WO2019081401A1

WO2019081401A1 - Quantum dots having a high absorption

Info

Publication number: WO2019081401A1
Application number: PCT/EP2018/078839
Authority: WO
Inventors: David MOCATTA; Amir Holtzman
Original assignee: Merck Patent GmbH
Current assignee: Merck Patent GmbH
Priority date: 2017-10-24
Filing date: 2018-10-22
Publication date: 2019-05-02
Anticipated expiration: 2020-04-24
Also published as: TW201930555A

Abstract

La présente invention concerne des points quantiques (QD) ayant une absorption élevée, un procédé de préparation desdits points quantiques, un support optique et un dispositif optique.The present invention relates to quantum dots (QD) having high absorption, a method of preparing said quantum dots, an optical medium and an optical device.

Description

Quantum dots having a high absorption

Field of the invention

The present invention relates to quantum dots (QD) having a high absorption, a method for the preparation of said quantum dots, optical medium and an optical device.

Background Art

Quantum dots are known in the prior arts. Quantum dots (QD) are a class of materials that offer various promising applications in fields related to light emission and absorption, e.g. in fields such as in-vivo imaging, light- emitting device manufacture, photodetection and solar energy conversion. For example, quantum dots may find application in transistors, solar cells, LEDs, diode lasers, medical imaging, quantum computing and a variety of other fields. Furthermore, QDs emitting in the visible electromagnetic spectrum may be of particular interest for lighting and display applications, e.g. for high brightness LEDs.

A quantum dot may be sufficiently small to exhibit distinct quantum mechanical properties. A single QD can for example contain about 100 to even 100000 atoms, having a diameter that ranges from about 10 to 50 or more atoms, e.g. a diameter in the range of about 2 to about 10

nanometers. For example, three-dimensional confinement of the

nanocrystal exciton states can be achieved, such that intermediate properties are obtained between those of the bulk material and discrete molecules. Therefore, the characteristics of a quantum dot may be closely related to its size and shape, e.g. the band gap, which determines the frequency range of emitted light, may be inversely related to its size. Monodisperse ensembles of QDs may feature a narrow, size-tunable emission spectrum, while also being particularly suitable for solution-based processing. Colloidal synthesis of nanocrystals may comprise the synthesis from precursor compounds in a solution. When heating the solution, the decomposed precursors form monomers that nucleate. Known QDs obtainable by colloidal synthesis may comprise binary compounds, such as lead sulfide, lead selenide, cadmium selenide, cadmium sulfide, indium arsenide and indium phosphide, or ternary compounds such as cadmium selenide sulfide. Particular nanocrystals known in the art may involve cadmium chalcogenide based materials where especially CdSe QDs synthesis is a fully mastered process. Such nanocrystal can be easily manufactured due to the simplicity of their synthesis, and may have a high optical quality.

However, cadmium is a toxic heavy element which may be subject to legal restrictions, e.g. by the EU OHS directive. Consequently, the use of such materials in large amounts is preferably avoided. Furthermore, the high toxicity may limit the applicability of cadmium chalcogenide based

materials, e.g. in in-vivo imaging. In addition to a low toxicity, a cost-efficient production at an industrial scale can also be considered highly

advantageous when scaling the use of nanocrystals from an academic setting to commercial product applications.

Cadmium-free alternatives for manufacturing quantum dots are known in the art, such as CulnS2 and InP. Particularly indium phosphide (InP) QDs are known that have emission characteristics similar to CdSe QDs, while advantageously having a lower toxicity. Methods for colloidally

manufacturing InP nanocrystals are known in the art.

US 2015/0083969 A1 discloses an lnP/ZnS(F) core/shell nanocrystal particle. WO 201 6/146719 A1 mentions a method for synthesizing nanoparticles by mixing a first precursor material comprising a first compound comprising a halide moiety and a metal or a metalloid, a second precursor material comprising a second compound comprising a polyatomic nonmetal, and a solvent and by heating up the mixture. US 8679543 B2 describes a coated InP/ZnS core /shell nanocrystal.

D. Gary et al, JACS, 201 6, 138, 1510-1513, describes single-crystal and electronic structure of a 1 .3nm Indium Phosphide nanoclusters (Magic- Sized nanoclusters) and a method for preparation of thereof.

D.Gary et al., Chem. Mater., 2015, 27, 1432-1441 , discloses InP quantum dots via magic sized cluster intermediates exhibiting no light emission.

J. Ning, U. Banin, ChemComm, 2017, 53, 2626-2629 describes Magic Size InP and InAs clusters, synthesis of thereof and shelling. A light emission is observed from InP/ZnS core/shell nanocrystals.

D. Gary et al, ChemComm, 201 6, 00, 1 61 discloses a reaction scheme between ln37P2o(02CR)si and primary amine.

Quantum dots obtainable according to prior art documents could be used. However, it is a permanent desire to improve the features of these quantum dots. Therefore, it is an object of embodiments of the present invention to provide quantum dots having a high absorption and efficiency.

It is an object of embodiments of the present invention to provide an efficient and/or cheap method for production of improved quantum dots.

The above objective is accomplished by quantum dots and a method for producing the same according to the present invention. Summary of the invention Surprisingly, the inventors have found that quantum dots (QD) based on indium phosphide (InP) exhibiting a ratio of the optical density of the first exciton peak maximum to the optical density of the trough on the high energy side of the first exciton peak of above 1 .80 and below 2.5 in the absorption spectrum measured at 25°using a toluene solution.

In another aspect, the present invention relates to quantum dots (QD) based on magic sized clusters of indium phosphide (MSC InP) exhibiting a ratio of the optical density of the first exciton peak maximum to the optical density of the trough on the high energy side of the first exciton peak of above 1 .80 and below 2.5 in the absorption spectrum measured at 25° using a toluene solution.

In another aspect, the present invention relates to a method for preparing QD being based on InP.

In another aspect, the present invention relates to a method for preparing QD being based on InP MSCs.

In another aspect, the present invention also relates to QD being obtainable by a method for preparing QD.

In another aspect, the present invention further relates to composition comprising QD being based on InP. In another aspect, the present invention also relates to an optical medium comprising QD being based on InP. In another aspect, the present invention further relates to composition comprising QD being based on InP MSCs.

In another aspect, the present invention also relates to an optical medium comprising QD being based on InP MSCs.

Detailed description of the invention The present invention provides quantum dots (QD) based on indium phosphide (InP) characterized in that the QD exhibit a ratio of the optical density of the first exciton peak maximum to the optical density of the trough on the high energy side of the first exciton peak of above 1 .80 and below 2.5 in the absorption spectrum measured at 25°using a toluene solution.

Quantum dots (QD) are well known in the art as described above.

Conventionally QD are a nanosized light emitting semiconductor material. According to the present invention, the term "nanosized" means the size in between 0,1 nm and 999 nm.

Thus, according to the present invention, the term ^"a nanosized light emitting semiconductor material^" is taken to mean that the light emitting material which size of the overall diameter is in the range from 0.5 nm to 999 nm. And in case of the material has elongated shape, the length of the overall structures of the light emitting material is in the range from 0.5 nm to 999 nm.

According to the present invention, the term "nano sized" means the size of the semiconductor material itself without ligands or another surface modification, which can show the quantum size effect. According to the present invention, a type of shape of the core of the nanosized light emitting material, and shape of the nanosized light emitting material to be synthesized are not particularly limited. For examples, spherical shaped, elongated shaped, star shaped, polyhedron shaped, pyramidal shaped, tetrapod shaped, tetrahedron shaped, platelet shaped, cone shaped, and irregular shaped nanosized light emitting materials can be synthesized. In some embodiments of the present invention, the QD exhibit a ratio of the peak maximum to the peak minimum of above 1 .80 and below 2.5 in the absorption spectrum at a wavelength in the range of 400 to 500 nm measured at 25°using a toluene solution. The ratio of the peak maximum to the peak minimum is the ratio of the OD of the first exciton peak and the trough on the lower wavelength side of that peak. Preferably, the ratio of the peak maximum to the peak minimum in the absorption spectrum is related to the first exciton peak.

Preferably, the data concerning the peak maximum in the absorption spectrum is obtained using a toluene solution of quantum material with an optical density (OD) of 0.09.

According to the present invention, the QD are based on indium phosphide (InP). Therefore, the present QD comprise a measurable amount of InP. Preferably, the QD comprise a centre area of InP. More preferably, the centre area of InP comprises a diameter in the range of 0.8 to 5.0 nm, preferably 0.9 nm to 3.0 nm, more preferably 1 .0 to 1 .5 nm. The size of the particles can be obtained by methods well known in the art. The particle size distribution is preferably assessed with Gatan Digital Micrograph software using images obtained from High Resolution Transmission

Electron Microscopy (HRTEM) and provided as arithmetic mean (number average). The sample preparation for performing the HRTEM can be performed by any conventional method. Preferably, the sample is purified before the measurement. E.g. 0.2ml of the crude sample is dissolved in 0.2ml of chloroform; 1 .6ml of acetone is then added and the mixture is precipitated by centrifuge (5 minutes, 5Krpm). Then the precipitant is dissolved in 0.5ml of chloroform, and 30uL from this solution is dropped on a Cu/C TEM grid with ultrathin amorphous carbon layer. The grid is dried in vacuum at 80°C for 1 .5h to remove the residues of the solvent as well as possible organic residues.

HRTEM and/or other TEM measurements are preferably carried out on a Tecnai F20 G2 machine equipped with EDAX Energy Dispersive X-Ray Spectrometer.

In a preferred embodiment, the QD are based on magic sized clusters comprising indium phosphide, more preferably the QD are based on magic sized clusters essentially consisting of indium phosphide (MSC InP). Magic sized clusters (MSC) are well known in the art. MSC have a well-defined composition and exhibit remarkable thermodynamic stability relative to similar sizes.

Preferably, the QD are based on a nanocrystal core, which consists solely of fused 6-membered rings with all phosphorus atoms coordinated to four indium atoms in a pseudo-tetrahedral arrangement. The nanocrystal core preferably have the formula [ln₂i P2o]³⁺, [ln₄₂P4o]⁶⁺, [I nesPeo]⁹*, [ln₈4Pso]¹²⁺, [ln₉₅P9o]¹⁵⁺, [ln₃i P₃o]³⁺, [Ι η₄ι Ρ ₀]³⁺, [Ι η₅ι Ρ₅ο]³⁺, [Ι η₆ι Ρ₆ο]³⁺, [ln₇i P7o]³⁺,

[l n8i Pso]³⁺, [l n9i Pgo]³⁺. I n this preferred embodiment the subset of atoms preferably possesses a C2 rotation axis that bisects two phosphorus atoms and a single indium atom located at the center of the particle, and measures approximately 1 .3 nm ^χ 1 .0 nm ^χ 1 .0 nm. A dihedral angle of 160 ± 3°is consistent along the longest straight In-P. The average In-P bond length in the [ln2i P2o]³⁺. core is 2.528 A (min 2.479 A, max 2.624 A), and the average P- In-P bond angle is 109.2°(min 97.7° , max 1 19.9^<).

Preferably, an additional 1 6 indium atoms are singly bound to this core through surface-exposed phosphorus atoms, with an average bond length of 2.482 A (min 2.450 A, max 2.515 A). Preferably, the sum of the single- bond covalent radii for In and P is 2.53 A and it is preferably inferred that the bonding in the inorganic core of this cluster may be best viewed as covalent in nature, with differences in bond lengths between In-P in the core and In-P at the surface arising from internal strain. The structure is preferably assessed using single-crystal X-ray diffraction at 25°C as well known in the art. (see J. Am. Chem. Soc. 201 6, 138, 1510-1513). It should be noted that the core of the present QD may comprise additional InP or areas having another structure. Preferably, the area comprising the preferred structure as mentioned above is at least 30% by volume, more preferably at least 50% by volume and even more preferably at least 70 % by volume.

According to a preferred embodiment, the quantum dots may comprise a core / shell structure. Consequently, the QD may comprise a shell of a semiconductor.

According to the present invention, the term ^"core / shell structure^" means the structure having a core part and at least one shell part covering said core.

In some embodiments of the present invention, said core / shell structure can be core / one shell layer structure, core / double shells structure or core / multishell structure. According to the present invention, the term ^"multishell^" stands for the stacked shell layers consisting of three or more shell layers. Each stacked shell layers of double shells and / or multishell can be made from same or different materials.

In some embodiments of the present invention, a quantum dot shell may comprise a shell of a semiconductor material comprising ll-VI, lll-V, or IV-VI semiconductors, or a combination of any of these.

In some embodiments, as a combination, ternary or quaternary materials of II, III, IV, V, VI materials of the periodic table can be used.

Preferably, the shell comprises or consists of a 1 ^st element of group 12 of the periodic table and a 2^nd element of group 1 6 of the periodic table, preferably, the 1 ^st element is Zn, and the 2^nd element is S, Se and/or the shell comprises or a consisting of a 1 ^st element of group 13 of the periodic table and a 2^nd element of group 15 of the periodic table, preferably, the 1 ^st element is In, and the 2^nd element is P, more preferably the shell comprises or a consisting of InP, GaP, ZnS, ZnSe or combinations of these materials, especially alloys of these materials, even more preferably ZnSe or the shell comprises a mixture of ZnS and ZnSe.

For example, CdSe/CdS, CdSeS/CdZnS, CdSeS/CdS/ZnS, ZnSe/CdS, CdSe/ZnS, InP/ZnS, InP/ZnSe, InP/ZnSe/ZnS, InZnP/ZnS, InZnPS/ ZnS, InZnP/ZnSe/ZnS, ZnSe/CdS, ZnSe/ZnS, GaP/ZnS, GaP/ZnSe,

GaP/ZnSe/ZnS, GaZnP/ZnS, GaZnPS/ ZnS, GaZnP/ZnSe/ZnS,

InGaP/ZnS, InGaP/ZnSe, InGaP/ZnSe/ZnS, or combination of any of these, can be used preferably. Preferably, the semiconducting material does not comprise Cd, more preferably the semiconducting material of the shell comprises ZnS and/or ZnSe, more preferably ZnSe or the shell comprises a mixture of ZnS and ZnSe.

According to a specific embodiment, the shell preferably comprises at least 20 % by weight, more preferably at least 40 % by weight, even more preferably at least 60 % by weight and most preferably at least 80 % by weight ZnSe based on the total weight of the shell. In a further embodiment, the shell preferably comprises at least 40 % by weight, more preferably at least 70 % by weight, even more preferably at least 80 % by weight and most preferably at least 90 % by weight ZnSe in a specific layer of the shell.

In an embodiment of the invention, the shell preferably has a thickness in the range of 0.3nm to 20nm, preferably 0.3nm to 10nm, more preferably 1 to 5nm, measured by taking images on a 120kV TEM and measuring the diameter of the quantum material for a sample of more than 50 particles and provided as arithmetic mean (number average). The measurement is preferably performed using imageJ software or the software mentioned above. Preferably, the shell thickness is calculated by subtracting the shelled particle thickness from the literature value of the MSCs e. g. 1 .0 or 1 .3nm and/or the particle being used for shelling. Furthermore, the particle size of the shelled particles can be determined as mentioned above before shelling.

In some embodiments of the invention, the size of the overall structures of the quantum dots, is from 1 nm to 100 nm, more preferably, it is from 1 nm to 30 nm, even more preferably, it is from 2 nm to 15 nm. The size is measured according to the method mentioned above and is based on the arithmetic mean (number average). In some embodiments of the present invention, the surface of the quantum dots can be over coated with one or more kinds of surface ligands.

Without wishing to be bound by theory it is believed that such a surface ligands may lead to disperse the nanosized material in a solvent more easily. In addition, the surface ligand may improve the features of the quantum dots such as efficiency, quantum yield, wavelength of the peak maximum and full width half maximum (FWHM). In some embodiments of the present invention, the QD preferably comprise a ligand. The surface ligands in common use include phosphines and phosphine oxides such as Trioctylphosphine oxide (TOPO), Trioctylphosphine (TOP), and Tributylphosphine (TBP); phosphonic acids such as

Dodecylphosphonic acid (DDPA), Tetradecylphosphonic acid (TDPA), Octadecylphosphonic acid (ODPA), and Hexylphosphonic acid (HPA);

amines such as Oleylamine, Dedecyl amine (DDA), Tetradecyl amine

(TDA), Hexadecyl amine (HDA), and Octadecyl amine (ODA), Oleylamine (OLA), alkenes, such as 1 -Octadecene (ODE), thiols such as hexadecane thiol and hexane thiol; mercapto carboxylic acids such as mercapto propionic acid and mercaptoundecanoicacid; carboxylic acids such as oleic acid, stearic acid, myristic acid; acetic acid and a combination of any of these. Polyethylenimine (PEI) also can be used preferably.

The ligands mentioned above, especially the acids, can be used in acidic form and/or as a salt. The person skilled in the art will be aware that the ligand will bind to the core in an appropriate manner, e.g. the acids may get deprotonated.

Examples of surface ligands have been described in, for example, the laid- open international patent application No. WO 2012/059931 A.

Preferably, the QD comprise a carboxylate ligand, more preferably a carboxylate ligand having 2 to 30 carbon atoms, preferably 4 to 24 carbon atoms, even more preferably 8 to 20 carbon atoms, most preferably 10 to 26 carbon atoms, even more preferably a carboxylate ligand selected from the group consisting of myristate, palmitate, laurate, stearate, oleate; and/or a phosphorus containing ligand, such as phosphine ligands, preferably alkyl phosphine ligands having 3 to 108 carbon atoms, e. g. Trioctylphosphine (TOP), phosphine oxide ligands, preferably alkyl phosphine oxide having 3 to 108 carbon atoms and/or phosphonate ligands, more preferably an alkyl phosphonate ligand having 1 to 36 carbon atoms, preferably 6 to 30 carbon atoms, even more preferably 10 to 24 carbon atoms, most preferably 12 or 20 carbon atoms in the alkyl group even more preferably a phosphonate ligand selected from the group consisting of octadecylphosphonate, dodecylphosphonate, tetradecylphosphonate, hexadecylphosphonate; and/or amines, preferably primary or secondary amines having 1 -36 carbon atoms, preferably 6 to 30.

In view of the ligands mentioned above, carboxylate ligands such as stearate and oleate and phosphine ligands, such as Trioctylphosphine oxide (TOPO), Trioctylphosphine (TOP), and Tributylphosphine (TBP) are preferred.

A further subject matter of the present invention is a method for preparing quantum dots (QD) being based on indium phosphide (InP), characterized by preparing magic size cluster (MSC) of InP (MSC InP). Preferably, the method provides quantum dots (QD) based on indium phosphide (InP) exhibiting a ratio of the optical density of the first exciton peak maximum to the optical density of the trough on the high energy side of the first exciton peak of above 1 .80 and below 2.5 in the absorption spectrum measured at 25°using a toluene solution. In addition thereto, the method provides the preferred embodiments of the quantum dots (QD) of the present invention as mentioned above and below.

The InP magic size cluster (MSC) can be prepared by any method known in the art. Preferably, the preparation of the MSC InP is achieved by a reaction mixture comprising a phosphorus precursor being selected from the group consisting of organic phosphine compounds, preferably alkylsilyl phosphine compounds having 1 to 3 silicon atoms preferably alkylsilyl phosphine compounds having 1 to 30 carbon atoms, preferably 1 to 10 carbon atoms, even more preferably 1 to 4 carbon atoms, most preferably 1 or 2 carbon atoms in the alkyl groups or aryl silyl phosphine compounds, preferably aryl silyl phosphine compounds having 1 -3 silicon atoms preferably aryl silyl phosphine compounds having 6 to 30 carbon atoms, preferably 6 to 18 carbon atoms, even more preferably 6 to 12 carbon atoms, most preferably 6 or 10 carbon atoms in the aryl groups.

In addition to a phosphorus precursor, the preparation of the MSC InP is preferably achieved by a reaction mixture comprising an indium precursor preferably being selected from the group consisting of indium carboxylates, more preferably indium carboxylates having 2 to 30 carbon atoms, preferably 4 to 24 carbon atoms, even more preferably 8 to 20 carbon atoms, most preferably 10 to 1 6 carbon atoms. The indium carboxylate is preferably selected from the group consisting of indium myristate, indium laurate, indium palmitate, indium stearate and indium oleate. Preferably, the phosphorous precursor comprises

tris(trimethylsilyl)phosphine and similar materials having an aryl, and/or alkyl group instead of the methyl unit, such as tris(triphenylsilyl)phosphine, tris(triethylsilyl)phosphine, tris(diphenylmethylsilyl)phosphine,

tris(phenyldimethylsilyl)phosphine, tris(triphenylsilyl)phosphine,

tris(triethylsilyl)phosphine, tris(diethylmethylsilyl)phosphine,

tris(ethyldimethylsilyl)phosphine. In a specific embodiment, the preparation of the MSC InP is preferably achieved by a reaction mixture comprising a phosphorus precursor and an indium precursor being different to the phosphorus precursor and the molar ratio of the phosphorus precursor to the indium precursor is preferably in the range of 1 :3 to 1 :1 , preferably 1 :2.5 to 1 :1 , even more preferably 1 :2 to 1 :1 . The preparation of the MSC InP is preferably achieved using a solvent. The solvent is not specifically restricted. Preferably, the solvent is selected from amines, aldehydes, alcohols, ketones, ethers, esters, amides, sulfur compounds, nitro compounds, hydrocarbons, halogenated hydro-carbons (e.g. chlorinated hydrocarbons), aromatic or heteroaromatic hydrocarbons, halogenated aromatic or heteroaromatic hydrocarbons and/or (cyclic) siloxanes, preferably cyclic hydrocarbons, terpenes, epoxides, ketones, ethers and esters. Preferably a non-coordinating solvent is used. Preferably, an alkane, more preferably a squalane is used as a solvent for the preparation of the MSC InP. Preferably , an alkane having 6 to 46 carbon atoms, more preferably 8 to 40 carbon atoms, even more preferably 12 to 34 carbon atoms, most preferably 1 6 to 30 carbon atoms is used as a solvent. More preferably, the alkane being used as a solvent is a decane, dodecane, tetradecane, hexadecane, octadecane, eicosane. docosane, hexamethyltetracosane. The alkane may be linear or branched with branched alkanes such as squalene being preferred.

In an embodiment of the present invention, the preparation of the MSC InP is preferably achieved by a reaction mixture comprising a solvent and the solvent comprises at least one alkene, preferably an alkene having 6 to 36 carbon atoms, more preferably 8 to 30 carbon atoms, even more preferably 12 to 24 carbon atoms, most preferably 1 6 to 20 carbon atoms. More preferably, the alkene is a 1 -alkene, such as 1 -decene, 1 -dodecene, 1 - Tetradecene, 1 -hexadecene, 1 -octadecene, 1 -eicosene. 1 -docosene. The alkene may be linear or branched.

Regarding the preparation step of the QD core and the MSC InP, alkenes are preferred in view of the other solvents mentioned above.

Surprising improvements can be obtained using a high reaction

temperature. Preferably, the preparation of the MSC InP is achieved at a temperature 1 10°C or above, more preferably 1 15°C o r above. Preferably, the preparation of the MSC InP is achieved at a temperature in the range of 1 10 to 180Ό, more preferably 1 15 to 140Ό. Preferably, the MSC InP exhibits an Exciton Peak of at least 370 nm, preferably at least 380 nm, in the absorbance spectrum measured at 25° using a toluene solution.

These data concern the MSC InP being achieved by the methods mentioned above and below and being preferably used as a starting material for the preparation of QD having the features mentioned above and below and preferably comprising a shell. Preferably, the QD having a shell exhibits an Exciton Peak of between 400-600nm, preferably between 440-500nm, in the absorption spectrum measured at 25°using a toluene solution.

In a preferred embodiment of the present invention, the preparation method of quantum dots (QD), especially the preparation of the Magic Size Cluster MSC of InP (MSC InP) preferably comprises a quenching step, wherein the quenching step more preferably includes a lowering of the temperature of a reaction mixture by at least 130 °C, preferably at least 150°C within a period of time less than 2 seconds, preferably less than 1 second. These data can be measured with any conventional method and is based on the average temperature decrease.

Preferably, the quenching step is performed by adding a solvent to the reaction mixture. More preferably, the solvent being added to the reaction mixture exhibits a temperature below 100 °C, more p referably below 50 °C, even more preferably below 30 °C, most preferably b elow 10 °C. Using the present method, it is possible to assess the temperature decrease based the temperature of the reaction mixture, the temperature of the solvent being added thereto, the volume of the reaction mixture, the volume of the solvent being added thereto and the time span during which the solvent being added to the reaction mixture. Furthermore, the temperature of any device being in contact with the reaction mixture may have an influence to the data mentioned above, e. g. the temperature and power output of the heating mantle if used.

Preferably, the volume ratio of the reaction mixture to the solvent being added to the reaction mixture is in the range of 4:1 to 1 :4 preferably 2:1 to 1 :2.

In a specific embodiment, the preparation of the MSC InP is preferably achieved in the presence of a carboxylate compound, more preferably carboxylate compound having 2 to 30 carbon atoms, preferably 4 to 24 carbon atoms, even more preferably 8 to 20 carbon atoms, most preferably 10 to 26 carbon atoms. More preferably, the carboxylate compound is a saturated carboxylate compound. The carboxylate compound could be added to the reaction mixture as a free acid or as a salt. Preferably, the carboxylate compound is added as a precursor, preferably an indium precursor wherein preferred indium precursors are disclosed above and below.

As mentioned above, preparation of the MSC InP is preferably achieved using specific precursors, solvents, and temperatures. This means that the MSC InP are preferably obtained by these measures. The obtained MSC InP can be used as starting materials for further modifying the features of the quantum dots and/or the MSC InP.

In a preferred embodiment, the MSC InP being prepared by a reaction mixture comprising a carboxylate compound in a first reaction step A) are preferably reacted with a ligand in a second reaction step B). Preferably, the ligand used in the second reaction step B) is a phosphonic acid, preferably an alkyl phosphonic acid having 1 to 36 carbon atoms, preferably 6 to 30 carbon atoms, even more preferably 10 to 24 carbon atoms, most preferably 12 or 20 carbon atoms in the alkyl group. The phosphonic acid can also be added as a salt. In a specific embodiment, the phosphonic acid is added as an indium salt. Preferably, an indium salt of an alkyl phosphonic acid having 1 to 36 carbon atoms, preferably 6 to 30 carbon atoms, even more preferably 10 to 24 carbon atoms, most preferably 12 or 20 carbon atoms in the alkyl group is used for the second reaction step B), such as indium octadecylphosphonate,

tetradecylphosphonate, indium dodecylphosphonate indium and indium hexylphosphonate.

In another embodiment, the MSC InP being prepared by a reaction mixture comprising a carboxylate compound in a first reaction step A) are preferably purified before performing the second step B). The purification is preferably performed by adding a solvent to the mixture obtained in the first reaction step A) and preferably precipitating the MSC InP. In a specific embodiment of the present invention, the magic size clusters (MSC) obtained in a reaction step and/or any product obtained using these MSC can be purified. This purification can be done as intermediate step or to obtain a purified quantum dots according to the present invention. According to a special embodiment, the purification can be achieved by dispersing 0.1 to 10 equivalents of the crude solution in 1 equivalent of a solvent (by volume), preferably a hydrocarbon solvent, e. g. toluene, hexane, pentane or chloroform. Then, 0.5 to 20 equivalents (by volume) of a cleaning solution such as a ketone, alcohol, preferably acetone, methanol, ethanol or propanol, more preferably an ketone, e. g. acetone is preferably added to the composition. The resultant suspension is preferably centrifuged for a time and at a speed sufficient for a useful precipitation. E.g. good results are achieved with 5 min at a speed of 5000 rpm.

In some embodiments of the present invention, the cleaning solution comprises one compound selected from one or more members of the group consisting of ketones, such as, methyl ethyl ketone, acetone, methyl amyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols, such as, methanol, ethanol, propanol, butanol, hexanol, cyclo hexanol, ethylene glycol; and pentane; halogenated hydrocarbons, such as chloroform;

xylene and toluene.

In a preferred embodiment of the present invention, the cleaning solution comprises three parts the crude solution with the QDs, the solvent and the anti-solvent. The solvent is typically a non-polar compound preferably an alkane or a benzene derivative such as toluene or a halogenated hydrocarbon, more preferably toluene, chloroform, hexane and pentane. The anti-solvent is typically a polar compound such as an alcohol, ester or nitrogen containing compound, preferably methanol, ethanol, isopropanol, butanol, ethyl acetate and acetonitrile. The ratios of the crude, solvent and anti-solvent are in the ranges of 2.5:2.5:1 to 1 :20:80.

In a preferred embodiment of the present invention, the cleaning solution comprises one or more of ketones to more effectively remove unreacted core precursors from the composition obtained in step A) and/or the composition obtained in step B) as mentioned above or any other reaction composition and remove e. g. the ligands leftovers.

More preferably, the cleaning solution contains one or more of ketones selected from the group consisting of methyl ethyl ketone, acetone, methyl amyl ketone, methyl isobutyl ketone, and cyclohexanone, and one more solvent selected from halogenated hydrocarbons, preferably chloroform, acetonitrile, ethyl acetate, xylene or toluene to remove unreacted core precursors from the composition obtained in step A) and/or the composition obtained in step B) as mentioned above or any other reaction composition and remove e. g. the ligands leftovers in the solution effectively. More preferably, the cleaning solution contains one or more of ketones selected from methyl ethyl ketone, acetone, methyl amyl ketone, methyl isobutyl ketone, and cyclohexanone, and chloroform.

In some embodiments of the present invention, the mixing ratio of ketones: chloroform can be 1 :2 - 20:1 in a molar ratio. Preferably it is 1 :1 - 5:1 to remove unreacted core precursors from the composition obtained in step A) and/or the ligands contained in the composition obtained in step B) as mentioned above or any other reaction composition and to remove e.g. the ligands leftovers in the solution.

More preferably, the cleaning removes the extra ligands and the unreacted precursor.

Preferably, the MSC InP being prepared by a reaction mixture comprising a carboxylate compound in the first reaction step A) is preferably reacted with a ligand in a second reaction step B) at a high temperature.

Preferably, the second reaction step B) is performed at a reaction temperature above 100°C, preferably at a reaction t emperature above 200°C, more preferably at a reaction temperature ab ove 300°C and even more preferably at a reaction temperature above 350Ό.

The upper temperature limit of the second reaction step B) is given by the temperature stability of the product. Preferably, the second reaction step B) is performed at a reaction temperature below 500°C, preferably at a reaction temperature below 450°C, more preferably a t a reaction temperature below 400°C and even more preferably at a reaction

temperature above 390°C.

The reaction step B) could be performed in a solvent. Preferably, the solvents mentioned above could be used for performing the reaction step B). More preferably, a non-coordinating solvent is used. Even more preferably, an alkane, especially a squalane having 6 to 46 carbon atoms, more preferably 8 to 40 carbon atoms, even more preferably 12 to 34 carbon atoms, most preferably 1 6 to 30 carbon atoms is used as a solvent is used as a solvent in reaction step B). Regarding the second reaction step B), alkanes are most preferred solvents.

According to a further aspect, the second reaction step B) is preferably stopped by quenching, preferably by lowering the temperature of a reaction mixture for preparing MSC InP by at least 130 Ό, p referably at least 150Ό within a period of time less than 2 seconds, preferably less than 1 second.

Preferably, the second reaction step B) is stopped by adding a solvent to the reaction mixture. Preferably, the solvent exhibits a temperature below 100 °C, more preferably below 50 Ό, even more pref erably below 30 °C, most preferably below 10 °C.

In a specific embodiment, the volume ratio of the reaction mixture of the second reaction step B) to a solvent being added to the reaction mixture of the second reaction step B) is preferably in the range of 4 to 1 preferably 2 to 1 .

According to a further aspect of the method of the present invention, a shell of a semiconductor is grown onto the magic size cluster comprising indium phosphide (MSC InP) and/or the quantum dots of the present invention as mentioned above and below. In some embodiments of the present invention, said shell comprises group 12 and group 1 6 elements of the periodic table. Preferably the shell comprises ZnS or ZnSe, more preferably ZnSe. Preferred embodiments regarding the shell are specified above and below. According to a specific embodiment of the method of the present invention, the Magic Size Cluster MSC of InP (MSC InP) preferably comprises a ligand, preferably a carboxylate ligand, more preferably a carboxylate ligand having 2 to 30 carbon atoms, preferably 4 to 24 carbon atoms, even more preferably 8 to 20 carbon atoms, most preferably 10 to 26 carbon atoms, even more preferably a carboxylate ligand selected from the group consisting of myristate, palmitate, laurate, stearate, oleate. These MSC InP are preferably used as a starting material for a preparing QD having a shell.

According to a specific embodiment of the method of the present invention, the Magic Size Cluster MSC of InP (MSC InP) preferably comprises a ligand, preferably a phosphorus containing ligand, such as phosphine ligands, preferably alkyl phosphine ligands having 3 to 108 carbon atoms, preferably trioctylphosphine, phosphine oxide ligands, preferably alkyl phosphine oxide having 3 to 108 carbon atoms and/or phosphonate ligands, more preferably an alkyl phosphonate ligand having 1 to 36 carbon atoms, preferably 6 to 30 carbon atoms, even more preferably 10 to 24 carbon atoms, most preferably 12 or 20 carbon atoms in the alkyl group, even more preferably a ligand selected from the group consisting of

Trioctylphosphine oxide (TOPO), Trioctylphosphine (TOP), and

Tributylphosphine (TBP); Dodecylphosphonic acid (DDPA),

Tetradecylphosphonic acid (TDPA), Octadecylphosphonic acid (ODPA), and Hexylphosphonic acid (HPA). These MSC InP are preferably used as a starting material for a preparing QD having a shell. In view of the disclosure mentioned above, the MSC InP comprising a phosphorus containing ligand are preferred in view of MSC InP comprising a carboxylate ligand as starting material for shelling. The preparation of the shell is preferably achieved using a solvent. The solvent is not specifically restricted. Preferably, the solvent is selected from amines, aldehydes, alcohols, ketones, ethers, esters, amides, sulfur compounds, nitro compounds, phosphorus compounds, hydrocarbons, halogenated hydro-carbons (e.g. chlorinated hydrocarbons), aromatic or heteroaromatic hydrocarbons, halogenated aromatic or heteroaromatic hydrocarbons and/or (cyclic) siloxanes, preferably cyclic hydrocarbons, terpenes, epoxides, ketones, ethers and esters. Preferably a non- coordinating solvent is used.

Preferably, an alkane, more preferably a squalane is used as a solvent for achieving a shell. Preferably , an alkane having 6 to 46 carbon atoms, more preferably 8 to 40 carbon atoms, even more preferably 12 to 34 carbon atoms, most preferably 1 6 to 30 carbon atoms is used as a solvent. More preferably, the alkane being used as a solvent is a decane, dodecane, tetradecane, hexadecane, octadecane, eicosane. docosane,

hexamethyltetracosane. The alkane may be linear or branched with branched alkanes such as squalane being preferred.

In an embodiment of the present invention, the preparation of the shell is preferably achieved by a reaction mixture comprising a solvent and the solvent comprises at least one alkene, preferably an alkene having 6 to 36 carbon atoms, more preferably 8 to 30 carbon atoms, even more preferably 12 to 24 carbon atoms, most preferably 1 6 to 20 carbon atoms. More preferably, the alkene is a 1 -alkene, such as 1 -decene, 1 -dodecene, 1 - Tetradecene, 1 -hexadecene, 1 -octadecene, 1 -eicosene. 1 -docosene. The alkene may be linear or branched. In a further embodiment of the present invention, the preparation of the shell is preferably achieved by a reaction mixture comprising a solvent and the solvent comprises at least one phosphorus compound, such as phosphine compounds, preferably alkyl phosphine compounds having 3 to 108 carbon atoms, phosphine oxide compounds, preferably alkyl phosphine oxide having 3 to 108 carbon atoms and/or phosphonate compounds, more preferably an alkyl phosphonate compounds having 1 to 36 carbon atoms, preferably 6 to 30 carbon atoms, even more preferably 10 to 24 carbon atoms, most preferably 12 or 20 carbon atoms in the alkyl group.

Preferably, Trioctylphosphine (TOP) is used as a solvent for the preparation of a shell. Regarding the preparation step of the shell, alkenes are preferred in view of the other solvents mentioned above. In a further preferred embodiment, the solvent for the preparation of the shell comprises a mixture of an alkene and a phosphorus compound. Preferably, the preparation of the shell is achieved at a temperature above 1 10 °C, preferably in the range of 1 10 to 400 °C, m ore preferably above 150 °C, even more preferably above 200Ό and most p referably above 220°C. In an embodiment of the present invention, t he preparation of the shell is preferably achieved at a temperature in the range of 100 to 400 °C, more preferably in the range of 150 to 350 °C, even more most preferably in the range of 180 to 300 °C, most preferably in t he range of 210 to

250 Ό.

In a specific embodiment of the present invention, the shell is preferably prepared by mixing MSC InP and a first precursor and heating up the obtained mixture and then adding a second precursor, preferably the first precursor comprises an element of group 12 of the periodic table and the second precursor comprises an element of group 1 6 of the periodic table. Preferably, the first precursor comprises Zn, and the second precursor comprises S, Se, preferably Se. In a further embodiment the first precursor comprises an element of group 13 of the periodic table and a the second precursor comprises an element of group 15 of the periodic table, preferably, the first precursor comprises In, and the second precursor comprises P. Preferred embodiments regarding the first and second precursors concerning the preparation of the shell are provided below. In a further embodiment of the present invention, the shell is preferably prepared by mixing MSC InP and a second precursor and heating up the obtained mixture and then adding a first precursor, preferably the first precursor comprises an element of group 12 of the periodic table and the second precursor comprises an element of group 1 6 of the periodic table. Preferably, the first precursor comprises Zn, and the second precursor comprises S, Se and/or the first precursor comprises an element of group 13 of the periodic table and a the second precursor comprises an element of group 15 of the periodic table, preferably, the first precursor comprises In, and the second precursor comprises P. Preferred embodiments regarding the first and second precursors concerning the preparation of the shell are provided below.

Preferably, the semiconductor precursor comprises a Zn compound and/or an In compound, preferably a Zn carboxylate, more preferably a zinc carboxylate having 2 to 30 carbon atoms, preferably 4 to 24 carbon atoms, even more preferably 8 to 20 carbon atoms, most preferably 10 to 26 carbon atoms, even more preferably a zinc carboxylate selected from the group consisting of Zn myristate, Zn palmitate, Zn laurate, Zn stearate, Zn oleate and/or an indium carboxylates, more preferably indium carboxylates having 2 to 30 carbon atoms, preferably 4 to 24 carbon atoms, even more preferably 8 to 20 carbon atoms, most preferably 10 to 1 6 carbon atoms even more preferably a indium carboxylate selected from the group consisting of In myristate, In palmitate, In laurate, In stearate, In oleate. Preferably, the semiconductor precursor comprises a S compound, preferably a sulfur solution and/or a sulfur suspension, a Se compound, preferably a Se solution and/or a Se suspension and/or an P compound, preferably an alkylsilyl phosphine more preferably

tris(trimethylsilyl)phosphine.

Preferably a sulfur solution, more preferably a S solution comprising a phosphorus containing solvent, e.g. trioctylphosphine is used as a semiconductor precursor.

Preferably, a Se suspension comprising a hydrocarbon solvent, e.g. an 1 - alkene, such as 1 -octadecene and/or an organic phosphine compounds, preferably alkyl phosphine compounds having 1 to 30 carbon atoms, preferably 1 to 10 carbon atoms, even more preferably 1 to 4 carbon atoms, most preferably 1 or 2 carbon atoms in the alkyl groups or aryl phosphine compounds having 6 to 30 carbon atoms, preferably 6 to 18 carbon atoms, even more preferably 6 to 12 carbon atoms, most preferably 6 or 10 carbon atoms in the aryl groups is used as a semiconductor precursor.

Preferably, an organic phosphine compound as mentioned above regarding the InP precursor, e.g. tris(trimethylsilyl)phosphine and similar materials having an aryl, and/or alkyl group instead of the methyl unit, such as tris(triphenylsilyl)phosphine, tris(triethylsilyl)phosphine,

tris(diphenylmethylsilyl)phosphine, tris(phenyldimethylsilyl)phosphine, tris(triphenylsilyl)phosphine, tris(triethylsilyl)phosphine,

tris(diethylmethylsilyl)phosphine, tris(ethyldimethylsilyl)phosphine dissolved in an organic solvent, preferably octadecene or squalane is used as a semiconductor precursor.

In another embodiment, the MSC InP being preferably prepared by a reaction mixture comprising a alkly phosphonate compound in a first reaction step A1 ) are reacted with a semiconductor precursor in a second reaction step B1 ). According to a further embodiment, the second reaction step B1 ) is performed by heating up a composition comprising a first precursor, preferably Zn compound and/or an In compound, to a temperature above 50°C, preferably above 90°C and a composition compr ising the reaction product from the first reaction step A1 ) and a second precursor, preferably a S and/or a Se and/or a P compound are injected into the composition comprising a first precursor. Preferably, the temperature of the composition comprising the second precursor comprises a temperature above 20°C, more preferably above 50°C at the time of the injec tion to the composition comprising the first precursor.

According to a further embodiment, the second reaction step B1 ) is performed by heating up a composition comprising a first precursor, preferably Zn compound and/or an In compound, to a temperature in the range of 50Ό to 300 , preferably in the range of 90Ό to 120 and a composition comprising the reaction product from the first reaction step A1 ) and a second precursor, preferably a S and/or a Se and/or a P compound are injected into the composition comprising a first precursor. The composition comprising the second precursor and the reaction product from the first reaction step A1 ) is preferably heated up to a temperature in the range of 20Ό to 120 , preferably in the range of 50Ό to 100 before mixing.

Preferably, the temperature of the reaction mixture is raised after the second precursor, preferably a S and/or a Se and/or a P compound is added, preferably to a temperature above 100°C, mor e preferably above 150°C, even more preferably above 200Ό and most pr eferably above 220°C. Preferably, the temperature of the reaction mixture is raised after the second precursor, preferably a S and/or a Se and/or a P compound is added, to a temperature in the range of 100°C to 30 0°C, more preferably in the range of 150°C to 280 °C, even more preferably in the range of 200°C to 260Ό and most preferably in the range of above 220Ό to 240 . According to another embodiment, the second reaction step B1 ) is performed by heating up a composition comprising a second precursor, preferably a S and/or a Se and/or a P compound, to a temperature above 50°C, preferably above 90°C and a composition compr ising the reaction product from the first reaction step A1 ) and a first precursor, preferably Zn compound and/or an In compound, is injected into the composition comprising a second precursor. Preferably, the temperature of the composition comprising the first precursor comprises a temperature above 20°C, more preferably above 50°C at the time of the injection to the composition comprising the second precursor.

According to another embodiment, the second reaction step B1 ) is performed by heating up a composition comprising a second precursor, preferably a S and/or a Se and/or a P compound, to a temperature in the range of 50Ό to 300 , preferably in the range of 90Ό to 120 and a composition comprising the reaction product from the first reaction step A1 ) and a first precursor, preferably Zn compound and/or an In compound, is injected into the composition comprising a second precursor. The composition comprising the first precursor is preferably heated up to a temperature in the range of 20°C to 120 °C, prefera bly in the range of 50°C to 100°C before mixing.

Preferably, the temperature of the reaction mixture is raised after the composition comprising first precursor, preferably Zn compound and/or an In compound, is added, preferably to a temperature above 100°C, more preferably above 150Ό, even more preferably above 200°C and most preferably above 220Ό. Preferably, the temperature of the reaction mixture is raised after the composition comprising first precursor, preferably Zn compound and/or an In compound, is added, preferably to a temperature in the range of 100°C to 300°C, more preferably in the range of 150°C to 280 Ό, even more preferably in the range of 200Ό to 260Ό and most preferably in the range of above 220Ό to 240Ό.

The reaction product of the first reaction step A1 ) can be purified before performing the second reaction step B1 ) for preparing a shell. Preferably, the purification is performed by adding a solvent and anti-solvent to the mixture obtained in the first reaction step A1 ) and preferably precipitating the MSC InP. For performing the Step B1 ) a mixture of the cleaned reaction product of Step A1 ) and a first precursor, preferably a Zn compound and/or an In compound, are preferably mixed and heated to a temperature above 50°C, preferably above 90°C and thereafter a composition comprising a second precursor, preferably a S compound, a Se compound and/or an P compound is added.

Further preferred embodiments regarding the purification, especially the adding of a solvent and the precipitation are provided above and added by reference thereto.

Preferably, the second reaction step B1 ) is stopped by lowering the temperature to room temperature. In a specific embodiment for preparing a shell, the second reaction step B1 ) is stopped by quenching, preferably by lowering the temperature of a reaction mixture for preparing MSC InP by at least 130 °C, preferably at least 150°C within a pe od of time less than 2 seconds, preferably less than 1 second. Preferred embodiments regarding the quenching, especially the adding of a solvent and the temperature of the solvent added are provided above and added by reference thereto. In another aspect, the present invention also relates to a method for preparing quantum dots comprising a core / shell structure, wherein the method comprises following steps (a), (b) and (c) in this sequence. (a) synthesis of a core in a solution,

(b) removing the extra ligands from the core

(c) coating the core with at least one shell layer using said solution obtained in step (b).

In another aspect, the present invention further relates to a composition comprising or consisting of the QD of the present invention, preferably semiconducting light emitting nanoparticle of the present invention and at least one additional material, preferably the additional material is selected from the group consisting of organic light emitting materials, inorganic light emitting materials, charge transporting materials, scattering particles, host materials, and matrix materials. A further embodiment of the present invention is a formulation comprising or consisting of the QD of the present invention, preferably semiconducting light emitting nanoparticle of the present invention and at least one solvent. Preferred solvents are mentioned above and below. In another aspect, the present invention further relates to the use of the QD of the present invention, preferably semiconducting light emitting

nanoparticle of the present invention, the composition of the present invention or the formulation of the present invention in an electronic device, optical device or in a biomedical device.

A further subject matter of the present invention are quantum dots (QD) being obtainable by a method of the present invention as described above and below.

Optical medium In another aspect, the present invention further relates to an optical medium comprising the nanosized light emitting material.

In some embodiments of the present invention, the optical medium can be an optical sheet, for example, a color filter, color conversion film, remote phosphor tape, or another film or filter.

According to the present invention, the term ^"sheet^" includes film and / or layer like structured mediums.

- Optical device

In another aspect, the invention further relates to an optical device comprising the optical medium. In some embodiments of the present invention, the optical device can be a liquid crystal display device (LCD), Organic Light Emitting Diode (OLED), backlight unit for an optical display, Light Emitting Diode device (LED), Micro Electro Mechanical Systems (here in after "MEMS"), electro wetting display, or an electrophoretic display, a lighting device, and / or a solar cell.

Further preferred embodiments of the present invention

Embodiment 1 : Quantum Dots (QD) based on Indium Phosphide (InP) characterized in that the QD exhibit a ratio of the optical density of the first exciton peak maximum to the optical density of the trough on the high energy side of the first exciton peak of above 1 .80 and below 2.5 in the absorption spectrum measured at 25°using a toluene solution, preferably the QD comprise centre area of InP, more preferably the centre area of InP comprises a diameter in the range of 0.8 to 5.0 nm, preferably 0.9 nm to 3.0 nm, more preferably 1 .0 to 1 .5 nm.

Embodiment 2: QD according to embodiment 1 , characterized in that the QD are based on magic sized clusters comprising indium phosphide, more preferably the QD are based on magic sized clusters essentially consisting of indium phosphide (MSC InP).

Embodiment 3: QD according to embodiment 1 or 2, characterized in that QD are based on a nanocrystal core, which consists solely of fused 6- membered rings with all phosphorus atoms coordinated to four indium atoms in a pseudo-tetrahedral arrangement, preferably the nanocrystal core have the formula [ln₂i P2o]³⁺, [ln ₂P4o]⁶⁺, [I nesPeo]⁹*, [ln₈4Pso]¹²⁺, [ln₉₅P9o]¹⁵⁺, [lnsi P₃₀]³⁺, [ln₄i P ₀]³⁺, [ln₅i P₅o]³⁺, [ln₆i P₆o]³⁺, [ln₇i P7o]³⁺, [ln₈i Pso]³⁺, and/or [Ι Π91 P₉₀]³⁺.

Embodiment 4: QD according to any one of embodiments 1 to 3,

characterized in that the QD exhibit a ratio of the peak maximum to the peak minimum of above 1 .80 and below 2.5 in the absorption spectrum at a wavelength in the range of 400 to 500 nm measured at 25°using a toluene solution.

Embodiment 5: QD according to any one of embodiments 1 to 4,

characterized in that the QD comprise a shell of a semiconductor.

Embodiment 6: Method for preparing QD being based on InP, characterized by preparing Magic Size Cluster MSC of InP (MSC InP).

Embodiment 7: Method for preparing QD according to embodiment 6, characterized in that the MSC InP exhibits an Exciton Peak of at least 370 nm, preferably at least 380 nm, in the absorbance spectrum measured at 25°using a toluene solution.

Embodiment 8: Method for preparing QD according to embodiment 6 or 7, characterized in that a shell of a semiconductor is grown onto the MSC InP. Embodiment 9: Method for preparing QD according to embodiment 8, characterized in that the shell comprises InP, ZnS or ZnSe, preferably ZnSe, or the shell comprises a mixture of ZnS and ZnSe. Embodiment 10: Method for preparing QD according to any one of embodiments 8 or 9, characterized in that the preparation of the shell is achieved by a reaction mixture comprising a solvent and the solvent comprises at least one alkene, preferably an alkene having 6 to 36 carbon atoms, more preferably 8 to 30 carbon atoms, even more preferably 12 to 24 carbon atoms, most preferably 1 6 to 20 carbon atoms.

Embodiment 1 1 : Method for preparing QD according to embodiment 10, characterized in that the alkene is a 1 -alkene. Embodiment 12: Method for preparing QD according to any one of embodiments 6 to 1 1 , characterized in that the preparation of the shell is achieved at a temperature above 1 10 °C, preferably in the range of 1 10 to 400 °C, more preferably above 150 Ό, even more pre ferably in the range of 150 to 300 Ό, most preferably in the range of 1 80 to 250 Ό.

Embodiment 13: Method for preparing QD according to any one of embodiments 6 to 12, characterized in that the MSC InP are prepared by a reaction mixture comprising a alkly phosphonate compound and/or alkyl phosphonic acid compound in a first reaction step A1 ) and the MSC InP obtained are reacted with a semiconductor precursor in a second reaction step B1 ).

Embodiment 14: Method for preparing QD according to embodiment 13, characterized in that the characterized in that the semiconductor precursor comprises a Zn compound and/or an In compound, preferably a Zn carboxylate, more preferably a zinc carboxylate having 2 to 30 carbon atoms, preferably 4 to 24 carbon atoms, even more preferably 8 to 20 carbon atoms, most preferably 10 to 26 carbon atoms, even more preferably a carboxylate ligand selected from the group consisting of myristate, palmitate, laurate, stearate, oleate and/or an indium

carboxylates, more preferably indium carboxylates having 2 to 30 carbon atoms, preferably 4 to 24 carbon atoms, even more preferably 8 to 20 carbon atoms, most preferably 10 to 1 6 carbon atoms.

Embodiment 15: Method for preparing QD according to embodiment 13 or 14, characterized in that the MSC InP being preferably prepared by a reaction mixture comprising a phosphonate compound and/or alkly phosphonic acid compound in a first reaction step A1 ) are purified before performing the second step B1 ).

Embodiment 1 6: Method for preparing QD according to any one of embodiments 13 to 15, characterized in that for performing the second step B1 ) a mixture of the reaction product of the first step A1 ) and a first precursor, preferably a Zn compound and/or an In compound are mixed and heated to a temperature above 50°C, preferably above 90°C and thereafter a composition comprising a second precursor, preferably a S compound, a Se compound and/or an P compound is added.

Embodiment 17: QD obtainable by a method according to any one of embodiments 6 to 1 6. Embodiment 18: Composition comprising QD according to any one of embodiments 1 to 5 and 17, and at least one additional material, preferably the additional material is selected from the group consisting of organic light emitting materials, inorganic light emitting materials, charge transporting materials, scattering particles, host materials, and matrix materials. Embodiment 19: Formulation comprising or consisting of the QD according to any one of embodiments 1 to 5 and 17 or the composition according to embodiment 18, and at least one solvent. Embodiment 20: Use of the QD according to any one of claims according to any one of embodiments 1 to 5 and 17, or the composition according to embodiment 18, or the formulation according to embodiment 19 in an electronic device, optical device or in a biomedical device. Embodiment 21 : An optical medium comprising the QD according to any one of embodiments 1 to 5 and 17 or the composition according to claim 18.

Embodiment 22: An optical device comprising the optical medium according to embodiment 21 .

Definition of Terms The term "semiconductor" means a material which has electrical

conductivity to a degree between that of a conductor (such as copper) and that of an insulator (such as glass) at room temperature.

The term "organic" means any material containing carbon atoms or any compound that containing carbon atoms ionically bound to other atoms such as carbon monoxide, carbon dioxide, carbonates, cyanides, cyanates, carbides, and thiocyanates.

The term "emission" means the emission of electromagnetic waves by electron transitions in atoms and molecules.

Advantages The quantum dots according to the invention and the optical media and/or the optical devices, obtainable therefrom are distinguished over the prior art by any one of the following surprising advantages:

1 . The optical media and/or the optical devices obtainable using the

quantum dots according to the invention exhibit very high stability and a very long lifetime compared with optical media and/or optical devices obtained using conventional quantum dots.

2. The quantum dots according to the invention can be processed using conventional methods, so that cost advantages can also be achieved thereby. 3. The quantum dots according to the invention are not subject to any particular restrictions, enabling the workability of the present invention to be employed comprehensively.

4. The quantum dots according to the invention provide a high color purity and a low FWHM.

5. The quantum dots according to the invention can be produced in a very rapid and easy manner using conventional methods, so that cost advantages can also be achieved thereby.

The quantum dots according to the invention are less toxic than conventional formulations and have a high environmental

acceptability. 7. The quantum dots according to the invention show a high emission in the visual range of the electromagnetic radiation. 8. The quantum dots according to the invention show a high absorption.

These above-mentioned advantages are not accompanied by an undue impairment of the other essential properties.

It should be pointed out that variations of the embodiments described in the present invention fall within the scope of this invention. Each feature disclosed in the present invention can, unless this is explicitly excluded, be replaced by alternative features which serve the same, an equivalent or a similar purpose. Thus, each feature disclosed in the present invention is, unless stated otherwise, to be regarded as an example of a generic series or as an equivalent or similar feature.

All features of the present invention can be combined with one another in any way, unless certain features and/or steps are mutually exclusive. This applies, in particular, to preferred features of the present invention. Equally, features of non-essential combinations can be used separately (and not in combination). It should furthermore be pointed out that many of the features, and in particular those of the preferred embodiments of the present invention, are themselves inventive and are not to be regarded merely as part of the embodiments of the present invention. For these features, independent protection can be sought in addition or as an alternative to each invention presently claimed.

The teaching on technical action disclosed in the present invention can be abstracted and combined with other examples. The invention is explained in greater detail below with reference to a working example, but without being restricted thereby. Working Examples

Working Example 1 : Preparation of quantum dots.

Preparation of ln(MA)3 Solution

In a typical synthesis, 0.93 g (3.20 mmol) of indium acetate and 2.65 g (1 1 .6 mmol) of myristic acid are weighed out into a 100 ml_, 14/20, three- neck round-bottom flask equipped with a thermowell, reflux condenser, and septum. The apparatus is evacuated with stirring and raised in temperature to 100°C. The solution is allowed to off-gas acetic acid under reduced pressure for approximately 12 h at 100 °C to genera te the ln(MA)3 solution. Afterward, the flask is filled with nitrogen, and a 20 ml_ portion of dry toluene is added.

Synthesis of InP MA MSCs from ln(MA)₃ Solution and PiSiMes

In a nitrogen filled glovebox, 465 μΙ_ of P(SiMe3)3 is added to 10 mL of dry toluene, drawn into a syringe and sealed with a rubber stopper. The ln(MA)3 flask is brought up to 1 10°C and the P(SiMe 3)3 solution is injected. The formation of MSCs is monitored via UV-vis of timed aliquots taken from the reaction solution until the MSCs is fully formed as indicated by no further changes in the UV-vis spectra. This procedure can be easily adapted for a wide variety of fatty carboxylic acids in place of myristic acid. InP MA MSCs Workup Procedure

After UV-vis confirmed formation of MSCs, the flask is cooled and then carefully evacuated until all of the toluene is removed. The flask is transferred into a nitrogen filled glovebox. The crude MSCs are

resuspended in toluene. The toluene solution is centrifuged to remove insoluble materials. The now transparent supernatant is transferred to a second centrifuge tube. Acetonitrile is added to the solution to precipitate the clusters. The suspension is centrifuged. The supernatant is decanted and discarded and the MSCs are redissolved in a minimal amount of toluene. Again acetonitrile is added, and the suspension is centrifuged. This is repeated for a total of four cycles of precipitation. Synthesis of InP ODPA MSCs from InP MA MSCs

In a typical synthesis, 0.234g of indium acetate and 0.484g, of

octadecylphosphonic acid are weighed out into a 50ml 14/20 3-neck round- bottom flask equipped with a stir bar, thermowell, reflux condenser, and septum. Dry squalane (5ml) is quickly injected into the 3-neck flask. The apparatus is evacuated and raised in temperature to 120 °C.

The solution is allowed to off-gas acetic acid under reduced pressure to generate the indium octadecylphosphonate solution for approximately 12 h at 120 °C. After this the flask is filled with nitr ogen, the temperature raised to 300 °C for a couple of minutes to form a clear, homogeneous solution, and finally the solution is cooled back to 120 ^<C a nd evacuated for another 2 h degassing step.

In the glovebox, a solution of 0.2g of purified InP MA MSCs in 2.5ml of squalane is prepared and drawn up into a plastic syringe and stoppered. The 3-neck flask is then filled with nitrogen and rapidly heated by setting the temperature controller to the maximum setting (450 °C). The InP MA MSCs solution is injected into the indium octadecylphosphonate solution when the temperature controller read 100 °C as the temperature of the solution is rising. Aliquots are taken during the reaction taking note of the time after injection and the temperature of the flask. Once the reaction solution reached a temperature of 350 °C, the tempe rature controller is set to 370 ^<C for further growth.

InP ODPA MSC Workup Procedure A Schlenk flask is filled with 25 ml_ of hexanes, briefly evacuated, and backfilled with nitrogen three times prior to the synthesis of the particles. After UV-vis confirmed complete conversion to the MSCs, the hot reaction mixture is drawn up into a 10 ml_ glass syringe. The solution is rapidly injected into hexanes under nitrogen.

Thereafter, the hexane is distilled off by heating under reduced pressure and then the temperature is raised to around 200°C to distill off the squalane.

ZnSe Growth onto InP ODPA Magic Sized Clusters Preparation of Se ODE composition.

0.0079 gr of Se powder are dissolved in 2ml ODE and mixed by using vortex.

Zinc oleate 0.1 M solution preparation

(a) Preparation of 0.4M zinc oleate solution:

1 . Into a 1 L flask 100.7 gr oleic acid, 137.1 gr of TOP and 9.105 gr of zinc oxide are weighed.

2. The flask is connected to a Schlenk line and put under reduced

pressure until 100 mTorr is reached.

3. The flask is heated to 150 ^°C and held under vacuum for 1 hour when the pressure stabilized.

4. The system is filled with argon and heated to 300^°C. After boiling it is cooled to 100^°C and pumped again.

5. After the pressure stabilized, the system is filled with argon again and heated to 320^°C. Once the solution is clear it is cooled to 150^°C and the formed water is removed by putting the system under reduced pressure, 100 mtorr. 6. Once the pressure stabilized, the flask is cooled to room temperature and stored; in inert conditions.

(b) The solution in (a) is diluted by adding 3 parts tricoctylphosphine to every 1 part, by volume, of solution (a).

Growth of ZnSe shell on the MSCs

0.75ml of octadecylphosphonate magic sized clusters are synthesized as mentioned above (see Chem. Mater. 2015, 27, 1432-1441 ) are cleaned by adding acetonitrile till turbidity and precipitated by centrifugation at

5000 rpm for 5 minutes. The precipitant is dissolved in 1 .5 ml toluene and 4.5 ml ODE.

From this solution 1 ml is taken for this synthesis, to which 2.25ml ODE is added. This solution is transferred to a 50 ml flask and vacuum pumped for 1 hour at 90 °C to remove the toluene. The system i s then put under argon atmosphere and cooled to room temperature.

0.3ml of the Zn(Oleate)2 /TOP solution as mentioned above are injected into the flask at RT, the flask is then heated to 1 00 Ό. After 27 minutes

0.24ml of the 0.05M ODE-Se suspension solution is injected. Then the flask is heated to 230Ό. After 44 minutes at 230 the p eak reached 452 nm and had a max/min of 1 .85. The quantum dots show a peak emission at 452nm and an optical density of the first exciton peak maximum to the optical density of the trough on the high energy side of the first exciton peak of 1 .85 using the methods mentioned above.

Claims

Patent Claims

Quantum Dots (QD) based on Indium Phosphide (InP) characterized in that the QD exhibit a ratio of the optical density of the first exciton peak maximum to the optical density of the trough on the high energy side of the first exciton peak of above 1 .80 and below 2.5 in the absorption spectrum.

QD according to claim 1 , characterized in that the QD are based on magic sized clusters comprising indium phosphide.

QD according to claim 1 or 2, characterized in that QD are based on a nanocrystal core, which consists solely of fused 6-membered rings with all phosphorus atoms coordinated to four indium atoms in a pseudo- tetrahedral arrangement

QD according to any one of claims 1 to 3, characterized in that the QD exhibit a ratio of the peak maximum to the peak minimum of above 1 .80 and below 2.5 in the absorption spectrum at a wavelength in the range of 400 to 500 nm.

QD according to any one of claims 1 to 4, characterized in that the QD comprise a shell of a semiconductor.

Method for preparing QD being based on InP, characterized by preparing Magic Size Cluster MSC of InP (MSC InP).

Method for preparing QD according to claim 6, characterized in that the MSC InP exhibits an Exciton Peak of at least 370 nm.

8. Method for preparing QD according to claim 6 or 7, characterized in that a shell of a semiconductor is grown onto the MSC InP.

9. Method for preparing QD according to claim 8, characterized in that the shell comprises InP, ZnS or ZnSe. 10. Method for preparing QD according to claim 8 or 9, characterized in that the preparation of the shell is achieved by a reaction mixture comprising a solvent and the solvent comprises at least one alkene.

1 1 . Method for preparing QD according to claim 10, characterized in that the alkene is a 1 -alkene.

12. Method for preparing QD according to any one of claims 6 to 1 1 ,

characterized in that the preparation of the shell is achieved at a temperature above 1 10 °C.

13. Method for preparing QD according to any one of claims 6 to 12,

characterized in that the MSC InP are prepared by a reaction mixture comprising an alkly phosphonate compound and/or alkyl phosphonic acid compound in a first reaction step A1 ) and the MSC InP obtained are reacted with a semiconductor precursor in a second reaction step

B1 ).

14. Method for preparing QD according to claim 13, characterized in that the characterized in that the semiconductor precursor comprises a Zn compound and/or an In compound, preferably a Zn carboxylate, more preferably a zinc carboxylate having 2 to 30 carbon atoms.

15. Method for preparing QD according to claim 13 or 14, characterized in that the MSC InP being preferably prepared by a reaction mixture comprising a phosphonate compound and/or alkly phosphonic acid compound in a first reaction step A1 ) are purified before performing the second step B1 ).

1 6. Method for preparing QD according to any one of claims 13 to 15, characterized in that for performing the second step B1 ) a mixture of the reaction product of the first step A1 ) and a first precursor, preferably a Zn compound and/or an In compound are mixed and heated to a temperature above 50°C.

17. QD obtainable by a method according to any one of claims 6 to 1 6. 18. Composition comprising QD according to any one of claims 1 to 5 and 17,

and at least one additional material.

Formulation comprising or consisting of the QD according to any one of claims 1 to 5,17 or the composition according to claim 18, and at least one solvent.

20. Use of the QD according to any one of claims according to any one of claims 1 to 5, 17, or the composition according to claim 18, or the formulation according to claim 19 in an electronic device, optical device or in a biomedical device.

21 .. An optical medium comprising the QD according to any one of claims 1 to 5, 17 or the composition according to claim 18.

22. An optical device comprising the optical medium according to claim 21 .