Vapor phase growth method of large-size ammonium fluoroborate single crystal

Abstract

The invention discloses a vapor phase growth method of a large-size ammonium fluoroborate single crystal, which comprises the following steps: weighing two or more compounds containing NH4, B, O and F as raw materials according to a stoichiometric ratio of 1: 4: 6: 1, uniformly mixing, adding a transport agent to obtain an initial mixture, and filling the initial mixture into a crystallization kettle; in the crystal growth stage, seed crystals are screened out or suspended by utilizing geometric elimination and temperature among crystal grains; the crystallization kettle is subjected to dynamic regulation and control heating in a temperature gradient area of a vertical tube furnace, and the dynamic regulation and control heating comprises the steps that the temperature of a high-temperature area and the temperature of a low-temperature area are independently increased or decreased, and the temperature gradient of a crystal growth area is dynamically controlled so that the temperature gradient can be matched with the temperature gradient needed in each stage of the crystal growth process; the raw materials are crystallized in the crystal growth area under the carrying of the transport agent, and the large-size ammonium fluoroborate crystal is obtained after growth. The method has the advantages of large single crystal size, simple operation and strong practicality, and is a good ammonium fluoborate single crystal growth process.

Description

Technical Field

[0001] The invention relates to the fields of crystal growth and functional materials, and in particular to a vapor phase growth method for a large-sized ammonium fluoroborate single crystal. Background Art

[0002] Deep ultraviolet nonlinear optical crystals have attracted worldwide interest because they generate coherent light with a wavelength below 200nm from the direct second harmonic generation output of solid-state lasers. Although many materials show nonlinear optical properties, only a few can be used for deep ultraviolet second harmonic generation. The molecular formula of ammonium fluoroborate is NH4B4O6F, abbreviated as ABF. It exhibits a sufficiently large second harmonic response and good phase matching. The excellent nonlinear optical properties mainly come from the fact that the nonlinear anion groups (BO3) and (BO3F) in the lattice are connected by shared oxygen atoms to form a (B4O6F) perpendicular to the a-axis. ∞ Two-dimensional layered structure, with layers connected by hydrogen bonds.

[0003] The neat and consistent arrangement of the structural elements of ammonium fluoroborate determines that it is a very excellent deep ultraviolet frequency doubling crystal. It is also another crystal that can produce deep ultraviolet laser (wavelength 158.9nm) output through direct frequency doubling after KBe2(BO3)F2 and RbBe2(BO3)F2. What's more, the raw materials used for ABF growth are non-toxic, and the grown crystals have good chemical stability and processing characteristics. Through the frequency doubling effect of ABF crystals, deep ultraviolet laser light sources for precision processing and measurement can be produced.

[0004] ABF is a non-isotropic molten compound and can be grown by the high-temperature molten salt method (also called the flux method). Since the interlayer spacing of ABF is relatively small and connected by a hydrogen bond network, its layered growth habit is not very serious. ABF crystals can be grown into millimeter-scale single crystals by the high-temperature molten salt method. The crystals cannot be cut and processed according to the phase matching angle to make non-prism-doubling devices. At present, ABF crystals grow by spontaneous nucleation, and it is particularly important to control the number of nuclei. However, since there is no rotation of the seed crystal during the growth process, the growth process basically relies on diffusion, the heat transfer and mass transfer are very weak, the crystal grows slowly, and there are many inclusions. In summary, there are problems in the growth and application of ABF crystals, such as difficult to control nucleation, many crystal nuclei, and small crystal size. Summary of the invention

[0005] In view of the problems existing in the above-mentioned prior art, the present invention aims to provide a method for vapor phase growth of large-sized ammonium fluoroborate single crystals to solve the problem of small size of ammonium fluoroborate single crystals grown by seedless crystal and molten salt method.

[0006] In order to achieve the above object, the present invention proposes a method for vapor phase growth of large-sized 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 in a metering ratio of 1:4:6:1, add a transfer agent after mixing, and obtain an initial mixture (ammonium fluoroborate polycrystals can also be used as the raw material), and put the initial mixture into a crystallization kettle;

[0009] S2, suspending seed crystals or spontaneous nucleation to select seed crystals;

[0010] Hanging seed crystals: hang seed crystals on the top of the crystallization kettle, then seal it, and put the sealed crystallization kettle into a vertical tube furnace or molten salt furnace. The vertical tube furnace or molten salt furnace is provided 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°C, the temperature of the low temperature zone is controlled at 20-300°C, and the temperature of the crystal growth zone is controlled at 300-400°C, and the temperature is kept for 1-5 days;

[0011] Spontaneous nucleation to select seed crystals includes two methods: geometric elimination between grains and temperature screening;

[0012] Geometric elimination between crystal grains: the top of the crystallization kettle is designed to be conical with a taper of 30-40%. The crystallization kettle is placed in a vertical tube furnace or a molten salt furnace. The vertical tube furnace or the molten salt furnace is provided 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°C, the temperature of the low temperature zone is controlled at 20-300°C, and the temperature of the crystal growth zone is controlled at 300-400°C. The temperature is kept for 1-10 days to screen out the seed crystals.

[0013] Temperature screening: Place the crystallization kettle in a vertical tube furnace or molten salt furnace, which is provided 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°C, the temperature of the low temperature zone is controlled at 20-300°C, and the temperature of the crystal growth zone is controlled at 300-400°C. After keeping the temperature for 1-10 days, perform temperature oscillation in the crystal growth zone to screen out the seed crystals.

[0014] S3, crystal growth;

[0015] The crystallization kettle is dynamically controlled and heated in the temperature gradient zone. The dynamic controlled heating is: the temperature gradient of the crystal growth zone is dynamically controlled by independently heating or cooling the temperature of the high temperature zone and the low temperature zone to match the temperature gradient required in each stage of the crystal growth process; the raw material is crystallized in the crystal growth zone under the carrier, and large-sized ammonium fluoroborate crystals are obtained after the crystal growth.

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

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

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

[0019] In the above scheme: the specific operation of the dynamic control heating is: the high temperature zone is programmed to heat up at a rate of 2-5°C / h, the low temperature zone is first programmed to heat up at a rate of 5-10°C / h for 5-10 hours, and then programmed to cool down at a rate of 15-20°C / h.

[0020] In the above scheme: the temperature gradient of the crystal growth zone is 1 to 40°C / cm;

[0021] The temperature gradient during the initial stage of crystal growth is 1 to 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 to 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 to 40° C. / cm.

[0024] In the above scheme: the high temperature zone, low temperature zone and uniform crystal growth zone include at least one independent heating zone, which is convenient for zone heating or cooling.

[0025] The beneficial effects of the present invention are:

[0026] 1. The gas phase method is adopted, and the seed crystals are suspended or selected by temperature oscillation and crucible shape, which is conducive to the growth of large-sized and structurally complete ABF crystals; 2. The temperature control is cleverly applied, and large-sized and 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, so that the crystals can achieve large-sized block growth (at least one dimension is greater than or equal to 30mm). The positive effect of the present invention is to grow high-optical quality ABF crystals with a size of 30mm×20mm×10mm or more; 4. The crystals can be cut and processed into frequency doubling devices in the direction of the phase matching angle, paving the way for their large-scale use and industrialization.

[0027] In summary, the ABF single crystal of the present invention has a stable structure and excellent frequency doubling performance; the high-resolution X-ray diffraction half-peak width is less than 40", indicating that the crystal has a high crystalline quality; the UV-visible near-infrared spectrophotometer shows that the transmittance of the unpolished a-sheet is as high as more than 85% in the 1500-200nm band; the Maker fringe method test shows that ABF has a large nonlinear optical frequency doubling response. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0029] Figure 2 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 test of the frequency doubling coefficient of the ammonium fluoroborate single crystal grown in Example 1. DETAILED DESCRIPTION

[0032] Example 1

[0033] B2O3 and NH4F compounds containing NH4, B, O and F are weighed as raw materials in a metering ratio of 1:4:6:1, and a transfer agent is added after mixing. The transfer agent is H3BO3, and the mass fraction of the transfer agent in the mixed raw materials is 10%.

[0034] The mixed raw materials are placed in a platinum crucible and sealed, and the sealed crucible is placed in a vertical three-stage molten salt furnace, where the raw materials are in the high temperature 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 1-5 days of heat preservation, the temperature is oscillated in the crystal growth zone (heating and cooling cycles are performed within the set temperature range) to screen out the seed crystals.

[0035] During the crystal growth process, dynamic regulation is performed, the high temperature zone is programmed to heat up at a rate of 5°C / h, and the low temperature zone is first programmed to heat up at a rate of 10°C / h for 5 hours, and then programmed to cool down at a rate of 15°C / h. By regulating the temperature of the high temperature zone and the low temperature zone within the set temperature range, the temperature gradient of the growth zone is dynamically regulated at 10-30°C / cm to match the real-time requirements of the crystal growth gradient.

[0036] After the crystal growth is completed, the temperature is lowered to room temperature at 50°C / h. Finally, ammonium fluoroborate crystal material is obtained, such as Figure 1 As shown, the size of the grown single crystal is 30mm×25mm×12mm. The crystal quality is good and the uniformity is good.

[0037] Example 2

[0038] B2O3 and NH4F compounds containing NH4, B, O, and F are weighed as raw materials in a metering ratio of 1:4:6:1, and a transfer agent is added after mixing to obtain an initial mixture. The transfer agent is NH4Cl, and the mass fraction of the transfer agent in the initial mixture is 5%.

[0039] The initial mixture is mixed in a mixer for 24 hours, and the mixed raw materials are put into a platinum crucible, and a seed crystal is hung on the top of the crucible, and then sealed. The sealed crucible is placed in a vertical three-stage molten salt furnace, and the raw materials are in the high temperature zone, and the corresponding part of the crucible for optimizing nucleation is in the 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℃, and the temperature is kept for 1-5 days.

[0040] During the crystal growth process, dynamic regulation is performed, the high temperature zone is programmed to heat up at a rate of 2°C / h, and the low temperature zone is programmed to heat up at a rate of 5°C / h for 10 hours, and then programmed to cool down at a rate of 15°C / h. By regulating the temperature of the high temperature zone and the low temperature zone within the set temperature range, the temperature gradient of the growth zone is dynamically regulated at 15-20°C / cm to match the real-time requirements of the crystal growth gradient.

[0041] After the crystal growth is completed, the temperature is lowered to room temperature at 50°C / h. Finally, ammonium fluoroborate crystal material is obtained, and the size of the grown single crystal is 30mm×25mm×10mm. The crystal quality is good and the uniformity is good.

[0042] Example 3

[0043] Weigh B2O3 and NH4F compounds containing NH4, B, O, and F as raw materials in a metering ratio of 1:4:6:1, and mix them to obtain an initial mixture. Put the initial mixture into an alumina ceramic crucible, suspend a seed crystal on the top of the crucible, and then seal it. Place the sealed crucible in a vertical three-stage molten salt furnace, with the raw materials in the high temperature zone, and the corresponding part of the crucible for optimizing nucleation is in the crystal growth zone. By adjusting the temperature field, the temperature in the high temperature zone is controlled at 300-550°C, the temperature in the low temperature zone is controlled at 20-300°C, and the temperature in the crystal growth zone is controlled at 300-400°C. Keep warm for 1-5 days to obtain a seed crystal.

[0044] During the crystal growth process, dynamic regulation is performed, the high temperature zone is programmed to heat up at a rate of 2°C / h, and the low temperature zone is first programmed to heat up at a rate of 5°C / h for 10 hours, and then programmed to cool down at a rate of 20°C / h. By regulating the temperature of the high temperature zone and the low temperature zone within the set temperature range, the temperature gradient of the growth zone is dynamically regulated at 10-30°C / cm to match the real-time requirements of the crystal growth gradient.

[0045] After the crystal growth is completed, the temperature is lowered to room temperature at 50°C / h. Finally, ammonium fluoroborate crystal material is obtained, and the size of the grown single crystal is 30mm×20mm×10mm. The crystal quality is good and the uniformity is good.

[0046] The ammonium fluoroborate single crystal obtained in Example 1 was subjected to structural and performance tests:

[0047] (a) The crystal was cleaved to obtain a sheet without step surface for high-resolution XRD diffraction test. The diffraction spectrum of ammonium fluoroborate single crystal shows that the half-peak width of the crystal is less than 40", and the crystal quality is high (see Figure 2 ).

[0048] (b) The obtained ammonium fluoroborate single crystal was cleaved into high quality a-sheet. The transmittance was tested by UV-visible near-infrared spectrophotometer. The transmittance spectrum showed that the transmittance in the 200-1500nm band was as high as 85% (see Figure 3 ).

[0049] (c) The obtained ammonium fluoroborate a sheet was placed on the self-built laser light path, and KDP was used as the reference sample for testing. Through fitting, it was found that the frequency response of ABF was 2.8 times that of KDP. (See Figure 4 ).

[0050] It can be seen from the above embodiments that the large-sized ABF single crystal grown by this method has high optical quality; the transmittance in the 200-1500nm band is as high as over 85%, with a high frequency doubling response, and the crystal has stable physical and chemical properties, is easy to process and preserve, and is expected to be applied to ultraviolet and deep ultraviolet laser frequency doubling conversion devices.

Claims

1. A method for growing large-size ammonium fluoroborate single crystals, characterized in that Grown by vapor phase method, including the following steps: S1. Raw material preparation; Weigh two or more compounds containing NH4, B, O, and F or ammonium fluoroborate polycrystals as raw materials in a metering ratio of 1:4:6:1, grind them uniformly, add a transfer agent, and obtain an initial mixture, and charge the initial mixture into a crystallization kettle; S2, suspending seed crystals or spontaneous nucleation to select seed crystals; Hanging seed crystals: hang seed crystals on the top of the crystallization kettle, then seal it, and put the sealed crystallization kettle into a vertical tube furnace or molten salt furnace. The vertical tube furnace or molten salt furnace is provided 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°C, the temperature of the low temperature zone is controlled at 20-300°C, and the temperature of the crystal growth zone is controlled at 300-400°C, and the temperature is kept for 1-10 days; Spontaneous nucleation to select seed crystals includes two methods: geometric elimination between grains and temperature screening; Geometric elimination between crystal grains: the top of the crystallization kettle is designed to be an inverted cone with a taper of 30-40%. The crystallization kettle is placed in a vertical tube furnace or a molten salt furnace. The vertical tube furnace or the molten salt furnace is provided 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°C, the temperature of the low temperature zone is controlled at 20-300°C, and the temperature of the crystal growth zone is controlled at 300-400°C. The temperature is kept for 1-5 days to screen out the seed crystals. Temperature screening: Place the crystallization kettle in a vertical tube furnace or molten salt furnace, which is provided 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°C, the temperature of the low temperature zone is controlled at 20-300°C, and the temperature of the crystal growth zone is controlled at 300-400°C. After keeping the temperature for 1-10 days, perform temperature oscillation in the crystal growth zone to screen out the seed crystals. S3, crystal growth; The crystallization kettle is dynamically controlled and heated in the temperature gradient zone. The dynamic controlled heating is: the temperature gradient of the crystal growth zone is dynamically controlled by independently heating or cooling the temperature of the high temperature zone and the low temperature zone to match the temperature gradient required in each stage of the crystal growth process; the raw material is crystallized in the crystal growth zone under the carrier, and large-sized ammonium fluoroborate crystals are obtained after the crystal growth.

2. The method for vapor phase growth of large-size ammonium fluoroborate single crystals according to claim 1, characterized in that: The mass percentage of the transmission agent in the initial mixture is 0-80%.

3. The method for vapor phase growth of large-size ammonium fluoroborate single crystals 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 vapor phase growth of large-size ammonium fluoroborate single crystals according to claim 1, characterized in that: The crystallization kettle is a platinum crucible, a gold crucible, an iridium crucible, a ceramic crucible, a quartz tube or a stainless steel crucible with a sealing structure.

5. The method for vapor phase growth of large-size ammonium fluoroborate single crystals according to claim 1, characterized in that: The specific operation of the dynamic control heating is: the high temperature zone is programmed to heat up at a rate of 2-5°C / h, the low temperature zone is first programmed to heat up at a rate of 5-10°C / h for 5-10 hours, and then programmed to cool down at a rate of 15-20°C / h.

6. The method for vapor phase growth of large-sized ammonium fluoroborate single crystals according to claim 5, characterized in that: The temperature gradient of the crystal growth zone is 1 to 40°C / cm; The temperature gradient during the initial stage of crystal growth is 1 to 30°C / cm; When the crystal grows to a size greater than 3 mm in at least one dimension, the temperature gradient is 1 to 25 °C / cm; When the crystal grows to a size greater than 10 mm in at least one dimension, the temperature gradient is 1 to 40° C. / cm.

7. The method for vapor phase growth of large-size ammonium fluoroborate single crystals 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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