WO2018097350A1 - TRIPLE-DOPED POLYCRYSTALLINE TRANSPARENT UPCONVERTING α-SIALON CERAMICS AND METHOD FOR PREPARING SAME - Google Patents

Abstract

The present invention relates to transparent α-SiAlON ceramics tri-doped with erbium, thulium, and holmium and a method for preparing the same. The ceramics are characterized in that upconversion occurs at at least one wavelength of 657 nm, 679 nm, and 805 nm when the ceramics are irradiated with light of 980 nm at room temperature. The observed hardness and fracture toughness of sintered α-SiAlON ceramics are higher than those of other commercial optically active polycrystalline transparent ceramics including YAG and Y₂O₃.

Description

Triple Doped Polycrystalline Translucent Upconverting Alphasialon Ceramics and Manufacturing Method Thereof

The present invention relates to alpha sialon ceramics having a translucent and upconverting property in a triple-doped visible region and an infrared region in which erbium, holmium and thulium are formed, and a method of manufacturing the same.

In the development of high-power laser diodes and short wavelength-emitting solid state lasers, upconversion light emission of erbium ion doped materials has attracted attention. Up with erbium ions (Er ^{3 +)} - conversion process has been shown to play an important role host material. Various host materials have been studied so far, for example, glass, polycrystalline powders, single crystals, thin films, nano-crystals and translucent ceramics have been investigated. C. Liu, J. Heo, Local Heating from Silver Nanoparticles and Its Effect on the Er ^{3 +} Upconversion in Oxyfluoride Glasses, J. Amer. Ceram. Soc., 93 (2010) 3349-53 and Y. Kishi, S. Tanabe, S. Tochino, G. Pezzotti, Fabrication and Efficient Infrared-to-Visible Upconversion in Transparent Glass Ceramics of Er-Yb Co-Doped CaF ₂ Nano -Crystals, J. Amer. Ceram. Soc., 88 (2005) 3423-26.

Most up-conversion materials are based on oxides and oxy-fluoride glasses. However, these materials exhibit poor chemical stability and mechanical properties and are therefore limited in their many applications. To overcome this problem of glass up-conversion materials, translucent polycrystalline ceramics have been introduced as up-conversion materials. Lanthanide-doped yttria and YAG materials exhibit up-conversion properties that can collect light in the infrared region that covers most of the solar spectrum and convert it to high energy wavelengths, which can be applied to solar cell windows. -Can also be applied to displays [see: S. Chen, Y. Wu, New opportunities for transparent Ceramics, Amer. Ceram. Soc. Bull., 92 (2013) 32-7 and T.R. Hinklin, S.C. Rand, R.M. Laine, Transparent, Polycrystalline Upconverting Nanoceramics: Towards 3-D Displays, Advanced Materials, 20 (2008) 1270-3].

On the other hand, sialon, a silicon nitride present with alumina, refers to a system associated with a silicon-aluminum-oxygen-nitrogen phase. The sialon ceramic material is different from silicon nitride because aluminum and oxygen are included in the crystal structure. Ceramic products made of sialon exhibit high strength even at high temperatures and have high hardness suitable for industrial applications. In particular, sialon has superior hardness to alumina at high temperatures. In addition to the aluminum and oxygen introduced into the structure, compounds such as yttria and magnesia are typically added to aid in sintering. During sintering, these compounds react with silica on the silicon nitride surface, intentionally added silica, or with silica present as an impurity.

These additional elements greatly increase the complexity of the phase relationships affecting the sialon material, thus making it more difficult to process the sialon material to achieve the desired properties. It is known that the phase chemistry of the sialon intergranular phase is more complex than that of silicon nitride ceramic systems. See F. Riley, J. Amer. Ceram. Soc. 83 [2] (2000) 259]. Almost completely densified sialon ceramics can be obtained at lower grain boundaries by the insertion of metal cations into the silicon nitride lattice. According to numerous documents and patents, intergranular phases are known to degrade the properties of ceramics because they generally lead to high temperature degradation and reduced strength. See U.S. Pat. No. 5,413,972 to Hwang et al; D. Dressler & R Riedel, Int. J. Refractory Metals & Hard Materials 15 (1997), pg. 13-47 especially pg. 23; and D. A. Bonnel et al., J. Amer. Ceram. Soc. 70 (1987), pg. 460].

The best known crystalline phases in the sialon family are the alpha and beta phases, which are based on the alpha and beta phases of silicon nitride. On sialon, some of the silicon and nitrogen atoms are replaced by aluminum and oxygen atoms.

The betasialon phase is generally represented by the formula Si _{6 - z} Al _z O _z N _{8 -z} , where 0 <z <4.2. In this structure, no additional metal ions are included in the crystal lattice.

The alpha sialon phase is generally represented by the formula Mx (Si, Al) ₁₂ (O, N) ₁₆ where x is 0 <x <2, M is an element such as Mg, Y, Ce, Sc, or other rare earth materials. Indicates. More specifically, stoichiometrically M _{m / v} Si _12-mn Al _{m + n} O _n N _16-n [GZ Cao and R. Metselaar, "α'-Sialon Ceramics: A Review", Chem. Mat. Vol. 3 No 2, 242-252 (1991), where v is the balance of M. Two formulas are used interchangeably in the present invention. Suitable M ions in this structure are not suitable in beta sialon structures.

Traditionally, alpha sialon represents equiaxed crystal grains in the microstructure of ceramics and is therefore used as a high strength material. The equiaxed microstructure has better light transmittance and higher intensity.

Many papers and patents, however, address the general problem of deterioration between grain boundaries of ceramics, which generally leads to high temperature degradation and a decrease in strength. U.S. Pat. No. 5,413,972 to Hwang et al; D. Dressler & R Riedel, Int. J. Refractory Metals & Hard Materials 15 (1997), pg. 13-47 especially pg. 23; and D. A. Bonnel et al., J. Amer. Ceram. Soc. 70 (1987), pg. 460). The alpha phase can accommodate other metal oxides, but the beta phase is not so that the alpha phase is an important phase for reducing the grain boundaries of the phase.

SUMMARY OF THE INVENTION An object of the present invention is to provide a triple doped sialon ceramic body having high temperature stability and strength while having excellent light transmission and upconversion light emission characteristics in the infrared region and the visible region. It is yet another object of the present invention to provide a method of making triple doped translucent sialon ceramics having upconversion properties.

In order to achieve the above object, the present invention is a ceramic molded body, (Ho, Tm, Er) _x Si _{12 -m- n} Al _{m + n} O _n N _{16 -n} (0 <x <2, 1.0 <m <1.5 And an alpha sialon crystal structure represented by 1.0 <n <1.5).

The weight ratio of Ho, Tm and Er may range from Ho: Tm: Er = 1: 1: 5 to 5: 5: 1.

The ceramic molded body is, Si _{6 -} can further include a _z Al _z O _z N _{8 -z} oxynitride glass phase structure of beta-SiAlON represented by (0 <z <4.2).

When the ceramic molded body is irradiated with light of 980 nm at room temperature, upconversion may occur at a wavelength of at least one of 560 nm, 657 nm, 679 nm, and 805 nm.

When the ceramic molded body is irradiated with light of 980 nm at room temperature, upconversion may occur at at least two wavelengths of 560 nm, 657 nm, 679 nm, and 805 nm.

When the ceramic molded body projects light of 980 nm at room temperature, downconversion may occur at a wavelength of 1530 nm.

The ceramic molded body may have an energy transfer efficiency of 96.4% or more at a wavelength of 1530 nm.

As another method for achieving the above object, the method for producing a ceramic molded body of the present invention, alpha-silicon nitride, Er ₂ O ₃ , Al ₂ O ₃ , Tm ₂ O ₃ , Ho ₂ O ₃ And mixing AlN powder to prepare a mixed powder, compressing the mixed powder to prepare a compact, and compressing the compact into a nitrogen atmosphere at a temperature of 1700 to 1900 ° C. at a pressure of 25 to 30 MPa. Firing; _Wherein , (Ho, Tm, Er) _x Si _{12 -mn} Al _{m + n} O _n N _16-n (0 <x <2, 1.0 <m <1.5, and 1.0 <n <1.5) It is achieved as a method of producing triple doped polycrystalline light transmissive alpha sialon ceramic shaped bodies comprising the indicated alpha sialon crystal structure.

The weight ratio of Ho, Tm and Er may range from Ho: Tm: Er = 1: 1: 5 to 5: 5: 1.

The ceramic molded body may have a thickness of 200 μm to 500 μm.

FIELD OF THE INVENTION The present invention relates to transparent alpha sialon ceramics doped with erbium, holmium and thulium, wherein the observed hardness and fracture toughness of the sintered alpha sialon ceramics are YAG, Y ₂ O ₃ and other commercial optically active polycrystalline light transmissive ones. Higher than ceramics.

In particular, it exhibits light transmittance and strong upconversion characteristics in the visible and infrared regions, and its energy transfer efficiency is also higher than that of the conventional single-doped or co-doped samples. Expected through triple doped alpha sialon with holmium and thulium.

1 is a graph showing an XRD pattern according to an embodiment of the present invention.

Figure 2 shows the HRTEM micrograph and SAD pattern according to an embodiment of the present invention.

3 is a graph showing an upconversion emission spectrum according to an embodiment of the present invention.

4 is a photograph for showing light transmittance of a sample according to an embodiment of the present invention.

5 is a graph showing an upconversion emission spectrum according to an embodiment of the present invention.

6 is a graph illustrating a downconversion emission spectrum according to an embodiment of the present invention.

7 is a graph showing an absorption spectrum according to an embodiment of the present invention.

8 is a graph showing radiation attenuation according to an embodiment of the present invention.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

The accompanying drawings are only examples as illustrated in order to explain the technical idea of the present invention in more detail, and thus the spirit of the present invention is not limited to the accompanying drawings.

Although sialon ceramics are well known as structural engineering materials, they are not well known for their optical properties. The inventors of the present invention have developed sialon ceramics different from the existing ones, which are naturally translucent and exhibit upconversion emission characteristics. Translucent sialon ceramics are produced under controlled composition and sintering conditions. The inventors have confirmed that the alpha sialon ceramics are stabilized with metal cations and manufactured alpha sialon ceramics stabilized with erbium cations.

Erbium is known to exhibit upconversion in a number of host materials, ie Y ₂ O ₃ , YAG and other oxide ceramic nanopowders. Alpha sialon has a unique crystal structure, which is suitable for metal ions in a unit cell and has two lattice positions to stabilize the structure. In the present invention, the erbium cation was doped at this lattice position and the physical and optical properties were studied.

In the present invention, erbium, holmium, and thulium were co-doped in triple, and the upconversion emission characteristics thereof were studied.

As shown in FIG. 1, the crystal phase was confirmed by XRD pattern analysis. The main crystalline phase was represented by alpha sialon and included small amounts of beta sialon, AlN polytype, and vitrified intergranular phases. Nevertheless, the sialon ceramics produced in the present invention are preferably considered as alpha sialon ceramics.

Through observation of the XRD pattern and the microstructure, it can be seen that the ceramic molded body may be represented by the following chemical formula.

(Ho, Tm, Er) _x Si _12-mn Al _{m + n} O _n N _16-n

Here, x, m and n are in the range of 0 <x <2, 1.0 <m <1.5 and 1.0 <n <1.5. (Ho, Tm, Er) includes all three cationic elements, and a small amount of other elements may be added during the manufacturing process or for other reasons. The weight ratio of Ho, Tm and Er is preferably in the range of Ho: Tm: Er = 1: 1: 5 to 5: 5: 1. In the present invention, Ho and Tm are doped at the same weight ratio, and the relative weight of Er Although the experiment was carried out in the form of adjusting the weight ratio, the scope of the present invention is not limited thereto, and even if the weight ratio of Ho and Tm is different, it is expected to exhibit similar characteristics. If the weight ratio of Er to Ho and Tm was larger or smaller than this, the upconversion characteristics by triple doping of erbium, holmium and thulium were not observed. It exhibited similar property values as one alpha sialon. Changes in the composition of sialon ceramics are basically designed based on the values of m and n, where m and n are SN bonds due to the combination of (Al-N) and (Al-O) in Si ₃ N ₄ . Each corresponds to a level to be replaced.

In Table 1 below, a sample was prepared using the sum of the weight ratios of erbium, holmium and thulium when m = n = 1.1 as Ho + Tm + Er = 11 wt%. T3), erbium-only sample (E3), holmium-only sample (H3), holmium-erbium co-doped sample (HE5), and thulium and erbium-doped sample (TE5) were also prepared and characterized. Was compared. In the present invention, m and n are each limited to the range of 1.0 to 1.5, but when m or n is less than 1.0, the upconversion characteristics are drastically reduced. In addition, as shown in FIG. 4, the transmittance in the visible light range was found between m and n of 1.0 to 1.5 based on the Tm, but the visible light transmittance of the m or n range of 2.0 was found to be close to zero. In the present invention, the visible light transmittance is an important characteristic, through which it was confirmed that m and n is preferably in the range 1.0 ~ 1.5.

Due to the nature of sialon, beta sialon may be partially produced at the interface of alpha sialon, and the chemical formula is as follows:

Si _6-z Al _z O _z N _8-z (0 <z <4.2)

Table 1 Erbium, holmium, and thulium concentrations in each sample code and each sample Sample code Holmium concentration (wt%) Erbium concentration (wt%) Thulium Concentration (wt%) H3 11.0 0.0 0.0 T3 0.0 0.0 11.0 E3 0.0 11.0 0.0 HE5 1.78 8.92 0.0 TE5 0.0 9.08 1.82 HTE55 1.78 7.13 1.78 HTE75 2.68 5.35 2.68 HTE11 3.57 3.57 3.57

The method for preparing the alpha sialon ceramic molded body co-doped with the erbium, holmium and thulium of the present invention is as follows:

a) alpha-silicon nitride, Er ₂ O ₃ , Al ₂ O ₃ , Tm ₂ O ₃ , Ho ₂ O ₃ And mixing the AlN powder to prepare a mixed powder;

b) compressing the mixed powder to produce a compacted product;

c) calcining the compacted body in a nitrogen atmosphere, at a temperature of 1700 to 1900 ° C. and a pressure of 25 to 30 MPa in a hot press method;

d) The step of cooling to room temperature after holding for 2 hours in the temperature range of 1700 ~ 1900 ℃.

In the above production method, the weight ratios of erbium, holmium and thulium were 1.78 to 7.13 wt%, respectively, and the sum of the erbium, holmium and thulium concentrations was approximately 11 wt%. The approximate meaning here is that it is difficult to fit 11 wt% mathematically, so that some errors may occur experimentally. As shown in Table 1, the weight ratio of thulium and erbium in the present invention was able to confirm the light conversion upconversion characteristics in the range of Ho: Tm: Er = 1: 1: 5 to 5: 5: 1. In addition, it is preferable that the thickness of the manufactured molded article is in the range of 200 to 500 μm. However, when the thickness of the molded product is made thinner than 200 μm, no suitable strength is obtained. Samples in the present invention used that made to a thickness of 200 μm. If the molded body is not in the temperature range and pressure range presented in step c), the permeability is low, or the strength is difficult to apply the application.

As shown in FIG. 2, microscopic observation using HRTEM confirmed that the crystal grains were similar to the existing alpha sialon. Thus, the alpha sialon of the present invention is a crystal structure stabilized by erbium, holmium and thulium ions. In addition, it can be seen from FIG. 2 that all samples are composed of isometric, isotropic polyhedral grains, which are general alpha sialon grain shapes. This grain shape allows for better optical light transmission. Translucent ceramics are required for various applications due to their excellent mechanical properties.

The luminescent properties of the translucent ceramics allow the material to be used in various applications. Luminescent ceramics are also known as phosphors. Such phosphorescent light-transmitting ceramics are light-transmissive in the visible light spectrum because these materials absorb different wavelengths of visible light at the emission center. In the case of sialon ceramics having a hexagonal structure, most of the light is scattered through grain boundaries. When the grain size is adjusted to 500 nm or less, it shows partial light transmittance in the visible region. However, the sialon ceramics produced in the present invention showed much higher light transmittance in the infrared region. The light transmittance varies with thickness, and the thinner it is, the higher the light transmittance in the visible region. Figure 4 is a photograph showing the light transmittance for a 500 μm thick HTE55 sample. As shown in FIG. 4, it was confirmed that the visible light transmittance was excellent.

The wavelength range of 200 to 2500 nm for the thulium-doped sample (T3), the erbium-doped sample (E3), the holmium-doped sample (H3), and the erbium, holmium and thulium triple-doped sample (HTE55). Absorption spectrum is shown in FIG. In the absorption spectra of the thorium-doped sample (T3) and the holmium-only sample (H3), no absorption band around 980 nm was observed. Therefore, traditional 980 nm pumping cannot be used for thulium doped alpha sialon or holmium doped alpha sialon. However, triple doped samples of erbium, holmium and thulium (HTE55) indicate that the co-doped samples can be excited by a 980 nm laser. In addition, several pairs of absorption bands can be observed in the visible region (approximately 400-700 nm), allowing for up-converted luminescence with erbium, holmium, and thulium through triple-doped alpha-sialon.

The light spectrum excited to the 980 nm laser at room temperature for each sample is shown in FIG. 5. 5 is an upconversion spectrum, and FIG. 6 is a downconversion spectrum. The only thulium doped only one sample (T3) and a holmium-doped sample (H3) did not show up-conversion emission, since there is ^{3 +} Ho and Tm ^{3 +} can be excited at 980nm. Erbium-doped sample (E3) showed strong green light, weak red light and infrared light emission. In FIG. 5B, a frequency downconversion band was observed around 1530 nm, and this downconversion can be applied to a near infrared communication window.

The emission spectra changed significantly in the triple doped samples of erbium, holmium and thulium (HTE55, HTE75, HTE11). In the triple doped samples strong red light emission appeared around 657 nm and 679 nm, while strong infrared light emission was around 805 nm.

In order to check and compare the upconversion performance of each sample in the present invention, the energy transfer efficiency was calculated using the emission lifetime at 1530 nm wavelength, and the respective values were compared, and the contents thereof are shown in Table 2 below. The light emission lifetime? Is obtained using a radiation attenuation curve generated during downconversion. 8 shows the radiation attenuation curve of downconversion occurring at 1530 nm.

The light emission life is calculated by Equation 1 below using a radiation attenuation curve.

Equation 1

Here, A, B ₁ , B ₂ , and B ₃ represent the amplitudes of the respective attenuation elements, and τ ₁ , τ ₂ , and τ ₃ represent the light emission lifetimes of the respective attenuation elements.

The energy transfer efficiency is related to the light emission life and is calculated by Equation 2 below.

Equation 2

Here, η is energy transfer efficiency, and τ _f and τ ₀ are light emission lifetimes with and without acceptor ions.

TABLE 2 Luminescence Life and Energy Transfer Efficiency of Each Sample Sample code Luminous Life Energy transfer efficiency (η) τ ₁ (㎲) τ ₂ (㎲) E3 2570 ± 10 - - HE5 731 ± 20 - 71.6% TE5 865 ± 31 - 66.3% HTE55 92.1 ± 0.7 224 ± 7 96.4%

Emission life in the Table 2 above, (τ _1, τ ₂₎ is a value calculated through equation (1) using the radiation attenuation curve of Figure 8, by using this, we calculated the energy transfer efficiency from the following expression (2). Based on the value of E3, the value of τ ₁ for the case of acceptor ion for Er is represented by τ _f in Equation 2. Where τ _{1 of} E3 becomes τ _o of Equation 2 and τ ₁ of the remaining samples is τ _f Becomes

In the energy transfer efficiency calculated through Equation 2 from the measured light emission lifetime, the HTE55 had an energy transfer efficiency of 96.4%. This is a significant improvement over the energy transfer efficiency of 66.3% of the co-doped erbium and thorium (TE5) and 71.6% of the co-doped holmium and erbium (HE5). Can be predicted. In the conventional doped sample only Er element, the electrons move from the ground state to the excited state, and the light emission life is long because the residence time is long. However, when Tm and Ho are triple doped with Er, the energy of Er's electrons moves to Tm or Ho, which reduces the time that the excited electrons stay in the excited state. When co-doped, the light emission life is reduced, resulting in high energy transfer efficiency, thereby obtaining a high upconversion effect.

This triple dope of erbium, holmium and thulium with a combination of high visible and infrared light transmittance, excellent upconversion and downconversion luminescence properties, moderately low phonon energy and excellent mechanical and thermochemical stability is expected to serve a variety of applications in the future. Application is possible.

The above-described embodiments are examples for explaining the present invention, but the present invention is not limited thereto. Those skilled in the art to which the present invention pertains will be capable of carrying out the present invention by various modifications therefrom, and the technical protection scope of the present invention should be defined by the appended claims.

Claims (10)

As a ceramic molded body, An alpha sialon crystal structure represented by (Ho, Tm, Er) _x Si _12-mn Al _{m + n} O _n N _16-n (0 <x <2, 1.0 <m <1.5 and 1.0 <n <1.5) A triple doped polycrystalline light transmissive alpha sialon ceramic molded article comprising. In claim 1, The weight ratio of the Ho, Tm and Er is in the range of Ho: Tm: Er = 1: 1: 5 ~ 5: 5: 1, the doped polycrystalline light-transmitting alpha sialon ceramics molded body. In claim 1, The ceramic molded body, _{Si 6 - z Al z O z} N 8 -z (0 <z <4.2) between the oxynitride glass phase of beta sialon structure further comprises a triple doped characterized in that the light transmitting polycrystalline upconverts alpha sialon ceramics represented by Molded body. In claim 1, The ceramic molded body, A triple-doped polycrystalline light upconverting alpha sialon ceramic molded body characterized by upconversion occurring at a wavelength of at least one of 560 nm, 657 nm, 679 nm, and 805 nm when irradiated with light of 980 nm at room temperature. In claim 1, The ceramic molded body, A triple doped polycrystalline light transmissive alpha sialon ceramic molded body characterized by upconversion at at least two wavelengths of 560 nm, 657 nm, 679 nm, and 805 nm when irradiated with light of 980 nm at room temperature. In claim 1, The ceramic molded body, A triple doped polycrystalline light transmissive alpha sialon ceramic molded body characterized by downconversion occurring at a wavelength of 1530 nm when projecting light of 980 nm at room temperature. In claim 1, The ceramic molded body is a triple doped polycrystalline light transmissive alpha sialon ceramic molded body, characterized in that the energy transfer efficiency at 1530 nm wavelength of 96.4% or more. Alpha-silicon nitride, Er ₂ O ₃ , Al ₂ O ₃ , Tm ₂ O ₃ , Ho ₂ O ₃ And mixing the AlN powder to prepare a mixed powder; Compressing the mixed powder to produce a compacted body; Calcining the compacted body in a nitrogen atmosphere at a temperature of 1700 to 1900 ° C. and a pressure of 25 to 30 MPa in a hot press method; Including; Formula: (Ho, Tm, Er) _x Si _{12 -m- n} Al _{m + n} O _n N _{16 -n} (0 <x <2, 1.0 <m <1.5, and 1.0 <n <1.5) A method of making a triple doped polycrystalline light upconverting alpha sialon ceramic molded body comprising an alpha sialon crystal structure. In claim 8, The weight ratio of the Ho, Tm and Er is in the range of Ho: Tm: Er = 1: 1: 5 ~ 5: 5: 1, the method of producing a triple doped polycrystalline light transmissive alpha sialon ceramic molded body. In claim 8, The ceramic molded body, A method of manufacturing a triple doped polycrystalline light transmissive alpha sialon ceramic molded body, characterized in that the thickness is 200 to 500 μm.

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