Crystal growth equipment and method for preparing KBBF group nonlinear optical crystal by using same

Abstract

The invention relates to crystal growth equipment and a method for preparing KBBF-family nonlinear optical crystals by using the same. The crystal growth equipment comprises a heating furnace, a gas source, a vacuum pump, a quartz tube with an opening in one end, a sealing device used for sealing the end opening of the quartz tube and a tee joint, a first connector of the tee joint enters the quartz tube through the sealing device, a second connector of the tee joint is used for being connected with the gas source, and a third connector of the tee joint is used for being communicated with the vacuum pump. According to the KBBF group nonlinear optical crystal prepared by adopting the method disclosed by the invention, the problem that the transmittance of the crystal is rapidly reduced near an ultraviolet absorption cutoff wavelength is remarkably improved, so that the KBBF group nonlinear optical crystal has a wider application prospect in a short-wave deep ultraviolet region lower than 180nm.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of crystal growth. More particularly, it relates to a crystal growth device and a crystal growth method. BACKGROUND

[0002] With the rapid development of semiconductor materials in recent years, deep ultraviolet lithography machines, chip processing and the like urgently need deep ultraviolet lasers, for example, lasers with a wavelength shorter than 200 nm. Compared with gas lasers and dye lasers, all-solid-state deep ultraviolet lasers have attracted much attention due to their higher beam quality, higher stability, more compact structure and lower maintenance cost. At present, one of the most effective methods to realize all-solid-state deep ultraviolet lasers is to expand the wavelength of mature and commercialized near-infrared lasers to the visible, ultraviolet and deep ultraviolet bands through the cascading frequency conversion technology of nonlinear optical crystals, such as frequency doubling and sum frequency generation technology. Commonly used nonlinear optical crystals include LiB3O5(LBO), CsLiB6O 10 (CLBO), KBe2BO3F2(KBBF), RbBe2BO3F2(RBBF), CsBe2BO3F2(CBBF) and other borate crystals. Among them, the KBBF, RBBF and CBBF fluorinated beryllium potassium borate family nonlinear optical crystals (hereinafter also abbreviated as KBBF family crystals, KBBF family nonlinear optical crystals) can realize ultraviolet and deep ultraviolet laser output through direct frequency doubling, and the shortest frequency doubling wavelengths are 161 nm, 171 nm and 205 nm, respectively. If the sum frequency generation method is used, the output wavelength can be shorter. At present, through the KBBF prism coupler device, 149.8 nm laser output has been realized by sum frequency generation. Shorter wavelength deep ultraviolet lasers have important application prospects in advanced scientific instruments such as super-high-resolution photoelectron spectrometers and frontier scientific fields such as optical clocks. Therefore, the fluorinated beryllium potassium borate family nonlinear optical crystals, especially the KBBF and RBBF crystals, have great application prospects in the short-wave deep ultraviolet region below 180 nm, and there is no other crystal that can compare with them at present.

[0003] However, the transmittance of the fluorinated beryllium potassium borate family nonlinear optical crystals, such as the KBBF crystal, near the ultraviolet absorption cutoff wavelength, for example, 155-165 nm, will rapidly decrease, which seriously affects the frequency conversion efficiency and short-wave output power, and even cannot produce effective power output. It has been found that with the increase of the thickness of the KBBF crystal, the ultraviolet cutoff wavelength of the KBBF crystal red shifts from 147 nm to 160 nm, which is caused by the non-intrinsic absorption of several transition metal ion impurities. In order to reduce the deep ultraviolet absorption of the KBBF crystal and improve the transmittance of the crystal, high-purity raw materials need to be used to reduce the impurity content in the crystal. However, this still cannot improve the problem of rapid decrease of the transmittance of the KBBF crystal near the ultraviolet absorption cutoff wavelength. SUMMARY

[0004] The application aims to provide a potassium fluoro-borato-beryllate family nonlinear optical crystal with high transmittance near the ultraviolet absorption cutoff wavelength.

[0005] In a first aspect, the application provides a crystal growth apparatus, comprising a heating furnace, a gas source, a vacuum pump, a quartz tube with one open end, a sealing device for sealing the open end of the quartz tube, and a tee joint,

[0006] The first interface of the tee joint enters the quartz tube through the sealing device, the second interface is used for connecting the gas source, and the third interface is used for communicating with the vacuum pump.

[0007] Preferably, the crystal growth apparatus further comprises a first valve arranged on the sealing device, a second valve arranged on the second interface of the tee joint, and a third valve arranged on the third interface of the tee joint.

[0008] Preferably, the crystal growth apparatus further comprises a pressure gauge arranged on the sealing device.

[0009] In a second aspect, the application provides an application of the crystal growth apparatus in the preparation of a potassium fluoro-borato-beryllate family nonlinear optical crystal, wherein the gas source is used for providing a reducing gas.

[0010] In a third aspect, the application provides a method for preparing a potassium fluoro-borato-beryllate family nonlinear optical crystal, wherein the potassium fluoro-borato-beryllate family nonlinear optical crystal is prepared by using the crystal growth apparatus as described above, and the method comprises the following steps:

[0011] Loading a raw material for growing a potassium fluoro-borato-beryllate family crystal into a crucible;

[0012] Placing the crucible containing the raw material into the quartz tube and sealing the open end of the quartz tube;

[0013] First injecting a reducing gas into the quartz tube after the first vacuumizing;

[0014] Heating the raw material to complete melting, and growing the crystal by using a spontaneous nucleation method.

[0015] Preferably, the method further comprises, after the first injection of the reducing gas, second vacuumizing the quartz tube and second injecting a reducing gas.

[0016] Preferably, the injection of the reducing gas comprises injecting the reducing gas to normal pressure.

[0017] Preferably, the potassium fluoro-borato-beryllate family nonlinear optical crystal is a KBBF, RBBF, or CBBF crystal.

[0018] Preferably, the raw material comprises a pre-synthesized potassium fluoro-borato-beryllate family polycrystal powder or a raw material for synthesizing a potassium fluoro-borato-beryllate family crystal, and a flux.

[0019] In a fourth aspect, this application provides a potassium fluoroborate group nonlinear optical crystal prepared by the method described above, wherein the Cu content in the crystal is less than the Cu element detection limit of the ICP-OES method.

[0020] The beneficial effects of this invention are as follows:

[0021] This invention discloses a crystal growth apparatus and a method for growing potassium fluoroborate beryllium fluoride group nonlinear optical crystals under a reducing atmosphere. During the KBBF crystal growth process, a redox reaction is conducted between a reducing gas and impurity ions to reduce the Cu content in the liquid phase. 2+ The valence state increases its ionic radius (Cu) 2+ Ionic radius 70 pm, Cu + The ionic radius (96 pm) was inhibited from entering the crystal lattice during the crystallization process of KBBF group crystals, effectively reducing the Cu content in the crystal. 2+ Impurities; at the same time, the method grows crystals in a closed environment of quartz tube, avoiding contamination from dust in the heating furnace air and refractory and insulation materials such as furnace chamber and furnace body, resulting in crystals with lower impurity content.

[0022] The KBBF family nonlinear optical crystal obtained by the method of this application significantly improves the problem of rapid transmittance decline of KBBF family crystals near the ultraviolet absorption cutoff wavelength, and has high transmittance in the deep ultraviolet, especially in the vicinity of 155-165nm, making KBBF family nonlinear optical crystals have a wider range of application prospects in the short-wavelength deep ultraviolet region below 180nm. Attached Figure Description

[0023] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings:

[0024] Figure 1 An exemplary schematic diagram of the crystal growth apparatus of this application is shown;

[0025] Figure 2 A photograph of the KBBF crystal of Embodiment 1 of this application is shown;

[0026] Figure 3 The deep ultraviolet transmittance curve of the KBBF crystal of Example 1 of this application is shown;

[0027] Figure 4 A photograph of the KBBF crystal of Embodiment 2 of this application is shown;

[0028] Figure 5 The deep ultraviolet transmittance curve of the KBBF crystal in Example 2 of this application is shown;

[0029] Figure 6A photo of KBBF crystal of Comparative Example 1 is shown;

[0030] Figure 7 A deep ultraviolet transmittance curve of KBBF crystal of Comparative Example 1 is shown;

[0031] wherein

[0032] 10 - heating furnace; 11 - quartz tube; 12 - furnace chamber; 13 - heat preservation structure; 14 - furnace shell; 15 - pressure gauge; 16 - crucible, 17 - temperature control element;

[0033] 21 - flange; 22 - sealing ring; 23 - cover; 24 - bolt;

[0034] 30 - tee joint; 31 - first interface; 32 - second interface; 33 - third interface; 34 - first valve; 35 - second valve; 36 - third valve;

[0035] 40 - gas source;

[0036] 50 - vacuum pump. DETAILED DESCRIPTION

[0037] In order to more clearly illustrate the present application, the present application will be further described below in conjunction with preferred embodiments and drawings. It should be clear that the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present application. In addition, unless otherwise specified, the raw materials used in the present application can be purchased from commercial suppliers, and any range recited in the present application includes the end values and any numerical value between the end values and any sub-range formed by any numerical value or end value.

[0038] The present application takes the preparation method of KBBF crystal as an example to illustrate the method for preparing potassium fluoro-borato-beryllate family nonlinear optical crystal.

[0039] The conventional crystal growth process is a process of solute transport and impurity removal. Since the raw material inevitably contains various impurity elements, if the impurity elements are close to the ion radius of the constant elements in the crystalline compound, the ion valence is consistent, or there is a larger gap in the lattice, the impurity elements are easy to enter the lattice during the solute transport process, replace the original element position or interstitially fill the gap. The introduced impurities will reduce the optical uniformity of the crystal, especially the transition metal impurities, which are also easy to produce absorption at different wavelengths in the deep ultraviolet region. In order to reduce the deep ultraviolet absorption of KBBF crystal and improve the transmittance of the crystal, high-purity raw materials need to be used to reduce the impurity content in the crystal. At present, although the highest purity of the raw material for preparing KBBF crystal has reached more than 99.00%, the impurities such as alkali metals, alkaline earth metals and various transition metals and heavy metal elements cannot be completely removed. In addition, during the crystal growth process, the environment around the crystal growth continuously contaminates the melt and introduces new impurities. The impurities in the KBBF crystal obtained by the conventional growth method are measured by ICP-OES, and the results show that the crystal contains Cu, Al, Na, Zn, Fe and Si, and the content is in the range of several to several hundred ppm. Among them, the absorption range of Cu ions is 160-165 nm in the deep ultraviolet band, which seriously affects the transmittance of KBBF crystal in this band range, and further affects the application of KBBF crystal in this band.

[0040] In view of this problem, the application provides a crystal growth device, application of the crystal growth device in preparation of potassium fluoro-borato-beryllate family nonlinear optical crystal, and a method for growing KBBF family nonlinear optical crystal in a reducing atmosphere. In the crystal growth process, the redox reaction between the reducing gas and the impurity ions reduces the valence of Cu 2+ and increases its ion radius, inhibits the entry of Cu elements into the lattice, and effectively reduces the Cu impurities in the crystal. At the same time, the method grows the crystal in a sealed environment of a quartz tube, avoiding the impurity pollution caused by dust in the surrounding air, furnace body material and heat preservation material, and the impurity content in the obtained crystal is significantly reduced. The Cu content in the crystal sample cannot be detected by ICP-OES, the Cu content in the remaining material is in the order of tens of ppm, and the transmittance of the crystal at 165 nm is greater than 30%. The KBBF family nonlinear optical crystal obtained by the method of the application effectively improves the transmittance of this type of crystal in the deep ultraviolet region, and removes the obstacles for its high-efficiency output in the short-wave deep ultraviolet band.

[0041] The first embodiment of the application provides a crystal growth device. Figure 1The structure of the crystal growth apparatus is shown in the example. The crystal growth apparatus comprises a heating furnace 10, a gas source 40, a vacuum pump 50, a quartz tube 11 with an open end, a sealing device for sealing the end of the quartz tube, and a tee joint 30. The heating furnace 10 comprises a furnace body composed of a resistance wire heating furnace chamber 12, a heat insulation structure 13, and a furnace shell 14. The quartz tube 11 is a hollow cylindrical structure with an open top end, which is placed in the heating furnace chamber and used to accommodate a crucible 16 for crystal growth.

[0042] The open end of the quartz tube is provided with a sealing device, which comprises a stainless steel flange 21, a sealing ring 22, a cover 23, and a bolt 24, and is used to seal the quartz tube. As a specific example, the sealing device is arranged outside the heating furnace. The cover 23 is provided with a plurality of openings, for example, a first gas pipeline, a first valve 34, and a pressure gauge 15, which are connected to the inside of the quartz tube through the openings respectively, and the first valve 34 is used to control the communication between the inside of the quartz tube and the atmosphere. The gas source 40, for example, a gas cylinder, is used to provide reaction gas to the inside of the quartz tube, the second interface 32 of the tee joint is connected to the gas source 40 through a second gas pipeline, and the second gas pipeline is provided with a second valve 35. The vacuum pump 50 is used to vacuumize the inside of the quartz tube, the third interface 33 of the tee joint is connected to the vacuum pump 50 through a third gas pipeline, and the third gas pipeline is provided with a third valve 36. By opening and closing the second valve and the third valve respectively, the inside of the quartz tube can be vacuumized and the gas from the gas source can be injected respectively.

[0043] A crucible 16 is arranged at the middle position of the bottom of the quartz tube, and the crucible is used to place raw materials for growing crystals, for example, mixed raw materials including crystal raw materials and fluxing agents, and a cover is arranged above the crucible. The materials of the crucible and the cover are, for example, platinum gold. The temperature control element 17 can be a thermocouple, for example, a platinum-platinum rhodium thermocouple. Those skilled in the art can choose other commonly used temperature control elements to replace, for example, a thermistor, a resistance temperature detector, an IC temperature sensor, etc., which are all within the protection scope of the present application.

[0044] As a specific example, the quartz tube 11 is in a hollow cylindrical shape, with a diameter of 12 cm, a height of 80 cm, and a wall thickness of 1 cm. The resistance wire heating furnace chamber has a diameter of 14 cm and a height of 60 cm, and the temperature of the furnace chamber is raised by heating with an electric furnace wire to melt the crystal raw materials and fluxing agents in the crucible. The heat insulation structure comprises a side wall heat insulation layer and a bottom heat insulation layer, and the heat insulation layer can be a multi-layer structure. The heat insulation materials used include, but are not limited to, glass fiber, asbestos, rock wool, silicate, etc., and other heat insulation materials that can play a heat insulation role can also be selected.

[0045] As a second embodiment of the present application, the gas source provides a reducing or weakly reducing gas, and the crystal growth apparatus can be applied to grow a potassium fluoro-borato-beryllate family nonlinear optical crystal. A person skilled in the art can select the type of reducing gas as needed, for example, CO, H2, CH4, etc., which can be a mixture of one or more reducing gases; or a mixture of a reducing gas and an inert gas such as N2, Ar, etc. The vacuum pump can make the vacuum degree in the quartz tube reach 10 -4 atmospheres. By repeatedly performing the operations of vacuumizing and introducing the reducing gas, the air in the quartz tube can be completely removed, so that the crystal growth is carried out in a reducing atmosphere. The gas pipeline diameter is, for example, 3-10 mm. In a specific embodiment, the gas pipeline diameter is 8 mm, and the reducing gas is, for example, a mixture of N2+(3-5)% H2. To avoid sticking of the crucible to the quartz tube, a layer of thermal insulation cotton can be placed between the quartz tube and the crucible.

[0046] A third embodiment of the present application provides a preparation method for preparing a potassium fluoro-borato-beryllate family crystal.

[0047] The crystal growth apparatus as described above is used to grow a potassium fluoro-borato-beryllate family crystal by spontaneous nucleation, and the following takes KBBF crystal as an example for illustration, which specifically includes the following steps:

[0048] The mixed raw materials obtained by mixing the pre-synthesized potassium fluoro-borato-beryllate polycrystal powder with the boron oxide and potassium fluoride composite fluxing agent are loaded into the crucible, and then the crucible containing the mixed raw materials is placed into the quartz tube, the upper end cover of the crucible is covered, and the top of the quartz tube is sealed by the sealing device. The second valve is closed and the third valve is opened to vacuumize the quartz tube, then the third valve is closed and the second valve is opened to introduce the reducing gas, and the operation of repeatedly vacuumizing and introducing the reducing gas to normal pressure is repeated twice. The air components in the quartz tube are completely removed, and the reducing gas is injected to normal pressure, and the second valve is closed;

[0049] A first temperature rising is performed to 800°C to completely melt the mixed raw materials in the crucible, and a constant temperature of, for example, 48 h is maintained to make the solution uniformly mixed; as the temperature rises, the gas pressure in the quartz tube slightly rises;

[0050] A second temperature lowering is performed to the vicinity of the saturation temperature;

[0051] A third temperature lowering is performed to start the crystal growth, and a spontaneous nucleation growth technique is adopted, and the temperature lowering interval is 50-100°C.

[0052] After the crystal growth is completed, the temperature of the heating furnace is slowly lowered to room temperature, the first valve is opened, the sealing device of the quartz tube is opened, and the crucible is taken out;

[0053] The crystal is separated from the melt by acid solution cleaning to obtain the KBBF crystal.

[0054] The fluoroborokryptite family polycrystal powder can be synthesized by a solid phase synthesis method commonly used in the art.

[0055] Further, the raw material for synthesizing the fluoroborokryptite family crystal is, for example, various fluorine-containing compounds, boron-containing compounds, beryllium-containing compounds, and the like that participate in the reaction, similar to KBF4, BeO, and H3BO3.

[0056] Further, when the reaction raw material is the fluoroborokryptite family polycrystal powder and the fluxing agent, the fluxing agent is selected from KF and B2O3, and the molar ratio of the fluoroborokryptite family polycrystal powder, KF, and B2O3 is 1:(3-6):(1-3). When the reaction raw material is the raw material for synthesizing the fluoroborokryptite family crystal and the fluxing agent, the fluxing agent is selected from KF and H3BO3, and the stoichiometric ratio of the mixed raw material, for example, KBF4, BeO, H3BO3, and KF, is 1:2:(3-6):(3-6), wherein H3BO3 is in excess, part of H3BO3 is a reactant, and part of H3BO3 is a fluxing agent.

[0057] Further, the first temperature increasing rate is 10-100°C / h; for example, the first temperature increasing rate can be 10°C / h, 20°C / h, 30°C / h, 40°C / h, 50°C / h, 60°C / h, 70°C / h, 80°C / h, 90°C / h, 100°C / h, and the like; the second temperature decreasing rate can be 10-100°C / h, preferably 30-50°C / h; for example, the second temperature decreasing rate can be 10°C / h, 20°C / h, 30°C / h, 40°C / h, 50°C / h, 60°C / h, 70°C / h, 80°C / h, 90°C / h, 100°C / h, and the like; the third temperature decreasing rate is 0.2-1°C / d, preferably 0.5-1°C / d; for example, the third temperature decreasing rate can be 0.2°C / d, 0.3°C / d, 0.4°C / d, 0.5°C / d, 0.6°C / d, 0.7°C / d, 0.8°C / d, 1°C / d, and the like. The crystal growth time is 50-100d, preferably 60-100d; for example, the crystal growth time can be 60d, 65d, 70d, 75d, 80d, 85d, 90d, 95d, 100d, and the like.

[0058] Further, the time for cooling to room temperature is 48-96h.

[0059] The method for preparing the fluoroborokryptite family nonlinear optical crystal according to the present application will be further described below through specific examples.

[0060] Raw material:

[0061] KBF4, sourced from Xilong Chemical Co., Ltd., has a purity of 99% and contains impurities such as SO4 and PO4.

[0062] BeO, sourced from Hunan Shuikoushan Metal Co., Ltd., with a purity of 99%, but impurity content was not provided;

[0063] H3BO3, sourced from Shanghai Aladdin Biochemical Technology Co., Ltd., with a purity of 99.5%, contains impurities such as As, Ca, Fe, and Pb.

[0064] B2O3, sourced from Merk in Germany, with a purity of 99.99%, contains impurities such as Cl, Pb, Ca, and Fe;

[0065] KF, sourced from Merk in Germany, has a purity of 99.99% and contains impurities such as SiF6, Fe, Pb, and Na.

[0066] Trace analysis:

[0067] Instrument: ThermoFisher (USA), Model: iCAP6300;

[0068] Detection method: ICP-OES;

[0069] The sample is dissolved in a solution, and the liquid sample is converted into an aerosol by an atomizer, which is then carried into the plasma torch by a carrier gas (argon). Under the action of a high-frequency magnetic field, the argon gas is ionized to form an ICP torch with a temperature as high as 6000-10000 K. The sample in the aerosol is rapidly atomized, ionized, and excited. When the excited atoms / ions transition from high energy levels to low energy levels, they release characteristic spectra of specific wavelengths (each element corresponds to a unique characteristic wavelength). After the spectra are separated by a spectroscopic system, the intensity of the characteristic spectral lines is measured by a detector. Combined with a standard curve, the content of the corresponding element in the sample can be calculated, and the element type can be determined by the spectral line wavelength.

[0070] Example 1

[0071] use Figure 1 The crystal growth apparatus shown spontaneously nucleates and grows KBBF crystals. The specific steps of the preparation method are as follows:

[0072] KBBF polycrystalline powder was prepared using a solid-state synthesis method. The solid-state synthesis equation is as follows:

[0073] 6BeO+3KBF4+2H3BO3→3KBe2BO3F2+2BF3↑+3H2O↑,

[0074] All reactants were thoroughly mixed according to stoichiometric ratio, sintered at 750°C, and kept at a constant temperature for 48 hours until the reaction was complete. The KBBF phase polycrystalline powder was confirmed by powder XRD.

[0075] The obtained KBBF polycrystalline powder is used as a growth raw material, mixed with fluxing agents KF and B2O3 in a molar ratio of 1:5:3 in a mortar, and after mixing, the raw materials are all poured into a platinum crucible. The platinum crucible is placed in the center of a quartz tube, and a platinum cover is placed above the crucible. The port of the quartz tube is sealed with a sealing device, and vacuum is slowly drawn to avoid dust flying out of the crucible at too high a speed. After vacuumizing, a mixture of nitrogen and hydrogen (4%) is slowly filled to normal pressure, and then vacuumized again. After the second vacuumizing, a reducing gas is filled to normal pressure, and the air in the quartz tube is completely removed.

[0076] The temperature is raised to 800°C at a rate of 50°C / h, and kept constant for 48 h to ensure that the high-temperature solution is fully mixed and uniform. As the temperature rises, the gas expands, and the pressure at high temperature is slightly higher than normal pressure. After the solution is fully mixed and uniform, the temperature is reduced in two stages at a rate of 60°C / h to the vicinity of the saturation point temperature (about 750°C), and then the crystal growth is started at a rate of 0.5°C / d. The crystal growth time is 40 d. After the crystal growth is completed, the furnace body is reduced to room temperature within 4 d to obtain KBBF crystals, as shown in Figure 2 , and the deep ultraviolet transmittance of the crystal is shown in Figure 3 . In the crystal growth process using the crystal growth equipment and the crystal preparation method of the present application, the Cu 2+ ions in the solution and the reducing gas undergo a redox reaction, and Cu 2+ is reduced to Cu + , and the Cu ion radius increases, making it difficult for Cu + to enter the crystal lattice. The obtained KBBF crystal has a transmittance of up to 32.0% at 165 nm (KBBF crystal thickness 0.5 mm). Using ICP-OES, American ThermoFisher, iCAP6300, to measure impurities, it is found that the obtained KBBF crystal has no detectable Cu element, i.e., the Cu content in the KBBF crystal obtained in Example 1 is less than the Cu element detection limit of the ICP-OES method.

[0077] Example 2

[0078] The KBBF crystal is grown by spontaneous nucleation using the crystal growth furnace shown in Figure 1 , and the specific steps of the preparation method are as follows:

[0079] The raw materials KBF4, BeO, H3BO3 and KF are mixed and ground in a mortar in a molar ratio of 1:2:5:7, and the excess KF and H3BO3 are used as fluxing agents. After mixing, the raw materials are poured into a platinum crucible, and the platinum crucible is placed in the center of a quartz tube. The port of the quartz tube is sealed with a sealing device, and vacuum is slowly drawn to avoid dust flying out of the crucible at too high a speed. After vacuumizing, a mixture of argon and hydrogen (5%) is slowly filled to normal pressure, and then vacuumized again. After the second vacuumizing, a reducing gas is filled to normal pressure, and the air in the quartz tube is completely removed.

[0080] The temperature was increased to 850℃ at a rate of 60℃ / h and held for 24 hours to ensure thorough mixing of the high-temperature solution. A second cooling phase was then implemented at 50℃ / h to bring the solution close to the saturation point (approximately 740℃) for this mixture. A third cooling phase was then initiated at a rate of 0.6℃ / day to allow crystal growth. During crystal growth, Cu in the solution... 2+ Ions and reducing gases undergo redox reactions, Cu 2+ Reduced to Cu + Increase the ionic radius, Cu + It is difficult to penetrate the crystal lattice, and the crystal growth time is 50 days. After the crystal growth is completed, the furnace is cooled to room temperature within 4 days to obtain KBBF crystals. See [link to KBBF crystal growth]. Figure 4 The deep ultraviolet transmittance of the crystal is as follows Figure 5 As shown, the obtained KBBF crystal has a transmittance of up to 32.2% at 165 nm (crystal thickness 0.5 mm). Impurities were measured using a Thermo Fisher iCAP6300 (USA), and no Cu was detected in the obtained KBBF crystal. That is, the Cu content in the KBBF crystal obtained in Example 2 is below the Cu detection limit of the ICP-OES method.

[0081] Comparative Example 1

[0082] KBBF polycrystalline powder, the same as in Example 1, was used as the crystal growth material. It was mixed and ground in a mortar with flux KF and B2O3 at a molar ratio of 1:5:3. The mixture was then poured into a platinum crucible. The platinum crucible was placed in the center of a quartz tube, and the ends of the quartz tube were sealed with a sealing device. The growth equipment was identical to that in Example 1, but the vacuuming and reducing gas injection steps were omitted, and the air atmosphere inside the quartz tube was maintained.

[0083] The temperature was increased to 850℃ at a rate of 40℃ / h and held for 24 hours to ensure thorough mixing of the high-temperature solution. A second cooling phase was then performed at 40℃ / h to bring the temperature close to the saturation point (approximately 740℃) for this solution ratio. A third cooling phase was then initiated at a rate of 0.6℃ / day to allow crystal growth for 50 days. After the crystal growth cycle was completed, the temperature was lowered to room temperature within 4 days to obtain KBBF crystals. (See attached image) Figure 6 After selecting transparent crystals and polishing them, the transmittance is measured. Figure 7 As shown, the transmittance at 165 nm is only 7.7% (crystal thickness 0.5 mm). Impurities were measured using ICP-OES (model: iCAP6300, manufacturer: ThermoFisher, USA), and the Cu element content was 15 ppm.

[0084] It can be seen that, by using the crystal growth device and the preparation method of the present application, the Cu element in the potassium fluoro-borato-beryllate crystal obtained is significantly reduced to below the Cu detection limit of iCAP6300, generally less than 1 ppm, and the transmittance of the KBBF crystal in the 160-165 nm waveband is significantly improved.

[0085] Obviously, the above embodiments of the present application are only examples for clearly illustrating the present application, and are not intended to limit the implementation manners of the present application. Based on the above description, other different forms of changes or variations can be made by those skilled in the art, and it is impossible to enumerate all the implementation manners here. Any obvious changes or variations derived from the technical solutions of the present application are still within the protection scope of the present application.

Claims

1. A crystal growth apparatus, characterized in that, Includes a heating furnace, a gas source, a vacuum pump, a quartz tube open at one end, a sealing device for sealing the end of the quartz tube, and a tee. The first port of the three-way valve is connected to the quartz tube through the sealing device, the second port is connected to the gas source, and the third port is connected to the vacuum pump.

2. The crystal growth apparatus according to claim 1, characterized in that, The crystal growth apparatus further includes a first valve disposed on the sealing device; a second valve disposed on the second interface pipe of the tee; and a third valve disposed on the third interface pipe of the tee.

3. The crystal growth apparatus according to claim 1, characterized in that, The crystal growth apparatus further includes a pressure gauge disposed on the sealing device.

4. The application of the crystal growth equipment according to claim 1 in the preparation of potassium fluoroborate group nonlinear optical crystals, characterized in that, The gas source is used to provide reducing gas.

5. A method for preparing a potassium fluoroborate group nonlinear optical crystal, comprising the following steps, using the crystal growth apparatus according to any one of claims 1-3: The raw materials used for growing potassium fluoroborate group crystals are loaded into the crucible; Place the crucible containing the raw material inside the quartz tube and seal the end of the quartz tube; The first vacuuming of the quartz tube followed by the first injection of reducing gas; The raw material is heated until completely melted, and the crystal is grown using a spontaneous nucleation method.

6. The method according to claim 5, characterized in that, The method further includes, after the first injection of reducing gas, evacuating the quartz tube a second time and injecting reducing gas a second time.

7. The method according to claim 5, characterized in that, The injected reducing gas includes injecting reducing gas to atmospheric pressure.

8. The method according to claim 5, characterized in that, The potassium fluoroborate group nonlinear optical crystal is a KBBF, RBBF, or CBBF crystal.

9. The method according to claim 5, characterized in that, The raw materials include pre-synthesized potassium fluoroborate polycrystalline powder or raw materials for synthesizing potassium fluoroborate crystals, as well as flux.

10. A potassium fluoroborate group nonlinear optical crystal prepared by the method of claim 5, characterized in that, The Cu content in the crystal is less than the Cu element detection limit of the ICP-OES method.

Images