Method for improving optical performance of BaGa4Se7 single crystal

Abstract

The invention discloses a method for improving the optical performance of a BaGa4Se7 single crystal, which comprises the following steps: raising the ambient temperature of the BaGa4Se7 single crystal to 300-1000 DEG C, and keeping the temperature for 5-60 days; and reducing the environment temperature to room temperature. According to the method, the BaGa4Se7 single crystal is subjected to component compensation, and the defect concentration in the BaGa4Se7 single crystal is reduced, so that the absorption coefficient is reduced, the optical quality of the BaGa4Se7 single crystal is improved, and the light scattering of the BaGa4Se7 single crystal is reduced.

Description

Technical Field

[0001] The present invention relates to the annealing field of barium gallium selenide single crystals. More specifically, it relates to a method for improving the optical properties of BaGa4Se7 single crystals. Background Art

[0002] Today, with the continuous development of military and civil applications, high-performance infrared nonlinear optical crystals play an increasingly important role. Currently, commercially available infrared nonlinear optical materials mainly include silver gallium sulfide (AgGaS2), silver gallium selenide (AgGaSe2), and zinc germanium phosphide (ZnGeP2). However, due to the low laser-induced damage threshold (LIDT) of AgGaQ2 (Q = S, Se), and the multi-photon absorption of ZnGeP2 for 1-2μm light sources, their applications are severely restricted. Therefore, people are committed to developing new materials to surpass existing commercial crystals. Barium gallium selenide (BaGa4Se7) crystal is a new type of infrared nonlinear optical crystal invented by Yao et al. in 2010. Compared with traditional commercial nonlinear optical crystals, BaGa4Se7 crystals have good comprehensive properties. Including a high laser-induced damage threshold (557MW / cm 2 , which is 3.6 times that of AgGaS2), a wide optical transmission range (0.47 - 18μm), and moderate birefringence (0.07). In addition, it can be pumped by a 1.064μm Nd:YAG commercial laser to generate widely tunable 3 - 5μm mid-infrared and 8 - 14μm long-wave infrared lasers. Therefore, BaGa4Se7 crystals can be regarded as a promising new type of infrared nonlinear optical crystal.

[0003] Currently, the vertical Bridgman technique (VB) and the horizontal gradient freeze technique (HFG) have been tried for growing large-sized BaGa4Se7 single crystals. The crystal grown by Yao et al. using the Bridgman technique in 2012 had a size of (diameter) × 30 (length) mm 3 , and in 2022, the size reached For a BaGa4Se7 device with a size of 10×10×15mm 3 , the absorption coefficient was 0.15cm -1 @10μm. P Schunemann et al. grew crystals without seeds by the horizontal gradient freeze technique in 2018, and the crystals had no scattering centers and retrograde solubility. However, the transmittance of a 2.3mm sample was lower than 60% throughout the transmission band, and the corresponding absorption coefficient was greater than 0.6cm -1 . The above data indicate that the quality of the grown crystals needs to be further improved.

[0004] During the crystal growth process, the high vapor pressure of selenium makes it easy to volatilize, resulting in incomplete system reactions, thus reducing the crystal quality and causing defects in the crystal. Therefore, optimizing the secondary annealing process for composition compensation, especially optimizing the annealing atmosphere, the quality of the annealed polycrystalline powder, adjusting the annealing temperature and holding time, is beneficial to reducing the thermal stress and existing defects in the crystal, as well as improving the optical quality of the crystal, thereby reducing the absorption coefficient and increasing the laser-induced damage threshold. Summary of the Invention

[0005] Based on the above facts, the object of the present invention is to provide a method for improving the optical properties of BaGa4Se7 single crystals. This method can well improve the quality of BaGa4Se7 single crystals, enhance their optical properties, and further reduce their absorption coefficient and increase the laser-induced damage threshold.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for improving the optical properties of BaGa4Se7 single crystals, comprising the following steps:

[0008] Raise the ambient temperature of the BaGa4Se7 single crystal to 300 - 1000 °C and hold at this temperature for 5 - 60 days;

[0009] Lower the ambient temperature to room temperature.

[0010] In this technical solution, no requirements are made for the source of the BaGa4Se7 single crystal. It can be a BaGa4Se7 single crystal prepared by various conventional methods such as the spontaneous crystallization method, the Bridgman - Stockbarger method, the horizontal gradient freezing technique, etc. Preferably, the BaGa4Se7 single crystal is a polished BaGa4Se7 single crystal.

[0011] In this technical solution, the ambient temperature refers to the temperature of the environment where the BaGa4Se7 single crystal is located. For example, when the BaGa4Se7 single crystal is placed in an annealing device, the ambient temperature at this time refers to the temperature of the BaGa4Se7 single crystal in the annealing device.

[0012] Furthermore, the temperature after heating is 500 - 1000 °C. In some specific examples, the temperature after heating includes but is not limited to 700 - 1000 °C, 750 - 950 °C, 750 - 820 °C, 820 - 950 °C, 750 °C, 820 °C, 950 °C, etc.

[0013] Furthermore, the heating rate is 30 - 60 °C / h. In some specific examples, the heating rate is 40 - 60 °C / h, 40 - 50 °C / h, 50 - 60 °C / h, 50 °C / h, etc.

[0014] In this technical solution, controlling the heating rate and the temperature after heating is beneficial to reducing the thermal stress generated in the BaGa4Se7 crystal and the existing defects, thereby improving its optical properties, reducing the absorption coefficient, and increasing the laser damage threshold. When the heating rate is higher than 60 °C / h, the temperature distribution inside the material will be uneven, which is likely to cause the concentration of thermal stress and the generation of stress cracks; when the heating rate is lower than 30 °C / h, the entire annealing process cycle will be prolonged, the efficiency will be reduced, and the energy consumption will increase; when the temperature after heating is higher than 1000 °C, the crystal will melt; when the temperature after heating is lower than 300 °C, the energy is too low to achieve component compensation and stress elimination in the crystal.

[0015] Furthermore, the cooling rate is 5-20 °C / h. In some specific examples, the cooling rate is 10-20 °C / h, 10-15 °C / h, 10 °C / h, etc.

[0016] In this technical solution, controlling the cooling rate and the temperature after cooling is beneficial to reducing the thermal stress generated in the BaGa4Se7 crystal and the existing defects, thereby improving its optical properties, further reducing the absorption coefficient, and increasing the laser damage threshold. When the cooling rate is higher than 20 °C / h, new thermal stress will be generated inside the crystal due to the too-fast cooling rate, making the annealing ineffective; when the cooling rate is lower than 5 °C / h, the entire annealing cycle will be prolonged, the efficiency will be reduced, and the energy consumption will increase. Furthermore, the method of cooling to room temperature is to naturally cool to room temperature after removing the heat source.

[0017] Furthermore, in this method, the BaGa4Se7 single crystal is in an annealing atmosphere, and the annealing atmosphere is selected from barium selenide atmosphere, barium gallium selenide atmosphere, gallium sesquiselenide atmosphere, selenium atmosphere, or vacuum condition. The annealing atmosphere can be flexibly selected according to the type of defects contained in the crystal.

[0018] It should be noted that in this method, during the entire process of heat preservation and cooling, the BaGa4Se7 single crystal is in the annealing atmosphere.

[0019] Furthermore, the annealing atmosphere is obtained by the volatilization of polycrystalline powders of barium selenide, barium gallium selenide, gallium sesquiselenide, or selenium. Under high-temperature conditions, the polycrystalline powders are volatilized into gases, which then enter the BaGa4Se7 single crystal to perform composition compensation on the single crystal.

[0020] Furthermore, the mass of the polycrystalline powder is 2%-10% of the mass of the BaGa4Se7 single crystal. When the mass of the polycrystalline powder is lower than 2% of the mass of the BaGa4Se7 single crystal, it is not sufficient to completely compensate for the defects; when the mass of the polycrystalline powder is higher than 10% of the mass of the BaGa4Se7 single crystal, it will cause additional doping defects.

[0021] Further, on the basis that the mass of the polycrystalline powder is 2%-10% of the mass of the BaGa4Se7 single crystal, the polycrystalline powder is preferably capable of completely covering the BaGa4Se7 single crystal.

[0022] Further, the method is carried out in an annealing device, and the structure of the annealing device includes:

[0023] A furnace chamber, a sleeve arranged in the furnace chamber, a glass crucible arranged in the sleeve for placing the BaGa4Se7 single crystal, and a glass stopper for sealing the glass crucible.

[0024] It can be understood that the ambient temperature of the BaGa4Se7 single crystal at this time refers to the temperature inside the furnace chamber of the annealing device.

[0025] The advantages of this annealing device include that the annealing powder and the crystal are in close contact, which is beneficial for component compensation, and the crucible used for annealing can be designed in any shape, and the annealing is not restricted by the crystal shape.

[0026] Further, the method includes the following steps:

[0027] Place the BaGa4Se7 single crystal and the polycrystalline powder of barium selenide, barium gallium selenide, gallium diselenide or selenium in a glass crucible, and seal the glass crucible with a glass stopper;

[0028] Heat the furnace chamber to 300-1000 °C and keep it at this temperature for 5-60 days;

[0029] Cool the furnace chamber to room temperature.

[0030] Even further, the method includes the following steps:

[0031] Further, the method includes the following steps:

[0032] Place the BaGa4Se7 single crystal and the polycrystalline powder of barium selenide, barium gallium selenide, gallium diselenide or selenium in a glass crucible, and seal the glass crucible with a glass stopper;

[0033] Heat the furnace chamber to 300-1000 °C at a rate of 30-60 °C / h and keep it at this temperature for 5-60 days;

[0034] Cool the furnace chamber to room temperature at a rate of 5-20 °C / h.

[0035] Further, the temperature after heating is 500-1000 °C.

[0036] The beneficial effects of the present invention are as follows:

[0037] The method for improving the optical properties of BaGa4Se7 single crystal in the present invention is the single-temperature-zone annealing method, which is beneficial to maintaining a constant temperature field, thereby better reducing crystal defects and improving the optical quality of the crystal. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The following further describes in detail the specific embodiments of the present invention with reference to the accompanying drawings.

[0039] Figure 1 The structural schematic diagram of an exemplary annealing device in the present invention is shown.

[0040] Figure 2 The transmission spectra of the BaGa4Se7 single crystal before and after treatment in Example 1 are shown.

[0041] Figure 3 The transmission spectra of the BaGa4Se7 single crystal before and after treatment in Example 2 are shown.

[0042] Figure 4 The transmission spectra of the BaGa4Se7 single crystal before and after treatment in Example 3 are shown.

[0043] Figure 5 The transmission spectra of the BaGa4Se7 single crystal before and after treatment in Example 4 are shown.

[0044] Figure 6 The morphology diagram of the BaGa4Se7 single crystal after treatment in Comparative Example 1 is shown. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0045] To more clearly illustrate the present invention, the following further describes the present invention with reference to preferred embodiments and the accompanying drawings. Similar components in the drawings are denoted by the same reference numerals. Those skilled in the art should understand that the content specifically described below is illustrative rather than restrictive, and should not be used to limit the protection scope of the present invention.

[0046] In this embodiment, the method for improving the optical properties of the BaGa4Se7 single crystal can be carried out in an annealing device as shown in Figure 1 The structure of the annealing device includes: a furnace chamber 1, a sleeve 2 arranged in the furnace chamber 1, a glass crucible 4 for placing the BaGa4Se7 single crystal arranged in the sleeve 2, and a glass stopper 3 for sealing the glass crucible 4.

[0047] In the specific operation process, the BaGa4Se7 single crystal 5 and the solid annealing atmosphere source 6 are both placed in the glass crucible 4.

[0048] In this method, the single-temperature-zone annealing method is adopted, which is beneficial to maintaining a constant temperature field; moreover, the glass crucible (preferably a quartz crucible) used for annealing can be designed in any shape, so the BaGa4Se7 single crystal does not have to be restricted by the shape during this process. More importantly, in this method, the annealing atmosphere to be used can also be adjusted according to the growth defects of the barium gallium selenide crystal, so as to maximize the annealing effect, improve the optical quality of the crystal, and reduce defects.

[0049] Example 1

[0050] A method for improving the optical properties of BaGa4Se7 single crystal includes the following steps:

[0051] 1) Place the polished BaGa4Se7 single crystal (before treatment) and BaSe polycrystalline powder accounting for 2 wt% of the mass of the BaGa4Se7 single crystal in the glass crucible of the annealing device;

[0052] 2) Heat the glass crucible to the temperature of 950 °C in the furnace of the annealing device at a rate of 50 °C / h, and anneal and hold at 950 °C for 20 days;

[0053] 3) After annealing, cool down to room temperature at a rate of 10 °C / h to obtain the product.

[0054] Characterize the optical quality of the BaGa4Se7 single crystal (after treatment) processed by the above method. Specifically, polish the BaGa4Se7 single crystal after the above treatment and conduct the test of the transmission spectrum. The results are as Figure 2 shown. It can be seen that, compared with the untreated BaGa4Se7 single crystal, the transmittance of the BaGa4Se7 single crystal processed by the above method at a wavelength of 4 microns has increased by 5%.

[0055] Example 2

[0056] A method for improving the optical properties of BaGa4Se7 single crystal includes the following steps:

[0057] 1) Place the polished BaGa4Se7 single crystal (before treatment) and BaGa4Se7 polycrystalline powder accounting for 2 wt% of the mass of the BaGa4Se7 single crystal in the glass crucible of the annealing device;

[0058] 2) Heat the glass crucible to the temperature of 750 °C in the furnace of the annealing device at a rate of 50 °C / h, and anneal and hold at 750 °C for 40 days;

[0059] 3) After annealing, cool down to room temperature at a rate of 10 °C / h to obtain the product.

[0060] Optical quality characterization was performed on the BaGa4Se7 single crystal (after treatment) processed by the above method. Specifically, the BaGa4Se7 single crystal after the above treatment was polished and the transmission spectrum was tested. The results are as Figure 3 shown. It can be seen that compared with the untreated BaGa4Se7 single crystal, the transmittance of the BaGa4Se7 single crystal processed by the above method at a wavelength of 4 μm has increased by 7%.

[0061] Example 3

[0062] A method for improving the optical properties of a BaGa4Se7 single crystal includes the following steps:

[0063] 1) Place the polished BaGa4Se7 single crystal (before treatment) and polycrystalline Ga2Se3 powder with a mass of 2 wt% of the BaGa4Se7 single crystal in a glass crucible of an annealing device;

[0064] 2) Heat the glass crucible at a rate of 50 °C / h to an annealing device furnace temperature of 950 °C and anneal and hold at 950 °C for 60 days;

[0065] 3) After annealing, cool to room temperature at a rate of 10 °C / h to obtain.

[0066] Optical quality characterization was performed on the BaGa4Se7 single crystal (after treatment) processed by the above method. Specifically, the BaGa4Se7 single crystal after the above treatment was polished and the transmission spectrum was tested. The results are as Figure 4 shown. It can be seen that compared with the untreated BaGa4Se7 single crystal, the transmittance of the BaGa4Se7 single crystal processed by the above method at a wavelength of 4 μm has increased by 6%.

[0067] Example 4

[0068] A method for improving the optical properties of a BaGa4Se7 single crystal includes the following steps:

[0069] 1) Place the polished BaGa4Se7 single crystal (before treatment) and polycrystalline Ga2Se3 powder that can completely submerge the BaGa4Se7 single crystal and has a content between 2 wt% and 10 wt% of the BaGa4Se7 single crystal mass in a glass crucible of an annealing device;

[0070] 2) Heat the glass crucible at a rate of 50 °C / h to an annealing device furnace temperature of 820 °C and anneal and hold at 820 °C for 30 days;

[0071] 3) After annealing, cool to room temperature at a rate of 10 °C / h to obtain.

[0072] Optical quality characterization was carried out on the BaGa4Se7 single crystal (after treatment) processed by the above method. Specifically, the BaGa4Se7 single crystal after the above treatment was polished and the transmission spectrum was measured. The results are as Figure 5 shown. It can be seen that, compared with the untreated BaGa4Se7 single crystal, the transmittance of the BaGa4Se7 single crystal processed by the above method at a wavelength of 4 microns increased by 12%.

[0073] Comparative Example 1

[0074] A method for improving the optical properties of BaGa4Se7 single crystal includes the following steps:

[0075] 1) Place the polished BaGa4Se7 single crystal and BaSe polycrystalline powder with a mass of 2 wt% of the BaGa4Se7 single crystal in a glass crucible of an annealing device;

[0076] 2) Heat the glass crucible at a rate of 50 °C / h to an annealing device furnace temperature of 1050 °C and anneal and hold at 1050 °C for 20 days;

[0077] 3) After annealing, cool down to room temperature at a rate of 10 °C / h to obtain.

[0078] Due to the annealing temperature reaching the melting point, the BaGa4Se7 single crystal processed by the above method is in a molten state, and the crystal picture is as Figure 6 shown.

[0079] Comparative Example 2

[0080] A method for improving the optical properties of BaGa4Se7 single crystal includes the following steps:

[0081] 1) Place the polished BaGa4Se7 single crystal and BaSe polycrystalline powder with a mass of 2 wt% of the BaGa4Se7 single crystal in a glass crucible of an annealing device;

[0082] 2) Heat the glass crucible at a rate of 50 °C / h to an annealing device furnace temperature of 250 °C and anneal and hold at 250 °C for 20 days;

[0083] 3) After annealing, cool down to room temperature at a rate of 10 °C / h to obtain.

[0084] Due to the too low annealing temperature, the BaGa4Se7 single crystal processed by the above method cannot achieve composition compensation for the BaGa4Se7 single crystal, thus making up for the defects.

[0085] Comparative Example 3

[0086] A method for improving the optical properties of BaGa4Se7 single crystal includes the following steps:

[0087] 1) Place the polished BaGa4Se7 single crystal and BaSe polycrystalline powder with a mass of 1 wt% of the BaGa4Se7 single crystal in a glass crucible of the annealing device;

[0088] 2) Heat the glass crucible at a rate of 50 °C / h until the temperature inside the annealing device furnace reaches 950 °C, and anneal and hold at 950 °C for 20 days;

[0089] 3) After annealing, cool down to room temperature at a rate of 10 °C / h to obtain the product.

[0090] Due to the too low content of the BaSe polycrystalline powder used, the BaGa4Se7 single crystal processed by the above method cannot achieve composition compensation for the BaGa4Se7 single crystal, thus making up for the defects.

[0091] Comparative Example 4

[0092] A method for improving the optical performance of a BaGa4Se7 single crystal, comprising the following steps:

[0093] 1) Place the polished BaGa4Se7 single crystal and BaSe polycrystalline powder with a mass of 12 wt% of the BaGa4Se7 single crystal in a glass crucible of the annealing device;

[0094] 2) Heat the glass crucible at a rate of 50 °C / h until the temperature inside the annealing device furnace reaches 950 °C, and anneal and hold at 950 °C for 20 days;

[0095] 3) After annealing, cool down to room temperature at a rate of 10 °C / h to obtain the product.

[0096] Due to the too high content of the BaSe polycrystalline powder used, the BaGa4Se7 single crystal processed by the above method results in additional doping defects.

[0097] Comparative Example 5

[0098] A method for improving the optical performance of a BaGa4Se7 single crystal, comprising the following steps:

[0099] 1) Place the polished BaGa4Se7 single crystal and BaSe polycrystalline powder with a mass of 2 wt% of the BaGa4Se7 single crystal in a glass crucible of the annealing device;

[0100] 2) Heat the glass crucible at a rate of 50 °C / h until the temperature inside the annealing device furnace reaches 950 °C, and anneal and hold at 950 °C for 20 days;

[0101] 3) After annealing, cool down to room temperature at a rate of 25 °C / h to obtain the product.

[0102] Due to the too fast cooling rate after annealing, the BaGa4Se7 single crystal processed by the above method has uneven thermal stress in the crystal and shows cracking phenomenon.

[0103] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is impossible to list all the implementation manners here. Any obvious changes or variations derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A method for improving the optical properties of BaGa4Se7 single crystal, characterized in that, It includes the following steps: Raise the ambient temperature of the BaGa4Se7 single crystal to 300 - 1000 °C and keep it at this temperature for 5 - 60 days; Lower the ambient temperature to room temperature.

2. The method according to claim 1, wherein The temperature after heating is 500 - 1000 °C.

3. The method according to claim 1, wherein The heating rate is 30 - 60 °C / h.

4. The method according to claim 1, wherein The cooling rate is 5 - 20 °C / h.

5. The method according to any one of claims 1 to 4, characterized in that, In this method, the BaGa4Se7 single crystal is in an annealing atmosphere, and the annealing atmosphere is selected from barium selenide atmosphere, barium gallium selenide atmosphere, gallium diselenide atmosphere, selenium atmosphere or vacuum condition.

6. The method according to claim 5, characterized in that, The annealing atmosphere is obtained by the volatilization of polycrystalline powders of barium selenide, barium gallium selenide, gallium diselenide or selenium.

7. The method according to claim 6, characterized in that, The mass of the polycrystalline powder is 2% - 10% of the mass of the BaGa4Se7 single crystal.

8. The method according to claim 1, characterized in that, This method is carried out in an annealing device, and the structure of the annealing device includes: A furnace chamber, a sleeve arranged in the furnace chamber, a glass crucible arranged in the sleeve for placing the BaGa4Se7 single crystal, and a glass stopper for sealing the glass crucible.

9. The method according to claim 8, characterized in that It includes the following steps: Place the BaGa4Se7 single crystal and polycrystalline powders of barium selenide, barium gallium selenide, gallium diselenide or selenium in the glass crucible and seal the glass crucible with a glass stopper; Raise the temperature of the furnace chamber to 300 - 1000 °C and keep it at this temperature for 5 - 60 days; Lower the temperature of the furnace chamber to room temperature.

10. The method according to claim 9, wherein The temperature after heating is 500 - 1000 °C.

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