A method for vapor phase growth of large-size ammonium fluoroborate single crystals

Abstract

This invention discloses a method for large-size ammonium fluoroborate single crystal vapor phase growth, comprising the following steps: weighing two or more compounds containing NH4, B, O, and F as raw materials in a stoichiometric ratio of 1:4:6:1, mixing them thoroughly, adding a transport agent to obtain an initial mixture, and loading the initial mixture into a crystallization vessel; during the crystal growth stage, seed crystals or suspended seed crystals are selected by geometric selection and temperature screening among the grains; the crystallization vessel is dynamically heated within the temperature gradient zone of a vertical tube furnace, the dynamic heating being achieved by independently raising or lowering the temperatures of the high-temperature and low-temperature zones to dynamically control the temperature gradient of the crystal growth zone, so as to match it with the temperature gradient required at each stage of the crystal growth process; the raw materials crystallize in the crystal growth zone under the transport agent, resulting in large-size ammonium fluoroborate crystals. This invention produces large-size single crystals, is simple to operate, and highly practical, representing a superior ammonium fluoroborate single crystal growth process.

Description

Technical Field

[0001] This invention relates to the fields of crystal growth and functional materials, and particularly to a method for the vapor phase growth of large-size ammonium fluoroborate single crystals. Background Technology

[0002] Deep ultraviolet (DUV) nonlinear optical crystals have attracted worldwide interest due to their ability to generate coherent light with wavelengths below 200 nm through direct second harmonic generation from solid-state lasers. Although many materials exhibit nonlinear optical properties, only a few can be used for DUV second harmonic generation. Ammonium fluoroborate, with the molecular formula NH4B4O6F, abbreviated as ABF, exhibits a sufficiently large second harmonic response and good phase matching. Its excellent nonlinear optical properties primarily stem from the shared oxygen atoms of the nonlinear anionic groups (BO3) and (BO3F) in the crystal lattice, forming a (B4O6F) structure perpendicular to the a-axis. ∞ It has a two-dimensional layered structure, with the layers connected by hydrogen bonds.

[0003] The uniform arrangement of ammonium fluoroborate (ABF) structural units makes it an excellent deep-ultraviolet (DLU) frequency-doubling crystal, and it is another crystal, following KBe2(BO3)F2 and RbBe2(BO3)F2, capable of generating LU laser output (wavelength 158.9 nm) through direct frequency doubling. Even better, the raw materials used for ABF growth are non-toxic, and the resulting crystals exhibit good chemical stability and processing characteristics. The frequency doubling effect of ABF crystals can be used to fabricate LU laser sources for precision machining and measurement.

[0004] ABF is a heterogeneous molten compound that can be grown using the high-temperature molten salt method (also called the flux method). Due to its relatively small interlayer spacing and the presence of a hydrogen bond network, ABF's layered growth habit is not particularly pronounced. ABF crystals can be grown into millimeter-sized single crystals using the high-temperature molten salt method. However, the crystals cannot be cut and processed according to phase-matching angles to fabricate prism-less frequency-doubling devices. Currently, ABF crystals are grown using spontaneous nucleation, making the control of the number of nuclei particularly important. Because there is no seed crystal rotation during growth, the process relies primarily on diffusion, resulting in very weak heat and mass transport, slow crystal growth, and numerous inclusions. In summary, ABF crystal growth and applications suffer from challenges such as difficulty in controlling nucleation, a large number of nuclei, and small crystal size. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention aims to provide a method for large-size ammonium fluoroborate single crystal vapor phase growth, so as to solve the problem of small size in seedless and molten salt methods for growing ammonium fluoroborate single crystals.

[0006] To achieve the above objectives, this invention proposes a method for the vapor phase growth of large-size ammonium fluoroborate single crystals, comprising the following steps:

[0007] S1. Raw material preparation;

[0008] Weigh two or more compounds containing NH4, B, O, and F as raw materials according to a stoichiometric ratio of 1:4:6:1, mix them thoroughly, and add a transport agent or not to obtain an initial mixture (ammonium fluoroborate polycrystalline material can also be used). Load the initial mixture into a crystallization vessel.

[0009] S2. Seed crystals are selected by suspension or spontaneous nucleation.

[0010] Suspended seed crystal: Suspend the seed crystal at the top of the crystallization vessel, then seal it. Place the sealed crystallization vessel into a vertical tube furnace or molten salt furnace. The vertical tube furnace or molten salt furnace is equipped with a temperature gradient zone, which includes a high-temperature zone, a low-temperature zone, and a crystal growth zone. By adjusting the temperature field, the temperature of the high-temperature zone is controlled at 300-550℃, the temperature of the low-temperature zone is controlled at 20-300℃, and the temperature of the crystal growth zone is controlled at 300-400℃. The temperature is maintained for 1-10 days.

[0011] Spontaneous nucleation screening of seed crystals includes two methods: geometric elimination between grains and temperature screening.

[0012] Geometric elimination of grains: The top of the crystallization vessel is designed as a cone with a taper of 30-40%. The crystallization vessel is placed in a vertical tube furnace or molten salt furnace, which has a temperature gradient zone, including a high-temperature zone, a low-temperature zone, and a crystal growth zone. By adjusting the temperature field, the temperature of the high-temperature zone is controlled at 300-550℃, the temperature of the low-temperature zone is controlled at 20-300℃, and the temperature of the crystal growth zone is controlled at 300-400℃. The temperature is maintained for 1-5 days, and seed crystals are screened out.

[0013] Temperature screening: The crystallization vessel is placed in a vertical tube furnace or molten salt furnace, which is equipped with a temperature gradient zone, including a high temperature zone, a low temperature zone, and a crystal growth zone. By adjusting the temperature field, the temperature of the high temperature zone is controlled at 300-550℃, the temperature of the low temperature zone is controlled at 20-300℃, and the temperature of the crystal growth zone is controlled at 300-400℃. After holding at this temperature for 1-10 days, temperature oscillation is performed in the crystal growth zone to screen out seed crystals.

[0014] S3, crystal growth;

[0015] The crystallization vessel is dynamically heated within a temperature gradient zone. This dynamic heating involves independently raising or lowering the temperatures of the high-temperature and low-temperature zones to dynamically control the temperature gradient of the crystal growth zone, ensuring it matches the temperature gradient required for each stage of the crystal growth process. The raw material crystallizes in the crystal growth zone under the transport agent, resulting in large-sized ammonium fluoroborate crystals.

[0016] In the above scheme, the mass percentage of the transport agent in the initial mixture is 0-80%.

[0017] In the above scheme, the transport agent is N2, H2O, HF, H3BO3, NH3·H2O, NH4F, NH4Cl, NH4Br, (NH4)2CO3, NH4HCO3 or (NH4)2SO4.

[0018] In the above scheme: the crystallization vessel is a platinum crucible, iridium crucible, ceramic crucible, quartz tube or stainless steel crucible with a sealed structure.

[0019] In the above scheme, the specific operation of the dynamic heating control is as follows: the high temperature zone is programmed to increase the temperature at a rate of 2-5℃ / h, the low temperature zone is programmed to increase the temperature at a rate of 5-10℃ / h for 5-10 hours, and then programmed to decrease the temperature at a rate of 15-20℃ / h.

[0020] In the above scheme, the temperature gradient of the crystal growth region is 1 to 40℃ / cm.

[0021] In the above scheme: the temperature gradient during the initial stage of crystal growth is 1–30 °C / cm;

[0022] When the crystal grows to a size greater than 3 mm in at least one dimension, the temperature gradient is 1–25 °C / cm.

[0023] When the crystal grows to a size greater than 10 mm in at least one dimension, the temperature gradient is 1–40 °C / cm.

[0024] In the above scheme: the high temperature zone, the low temperature zone and the homogeneous crystal growth zone include at least one independent heating zone, which facilitates zoned heating or cooling.

[0025] The beneficial effects of this invention are:

[0026] 1. The gas-phase method is adopted, and seed crystals are selected by suspending them or by using temperature oscillation and crucible shape, which facilitates the growth of large-sized and structurally complete ABF crystals; 2. Temperature control is cleverly applied, and large-sized, high-quality ABF single crystals are obtained by adjusting the temperature gradient at different stages; 3. The layered growth habit of ABF crystals can be overcome, enabling large-sized bulk crystal growth (at least one dimension is greater than or equal to 30mm). The positive effect of this invention is the growth of high-optical-quality ABF crystals with a size of 30mm × 20mm × 10mm or larger; 4. The crystals can be cut and processed into frequency doubling devices according to the phase matching angle direction, paving the way for their large-scale use and industrialization.

[0027] In summary, the ABF single crystal structure of this invention is stable and has excellent frequency doubling performance; the full width at half maximum (FWHM) of the high-resolution X-ray diffraction is less than 40″, indicating that the crystal has high crystal quality; the UV-Vis-NIR spectrophotometer shows that the transmittance of the unpolished a-sheet is as high as 85% or more in the 1500-200 nm band; the Maker fringe method test shows that the ABF has a large nonlinear optical frequency doubling response. Attached Figure Description

[0028] Figure 1 It is the ammonium fluoroborate single crystal material grown in Example 1.

[0029] Figure 2 This is the rocking curve of the ammonium fluoroborate single crystal grown in Example 1.

[0030] Figure 3 This is the transmission spectrum of the ammonium fluoroborate single crystal grown in Example 1.

[0031] Figure 4 This is a frequency doubling coefficient test of the ammonium fluoroborate single crystal grown in Example 1. Detailed Implementation

[0032] Example 1

[0033] Weigh B2O3 and NH4F compounds containing NH4, B, O and F in a stoichiometric ratio of 1:4:6:1 as raw materials, mix them well, and then add a transport agent, H3BO3, with a mass fraction of 10% in the mixed raw materials.

[0034] The mixed raw materials are placed in a platinum crucible and sealed. The sealed crucible is then placed in a vertical three-section molten salt furnace, with the raw materials in the high-temperature zone. By adjusting the temperature field, the temperature in the high-temperature zone is controlled at 300-550℃, the temperature in the low-temperature zone at 20-300℃, and the temperature in the crystal growth zone at 300-400℃. After holding at these temperatures for 1-10 days, temperature oscillation is performed in the crystal growth zone (heating and cooling cycles are performed within the set temperature range) to select seed crystals.

[0035] During crystal growth, dynamic control is implemented. The high-temperature zone is programmed to heat up at a rate of 5℃ / h, while the low-temperature zone is programmed to heat up at a rate of 10℃ / h for 5 hours, followed by a programmed cooling rate of 15℃ / h. By adjusting the temperatures of the high-temperature and low-temperature zones within a set temperature range, the temperature gradient in the growth zone is dynamically controlled within 10-30℃ / cm to match the real-time gradient requirements of crystal growth.

[0036] After crystal growth, the temperature was lowered to room temperature at a rate of 50℃ / h. This ultimately yielded ammonium fluoroborate crystalline material, such as... Figure 1 As shown, the grown single crystal has a size of 30 mm × 25 mm × 12 mm. The crystal quality is good and the uniformity is excellent.

[0037] Example 2

[0038] Weigh out B₂O₃ and NH₄F compounds containing NH₄, B, O, and F in a stoichiometric ratio of 1:4:6:1, mix them thoroughly, and then add a transport agent to obtain an initial mixture. The transport agent is NH₄Cl, and its mass fraction in the initial mixture is 5%.

[0039] The initial mixture is thoroughly mixed in a mixer for 24 hours. The resulting mixture is then placed in a platinum crucible, with a seed crystal suspended on top. The crucible is then sealed and placed in a vertical three-section molten salt furnace. The raw material is positioned in the high-temperature zone, while the corresponding portion of the crucible for optimized nucleation is in the crystal growth zone. By adjusting the temperature field, the high-temperature zone is controlled at 300-550℃, the low-temperature zone at 20-300℃, and the crystal growth zone at 300-400℃, and the temperature is maintained for 1-10 days.

[0040] During crystal growth, dynamic control is implemented. The high-temperature zone is programmed to heat up at a rate of 2℃ / h, while the low-temperature zone is programmed to heat up at a rate of 5℃ / h for 10 hours, followed by a programmed cooling rate of 15℃ / h. By adjusting the temperatures of the high-temperature and low-temperature zones within a set temperature range, the temperature gradient in the growth zone is dynamically controlled at 15-20℃ / cm to match the real-time gradient requirements of crystal growth.

[0041] After crystal growth, the temperature was lowered to room temperature at a rate of 50℃ / h. Ammonium fluoroborate crystal material was finally obtained, with single crystals measuring 30 mm × 25 mm × 10 mm. The crystals exhibited good quality and uniformity.

[0042] Example 3

[0043] Weigh out B2O3 and NH4F compounds containing NH4, B, O, and F in a stoichiometric ratio of 1:4:6:1 as raw materials, and mix them thoroughly to obtain an initial mixture. Place the initial mixture into an alumina ceramic crucible, suspend a seed crystal on top of the crucible, and then seal it. Place the sealed crucible in a vertical three-section molten salt furnace, with the raw materials in the high-temperature zone and the corresponding part of the crucible for optimized nucleation in the crystal growth zone. Adjust the temperature field to control the high-temperature zone temperature at 300-550℃, the low-temperature zone temperature at 20-300℃, and the crystal growth zone temperature at 300-400℃, and hold at these temperatures for 1-10 days.

[0044] During crystal growth, dynamic control is implemented. The high-temperature zone is programmed to heat up at a rate of 2℃ / h, while the low-temperature zone is programmed to heat up at a rate of 5℃ / h for 10 hours, followed by a programmed cooling rate of 20℃ / h. By adjusting the temperatures of the high-temperature and low-temperature zones within a set temperature range, the temperature gradient in the growth zone is dynamically controlled within 10-30℃ / cm to match the real-time gradient requirements of crystal growth.

[0045] After crystal growth, the temperature was lowered to room temperature at a rate of 50℃ / h. Ammonium fluoroborate crystal material was finally obtained, with single crystals measuring 30 mm × 20 mm × 10 mm. The crystals exhibited good quality and uniformity.

[0046] The structure and properties of the ammonium fluoroborate single crystal obtained in Example 1 were tested:

[0047] (a) A stepless surface 'a' of the crystal was cleaved for high-resolution XRD diffraction testing. The diffraction pattern of the ammonium fluoroborate single crystal showed a full width at half maximum (FWHM) of less than 40″, indicating high crystal quality (see [reference]). Figure 2 ).

[0048] (b) The obtained ammonium fluoroborate single crystals were cleaved to produce high-quality sheet a. Transmittance was measured using a UV-Vis-NIR spectrophotometer. The transmittance spectrum showed that the transmittance was as high as 85% in the 200-1500 nm wavelength range (see...). Figure 3 ).

[0049] (c) The obtained ammonium fluoroborate a-plate was placed on a self-built laser optical path, and tested using KDP as a reference sample. Through fitting, the octave response of ABF was found to be 2.8 times that of KDP. (See...) Figure 4 ).

[0050] As can be seen from the above embodiments, the large-size ABF single crystals grown by this method have high optical quality; the transmittance in the 200-1500nm band is as high as 85% or more, and it has a high frequency doubling response. Moreover, the crystal has stable physical and chemical properties, is easy to process and store, and is expected to be applied to ultraviolet and deep ultraviolet laser frequency doubling devices.

Claims

1. A method for growing large-size ammonium fluoroborate single crystals, characterized in that... Growth via vapor phase includes the following steps: S1. Raw material preparation; Weigh two or more compounds containing NH4, B, O, and F, or ammonium fluoroborate polycrystalline material, according to a stoichiometric ratio of 1:4:6:

1. Grind them evenly and then add a transport agent or not to obtain an initial mixture. Load the initial mixture into a crystallization vessel. S2. Seed crystals are selected by suspension or spontaneous nucleation. Suspended seed crystal: Suspend the seed crystal at the top of the crystallization vessel, then seal it. Place the sealed crystallization vessel into a vertical tube furnace or molten salt furnace. The vertical tube furnace or molten salt furnace is equipped with a temperature gradient zone, which includes a high-temperature zone, a low-temperature zone, and a crystal growth zone. By adjusting the temperature field, the temperature of the high-temperature zone is controlled at 300-550℃, the temperature of the low-temperature zone is controlled at 20-300℃, and the temperature of the crystal growth zone is controlled at 300-400℃. The temperature is maintained for 1-10 days. Spontaneous nucleation screening of seed crystals includes two methods: geometric elimination between grains and temperature screening. Geometric elimination of grains: The top of the crystallization vessel is designed as an inverted cone with a taper of 30-40%. The crystallization vessel is placed in a vertical tube furnace or molten salt furnace, which has a temperature gradient zone, including a high-temperature zone, a low-temperature zone, and a crystal growth zone. By adjusting the temperature field, the temperature of the high-temperature zone is controlled at 300-550℃, the temperature of the low-temperature zone is controlled at 20-300℃, and the temperature of the crystal growth zone is controlled at 300-400℃. The temperature is maintained for 1-5 days, and seed crystals are screened out. Temperature screening: The crystallization vessel is placed in a vertical tube furnace or molten salt furnace, which is equipped with a temperature gradient zone, including a high temperature zone, a low temperature zone, and a crystal growth zone. By adjusting the temperature field, the temperature of the high temperature zone is controlled at 300-550℃, the temperature of the low temperature zone is controlled at 20-300℃, and the temperature of the crystal growth zone is controlled at 300-400℃. After holding at this temperature for 1-10 days, temperature oscillation is performed in the crystal growth zone to screen out seed crystals. S3, crystal growth; The crystallization vessel is dynamically heated within a temperature gradient zone. This dynamic heating involves independently raising or lowering the temperatures of the high-temperature and low-temperature zones to dynamically control the temperature gradient of the crystal growth zone, ensuring it matches the temperature gradient required for each stage of the crystal growth process. The raw material crystallizes in the crystal growth zone under the transport agent, resulting in large-sized ammonium fluoroborate crystals.

2. The method for large-size ammonium fluoroborate single crystal vapor phase growth according to claim 1, characterized in that: The transport agent accounts for 0-80% by mass in the initial mixture.

3. The method for large-size ammonium fluoroborate single crystal vapor phase growth according to claim 2, characterized in that: The transport agent is N2, H2O, HF, H3BO3, NH3·H2O, NH4F, NH4Cl, NH4Br, (NH4)2CO3, NH4HCO3 or (NH4)2SO4.

4. The method for large-size ammonium fluoroborate single crystal vapor phase growth according to claim 1, characterized in that: The crystallization vessel is a platinum crucible, gold crucible, iridium crucible, ceramic crucible, quartz tube, or stainless steel crucible with a sealed structure.

5. The method for large-size ammonium fluoroborate single crystal vapor phase growth according to any one of claims 1-3, characterized in that: The specific operation of the dynamic heating control is as follows: the high temperature zone is programmed to increase in temperature at a rate of 2-5℃ / h, the low temperature zone is programmed to increase in temperature at a rate of 5-10℃ / h for 5-10 hours, and then programmed to decrease in temperature at a rate of 15-20℃ / h.

6. The method for large-size ammonium fluoroborate single crystal vapor phase growth according to claim 5, characterized in that: The temperature gradient in the crystal growth region is 1–40 °C / cm.

7. The method for large-size ammonium fluoroborate single crystal vapor phase growth according to claim 6, characterized in that: The temperature gradient during the initial stage of crystal growth is 1–30 °C / cm. When the crystal grows to a size greater than 3 mm in at least one dimension, the temperature gradient is 1–25 °C / cm. When the crystal grows to a size greater than 10 mm in at least one dimension, the temperature gradient is 1–40 °C / cm.

8. The method for large-size ammonium fluoroborate single crystal vapor phase growth according to claim 1, characterized in that: The high-temperature zone, low-temperature zone, and crystal growth zone include at least one independent heating zone.

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