An annealing method for improving the quality of Li2Ga2GeS6 crystals

Abstract

The present application relates to the technical field of post-treatment of growth of mid-infrared nonlinear optical chalcogenide crystals, and provides an annealing method for improving the quality of Li2Ga2GeS6 crystals. The Li2Ga2GeS6 crystals and a buffer source of the same component are physically separated and encapsulated in a sealed container for annealing. In the annealing process, the buffer source can release Li, Ga, Ge and S gas phase components, establish a multi-component intrinsic atmosphere matching the LGGS crystal, simultaneously adjust the component deviation related to the sulfur vacancy, interstitial sulfur and Li / Ga / Ge anti-site defects, stabilize the chemical potential of all components in the system, realize the homogenization of the components in the crystal, and release the thermal stress introduced by the crystal growth, so as to effectively improve the crystal quality. The annealing method has a wide application range, a wide process window, and is convenient for large-scale implementation in a multi-temperature zone tube furnace, and has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of post-growth processing technology for mid-infrared nonlinear optical chalcogenide crystals, and particularly to an annealing method for improving the quality of Li2Ga2GeS6 crystals. Background Technology

[0002] Nonlinear optical crystals are core functional materials for achieving infrared laser frequency conversion, and have significant application value in fields such as infrared detection, environmental monitoring, optoelectronic countermeasures, and laser medicine. Li₂Ga₂GeS₆ (LGGS) crystal is a non-centrosymmetric orthorhombic sulfide mid-infrared nonlinear optical crystal. This crystal possesses a wide infrared transmission spectrum, a large band gap, a high second-order nonlinear optical coefficient, and excellent resistance to laser damage. It is highly suitable for mid-infrared frequency doubling, difference frequency generation, optical parametric oscillation, and optical parametric amplification under near-infrared laser pumping conditions, making it a highly promising candidate crystal material for medium- and high-power mid-infrared laser frequency conversion devices.

[0003] Currently, LGGS crystals are typically grown using the Bridgman process in a sealed system. During crystal growth and subsequent cooling, components such as lithium and sulfur within the system tend to volatilize at high temperatures; simultaneously, the temperature gradient during growth introduces significant thermal stress within the crystal. These factors combined lead to the formation of various defects within the crystal, including sulfur vacancies, Li / Ga / Ge antisite defects, dislocations, microcracks, compositional segregation, and heterogeneous micro-inclusions. These defects increase scattering loss, thermally induced birefringence, and decrease the laser damage threshold, severely limiting the practical performance of LGGS crystals in medium- and high-power laser frequency conversion devices.

[0004] Annealing is a common post-processing technique for repairing crystal growth defects and improving the optical quality of crystals. However, in LGGS crystals, Li, Ga, and Ge are all prone to volatilization and loss at high temperatures, and current annealing methods are unable to stabilize the chemical potential of all components, thus failing to effectively improve crystal quality. Summary of the Invention

[0005] In view of this, the present invention provides an annealing method for improving the quality of Li2Ga2GeS6 crystals. The present invention physically separates the Li2Ga2GeS6 crystal and a Li2Ga2GeS6 homogeneous composition buffer source and encapsulates them in a sealed container for annealing. This reduces crystal defects through composition homogenization, improves crystal transmittance, optical uniformity, processing integrity, and laser operating stability, effectively improving crystal quality.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: An annealing method for improving the quality of Li2Ga2GeS6 crystals includes the following steps: The Li2Ga2GeS6 crystal is placed in a first container, and the first container containing the Li2Ga2GeS6 crystal is placed in a second container. A homogeneous buffer source of the Li2Ga2GeS6 crystal is added between the outer wall of the first container and the inner wall of the second container. The second container is then sealed and annealed. The annealing temperature is 650~800℃ and the holding time is 70~150h.

[0007] Preferably, before placing the Li2Ga2GeS6 crystal in the first container, the process further includes cleaning the Li2Ga2GeS6 crystal and then purging it with an inert gas.

[0008] Preferably, the first container is made of corundum and the second container is made of quartz; the inner wall of the second container is provided with a pyrolysis carbon layer.

[0009] Preferably, the first container is a corundum crucible, and the second container is a quartz ampoule; the inner diameter of the second container is 16~50mm, and the wall thickness is 1~3mm.

[0010] Preferably, the homogeneous component buffer source is a polycrystalline material of Li2Ga2GeS6, or a mixture of Li2S, GeS2 and Ga2S3; the molar ratio of Li2S, GeS2 and Ga2S3 in the mixture is 1:(2~4):1.

[0011] Preferably, the mass of the homogeneous component buffer source is 0.5 to 2 times the mass of the Li2Ga2GeS6 crystal.

[0012] Preferably, the annealing is performed under vacuum conditions.

[0013] Preferably, the annealing procedure is as follows: first, the temperature is increased to 100-150℃ at a rate of 20-40℃ / h and held for 2-6 hours; then, the temperature is increased to 350-450℃ at a rate of 20-40℃ / h and held for 2-8 hours; subsequently, the temperature is increased to 650-800℃ at a rate of 10-30℃ / h and held for 70-150 hours.

[0014] Preferably, after annealing, the annealed crystal is further cooled; the cooling procedure is as follows: cooling to 80-150°C at a rate of 2-30°C / h, and then cooling to room temperature with the furnace.

[0015] Preferably, the Li2Ga2GeS6 crystal is a grown ingot, a directionally cut crystal block, or an optical wafer that has been ground and polished.

[0016] This invention provides an annealing method for improving the quality of Li2Ga2GeS6 crystals, comprising the following steps: A Li₂Ga₂GeS₆ crystal is placed in a first container, and the first container containing the Li₂Ga₂GeS₆ crystal is placed in a second container. A homogeneous buffer source of the Li₂Ga₂GeS₆ crystal is added between the outer wall of the first container and the inner wall of the second container. The second container is then sealed and annealed. The annealing temperature is 650~800℃, and the holding time is 70~150h. In this invention, the Li₂Ga₂GeS₆ crystal and the homogeneous buffer source are physically separated and encapsulated in a sealed container for annealing. During the annealing process, the buffer source can release the gaseous components of Li, Ga, Ge, and S, establishing a multi-component intrinsic atmosphere that matches the LGGS crystal. This can simultaneously adjust the component deviations related to sulfur vacancies, interstitial sulfur, and Li / Ga / Ge antisite defects, stabilize the chemical potential of all components in the system, achieve component homogenization inside the crystal, and release the thermal stress introduced by crystal growth. The annealing method of this invention can be used to process various forms of Li2Ga2GeS6 crystals, including ingots, ingots, and polished optical wafers. It can effectively reduce scattering loss within the crystal, improve the crystal's transmittance and optical uniformity, enhance the integrity of crystal processing, and improve the stability of the crystal during laser operation. Furthermore, the annealing parameters of this invention are lower than the melting point of Li2Ga2GeS6 crystals, providing a wide process window and facilitating scale-up implementation in multi-temperature zone tube furnaces.

[0017] Furthermore, by isolating the crystal with a carbon layer on the inner wall of the container, physically partitioning the crystal and the buffer source, and using a low-water-oxygen loading operation, the present invention can reduce the reaction of lithium sulfides with quartz and oxygen contamination, while preventing the crystal from coming into contact with external moisture, thus preventing hydrolysis, deliquescence and deterioration of the crystal, and further ensuring the quality of the crystal. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the loading method of Li2Ga2GeS6 crystal and homogeneous composition buffer source, where 1-second container, 2-fractured carbon layer, 3-first container, 4-Li2Ga2GeS6 crystal, and 5-homogeneous composition buffer source. Figure 2 The Raman spectra of the wafer before and after annealing in Example 2; Figure 3 The fluorescence spectra of the wafer before and after annealing in Example 2; Figure 4 The ultraviolet-visible transmission spectra of the wafer before and after annealing in Example 2; Figure 5 The ultraviolet-visible transmission spectra of the wafers before and after annealing in Comparative Examples 1 and 2 are shown. Detailed Implementation

[0019] In this invention, "homogeneous component buffer source" refers to a solid material that can provide gaseous components of Li, Ga, Ge and S related to the composition of LGGS to a closed system at the annealing temperature and buffer the chemical potential of each component near the crystal surface; "physical separation" means that there is no solid contact between the crystal and the buffer source, but the space where the two are located is kept gaseous through the internal cavity of the container.

[0020] This invention provides an annealing method for improving the quality of Li2Ga2GeS6 crystals, comprising the following steps: The Li2Ga2GeS6 crystal is placed in a first container, and the first container containing the Li2Ga2GeS6 crystal is placed in a second container. A homogeneous buffer source of the Li2Ga2GeS6 crystal is added between the outer wall of the first container and the inner wall of the second container. The second container is then sealed and annealed. The annealing temperature is 650~800℃ and the holding time is 70~150h.

[0021] In this invention, the Li2Ga2GeS6 crystal can be a grown ingot, a directionally cut crystal block, or an optical wafer that has been ground and polished.

[0022] In this invention, before placing the Li2Ga2GeS6 crystal in the first container, the process further includes: cleaning the Li2Ga2GeS6 crystal and then purging it with an inert gas; the inert gas is preferably argon; the cleaning specifically involves using a dust-free wiping material to remove surface particles; in a specific embodiment of this invention, after argon purging, the crystal is preferably transferred to a glove box for pre-drying. In this invention, operations such as weighing raw materials, loading, and unsealing after annealing are all performed in an anhydrous and oxygen-free glove box to minimize the deliquescence of the LGGS crystal; the water content in the glove box is no higher than 0.01 ppm, and the oxygen content is no higher than 0.01 ppm.

[0023] In this invention, the material of the first container is preferably corundum; in a specific embodiment of this invention, the first container is preferably a corundum crucible; the corundum crucible is preferably baked at 100~200℃ for 2~6 h before use, and then stored in a glove box after cooling.

[0024] In this invention, the material of the second container is preferably quartz; the inner wall of the second container is preferably provided with a cracked carbon layer. The continuous cracked carbon layer on the inner wall of the second container can reduce the reaction and oxygen pollution caused by direct contact between lithium sulfides and quartz; the cracked carbon layer on the inner wall of the second container is preferably prepared by acetone cracking method; the specific conditions of the acetone cracking method are not particularly required, and those well known to those skilled in the art can be used; the inner diameter of the second container is preferably 16~50mm, specifically 20, 30 or 40mm, and the wall thickness is preferably 1~3mm, specifically 1, 2 or 3mm; the outer diameter of the first container is smaller than the inner diameter of the second container; in a specific embodiment of this invention, the second container is preferably a quartz ampoule.

[0025] In this invention, the homogeneous component buffer source is preferably Li2Ga2GeS6 polycrystalline material, or a mixture of Li2S, GeS2 and Ga2S3; the molar ratio of Li2S, GeS2 and Ga2S3 in the mixture is preferably 1:(2~4):1, specifically 1:2:1, 1:3:1 or 1:4:1; in a specific embodiment of this invention, when Li2Ga2GeS6 polycrystalline material is used as the homogeneous component buffer source, it is preferable to crush the polycrystalline material into particles of 0.2~3mm and pre-dry it.

[0026] In this invention, the mass of the homogeneous component buffer source is preferably 0.5 to 2 times the mass of the Li2Ga2GeS6 crystal, specifically 0.5, 1, 1.5 or 2 times; the total volume of the homogeneous component buffer source is preferably no more than one-third of the effective inner cavity volume of the second container.

[0027] In this invention, the loading method of the Li2Ga2GeS6 crystal and the homogeneous composition buffer source is as follows: Figure 1 As shown, this invention physically separates a Li₂Ga₂GeS₆ crystal and a homogeneous buffer source within a sealed container. The Li₂Ga₂GeS₆ crystal and the homogeneous buffer source are isolated by a first container, allowing the gaseous components to diffuse while preventing solid particles from contacting the crystal. Annealing under these physically separated conditions ensures that the Li, Ga, Ge, and S gaseous components released by the buffer source at high temperatures can diffuse freely within the sealed container, regulating the chemical potential of each component and achieving component homogenization within the crystal. Furthermore, it avoids direct contact between the crystal and the solid particles of the buffer source, preventing contamination of the crystal surface and ensuring the surface integrity and optical quality of the crystal after annealing.

[0028] In this invention, the annealing is preferably performed under vacuum conditions; in a specific embodiment of this invention, after the loading is completed, the second container is preferably evacuated and backfilled with high-purity argon in the glove box transition chamber in sequence, repeated 2-3 times, and then evacuated to 1×10 using an oxyhydrogen flame.-3 The pressure is below 100 Pa and then melt-sealed. After melting and sealing, check the continuity of the seal and the appearance of the container. After confirming that there are no cracks, proceed with annealing.

[0029] In this invention, the annealing temperature is preferably 650~800℃, specifically 650℃, 700℃, 750℃ or 800℃, and the holding time is preferably 70~150h, specifically 70, 80, 100, 120, 130 or 140h; specifically, the annealing procedure is preferably as follows: first, the temperature is increased to 100~150℃ (specifically 120℃, 130℃ or 140℃) at a rate of 20~40℃ / h (specifically 20, 30 or 40℃ / h) and held for 2~6h (specifically 4 or 5h); then, the temperature is increased to 350~450℃ (specifically 380℃, 400℃ or 420℃) at a rate of 20~40℃ / h (specifically 20, 30 or 40℃ / h) and held for 2~8h. The annealing process, performed under the above conditions, can establish equilibrium vapor partial pressures containing Li, Ga, Ge, and S components in a closed system, promoting component homogenization, point defect migration, and thermal stress release within the crystal, while suppressing non-stoichiometric volatilization of each component during annealing.

[0030] In this invention, the annealing can be performed in a programmable box furnace or a multi-zone tube annealing furnace.

[0031] In this invention, after annealing, the annealed crystal is further cooled. The preferred cooling procedure is to cool to 80-150°C at a rate of 2-30°C / h, followed by furnace cooling to room temperature. In a specific embodiment of this invention, it is preferable to first cool to 400-500°C (specifically 400°C or 450°C) at a rate of 2-5°C / h (specifically 10°C / h), then cool to 80-150°C (specifically 120°C), and finally furnace cooling to room temperature. In a specific embodiment of this invention, for ingots with a diameter greater than 15 mm or crystal blocks with a length greater than 20 mm, the cooling rate within the 650-500°C range is preferably no higher than 3°C / h to reduce thermal stress caused by the temperature gradient.

[0032] After cooling, the container is preferably transferred to a glove box for unsealing to observe the crystal surface. The annealed crystal is then stored in a dry, inert atmosphere-sealed container until subsequent cutting, grinding, polishing, or optical performance testing.

[0033] In a specific embodiment of the present invention, ultraviolet-visible-near-infrared transmission spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction rocking curves, and fluorescence spectroscopy tests can be performed on the crystals before and after annealing to compare the changes in crystal properties and thus evaluate the effect of annealing. Based on the above test results, the most suitable annealing temperature, holding time, and buffer source and other process parameters can be determined comprehensively.

[0034] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0035] In the following examples, the same sample, the same thickness, and the same measurement position were used to compare the results before and after annealing. The specific test items included at least the following two items: (1) Appearance and scattering inspection: Observe the distribution of scattering points, streaks, cracks and residual stress inside the crystal under visible light transmission, side illumination and orthogonal polarization conditions.

[0036] (2) Transmission spectrum: The transmittance in the range of 0.35~1.5 μm was measured by a UV-Vis-NIR spectrophotometer, and the transmittance in the range of 1.5~16 μm was measured by a Fourier transform infrared spectrometer.

[0037] (3) Raman spectroscopy: Measured at 50~500 cm under the same laser power, integration time and polarization conditions. -1 Raman spectra of the range were compared, including baseline, characteristic peak positions, peak intensity ratios, and full width at half maximum (FWHM).

[0038] (4) Crystal integrity: Select the same crystal plane and the same diffraction peak to measure the full width at half maximum (FWHM) of the high-resolution X-ray rocking curve.

[0039] (5) Component homogeneity: Energy dispersive spectroscopy (EDS) or electron probe microanalysis was performed at multiple locations along the crystal axis and radial direction to compare the relative content fluctuations of the main elements other than Li, Ga, Ge, and S; if necessary, secondary ion mass spectrometry (DIMS) or inductively coupled plasma mass spectrometry (ICP-MS) was used for auxiliary analysis of Li content. No relevant test results were available. (6) Photoluminescence and laser stability: Compare fluorescence spectra at the same excitation wavelength and temperature; for samples used in laser devices, damage threshold or stability tests before and after annealing can be performed using a 1.064 μm pulsed laser with the same spot size, pulse width and repetition frequency.

[0040] In the following embodiments, Li2Ga2GeS6 is referred to as LGGS.

[0041] Example 1: Annealing of a 0.5mm thick polished LGGS wafer The LGGS wafer to be tested was polished on both sides, and the wafer mass was recorded as m. Surface particles were removed using a dust-free wiping material, and the wafer was then purged with dry argon gas. Afterward, the wafer was transferred to a glove box (with water and oxygen content not exceeding 0.01 ppm) for pre-drying for 4 hours. 0.5 m of LGGS polycrystalline material with a particle size of 0.5–2 mm was used as a homogeneous composition buffer source.

[0042] In a quartz ampoule with a cracked carbon layer on the inner wall, the wafer is vertically inserted into a corundum crucible; a buffer source is uniformly placed between the corundum crucible and the quartz ampoule.

[0043] The quartz ampoule underwent three cycles of vacuuming and argon backfilling, ultimately reaching a vacuum level of 1×10⁻⁶. -3 The quartz ampoule was placed in an annealing furnace and heated to 120°C at a rate of 30°C / h and held for 4 hours. The temperature was then increased to 400°C at a rate of 30°C / h and held for 4 hours. Subsequently, the temperature was increased to 650°C at a rate of 20°C / h and held for 70 hours. After the holding period, the temperature was decreased to 400°C at a rate of 5°C / h, then decreased to 120°C at a rate of 10°C / h, and finally cooled to room temperature in the furnace.

[0044] The quartz ampoule was unsealed inside the glove box, and the wafer was placed in a dry, sealed container.

[0045] Example 2: Annealing of a 1.0mm thick polished LGGS wafer The LGGS wafer to be tested was polished on both sides, and the wafer mass was recorded as m. Surface particles were removed using a dust-free wiping material, and the wafer was then purged with dry argon gas. Afterward, the wafer was transferred to a glove box (with water and oxygen content not exceeding 0.01 ppm) for pre-drying for 4 hours. 0.5 m of LGGS polycrystalline material with a particle size of 0.5–2 mm was used as a homogeneous composition buffer source.

[0046] In a quartz ampoule with a cracked carbon layer on the inner wall, a wafer is vertically inserted into an alumina crucible; a homogeneous buffer source is uniformly packed between the alumina crucible and the quartz ampoule.

[0047] The quartz ampoule underwent three cycles of vacuuming and argon backfilling, ultimately reaching a vacuum level of 1×10⁻⁶. -3 The ampoule was heated to below Pa and then sealed. It was placed in an annealing furnace, heated to 120°C at 30°C / h and held for 4 hours, then heated to 400°C at 30°C / h and held for 4 hours, followed by heating to 750°C at 20°C / h and holding for 100 hours. After the holding period, the temperature was lowered to 400°C at 5°C / h, then lowered to 120°C at 10°C / h, and then cooled to room temperature in the furnace.

[0048] The quartz ampoule was unsealed inside the glove box, and the wafer was placed in a dry, sealed container.

[0049] Example 3: Annealing of a 2.0mm thick polished LGGS wafer The LGGS wafer to be tested was polished on both sides, and the wafer mass was recorded as m. Surface particles were removed using a dust-free wiping material, and the wafer was purged with dry argon gas. The wafer was then transferred to a glove box (with water and oxygen content not exceeding 0.01 ppm) for pre-drying for 4 hours. 0.5 m of LGGS polycrystalline material with a particle size of 0.5–2 mm was used as a homogeneous composition buffer source.

[0050] In a quartz ampoule with a cracked carbon layer on the inner wall, the wafer is vertically inserted into a corundum crucible; a buffer source is evenly packed between the corundum crucible and the quartz ampoule.

[0051] The quartz ampoule underwent three cycles of vacuuming and argon backfilling, ultimately reaching a vacuum level of 1×10⁻⁶. -3 The ampoule was heated to below Pa and then sealed. It was placed in an annealing furnace, heated to 120°C at 30°C / h and held for 4 hours, then heated to 400°C at 30°C / h and held for 4 hours, followed by heating to 800°C at 20°C / h and holding for 150 hours. After the holding period, the temperature was lowered to 400°C at 5°C / h, then lowered to 120°C at 10°C / h, and then cooled to room temperature in the furnace.

[0052] The quartz ampoule was unsealed inside the glove box, and the wafer was placed in a dry, sealed container.

[0053] Comparative Example 1: Vacuum annealing without a homogeneous buffer source An LGGS wafer with the same position, size, and thickness as that in Example 2 was selected. No homogeneous component buffer source was placed, and the remaining assembly, vacuuming, heating, holding, and cooling conditions were the same as in Example 2. This sample was used to evaluate the volatilization of crystal components and defect changes under a closed vacuum environment, and the results were compared with the annealing results of Example 2.

[0054] Comparative Example 2: Annealing using only a single sulfur source An LGGS wafer with the same position, size, and thickness as that in Example 2 was selected. Elemental sulfur was used as the sole atmosphere source, without adding a homogeneous buffer source containing Li, Ga, and Ge. The remaining assembly, vacuuming, heating, holding, and cooling conditions were the same as in Example 2. This sample was used to evaluate the volatilization of crystal components and defect changes under a sealed vacuum environment, and the results were compared with the annealing results of Example 2.

[0055] Test Example 1 The Raman spectrum, fluorescence spectrum, and UV-Vis transmission spectrum of the wafer in Example 2 before and after annealing were tested using the aforementioned method. The test results are as follows: Figures 2-4 As shown.

[0056] Figure 2The images show the Raman spectra of the wafer before and after annealing in Example 2. According to... Figure 2 It can be seen that the peak positions of the characteristic Raman peaks of the crystal remain basically consistent before and after annealing, and the main crystal lattice remains stable. After annealing, the relative intensity of each characteristic peak is improved as a whole, and the half-width of the characteristic peak is narrowed, indicating that after annealing, the point defects inside the crystal are significantly reduced and the crystal integrity is improved.

[0057] Figure 3 The fluorescence spectra of the wafer before and after annealing in Example 2 are shown. According to... Figure 3 It can be seen that after annealing, the peak position of the crystal fluorescence peak shifts slightly to blue, the fluorescence peak intensity is significantly increased, and the tailing emission in the long-wavelength direction is significantly weakened. This indicates that the annealing treatment effectively reduces the internal defect centers of the crystal, suppresses defect-related intrinsic emission, increases the proportion of intrinsic emission of the crystal, and significantly improves the crystal quality.

[0058] Figure 4 The image shows the UV-Vis transmission spectra of the wafer before and after annealing in Example 2. According to... Figure 4 It can be seen that the transmittance of the crystal after annealing is significantly higher than that before annealing in the entire test wavelength range, and the transmittance in the long wavelength region is particularly significantly improved. This indicates that annealing effectively reduces the light scattering loss caused by internal defects in the crystal, and the optical transmittance performance of the crystal is significantly improved.

[0059] Following the same method, the Raman spectrum, fluorescence spectrum, and UV-Vis transmission spectrum of the wafers in Examples 1 and 3 before and after annealing were tested. The results were similar to those in Example 2, showing that the quality of the crystals was significantly improved after annealing.

[0060] The surface of the wafers after annealing in Examples 1-3 was inspected, and the results showed that there were no deposits or corrosion spots. This indicates that the loading and annealing process of the present invention can effectively prevent crystals from being contaminated or corroded, and can well protect the surface quality of the crystals.

[0061] The UV-Vis transmission spectra of the wafers in Comparative Examples 1 and 2 before and after annealing were tested and compared with the UV-Vis transmission spectra of Example 2. The results are as follows. Figure 5 As shown. Figure 5 In Comparative Example 1, vacuum annealing without a homogeneous component buffer source was used; in Comparative Example 2, annealing with a single sulfur source was used; and in Example 2, annealing with a homogeneous component buffer source was used. Figure 5It can be seen that, compared with the un-annealed sample, the transmittance of the vacuum-annealed sample without a buffer source in Comparative Example 1 only increased slightly; the transmittance of the sample annealed with a single sulfur source in Comparative Example 2 increased to a greater extent than that in Comparative Example 1, but the increase was still small; while the sample annealed with the homogeneous component buffer source of this invention showed the most significant increase in transmittance across the entire test wavelength range. This comparative result indicates that simple vacuum annealing easily causes the volatilization of multiple components in the crystal, and annealing with only a single sulfur source can only control the chemical potential of sulfur, unable to simultaneously stabilize the Li, Ga, and Ge components, resulting in limited defect repair capabilities; the homogeneous component buffer source annealing of this invention can establish a multi-component balanced atmosphere, minimizing internal scattering loss in the crystal and significantly improving the optical transmittance of the crystal.

[0062] The dimensions, mass, heating and cooling rates, and holding times listed in the above embodiments can be adjusted proportionally or adaptively according to the crystal size, initial defect state, ampoule volume, and furnace temperature field. As long as an LGGS homogeneous component buffer source that is physically separated from the crystal but gas-connected to it is used, and the LGGS crystal is annealed at a high temperature below its melting point under low water and oxygen closed conditions, and controlled slow cooling is adopted, all of these are implementation methods of the present invention.

[0063] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An annealing method for improving the quality of Li2Ga2GeS6 crystals, characterized in that, Includes the following steps: The Li2Ga2GeS6 crystal is placed in a first container, and the first container containing the Li2Ga2GeS6 crystal is placed in a second container. A homogeneous buffer source of the Li2Ga2GeS6 crystal is added between the outer wall of the first container and the inner wall of the second container. The second container is then sealed and annealed. The annealing temperature is 650~800℃ and the holding time is 70~150h.

2. The annealing method according to claim 1, characterized in that, Before placing the Li2Ga2GeS6 crystal in the first container, the process further includes cleaning the Li2Ga2GeS6 crystal and then purging it with inert gas.

3. The annealing method according to claim 1, characterized in that, The first container is made of corundum, and the second container is made of quartz; the inner wall of the second container is provided with a layer of cracked carbon.

4. The annealing method according to claim 1 or 3, characterized in that, The first container is a corundum crucible, and the second container is a quartz ampoule; the inner diameter of the second container is 16~50mm, and the wall thickness is 1~3mm.

5. The annealing method according to claim 1, characterized in that, The homogeneous component buffer source is a polycrystalline material of Li2Ga2GeS6, or a mixture of Li2S, GeS2 and Ga2S3; the molar ratio of Li2S, GeS2 and Ga2S3 in the mixture is 1:(2~4):

1.

6. The annealing method according to claim 1, characterized in that, The mass of the homogeneous component buffer source is 0.5 to 2 times the mass of the Li2Ga2GeS6 crystal.

7. The annealing method according to claim 1, characterized in that, The annealing is performed under vacuum conditions.

8. The annealing method according to claim 1, characterized in that, The annealing procedure is as follows: first, heat the temperature to 100-150℃ at a rate of 20-40℃ / h and hold for 2-6 h; then heat the temperature to 350-450℃ at a rate of 20-40℃ / h and hold for 2-8 h; subsequently, heat the temperature to 650-800℃ at a rate of 10-30℃ / h and hold for 70-150 h.

9. The annealing method according to claim 1, characterized in that, After annealing, the annealed crystal is cooled. The cooling process is as follows: cooling to 80-150°C at a rate of 2-30°C / h, and then cooling to room temperature with the furnace.

10. The annealing method according to claim 1, characterized in that, The Li2Ga2GeS6 crystal can be a grown ingot, a directionally cut crystal block, or an optical wafer that has been ground and polished.

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