A method for growing large-size single crystals of alkali metal borophosphate compounds

Abstract

The present invention provides a large-size single crystal growth method of an alkali metal borophosphate compound, and belongs to the technical field of single crystal growth methods. The present invention adopts a method combining a Czochralski method and a crucible rotation method to prepare an alkali metal borophosphate compound. The Czochralski method greatly improves the growth rate of the crystal and realizes the large-size preparation of the single crystal. The crucible rotation method effectively inhibits multi-nuclear condensation during crystal growth, so that the internal uniformity of the obtained large-size single crystal is better, the blank utilization rate is higher, and the growth quality of the crystal is significantly improved. The two are combined to obtain high-quality, large-size alkali metal borophosphate compound single crystals; the use of self-fluxing agents and self-in-system additives significantly reduces the viscosity of the melt while avoiding the reduction in single crystal quality caused by the introduction of elements outside the system, which is conducive to the acceleration of the pulling rate and the growth of large-size high-quality single crystals; annealing treatment ensures the quality of the single crystal, reduces cracks in the cutting process or breaks in actual use.

Description

Technical Field

[0001] The invention belongs to the technical field of single crystal growth methods, and in particular relates to a large-size single crystal growth method for an alkali metal borophosphate compound. Background Art

[0002] In the spectrum, wavelengths between 300 and 100 nm are called deep ultraviolet light. Due to the high energy of a single photon, deep ultraviolet lasers can break chemical bonds when interacting with materials, thus processing materials at the molecular level, and very little heat is generated in the process, so they are figuratively called "cold processing." In addition, the absorption efficiency of the obtained materials for shorter wavelengths is usually higher. Based on this principle, deep ultraviolet lasers have higher working efficiency. How to efficiently obtain stable deep ultraviolet laser output becomes a key issue to achieve the above goals.

[0003] At present, the mainstream technology route for obtaining deep ultraviolet lasers is to use the frequency conversion technology of nonlinear optical crystals. As a deep ultraviolet optical crystal with excellent performance, it must have the following characteristics: non-centrosymmetric structure, short cutoff edge, large frequency conversion coefficient, easy growth of large-sized single crystals and good chemical stability. Recent studies have shown that Cs 3 [(BOP) 2 (B 3 O 7 ) 3 ](CBPO) has excellent properties and is an excellent deep ultraviolet nonlinear optical crystal. However, the existing preparation of Cs 3 [(BOP) 2 (B 3 O 7 ) 3 ] method cannot obtain large-sized single crystals, and when the size of the single crystal increases, its quality cannot be guaranteed.

[0004] Therefore, there is an urgent need for a large-size single crystal growth method of an alkali metal borophosphate compound that can ensure the single crystal quality to solve the above problems. Summary of the invention

[0005] In order to solve the above technical problems, the present invention proposes a large-size single crystal growth method of an alkali metal borophosphate compound.

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

[0007] The present invention provides a large-size single crystal growth method of an alkali metal borophosphate compound, comprising the following steps:

[0008] (1) placing a raw material for preparing an alkali metal borophosphate compound, a self-fluxing agent and an additive into a crucible for melting to obtain a mixed melt;

[0009] (2) The mixed melt obtained in step (1) is cooled to a critical point of crystal floating, and then a seed crystal is added to the mixed melt for crystal growth, while the seed crystal is pulled at a pulling speed of 0.2 to 3.5 mm / day, and the crucible is rotated at a rotation rate of -100 rpm to 100 rpm. After the crystal growth is completed, the crystal is pulled out of the mixed melt liquid surface, and annealed to obtain a large-sized alkali metal borophosphate compound single crystal.

[0010] Preferably, the raw materials for preparing the alkali metal borophosphate compound in step (1) include a cesium source, a boron source and a phosphorus source; the molar ratio of the cesium source, the boron source and the phosphorus source is 3:(11-22):(2-4).

[0011] Preferably, the cesium source comprises Cs 2 CO 3 or CsOH; the phosphorus source includes NH 4 H 2 PO 4 or P 2 O 5 ; The boron source includes B 2 O 3 or H 3 BO 3 .

[0012] Preferably, the self-fluxing agent in step (1) comprises B 2 O 3 , H 3 BO 3 NH 4 H 2 PO 4 , P 2 O 5 and Cs 2 O; in actual operation, when the phosphorus source is NH 4 H 2 PO 4 When the self-service flux is selected P 2 O 5 When the phosphorus source is P 2 O 5 When the self-service flux is NH 4 H 2 PO 4 ; When the boron source is B 2 O 3 or H 3 BO 3 When the self-service flux is selected H 3 BO 3 or B 2 O 3That is to say, the raw material and the self-fluxing agent cannot be the same material; the amount of the self-fluxing agent is 0.01 to 60% of the mass of the raw material for preparing the alkali metal borophosphate compound.

[0013] Preferably, the additive in step (1) includes CsF, CsCl, CsBr, CsOH, CsNO 3 , Cs 2 O and Cs 2 CO 3 One or more of the above; the amount of the additive is 0.01 to 15% of the mass of the raw material for preparing the alkali metal borophosphate compound.

[0014] Preferably, the melting temperature in step (1) is 820-900° C. and the melting time is 20-48 hours.

[0015] Preferably, the temperature of the critical point of crystal floating in step (2) is 550-680°C.

[0016] Preferably, the cooling procedure for cooling the mixed melt to the critical point of floating crystal in step (2) is: the mixed melt is cooled to 680-750°C at room temperature, and then cooled to the critical point of floating crystal at a cooling rate of 0.8-1°C / day in the first week and 0.4-0.6°C / day thereafter.

[0017] Preferably, the annealing temperature in step (2) is 400-600° C. and the time is 48-100 h.

[0018] Compared with the prior art, the present invention has the following advantages and technical effects:

[0019] The present invention adopts a method combining a pulling method with a crucible rotation method to prepare an alkali metal borophosphate compound. The pulling method greatly improves the growth rate of the crystal and realizes the large-size preparation of the single crystal. The crucible rotation method effectively inhibits the multi-nuclear condensation during the crystal growth, so that the internal uniformity of the obtained large-size single crystal is better, the blank utilization rate is higher, and the growth quality of the crystal is significantly improved. By combining the two, high-quality, large-size alkali metal borophosphate compound single crystals are obtained. The present invention significantly reduces the viscosity of the melt by using a self-fluxing agent and an additive in the system, which is helpful for the acceleration of the pulling rate and the growth of large-size single crystals. The present invention ensures the quality of the single crystal by annealing the grown crystal, thereby effectively reducing the occurrence of cracks in the cutting process or the occurrence of fractures in actual use. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0021] Figure 1 A schematic diagram of an apparatus used in a large-size single crystal growth method of an alkali metal borophosphate compound provided by the present invention;

[0022] Among them, 1 is a crystal growth furnace, 2 is a rotating seed crystal pulling rod, 3 is a seed crystal, 4 is a crucible, 5 is a crucible rotating device, and 6 is a temperature control device;

[0023] Figure 2 A schematic diagram of an apparatus used in a large-size single crystal growth method of an alkali metal borophosphate compound provided in Example 1 of the present invention;

[0024] Among them, 1 is a lifting device, 2 is a rotating lifting device, 3 is a seed crystal rod, 4 is a crystal growth furnace, and 5 is a base support;

[0025] Figure 3 This is a working principle diagram of a 532nm laser (Z cavity) in Example 4 of the present invention;

[0026] Among them, 1-4 are reflectors, 5 is an acousto-optic modulator, 6 is a gain crystal, 7 is a frequency doubling crystal, 8 is a green light reflector (1), and 9 is a green light reflector (2);

[0027] Figure 4 This is a working principle diagram of a 532nm laser (V cavity) in Example 5 of the present invention;

[0028] Among them, 1-3 are reflectors, 4 is an acousto-optic modulator, 5 is a gain crystal, 6 is a frequency doubling crystal, 7 is a green light reflector (1), and 8 is a green light reflector (2);

[0029] Figure 5 This is a schematic diagram of a 266 nm laser in Example 6 of the present invention;

[0030] Among them, 1-3 are reflectors, 4 is an acousto-optic modulator, 5 is a gain crystal, 6 is a frequency doubling crystal (1), 7 is a green light reflector (1), 8 is a green light reflector (2), and 9 is a frequency doubling crystal (2). DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] The embodiment of the present invention provides a large-size single crystal growth method of an alkali metal borophosphate compound, comprising the following steps:

[0034] (1) placing a raw material for preparing an alkali metal borophosphate compound, a self-fluxing agent and an additive into a crucible for melting to obtain a mixed melt;

[0035] (2) The mixed melt obtained in step (1) is cooled to the critical point of crystal floating, and then a seed crystal is added to the mixed melt for crystal growth. At the same time, the seed crystal is pulled at a pulling speed of 0.2 to 3.5 mm / day and the crucible is rotated at a rotation rate of -100 rpm to 100 rpm. After the crystal growth is completed, the crystal is pulled out of the mixed melt liquid surface and annealed to obtain a large-sized alkali metal borophosphate compound single crystal.

[0036] The apparatus used in the large-size single crystal growth method of the alkali metal borophosphate compound provided by the present invention is as follows: Figure 1 As shown, it can be seen that the device includes a crystal growth furnace, a rotating seed crystal pulling rod, a seed crystal, a crucible, a crucible rotating device and a temperature control device.

[0037] In a preferred embodiment, the raw materials for preparing the alkali metal borophosphate compound include a cesium source, a boron source and a phosphorus source.

[0038] In a preferred embodiment, the cesium source comprises Cs 2 CO 3 or CsOH; the phosphorus source includes NH 4 H 2 PO 4 or P 2 O 5 ; The boron source includes B 2 O 3 or H 3 BO 3 .

[0039] In a preferred embodiment, the molar ratio of the cesium source, the boron source and the phosphorus source is 3:(11-22):(2-4).

[0040] In a preferred embodiment, the self-fluxing agent comprises B 2 O 3 , H 3 BO 3 NH 4 H 2 PO 4 , P 2 O 5 and Cs 2 One or more of O, preferably B 2 O 3 , H 3 BO3 and P 2 O 5 The present invention adopts the self-fluxing agent to be infinitely miscible with the raw materials for preparing the alkali metal borophosphate compound, so that the ratio can be easily adjusted without introducing impurities, and can also solve the problem of B 2 O 3 or H 3 BO 3 The problem of high viscosity.

[0041] In a preferred embodiment, the amount of the self-fluxing agent is 0.01-60% of the mass of the raw material for preparing the alkali metal borophosphate compound, preferably 20-40%, and more preferably 20-30%. The present invention controls the amount of the self-fluxing agent within the above range. If the amount is lower than the above range, the growth temperature of the system will be too high, volatilization will occur, and the probability of defects such as flocculent inclusions during crystal growth will increase. If the amount is higher than the above range, a miscellaneous crystal phase will appear, affecting the normal growth of the CBPO ​​crystal, and at the same time, the growing crystal will be prone to defects such as block inclusions.

[0042] In a preferred embodiment, the additive includes CsF, CsCl, CsBr, CsOH, CsNO 3 , Cs 2 O and Cs 2 CO 3 One or more of the following, preferably CsF, CsOH and CsNO 3 The present invention adopts the above-mentioned additives to significantly reduce the viscosity of the melt, which is helpful to increase the pulling rate and the growth of large-sized single crystals.

[0043] In a preferred embodiment, the amount of the additive is 0.01-15% of the mass of the raw material for preparing the alkali metal borophosphate compound, preferably 5-10%. The present invention controls the amount of the additive within the above range. If the amount is lower than the above range, the melt viscosity will increase, the crystal growth rate will decrease, and the probability of defects such as block inclusions will increase. If the amount is higher than the above range, the melt will volatilize, and the probability of defects such as flocculent inclusions will increase during crystal growth.

[0044] In a preferred embodiment, the crucible is a platinum crucible of φ120 mm×100 mm.

[0045] In a preferred embodiment, the melting temperature is 820-900° C. and the melting time is 20-48 hours.

[0046] In a preferred embodiment, the temperature of the critical point of crystal floating is 550-680°C, preferably 630-650°C.

[0047] In a preferred embodiment, the cooling procedure for cooling the mixed melt to the critical point of crystal floating is as follows: the mixed melt is cooled to 680-750°C at room temperature, and then cooled to the critical point of crystal floating at a cooling rate of 0.8-1°C / day in the first week and 0.4-0.6°C / day thereafter.

[0048] In a preferred embodiment, the pulling speed is 0.2-3.5 mm / day, preferably 0.5-2 mm / day, and more preferably 0.2-1.1 mm / day. After the lateral size of the crystal increases to the desired size, or the lateral growth rate of the crystal decreases, the radial size of the crystal is increased by controlling the pulling speed, and the size increase rate of the crystal is further increased to obtain a larger CBPO ​​single crystal.

[0049] In a preferred embodiment, the rotation rate of the crucible is -100 rpm to 100 rpm, preferably -50 rpm to 50 rpm. The present invention increases the melt convection by controlling the rotation rate of the crucible, making the melt temperature distribution more uniform and the material transport rate stable, thereby growing a single crystal with better quality and larger size.

[0050] In a preferred embodiment, the seed crystal is rotated while being pulled; the rotation speed of the seed crystal is 4 to 35 rpm, preferably 4 to 20 rpm, and more preferably 4 to 10 rpm.

[0051] In a preferred embodiment, the size of the seed crystal is φ3×10 mm to 10×10 mm.

[0052] In a preferred embodiment, the annealing temperature is 400-600° C. and the time is 48-100 hours. The present invention ensures the quality of the single crystal through annealing treatment, thereby effectively reducing cracks in the cutting process or breakage in actual use.

[0053] In a preferred embodiment, the molecular formula of the large-sized alkali metal borophosphate compound crystals is Cs 3 [(BOP) 2 (B 3 O 7 ) 3 ], molecular weight is 947.58, space group is R3, unit cell parameters are a=b=11.3066(9), c=13.9539(13), α=β=90°, γ=120°, Z=3.

[0054] The present invention adopts a method combining a pulling method with a crucible rotation method to prepare an alkali metal borophosphate compound. The pulling method greatly improves the growth rate of the crystal and realizes the large-size preparation of the single crystal. The crucible rotation method effectively inhibits the multi-nuclear condensation during the crystal growth, so that the internal uniformity of the obtained large-size single crystal is better, the blank utilization rate is higher, and the growth quality of the crystal is significantly improved. By combining the two, high-quality, large-size alkali metal borophosphate compound single crystals are obtained. The present invention significantly reduces the viscosity of the melt by using a self-fluxing agent and an additive, which is helpful for the acceleration of the pulling rate and the growth of large-size single crystals. The present invention ensures the quality of the single crystal by annealing the grown crystal, thereby effectively reducing the occurrence of cracks in the cutting process or the occurrence of fractures in actual use.

[0055] The room temperature in the embodiments of the present invention refers to "25±2°C".

[0056] Unless otherwise specified, the raw materials in the examples of the present invention were purchased from commercial sources.

[0057] Example 1

[0058] A large-size single crystal growth method of an alkali metal borophosphate compound comprises the following steps:

[0059] (1) Weigh Cs in a molar ratio of 3:22:4 2 CO 3 , H 3 BO 3 and P 2 O 5 As a raw material for preparing an alkali metal borophosphate compound, the raw material for preparing an alkali metal borophosphate compound is mixed with B 2 O 3 and CsF were mechanically mixed and pre-pressed in sequence, and then placed in a φ120mm×100mm platinum crucible, heated to 850°C, and kept at a constant temperature for 30 hours to obtain a mixed melt; wherein, B 2 O 3 The amount of is 20% by weight of the raw material for preparing the alkali metal borophosphate compound, and the amount of CsF is 5% by weight of the raw material for preparing the alkali metal borophosphate compound;

[0060] (2) The mixed melt obtained in step (1) is cooled to 700°C at room temperature, and then cooled to the critical point of floating crystal at a cooling rate of 0.8°C / day in the first week and 0.4°C / day thereafter, and then a seed crystal of φ10×10 mm is added for crystal growth. After the surface of the seed crystal is slightly melted, the cooling rate is adjusted to 2°C / day, and at the same time, the seed crystal is pulled at a pulling speed of 1.1 mm / day, and the crucible is rotated at a rotation rate of -10 rpm, and the rotation speed of the seed crystal is 8 rpm. After the crystal growth is completed, the crystal is pulled out of the mixed melt liquid surface, cooled to room temperature within 48 hours, and then annealed at 400°C for 48 hours to obtain a Cs crystal with a size of 65 mm×48 mm×31 mm. 3 [(BOP) 2 (B 3 O 7 ) 3 ](CBPO) single crystal.

[0061] Example 2

[0062] A large-size single crystal growth method of an alkali metal borophosphate compound comprises the following steps:

[0063] (1) Weigh CsOH and H in a molar ratio of 3:11:2. 3 BO 3 and NH 4 H 2 PO 4 As a raw material for preparing an alkali metal borophosphate compound, the raw material for preparing an alkali metal borophosphate compound, a self-fluxing agent and an additive are mechanically mixed and pre-pressed in sequence, and then placed in a φ120mm×100mm platinum crucible, heated to 820°C, and kept at a constant temperature for 48 hours to obtain a mixed melt; wherein the self-fluxing agent is B 2 O 3 and P 2 O 5 , B 2 O 3 and P 2 O 5 The molar ratio of the self-fluxing agent is 4:1, and the amount of the self-fluxing agent is 30% of the mass of the raw material for preparing the alkali metal borophosphate compound; the additive is CsNO 3 and CsOH, CsNO 3 The molar ratio of CsOH to CsOH is 3:1, and the amount of the additive is 5% of the mass of the raw material for preparing the alkali metal borophosphate compound;

[0064] (2) The mixed melt obtained in step (1) is cooled to 680°C at room temperature, and then cooled to the critical point of floating crystal at a cooling rate of 1°C / day in the first week and 0.6°C / day thereafter, and then a seed crystal of φ3×10 mm is added for crystal growth. After the surface of the seed crystal is slightly melted, the cooling rate is adjusted to 1.5°C / day, and at the same time, the seed crystal is pulled at a pulling speed of 0.5 mm / day, and the crucible is rotated at a rotation rate of -15 rpm, and the rotation speed of the seed crystal is 4 rpm. After the crystal growth is completed, the crystal is pulled out of the mixed melt liquid surface, cooled to room temperature within 80 hours, and then annealed at 400°C for 48 hours to obtain Cs with a size of 65 mm×45 mm×30 mm. 3 [(BOP) 2 (B 3 O 7 ) 3 ](CBPO) single crystal.

[0065] Comparative Example 1

[0066] A method for growing large-size single crystals of alkali metal borophosphate compounds using Figure 2 The device shown comprises a lifting device 1, a rotating lifting device 2, a seed crystal rod 3, a crystal growth furnace 4 and a base support 5. The method comprises the following steps:

[0067] (1) 326g of Cs 2 CO 3 , 256g B 2 O 3 and 154 g of NH 4 H 2 PO 4 (Cs 2 CO 3 , B 2 O 3 and NH 4 H 2 PO 4 The molar ratio is 3:11:4) and then the mixture is mechanically mixed and pre-sintered, and then placed in a φ120mm×100mm platinum crucible, heated to 900°C, and kept at a constant temperature for 20 hours to obtain a mixed melt;

[0068] (2) The mixed melt obtained in step (1) is cooled to 750°C at room temperature, and then cooled to the critical point of floating crystal at a cooling rate of 2°C / day in the first week and 1°C / day thereafter, and then a seed crystal of φ10×10 mm is added for crystal growth. After the surface of the seed crystal is slightly melted, the cooling rate is adjusted to 0.6°C / day. After the crystal growth is completed, the crystal is lifted from the surface of the mixed melt, cooled to room temperature within 48 hours, and then allowed to stand for 3 days, and then annealed at 400°C for 48 hours to obtain Cs with a size of 25 mm×15 mm×10 mm.3 [(BOP) 2 (B 3 O 7 ) 3 ](CBPO) single crystal.

[0069] Example 3

[0070] Any CBPO ​​single crystal obtained in Example 1-2 is oriented, roughly ground, finely polished, and coated to form a single crystal device. Figure 3 As shown, it is placed at position 7 and adopts the intra-cavity frequency conversion method. The laser light source with a wavelength of 1064nm is used as the fundamental frequency light ω. After it is injected into the frequency doubling crystal 7, the frequency doubling light 2ω with a wavelength of 532nm is generated, which is reflected by the green light reflectors 8 and 9 to output 532nm green laser.

[0071] Example 4

[0072] Any CBPO ​​single crystal obtained in Example 1-2 is oriented, roughly ground, finely polished, and coated to form a single crystal device. Figure 4 As shown, it is placed at position 6 and adopts the intra-cavity frequency conversion method. The laser light source with a wavelength of 1064nm is used as the fundamental frequency light ω. After it is injected into the frequency doubling crystal 6, it generates the frequency doubling light 2ω with a wavelength of 532nm, which is reflected by the green light reflectors 7 and 8 to output 532nm green laser.

[0073] Example 5

[0074] Any CBPO ​​single crystal obtained in Example 1-2 is oriented, roughly ground, finely polished, and coated to form a single crystal device. Figure 5 As shown, it is placed at position 9, with a laser light source with a wavelength of 1064nm as the fundamental frequency light ω, which is shot into the frequency doubling crystal 6 (the crystal can be other doubled frequency crystals or CBPO ​​crystals), and generates doubled frequency light 2ω with a wavelength of 532nm. The green light reflectors 7 and 8 reflect and output 532nm green laser light, which is shot into the frequency doubling crystal 9 to generate quadruple frequency light 4ω with a wavelength of 266nm.

[0075] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A method for growing large-size single crystals of alkali metal borophosphate compounds, characterized in that: The following steps are involved: (1) placing raw materials for preparing alkali metal borophosphate compounds, self-fluxing agents and additives in a crucible for melting to obtain a mixed melt; the self-fluxing agent comprises one or more of B2O3, H3BO3, NH4H2PO4, P2O5 and Cs2O; the amount of the self-fluxing agent is 0.01 to 60% of the mass of the raw materials for preparing alkali metal borophosphate compounds; the additive comprises one or more of CsF, CsCl, CsBr, CsOH, CsNO3, Cs2O and Cs2CO3; the amount of the additive is 0.01 to 15% of the mass of the raw materials for preparing alkali metal borophosphate compounds; (2) The mixed melt obtained in step (1) is cooled to a critical point of crystal floating, and then a seed crystal is added to the mixed melt for crystal growth, while the seed crystal is pulled at a pulling speed of 0.2 to 3.5 mm / day, and the crucible is rotated at a rotation rate of -100 rpm to 100 rpm. After the crystal growth is completed, the crystal is pulled out of the mixed melt liquid surface, and annealed to obtain a large-sized alkali metal borophosphate compound single crystal.

2. The large-size single crystal growth method of the alkali metal borophosphate compound according to claim 1, characterized in that: The raw materials for preparing the alkali metal borophosphate compound in step (1) include a cesium source, a boron source and a phosphorus source; the molar ratio of the cesium source, the boron source and the phosphorus source is 3:(11-22):(2-4).

3. The large-size single crystal growth method of the alkali metal borophosphate compound according to claim 2, characterized in that: The cesium source includes Cs2CO3 or CsOH; the phosphorus source includes NH4H2PO4 or P2O5; and the boron source includes B2O3 or H3BO3.

4. The large-size single crystal growth method of the alkali metal borophosphate compound according to claim 1, characterized in that: The melting temperature in step (1) is 820-900° C. and the melting time is 20-48 hours.

5. The large-size single crystal growth method of the alkali metal borophosphate compound according to claim 1, characterized in that: The temperature of the critical point of crystal floating in step (2) is 550-680°C.

6. The large-size single crystal growth method of the alkali metal borophosphate compound according to claim 1, characterized in that: The cooling procedure for cooling the mixed melt to the critical point of crystal floating in step (2) is as follows: the mixed melt is cooled to 680-750°C at room temperature, and then cooled to the critical point of crystal floating at a cooling rate of 0.8-1°C / day in the first week and 0.4-0.6°C / day thereafter.

7. The large-size single crystal growth method of the alkali metal borophosphate compound according to claim 1, characterized in that: The annealing temperature in step (2) is 400-600° C. and the annealing time is 48-100 hours.

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