MXPA99004002A - Compound with base of an alkaline-earth, sulphur and aluminium, gallium or indium, method of preparing same and use as luminophore - Google Patents

Abstract

The invention concerns a compound with a base of an alkaline-earth, sulphur and aluminium, gallium or indium, method for preparing same and use as luminophore. The compound is of formula AB2S4 in which A represents an alkaline-earth, B aluminium, gallium or indium, and it is characterised in that it is in the form of a powder residual content of oxygen not more than 1.5%and consists of particles of average size not more than 10&mgr;m. This compound is obtained by a method consisting in the following steps:forming a solution or a suspension containing salts of elements A and B, drying the solution or suspension by pulverisation;reacting the product obtained from the preceding step with carbon disulphide or with a mixture of hydrogen sulphide and carbon disulphide. The compound can be used as luminophore, in particular in cathodoluminescence.

Description

COMPOUNDS BASED ON AN ALKALINOTERREAL METAL.

FN SULFUR AND ALUMINUM. IN GALICIA OR IN INDIO. YOUR PROCESS OF PREPARATION AND ITS USE AS A LUMINIFER The present invention relates to a compound based on an alkaline earth metal, sulfur or aluminum, gallium or indium, a process for its preparation and its use as a luminifer. The fields of luminescence and electronics have recently undergone significant developments. Mention can be made, as an example of them, to the development of cathodoluminescent systems for novel exhibition and lighting techniques. One concrete application is that of replacing existing television screens with flat screens. These novel applications require luminiferous materials that exhibit increasingly improved properties. Thus, in addition to its ~ luminescence property, these materials are required to have specific characteristics of morphology or of particular size, with the In order to facilitate, in particular, its use in the desired applications. More specifically, luminifers that are micronic in size and that have, optionally, a narrow particle size distribution are required. The alkaline earth metal thiogalates are known as luminifers. These products are prepared from a mixture of salts or oxides of the various constituents, by heating at high temperature, in the presence of a flux. This method of preparation produces products that are large in size and often have a very wide particle size distribution. The object of the invention is to provide products of this type, with a small particle size. For this purpose, the compound of the invention, in a first embodiment, corresponds to the formula AB2S (1), in which A represents one or more alkaline earth metals and B is at least one element, taken from the group comprising aluminum, gallium or indium, and is characterized because it is provided in the form of a powder with a residual oxygen content of no more than 1.5%, more particularly, no more than 1%. According to a second embodiment, the compound of the invention corresponds to formula (1) and is characterized in that it is provided in the form of a powder composed of whole or unmilled particles, with an average size not greater than 10 μm. The invention also relates to a process for the preparation of such a compound, which is characterized in that it contains the following steps .- "forming a solution or a suspension comprising salts of elements A and B and, optionally, of the element of contamination o- impurities, - "the solution or the suspension is dried -by atomization; * the product obtained in the preceding step is reacted with the carbon disulfide or with a mixture of hydrogen sulfide and the carbon disulfide. Finally, the invention relates to the use as a luminifer, in particular in the catodoluminescence, of a compound, as described above.

Other features, details and advantages of the invention will become more fully apparent from reading the following description and the accompanying drawings, in which: "Figure 1 is an X-ray spectrum of a compound according to the As explained above, the compound of the invention is provided in the form of a powder and corresponds to the formula (1) AB2S 4. In this formula, A is an alkaline earth metal (Group lia of the Periodic Table). Periodic of the Elements, to which reference is made, here and through the description, that published in the Supplement to the Bulletin of the Société Chimique de France, No. 1 (January 1966). A can also be magnesium, calcium or barium. "B can be aluminum, gallium or indium .. B can be particularly gallium. According to a specific embodiment, the compound of the invention is preferably a strontium thiogalate. The invention also relates to compounds in which A represents various alkaline earth metals.

Similarly, B may represent a combination of at least two of the aluminum, gallium or indium elements. The compound of the invention may comprise one or more contaminants. The contaminant or impurity element is understood to mean, in this case, any element that can confer to the compound of the formula (1), luminescence properties in a given application of the compound as luminiferous. Without the desire to be restricted by theory, it can be thought that the polluting element can replace the alkaline earth metal. The amount of the contaminant element is usually no greater than 10 atomic%, with respect to the alkaline-earth metal element. More particularly, this contaminant element can be selected from the divalent manganese, divalent rare earth metals and the group comprising trivalent rare earth metals in combination with an alkali metal. In the case of trivalent rare earth metals, the presence of an alkali metal is necessary to compensate for the excess charge of the rare earth metal. This alkali metal can be particularly sodium.

The rare earth metals are understood to be the elements of the group composed of yttrium and the elements of the Periodic Table with an atomic number between 57 and 71 inclusive. The contaminant element can be more particularly europium (II), ytterbium (II) or cerium (III), in combination with an alkali metal. According to a first embodiment, the compound of the invention is characterized by "its low residual oxygen content.This content, in fact, is lower than that of the compounds of the prior art.This low level of residual oxygen may be a of the reasons for the advantageous luminescent properties = of the product of the invention As indicated above, this residual content is not greater than 1.5%, more particularly not more than 1%, expressed as the weight of oxygen with respect to the total weight of the compound According to a second embodiment of the invention, the compound of the invention is characterized by its morphology In accordance with this embodiment, the compound comprises particles with an average size of not more than 10 μm. the size characteristics and the particle size distribution are measured by the laser diffraction technique, which uses a particle sorter of the type Cilas HR 850 (volume distribution). This average size can be more particularly not more than 5 μm and more particularly not more than 4 μm. The particles for which the size has been given before, are unmilled or whole particles. The photographs of the scanning electron microscope make it possible to show that these particles do not have a broken or fragmented appearance, which is exhibited by the particles that have been subjected to grinding. Similarly, these photographs show that these particles also do not exhibit adhesion on their surfaces, to particles of markedly finer size, as it can be the case of the result of grinding, where the fine particles created by grinding can be added to larger particles. . However, it should be noted that the powder constituting the product of the invention may have simply been deagglomerated.

The compounds, according to the first embodiment, can, of course, exhibit particle size characteristics that have been supplied precisely in the foregoing, in combination with the characteristics of the residual oxygen content. Similarly, those of the second embodiment may also exhibit, in combination with the particle size characteristics, the oxygen content of the compounds of the first embodiment. All the additional features that will be given now apply to both modalities. According to a preferred alternative form of the invention, the compound exhibits a narrow particle size distribution. Thus, the index of dispersion is not greater than 0.7, it may be particularly not greater than 0.6.

The dispersion index is understood to mean the ratio: s / m = (de4 - d16) / 2d50 where: ~ d84 is the diameter of the particles for which 84% of the particles have a diameter below d84; dis is the diameter of the particles for which 16% of particles have a diameter below d50 is the average diameter of the particles.

The compounds of the invention can be comprised of particles with a substantially spherical configuration, for which the diameter corresponds to the average sizes given above. Other characteristics of the compounds of the invention are that they are provided in the form of a pure crystallographic phase, it is possible to show this purity by the X-ray diffraction spectra of the compounds. In the specific case of strontium thiogalate, this crystallographic phase is a cubic phase. The process for the preparation of the compounds of the invention will now be described. The first stage of the process is to form a solution or suspension comprising the salts of the elements A and B and, optionally, the pollutant element. The use is generally made of inorganic salts, such as nitrates, sulfates or -chlorides or alternatively hydroxides. The use can, optionally, of organic salts, but it is preferable, in this case, to use salts that exhibit few carbon atoms, such as carbonates or acetates. The salts are placed in a liquid medium, preferably water, in order to form a solution or a suspension. The next step consists in drying the prepared solution or suspension. This drying is carried out by atomization. - Spray drying is understood to mean the spray drying of the mixture in a hot atmosphere (spray drying). The atomization can be carried out by means of any known atomizer per se, for example, a sprinkler nozzle of shower head or another type. It is also possible to use the so-called rotary atomizers. Special reference can be made to the various spray techniques. capable of being used in the present process, to the standard work by Masters entitled "Drying by Spraying" (second edition, 1976, published by George Godwin, London). It should be noted that it is also possible to carry out the atomization / drying operation by means of an "instant" reactor, for example of the type developed by the applicant company and described especially in the French patent applications Nos. 2,257,326, 2, 4197754 and 2,431,321. In this case, the treated gases (hot gases) are driven with a helical movement and flow in a vortex weir. The mixture to be dried is injected along the "path that joins the axis of symmetry of the helical trajectories of the gases, which makes possible the complete transfer of the amount of movement of the gases to the mixture The gases, in fact, provide thus a double function: on the one hand, the spraying, that is, the conversion of the initial mixture into fine droplets and, on the other hand, the drying of the obtained droplets. , the extremely low residence time (usually less than about 1/10 of a second) of the particles in the reactor it has the advantage, among others, of limiting the possible risks of overheating, as a result of an excessively prolonged contact with the gases. With respect to the instantaneous reactor, mentioned above, reference can be made, in particular, to Figure 1 of French Patent Application 2,431,321. This instantaneous reactor "consists of a combustion chamber and a contact chamber composed of a cone junction body or a truncated cone, the upper part of which diverges.The combustion chamber emerges inside the contact chamber through via a reduced passage The upper part of the combustion chamber is equipped with an opening, which allows the introduction of the fuel phase, and the combustion chamber includes an internal coaxial cylinder, thus defining the inside of the combustion chamber , a central annular region and an annular peripheral region, exhibiting _ perforations mainly placed towards the upper part of the device.The chamber comprises at least six perforations distributed over at least one circle, but preferably on several circles, which are axially spaced. The total surface area of the perforations, located in the lower part of the chamber, can be very low, in the order of 1/10 to 1/100 of the total surface area of the perforations of the internal coaxial cylinder. The perforations are usually circular and are very thin. Preferably, the ratio of the diameter of the latter to the thickness of the wall is not less than 5, the minimum thickness of the wall being limited only by mechanical constraints. Finally, an angled tube emerges within the reduced passage, the end of which opens within the axis of the central region. The gaseous phase driven with a helical movement (subsequently known as the helical phase) is composed of a gas, generally air, introduced into it. of a hole made in the annular region, this orifice is preferably placed in the lower part of the region. In order to obtain a helical phase in the reduced passage, the gas phase is introduced preferably at low pressure within the aforementioned orifice, that is to say at a pressure below 1 bar and more particularly at a pressure between 0.2 and 0.5 bar above the pressure existing in the contact chamber. The speed of this helical phase is generally between 10 and 100 m / s and preferably between 30 and 60 m / s. Likewise, a fuel phase, which can, in particular, be methane, is injected axially via the aforementioned opening, into the central region at a speed of approximately 100 to 250 m / s.

The forced passage of the gases within the reduced passage takes place subsequently, according to an arrangement of trajectories coinciding with the families of the hyperboloid generators. These generators are based on a family of circles, of rings that are small = in size, located near and below the reduced passage, before divergence in all directions. The mixture, which is to be treated, is then introduced in liquid form by means of the aforementioned tube. The liquid is then divided into a multitude of drops, each of which is transported by a volume of gas and subject to a movement that creates a centrifugal effect. He The flow rate of the liquid is usually between 0.03 and 10 m / s. The ratio of the amount of specific movement to the helical phase to that of the liquid mixture must be high. In particular, it is not less than 100 and preferably is between 1000 and 10,000. The amounts of movement within the reduced passage are calculated as a function of the regimes of the inflow of gas and of the mixture to be treated, and of the cross section of the passage. An increase in the flow regimes results in an enlargement in the size of the drops. Under these conditions, the specific movement to gases is imposed in its direction and its intensity in the drops of the mixture to be treated, which have been separated from each other in the convergence region of the two currents. Also, the speed of the liquid mixture is reduced to the minimum necessary to obtain a continuous flow. The atomization generally takes place with a solid exit temperature between 90 and 150 ° C.

The final stage of the process consists of the sulfuration of the product obtained in the conclusion of the drying. This sulfiding is carried out by reacting the product obtained in the preceding step with carbon disulfide, hydrogen sulfide or with a mixture of hydrogen sulfide and carbon disulfide. The sulfiding reaction is carried out at a temperature between 600 and 1000 ° C, preferably around SOO ^ C. In the case of a mixture of hydrogen sulphide and carbon disulfide, the respective proportions of CS2 and H2S can vary within wide proportions. The flow rate of the sulfur gas (CS2, HaS or CS3 and H2S) is usually selected so that the amount of CS3 or H2S injected into the system during the reaction, ie between the start of the temperature rise (starting at thermal cycle) and the end of the stationary phase at high temperature, is enough to convert all the precursor into sulfur. A molar ratio ([sulfur gas] / [A] + [B]) greater than 4 generally makes it possible to meet this requirement.

The sulfur gas can be used with an inert gas, such as argon or nitrogen. The duration of the reaction corresponds to the time necessary to obtain the desired sulfide. At the conclusion of the heating, the formed sulfur is recovered. Additional alternative forms of the compound, according to the invention, will now be described. In the case of these alternative forms, all the characteristics of the compound that have already been described will also apply. According to a first of these alternative forms, the compound is provided in the form of a powder, which particles comprise a layer based on at least one transparent oxide. This layer covering the particles may not be perfectly continuous or homogeneous. However, preferably the particles, which constitute the compound, according to this alternative form, comprise a transparent oxide coating layer, which is uniform and of a controlled thickness. The transparent oxide is understood means, in this case, an oxide which, once deposited on the particle, in the form of a more or less fine film, only absorbs light rays in the visible region in a very small extension or nothing. Furthermore, it should be noted that the term "oxide", which is used for convenience through the present description, refers to this alternative form, and it should be understood that it also covers the oxides of the hydrated type. These oxides, or hydrated oxides, can be amorphous and / or crystalline. Mention may be made more particularly, as examples of such oxides, to silicon oxide (silica), aluminum oxide (alumina), zirconium oxide (zirconia), titanium oxide, zirconium silicate, ZrSI0 (zircon) and oxides of rare earth metals. According to a preferred alternative form, the coating layer is based on silica. More advantageously still, this layer is essentially and preferably composed of only silica The process for the preparation of a transparent oxide compound, according to this alternative form, consists essentially in bringing the starting compound into contact with the oxide precursor transparent, as mentioned above, and to precipitate the transparent oxide.

"Starting compound" is understood to mean the compound obtained by following the process of preparation and sulfidation, described above, and after optional deagglomeration. Examples of processes will be given below for the various types of transparent oxides. In the case of silica, mention may be made of the preparation of the silica by hydrolysis of an alkyl silicate, forming a reaction mixture by mixing water, alcohol, the compound, which is then suspended and, optionally, a base , an alkali metal fluoride or an ammonium fluoride, which can act as a catalyst for the condensation of the silicates. The alkyl silicate is then introduced. A preparation can also be carried out by reaction of the compound, of a silicate, of the type of alkali metal silicate, and of an acid. In the case of a layer based on alumina, the compound, an aluminate and an acid can be reacted, whereby the alumina precipitates. This precipitation can also be obtained by bringing together and reacting the compound, an aluminum salt and a base.

Finally, alumina can be formed by hydrolysis of an aluminum alcdxide. With respect to titanium oxide, it can be precipitated by introducing, within the aqueous / alcoholic suspension of the compound, a titanium salt, "such as TiCl 4, TiOCl 3 or TiOS 0, on the one hand, and" one kiss, on the other. It is also possible to carry out the preparation, for example, by hydrolysis of an alkyl titanate or precipitation of a titanium sol. Finally, in the case of a layer based on zirconium oxide, it is possible to carry out the preparation by cohydrolysis or coprecipitation of a suspension of the compound, in the presence of an organometallic zirconium compound, for example a zirconium alkoxide, such as zirconium isopropoxide. According to another alternative form, the compound of the invention is provided in the form of a powder, the particles of which comprise a zinc compound deposited on its surfaces. This zinc compound may have been obtained by the reaction of a zinc precursor with the ammonia and / or an ammonium salt. The form under which this zinc compound is provided in the product ofthe invention is not known exactly. However, - in some cases, it can be thought that zinc is present in the form of a zinc-ammonia complex, of the formula: "Zn (NH3) X (A) y, in which A represents an anion, such as OH ", Cl-, the acetate anion or, alternatively, a mixture of anions, x is not greater than 4 and is 2. The zinc-containing compound can be obtained by bringing the starting compound into contact with a precursor of zinc and ammonia and / or an ammonium salt. This contacting operation makes it possible to precipitate the zinc compound on particles constituting the starting compound. The zinc precursor can be a zinc oxide or a zinc hydroxide, which is used in suspension. This precursor can also be a zinc salt, preferably a soluble salt. This may be a salt of an inorganic acid, such as a chloride, or, alternatively, a salt of an organic acid, such as an acetate. Of course, the invention also refers to the combination of alternative forms, which have just been described. Thus, it is possible to consider a compound, whose particles comprise a "layer of oxide with, in addition, zinc." In particular, zinc can be included in the oxide layer or located on the surface of the latter. "Several processes for the preparation of the compounds can be considered. , whose particles comprise zinc with an oxide layer. In a first case, the starting compound, a zinc precursor, ammonia and / or an ammonium salt, and a precursor of the transparent oxide, are brought into contact, then the zinc compound is deposited on the starting composition and the transparent oxide is precipitated on the starting compound, otherwise, in a first step, the starting compound and a precursor of a transparent oxide are brought into contact and this transparent oxide is precipitated on the starting compound and then, in a second step, the compound, thus obtained, is brought into contact with a zinc precursor and ammonia and / or an ammonium salt, and this zinc compound is deposited According to another process, "the compound, the precursor of zinc, ammonia and / or ammonium salt and, if If appropriate, the precursor of the transparent oxide is contacted in the presence of n alcohol. This used alcohol is generally selected from aliphatic alcohols, such as, for example, butanol or ethanol. The alcohol can, in particular, be introduced with the zinc precursor in the form of an alcoholic solution of zinc. According to still another type of process, the compound, the zinc precursor, the ammonia and / or the ammonium salt and, if appropriate, the transparent oxide precursor, are contacted in the presence of a dispersant. This purpose of this dispersant is to prevent the agglomeration of the particles of the compound, when they are suspended for the previously described treatments. It is also possible to operate in more concentrated mixtures. Also promote the formation of a homogeneous layer of transparent oxide in all particles. This dispersant can be selected from the group of dispersants, which disperse by a steric effect and in particular by non-ionic polymers, soluble in water or soluble in organic substances, mention can be made, as the dispersant, of cellulose and its constituents. derivatives, polyacrylamides, polyethylene oxides, polyethylene glycols, polyoxyethylenated polypropylene glycols, polyacrylates, polyoxyethylenated alkylphenols, polyoxyethylenated long chain alcohols, polyvinyl alcohols, alkanolamides, dispersants of the polyvinylpyrrolidone type or compounds based on xanthan gum. Furthermore, it can be noted that it would be advantageous to treat the suspension obtained from the mixture of the reactants with ultrasound. Finally, the product obtained at the end of the operations, described above, can be washed with water or alcohol. It can also be dried in the air or, alternatively, under vacuum. It should be noted, for the additional alternative forms, that they have been justly described, ie the compounds in which the particles comprise a transparent oxide and / or a zinc compound, on their surface, than the residual oxygen contents, given above. , will still apply to the general compound (particles + transparent oxide and / or zinc compound) but to the starting compound, ie the particles without the transparent oxide or the zinc compound. As a result of their properties, the compounds, described above or as obtained by the processes that have been justly studied, can be used as luminiferous agents, in particular in cathodoluminescence, that is to say in applications involving excitations of the electronic type. They can thus be used in the manufacture of any device that operates under this principle, such as the flat screen FED or VFD, projection screens or television screens. The use of the compounds of the invention in this type of devices takes place in accordance with well-known techniques, "for example by depositing on screens by sedimentation, screen printing or electrophoresis." Finally, the invention is applied to the aforementioned devices, which they employ the catodoluminescence and comprise a compound according to the invention, and respective examples will be given below.

In these examples, the size of the particles was measured according to the aforementioned technique. Furthermore, it is specified that the measurement was carried out in a dispersion of the product in 0.05% by weight of an aqueous solution of sodium hexametaphosphate, which has been submitted in advance to the treatment with an ultrasonic probe (probe with a tip with diameter of 13 mm, 20 kHz, 120) for 3 minutes. The coordinates of a chromaticity are given in the system as defined by the Commission Internationale d'Eclairage (International Lighting Commission) and listed in the Recueil des Normes Fran? Aises [Compendium of French Standards] (APNOR), colorimetric color No X08-12 (1983). The oxygen content was determined by the analysis with "a Leco® device.

E-lemplo 1: Synthesis of Sr0.ssCeo.o? Nao.o?) Ga2S4 A mixture of nitrates "of cerium (III), gallium, strontium and sodium, in the proportions corresponding to those of the desired compound, was atomized with a Büchi® device, the inlet temperature is 210 ° C, while the outlet temperature is 110 ° C. The presence The sodium in the material allows the excess load due to the substitution of the cerium for a fraction of the strontium, to be compensated. 10 g of the powder obtained were placed in a crystalline carbon tundish (bed thickness of 1 cm), which is then introduced into a leak-proof sulfur oven. The gaseous reaction mixture consists of argon (50% by volume), CS2 (30%) and H2S (20%). The flow rate of the gas mixture is 10 1 / h. The thermal cycle is as follows: elevation at 8 ° C / min from ambient temperature to 800 ° C, then a stationary phase of 30 minutes at 800 ° C, under a mixture of H2 s / cs2 and then a drop of 8 ° C / min under argdn, at a temperature of 60 ° C, in which the oven can be opened and the product collected. The product is supplied in the form of a pure phase powder, with a cubic crystallographic structure. The average particle size is 4 μm. The dispersion index is 0.6. The oxygen content of the product is 1.1%.

Strontium thiogalate with cerium and sodium impurities exhibited an intense luminence in the blue color, when placed under a UV excitation (254 nm) or under electronic excitation.

EXAMPLE 2: Synthesis of (Sro.95Euo.05) Ga2S4 The same experimental procedure was followed for the synthesis of this compound. The highly reducing medium- makes it possible to include the europium with oxidation number two, directly at the strontium site.The product is provided in the form of a physically pure powder with a cubic crystallographic structure, whose X-ray spectrum is given in Figure 1. The average particle size is 3.3 μm, the dispersion index is 0.66, the oxygen content of the product is 1.1%, the strontium thiogalate with impurities of europium, luminesce in the green, when Place under excitation of UV light (254 mm) or under electronic excitation.

EXAMPLE 3 This example relates to the application in the low-voltage luminescence of the compounds of Examples 1 and 2. The products were deposited by screen printing on a transparent substrate with a loading level of 1 mg / cm 2. The efficacy of the thiogalate with cerium impurities of Example 1, under the low voltage electronic excitation (V = 400 v) was studied as a function of the current density. In the range of current densities studied (100 to 500 μA / mm *), no variation was observed in the response of the luminifer, which is 1.0 lm / W. This is a high efficiency, taking into account the low level of loading of the products in the substrate. The colorimetric coordinates are suitable for the production of a blue luminifer: x = 0.124 and y = 0.131. Under the same excitation conditions, the luminous efficiency of the product of Example 2, with europium impurities, is 6 lm / W and the green emission was characterized by the following colorimetric coordinates: x = 0.25 and y = 0.71.

EXAMPLE 4 This example relates to the preparation of a compound, according to the invention, "comprising a layer of zinc oxide and silica." Strontium thiogalate with impurities of 5% europium -of Example 2, was used as the Starting compound The treatment of the oxide layer deposit is as follows: Polyvinylpyrrolidone (PVP) was dissolved in the ethanol The strontium thiogalate was added to this solution The suspension obtained was dispersed using ultrasound, and the ammonia solution and then the zinc precursor were subsequently added in. The ethyl silicate was introduced continuously in two hours.After the introduction * of the ethyl silicate, maturation was carried out for two hours. obtained, washed with ethanol by filtration and then dried at 50 ° C for twelve hours.The reagents were used in the following proportions: _7__ SrGa2S4 200 Ethanol (95%) 643 Ammonia (32%) 100 Zinc oxide 20 Ethyl silicate 32 PVP 10 (Company Aldrich) 5 Molecular Weight = 10000 - An encapsulated product was obtained by a mixed layer of silica / zinc.

EXAMPLE 5 This example relates to the preparation of a compound according to the invention, comprising a layer of silica. The same starting compound was used as in Example 4, and the preparation was carried out in the same manner, but without using a zinc precursor. The reagents were used in the following proportions: g / kg SrGa2S4 200 Ethanol (95%) 663 Ammonia (32%) 100 Ethyl silicate 32 - PVP KIO (Aldrich Company) 5 Molecular Weight = 10000 A product encapsulated by a silica layer was obtained.

Claims (21)

1. CLAIMS 1. A compound of the formula AB ^, in which A represents one or more alkaline earth metals and B represents at least one element selected from aluminum, gallium and indium, characterized in that it is in the form of a powder, with a Residual oxygen content not greater than-1.5%, more particularly not greater than 1%.;
2. 2. A compound, according to the claim 1, characterized in that it is in the form of a compound in unmilled particle powder, with an average size not greater than 10 μm. ! '
3. 3. A compound of the formula AB2S4, in which A i represents one or more alkaline earth metals and B is at 'less an element taken from the group comprising aluminum, gallium or indium, characterized in that it is provided in the form of a powder, composed of whole or unground particles, with an average size not exceeding 10 μm. !
4. 4. A compound, according to the claim 3, characterized in that it has a residual oxygen content of not more than 1.5%, more particularly not greater! from 1%.
5. 5. A compound, according to any of the preceding claims, characterized in that it comprises at least one contamination element, which confers luminescence properties on said compound.
6. 6. A compound, according to any of the preceding claims, characterized in that the particles have an average size no greater than 5 μm.
7. 7. A compound, according to any of the preceding claims, characterized in that the particles have a substantially spherical configuration.
8. 8. A compound, according to any of the preceding claims, characterized in that the particles have a dispersion index, s / m not greater than 0.7.
9. 9. A compound, according to any of the preceding claims, characterized in that it has a pure crystallographic phase.
10. 10. A compound, according to any of the preceding claims, characterized in that B is gallium.
11. 11. A compound, according to any of the preceding claims, characterized in that A is strontium.
12. 12. A compound, according to any of claims 10 and 11, characterized in that it has a pure cubic crystallographic phase.
13. 13. A compound according to any of claims 5 to 11, characterized in that the pollution element is selected from the divalent manganese, divalent rare earth metals and the group comprising the trivalent rare earth metals, combined with a metal alkaline, this pollution element being more particularly europium (II), ytterbium, in combination with an alkali metal.
14. 14. A compound according to any of the preceding claims, characterized in that the particles comprise a layer based on at least one transparent oxide.
15. 15. A compound, according to any of the preceding claims, characterized in that it is in the form of a powder, the particles of which comprise a zinc compound on its surface
16. 16. A compound, according to claim 15, characterized in that the compound Zinc has been obtained by the reaction of a zinc precursor with ammonia or an ammonium salt
17. 17. Process for the preparation of a compound, according to one of claims 1 to 13, characterized in that it comprises: a solution or suspension, which includes salts of elements A and B and, optionally, a contamination element; "dry the solution or suspension by means of atomization; • react the product obtained, in the preceding stage, with carbon disulfide, hydrogen sulfide or with a mixture of hydrogen sulfide and carbon disulfide.
18. 18. The process according to claim 17, characterized in that the reaction with the gas mixture is carried out at a temperature of 600 to 1000 ° C
19. 19. The process, according to claims 17 or 18, characterized in that the nitrates are used as the salts.
20. 20. The use of a compound, according to any of claims 1 to 16, as a luminiferous, in particular in the cataodoluminescence.
21. 21. Device employing cathode-luminescence, characterized in that it comprises a compound according to any of claims 1 to 16.