CN106149051A - The thermal control Bridgman method single-crystal growing apparatus of fluoride single crystal body and method - Google Patents

Abstract

The present invention relates to a thermally controlled Bridgman method single crystal growth device and method for fluoride single crystals, wherein the furnace body system has a furnace cavity, a furnace bottom plate with a hole in the center, and a vacuum pipeline communicating with the furnace cavity, The central opening of the furnace bottom plate is connected with the cavity of the furnace cavity. The furnace cavity and the furnace bottom plate are double-layered, and the middle interlayer is arranged with a cooling water channel; The heaters and insulation screens on the upper and lower sides of the plate form three temperature zones: the upper high temperature zone, the middle gradient zone and the lower low temperature zone through the heat shield; The lower end of the column is connected with the lowering transmission device of the crucible, and the upper end passes through the central opening of the furnace bottom plate and extends into the interior of the furnace cavity to support the crucible bracket. Cooling water flows through the crucible water-cooled support column. The water temperature can be adjusted independently in real time.

Description

Apparatus and method for thermally controlled Bridgman single crystal growth of fluoride single crystal

technical field

The invention belongs to the technical field of crystal growth, and in particular relates to a thermally controlled Bridgman method single crystal growth device and method for fluoride single crystals.

Background technique

Fluoride crystals (such as CaF ₂ , SrF ₂ , MgF ₂ , BaF ₂ and LaF ₂ , etc.) are very important solid-state laser matrix materials. Compared with oxide matrix materials, fluoride has the following characteristics: fluoride crystal has a very wide transmission range, from far ultraviolet to mid-infrared; the refractive index of fluoride crystal is relatively low, which can minimize the surface of the spectrum used Reflectivity and limiting nonlinear effects under high-intensity laser pumping; low phonon energy can reduce the probability of non-radiative transitions between energy levels and improve radiation quantum efficiency. Therefore, the fluoride crystal doped with trivalent rare earth ions is an ideal system for people to engage in basic theoretical research work such as crystal structure defects, ion kinetic properties, and luminescent properties. Although the thermal and mechanical properties of most fluoride crystals are not as good as those of oxide crystal materials, their combination with low thermal load LD pump sources is very conducive to the establishment of high-power miniaturized all-solid-state low-to-medium power lasers.

At present, the technologies that can industrially grow large-sized fluoride crystals mainly include temperature gradient method (TGT), crucible descent method (B-S) and pulling method (Cz), but they all have their limitations when growing fluoride single crystals.

There is no relative movement between the crucible and the thermal field during the crystal growth process of the temperature gradient method, and the crystallization is completely transported by diffusion, and it is difficult to release the latent heat of crystallization with the increase of the crystal growth height; at the same time, the growth rate is also difficult to control, and the components are prone to overcooling, and eventually As a result, the quality of crystallization is poor, and it is difficult to obtain large-size optical-grade crystals.

The crystal size grown by the traditional crucible descending method is much larger than that of the temperature gradient method, but at present, there is basically no special cooling treatment for the seed crystal part of the traditional crucible descending furnace or the cooling effect is not very ideal, resulting in a small temperature gradient. In addition, the thermal conductivity of fluoride laser crystals is generally relatively low, so the latent heat of crystallization in the early stage of crystal growth is difficult to conduct efficiently through the seed crystal, and polycrystalline nucleation is very easy to occur in the early stage of shouldering; and as the solid-liquid interface The release of latent heat of crystallization becomes more difficult, resulting in the solid-liquid interface is often concave and accompanied by large temperature fluctuations, resulting in extremely uneven distribution of solutes and an increase in crystal defects.

The size of the fluoride single crystal grown by the pulling method is much smaller than that of the first two types, and the thermal stress of the crystal grown by the large temperature field gradient is also much larger, so it is not easy to obtain a large-sized optical grade single crystal.

To sum up, the current crystal growth technology cannot effectively solve the problem of the difficulty in releasing the crystallization latent heat generated when growing large-sized fluoride single crystals. As a result, the solid-liquid interface is difficult to control during the crystal growth process, and the temperature fluctuates greatly, resulting in uneven distribution of dopant ions, which seriously affects the crystallization quality of the crystal.

Contents of the invention

Aiming at the problems in the prior art that it is difficult to release latent heat of crystallization during the growth of fluoride single crystals, and the solid-liquid interface is often concave and unstable, the present invention aims to provide a thermally controlled Bridgman method for single crystal growth of fluoride single crystals Devices and methods to solve the problem of difficult release of latent heat of crystallization during the growth of large-sized fluoride single crystals; combined with reasonable process parameters, to ensure that the solid-liquid interface is always slightly convex as the crystal grows, improving the crystallization quality of fluoride single crystals .

In order to achieve the purpose of the above invention, one aspect of the present invention provides a thermally controlled Bridgman method single crystal growth device for fluoride single crystals, including: a furnace system, a heating and heat preservation system and a crucible lowering system, the furnace body The system has a furnace cavity, a furnace bottom plate with an opening in the center, and a vacuum pipeline communicating with the furnace cavity. The central opening of the furnace bottom plate communicates with the cavity of the furnace cavity, and the furnace cavity and the The bottom plates of the furnace are all double-layer structures, and the middle interlayer is arranged with a cooling water channel; the heating and heat preservation system is arranged in the furnace cavity, and is equipped with a heat insulation board, a heater and a heat preservation screen respectively located on the upper and lower sides of the heat insulation board, Three temperature zones, the upper high temperature zone, the middle gradient zone and the lower low temperature zone, are formed through the heat shield; the crucible lowering system includes a crucible water-cooled support column and a crucible lowering transmission device, and the lower end of the crucible water-cooled support column is connected to the lower end of the crucible The crucible is connected to the lowering transmission device, and the upper end passes through the central opening of the furnace floor and extends into the interior of the furnace cavity to support the crucible bracket. Cooling water circulates in the crucible water-cooled support column, and the crucible water-cooled support The flow rate and water temperature of the column cooling water can be adjusted independently in real time.

According to the present invention, an appropriate temperature gradient is established through independent heating of the upper and lower regions, which is conducive to the formation of a stable temperature field, and real-time control of the water flow and water temperature of the cooling water of the crucible water-cooled support column at different stages of crystal growth, The ability to release latent heat of crystallization is greatly improved, making the solid-liquid interface more stable.

Adopting the thermally controlled Bridgman method single crystal growth device of the present invention can effectively avoid the phenomenon of easy polycrystalline growth in the early stage of fluoride crystal growth, solve the difficult problem of crystallization latent heat release in the crystal growth stage, and control the solid-liquid interface shape of crystal growth , which is conducive to the uniform distribution of dopant ions and the growth of large-sized, high-optical-uniform fluoride single crystals.

Moreover, in the present invention, it is also possible that the crucible water-cooled support column includes a stainless steel water-cooled rod wrapped by a molybdenum tube, and there is a gap of 2-4 mm between the stainless steel water-cooled rod and the surrounding molybdenum tube.

According to the present invention, the molybdenum tube can shield the high-temperature direct radiation stainless steel water-cooling rod in the furnace cavity, enhance the water-cooling effect of the latter, and facilitate the release of crystallization latent heat during crystal growth.

Moreover, in the present invention, it is also possible that the material of the furnace cavity is stainless steel, and its single layer thickness is 6-10 mm.

According to the present invention, the material of the furnace cavity is stainless steel and its thickness is 6-10 mm, so that the corrosion resistance and compression and deformation resistance are stronger under the fluoride crystal growth environment (containing fluorine).

Moreover, in the present invention, it is also possible that the material of the heat insulation board is graphite board, molybdenum board, tungsten board or zirconia board, and the heat insulation screen includes graphite screen, molybdenum screen, tungsten screen or tungsten-molybdenum combination screen, and the heater includes a graphite heating body.

According to the present invention, the thermal insulation board is made of graphite, molybdenum or tungsten material with high reflectivity or zirconia, a thermal insulation material with low thermal conductivity, which can increase the temperature gradient of the upper and lower temperature zones; Molybdenum metal material has strong energy-saving effect and is easy to process; graphite heater is easy to process and low in cost.

Moreover, in the present invention, the crucible bracket may be used for fixing the crucible and may be a zirconia bracket.

According to the present invention, the crucible bracket is a zirconia bracket, and the zirconia can have a good thermal insulation effect, increase the temperature gradient, and enhance the heat conduction effect of the seed crystal.

Moreover, in the present invention, it may also be that the cooling water of the crucible water-cooled support column is provided by a separate cooling water system, and the flow rate and water temperature of the cooling water provided by the cooling water system can be adjusted independently in real time; the cooling water The control range of the flow rate is 1-8m ³ /h, the control range of the water temperature of the cooling water is -15-20°C, and the fluctuation range of the water temperature is less than 0.2°C.

According to the present invention, the cooling water of the crucible water-cooled support column is provided by an independent cooling water system, which is conducive to the real-time regulation of the water flow and water temperature of the cooling water of the crucible water-cooled support column at different stages of crystal growth, and greatly improves the release of crystallization latent heat ability to make the solid-liquid interface more stable.

Another aspect of the present invention also provides a method for preparing a fluoride single crystal using the above thermally controlled Bridgman method single crystal growth device, the method comprising:

(1) Place the fluoride single crystal raw material in a crucible with a seed crystal at the bottom, and then fix the crucible on the crucible bracket on the crucible water-cooled support column inside the furnace cavity;

(2) Raise the crucible to an appropriate position in the high temperature zone, close the furnace chamber and start vacuuming, and start heating up the chemical material when the vacuum degree is ≤5*10 ^-3 pa;

(3) Adjust the heating power of the upper and lower heaters to establish a suitable temperature gradient area, and adjust the position of the crucible to melt the top part of the seed crystal, and lower the crucible to start crystal growth after constant temperature for 5-10 hours;

(4) With the growth of the crystal, gradually increase the water flow rate of the water-cooled rod and reduce the temperature of the cooling water until the equal-diameter growth of the crystal ends;

(5) After the crystal growth is completed, by adjusting the heating power of the heater, gradually reduce the water flow rate of the water-cooled rod, increase the temperature of the cooling water, and reduce the temperature of the crucible by adjusting the position of the crucible. The temperature gradient at the upper and lower ends realizes near-zero temperature gradient annealing.

According to the method of the present invention, the gradient size of the temperature gradient area is formed by automatically adjusting the heating power of the upper and lower heaters, which can effectively avoid the change of the gradient size caused by the change of the crucible position during the crucible lowering process. The materialization process is completed in the high temperature zone, and the crystallization process is completed in the temperature gradient zone. During annealing, by adjusting the heating power of the upper and lower heaters and the position of the crucible, annealing with a near-zero temperature gradient can be achieved, which is more conducive to the release of crystal thermal stress.

Also, in the present invention, the crucible may be a graphite crucible, and the crucible bracket may be a zirconia bracket whose outside is wrapped with tungsten or molybdenum sheets.

According to the present invention, wrapping the zirconia bracket with tungsten or molybdenum sheets can effectively shield heat radiation and enhance the heat conduction effect of the seed crystal.

Moreover, in the present invention, the gradient in the temperature gradient zone may be 20-40° C./cm, and the descending speed of the crucible may be 0.5-1.5 mm/h.

Furthermore, in the present invention, it is also possible to gradually increase the water flow rate of the water-cooled rod while decreasing the temperature of the cooling water during the process from the shoulder growth of the crystal to the end of the equal-diameter growth.

Compared with the existing crucible descending method device and growth method, the present invention has the advantage that a suitable temperature gradient is established through independent heating of the upper and lower regions, which is conducive to the formation of a stable temperature field. In particular, a unique design is made for the crucible water-cooled support column: the cooling water is provided by an independent cooling water system, and the water flow and water temperature of the cooling water of the crucible water-cooled support column are regulated in real time at different stages of crystal growth, which greatly improves the latent heat of crystallization The release ability makes the solid-liquid interface more stable; the outside of the crucible water-cooled support column is wrapped with molybdenum tubes, which can effectively shield the direct heat radiation in the furnace cavity, and significantly enhance the heat conduction of the crucible water-cooled support column. The annealing stage can achieve near-zero temperature gradient annealing, which is more conducive to the release of crystal thermal stress.

The above contents and other objects, features and advantages of the present invention will be better understood according to the following detailed description and with reference to the accompanying drawings.

Description of drawings

1 is a schematic structural view of a thermally controlled Bridgman method single crystal growth device for a fluoride single crystal according to an embodiment of the present invention;

Fig. 2 is a schematic diagram of the heat exchange system of the crucible water-cooled support column in the thermally controlled Bridgman method single crystal growth device shown in Fig. 1;

Reference signs: 1. Bell-type furnace cavity; 2. Furnace bottom plate; 3. Vacuum pipe; 4. Upper heating element; 5. Lower heating element; 6. Upper heat preservation screen; 7. Lower heat preservation screen; 8. Bottom heat screen; 9. upper temperature control thermocouple; 10. lower temperature control thermocouple; 11. upper monitoring thermocouple; 12. lower monitoring thermocouple; 13. crucible; 14. heat shield; 15. zirconia support; 16. Molybdenum tube; 17, stainless steel water cooling rod; 18, crucible lowering transmission device; crucible water cooling support column 19; cooling water system 20; water storage tank 21; refrigeration system 22; water flow controller 23.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings and the following embodiments. It should be understood that the accompanying drawings and the following embodiments are only used to illustrate the present invention, not to limit the present invention.

The present invention aims at the problems in the prior art that it is difficult to release the latent heat of crystallization during the growth of fluoride single crystals, and the solid-liquid interface is often concave and unstable, and provides a thermally controlled Bridgman method single crystal growth device for fluoride single crystals , including: a furnace body system, a heating and heat preservation system and a crucible lowering system, the furnace body system has a furnace chamber, a furnace bottom plate with an opening in the center, and a vacuum pipeline communicated with the furnace chamber, the center of the furnace bottom plate The opening is connected with the cavity of the furnace cavity, the furnace cavity and the furnace bottom plate are double-layered, and the middle interlayer is arranged with a cooling water channel; the heating and heat preservation system is arranged in the furnace cavity, and has a Plates, heaters and insulation screens respectively located on the upper and lower sides of the heat insulation board, through the heat insulation board, three temperature zones are formed: the upper high temperature zone, the middle gradient zone and the lower low temperature zone; the crucible descending system includes a crucible Water-cooled support column and crucible lowering transmission device, the lower end of the crucible water-cooling support column is connected with the crucible lowering transmission device, and the upper end passes through the central opening of the furnace bottom plate and extends into the interior of the furnace cavity to support the crucible The bracket, cooling water flows through the crucible water-cooled support column, and the flow rate and water temperature of the cooling water of the crucible water-cooled support column can be independently adjusted in real time.

According to the present invention, an appropriate temperature gradient is established through independent heating of the upper and lower regions, which is conducive to the formation of a stable temperature field, and real-time control of the water flow and water temperature of the cooling water of the crucible water-cooled support column at different stages of crystal growth, The ability to release latent heat of crystallization is greatly improved, making the solid-liquid interface more stable.

FIG. 1 shows a schematic structural diagram of a thermally controlled Bridgman method single crystal growth device for fluoride single crystals according to an embodiment of the present invention.

As shown in FIG. 1 , the thermally controlled Bridgman method single crystal growth device of this embodiment includes a furnace body system, a heating and heat preservation system and a crucible lowering system. The furnace system is a closed furnace system, including a furnace cavity 1 , a furnace floor 2 with a hole in the center and a vacuum pipe 3 . The furnace chamber 1 can be formed as a bell jar type furnace chamber, and the vacuum pipeline 3 communicates with the furnace chamber 1 . The central opening of the furnace bottom plate 2 is connected with the cavity of the furnace cavity 1, and both the furnace cavity 1 and the furnace bottom plate 2 are double-layered, and a cooling water channel is arranged in the middle interlayer. The cooling water channel is, for example, a spiral cooling water channel.

The heating and heat preservation system includes a heat insulation board 14, two upper and lower independent heaters 4, 5 and heat preservation screens 6, 7, forming three temperature zones: the upper high temperature zone A, the middle gradient zone B and the lower low temperature zone C. The high temperature area A is the area above the heat shield 14 , the low temperature area C is the area below the heat shield 14 , and the gradient area B is the area near the heat shield 14 . In addition, a bottom heat shield 8 may also be provided below the lower low temperature zone C.

The upper and lower two heaters 4 and 5 can be graphite heating elements, for example, the heating power of the heating element can be independently controlled by the upper temperature control thermocouple 9 and the lower temperature control thermocouple 10 respectively, and the upper monitoring thermocouple 11 and the lower monitoring Thermocouple 12 can play the role of monitoring. A reasonable temperature gradient can be established through the feedback values of the upper and lower temperature control thermocouples 9, 10 and the two monitoring thermocouples 11, 12. In the process of crystal growth, the raw material melts in the high temperature zone A, crystallizes in the gradient zone B, and keeps warm in the low temperature zone C.

The crucible lowering system includes a crucible water-cooled support column 19 and a crucible lowering transmission device 18 . In the embodiment shown in Fig. 1, the crucible water-cooled support column 19 can be composed of stainless steel water-cooled rods 17 wrapped by molybdenum tubes 16, and the molybdenum tubes 16 can shield the high-temperature direct radiation stainless steel water-cooled rods 17 in the furnace cavity 1, and strengthen the latter The water cooling effect is beneficial to the release of latent heat of crystallization during crystal growth. The lower end of the crucible water-cooled support column 19 is connected with the crucible lowering transmission device 18 , and the upper end passes through the central opening of the furnace floor 2 and extends into the furnace cavity 1 to support the crucible bracket 15 . The cooling water of the crucible water-cooled support column 19 in the present invention is provided by an independent cooling water system 20, and the water flow rate and water temperature of the cooling water can be adjusted in real time according to the requirements of the growth process.

The cooling water system 20 of the independent crucible water-cooled support column described in this embodiment is shown in FIG. 2 , including a small water storage tank 21 , a refrigeration system 22 and a water flow controller 23 . The hot water flowing out of the crucible water-cooling support column 19 first enters a small water storage tank 21 with a volume of 1 ^m3 , and then flows into the refrigeration system 22 on the other side of the water storage tank 21, and the cooling water flowing out from the refrigeration system 22 passes through the water flow controller 23 Then it flows into the crucible water-cooled support column 19. The refrigeration system 20 can adjust the temperature of the outflowing water according to the process requirements, the water temperature control range is -15-20°C, and the fluctuation range of the water temperature is less than 0.2°C. The water flow controller can adjust the outflow water flow according to the process requirements, and the control range is 1-8m ³ /h.

The device for growing a fluoride single crystal by thermally controlled Bridgman method and the method for preparing a fluoride single crystal using the device will be further described in detail below according to different embodiments.

Example 1

To grow _CaF2 single crystal, the specific preparation method is as follows:

8Kg _CaF crystal raw material and 80g PbF powder are evenly mixed and packed into a graphite crucible ₁₃ with a CaF crystal seed crystal at the bottom, then the crucible ₁₃ is fixed on the crucible water-cooled support column 19 inside the furnace cavity 1 for oxidation Zirconium bracket 15, where PbF ₂ acts as an oxygen scavenger. Raise the crucible 13 to an appropriate position in the high temperature zone A (the upper end surface of the seed crystal is slightly higher than the heat shield 14), close the furnace chamber 1 and start vacuuming, and start to vacuum at 50°C/h when the vacuum degree is ≤5*10 ^-3 pa Raise the temperature of the chemical material at a certain rate; when the temperature of the monitoring thermocouple at the seed crystal position reaches 800° C., keep the temperature for 10 hours to fully remove the oxygen component inside the crucible 13 . Then continue to heat up at a rate of 50°C/h. By adjusting the heating power of the upper and lower heating elements 4 and 5, the temperature gradient in the temperature gradient area B is 25°C/cm. When the temperature of the monitoring thermocouple at the seed crystal position After reaching 1360-1380°C, the temperature was kept constant for 5 hours to ensure that the raw materials were fully melted and mixed, and then the crucible 13 was lowered at a speed of 1.2 mm/h to start crystal growth. The water flow rate of the water-cooled rod 17 at the initial stage of crystal growth was set at 1.5 m ³ /h, and the temperature was 15°C; during the process from the beginning of the shouldering to the end of the shouldering, the water flow rate of the water-cooled rod 17 gradually increased from 1.5 m ³ /h As large as 3m ³ /h, the cooling water temperature is gradually reduced from 15°C to 10°C. During the process from the end of shouldering to the end of equal-diameter growth, the water flow rate of the water-cooled rod 17 gradually increased from 3m ³ /h to 6m ³ /h, and the cooling water temperature gradually decreased from 10°C to 5°C. After the crystal growth is over, by adjusting the heating power of the upper and lower heating elements 4 and 5, the water flow rate of the water cooling rod 17 is gradually reduced, the temperature of the cooling water is increased, and the position of the crucible 13 is adjusted at the same time to reduce the temperature of the upper and lower ends of the crucible 13 Gradient, to achieve near-zero temperature gradient annealing.

Example 2

To grow Yb, Na:CaF ₂ single crystals, the specific preparation method is as follows:

6 Kg Yb, Na co-doped CaF ₂ crystal raw materials and 60g PbF ₂ powders are uniformly mixed and packed into a graphite crucible 13 with CaF ₂ crystal seed crystals at the bottom, then the crucible 13 is fixed to the crucible water-cooled inside the furnace cavity 1 On the zirconia bracket 15 on the support column 19, where PbF ₂ acts as an oxygen scavenger. Raise the crucible 13 to an appropriate position in the high temperature zone A (the upper end surface of the seed crystal is slightly higher than the heat shield 14), close the furnace chamber 1 and start vacuuming, and start to vacuum at 50°C/h when the vacuum degree is ≤5*10 ^-3 pa Raise the temperature of the chemical material at a certain rate; when the temperature of the monitoring thermocouple at the seed crystal position reaches 800° C., keep the temperature for 10 hours to fully remove the oxygen component inside the crucible 13 . Then continue to heat up at a rate of 50°C/h. By adjusting the heating power of the upper and lower heating elements 4 and 5, the temperature gradient in the temperature gradient area B is 25°C/cm. When the temperature of the monitoring thermocouple at the seed crystal position After reaching 1360-1380°C, the temperature was kept constant for 10 hours to ensure that the raw materials were fully melted and mixed, and then the crucible 13 was lowered at a speed of 1 mm/h to start crystal growth. The water flow rate of the water-cooled rod 17 at the initial stage of crystal growth was set at 1.5 m ³ /h, and the temperature was 15°C; during the process from the beginning of the shouldering to the end of the shouldering, the water flow rate of the water-cooled rod 17 gradually increased from 1.5 m ³ /h to 1.5 m 3 /h. As large as 3.5 m ³ /h, the cooling water temperature is gradually reduced from 15°C to 8°C. During the process from the end of shouldering to the end of equal-diameter growth, the water flow rate of the water-cooled rod 17 gradually increased from 3.5 m ³ /h to 6 m ³ /h, and the cooling water temperature gradually decreased from 8°C to 1°C. After the crystal growth is over, by adjusting the heating power of the upper and lower heating elements 4 and 5, the water flow rate of the water cooling rod 17 is gradually reduced, the temperature of the cooling water is increased, and the position of the crucible 13 is adjusted at the same time to reduce the temperature of the upper and lower ends of the crucible 13 Gradient, to achieve near-zero temperature gradient annealing.

Example 3

To grow _SrF2 single crystal, the specific preparation method is as follows:

8Kg _SrF crystal raw material and 80g PbF powder are evenly mixed and loaded into a crucible ₁₃ made of graphite with SrF crystal seed crystals at the bottom, then the crucible ₁₃ is fixed on the crucible water-cooled support column 19 inside the furnace cavity 1 for oxidation Zirconium bracket 15, where PbF ₂ acts as an oxygen scavenger. Raise the crucible 13 to an appropriate position in the high temperature zone A (the upper end surface of the seed crystal is slightly higher than the heat shield 14), close the furnace chamber 1 and start vacuuming, and start to vacuum at 50°C/h when the vacuum degree is ≤5*10 ^-3 pa Raise the temperature of the chemical material at a certain rate; when the temperature of the monitoring thermocouple at the seed crystal position reaches 800° C., keep the temperature for 10 hours to fully remove the oxygen component inside the crucible 13 . Then continue to heat up at a rate of 50°C/h. By adjusting the heating power of the upper and lower heating elements 4 and 5, the temperature gradient in the temperature gradient area is 25°C/cm. When the temperature of the monitoring thermocouple at the seed crystal reaches After 1460-1480°C, the temperature is kept constant for 6 hours to ensure that the raw materials are fully melted and mixed, and then the crucible 13 is lowered at a speed of 1.5 mm/h to start crystal growth. The water flow rate of the water-cooled rod 17 at the initial stage of crystal growth was set at 1.2m ³ /h, and the temperature was 15°C; during the process from the beginning of the shouldering to the end of the shouldering, the water flow rate of the water-cooling rod 17 gradually increased from 1.5m ³ /h As large as 3m ³ /h, the cooling water temperature is gradually reduced from 15°C to 10°C. During the process from the end of shouldering to the end of equal-diameter growth, the water flow rate of the water-cooled rod 17 gradually increased from 3m ³ /h to 6.5m ³ /h, and the cooling water temperature gradually decreased from 10°C to 5°C. After the crystal growth is over, by adjusting the heating power of the upper and lower heating elements 4 and 5, the water flow rate of the water cooling rod 17 is gradually reduced, the temperature of the cooling water is increased, and the position of the crucible 13 is adjusted at the same time to reduce the temperature of the upper and lower ends of the crucible 13 Gradient, to achieve near-zero temperature gradient annealing.

Example 4

To grow Nd, Y:SrF ₂ single crystal, the specific preparation method is as follows:

6Kg Nd, Y co-doped SrF ₂ crystal raw materials and 60g PbF ₂ powders are evenly mixed and packed into a crucible 13 made of graphite with SrF ₂ crystal seed crystals at the bottom, and then the crucible 13 is fixed on the crucible water-cooled support inside the furnace cavity 1 Zirconia bracket 15 on column 19 with PbF ₂ as oxygen scavenger. Raise the crucible 13 to an appropriate position in the high temperature zone A (the upper end surface of the seed crystal is slightly higher than the heat shield 14), close the furnace chamber 1 and start vacuuming, and start to vacuum at 50°C/h when the vacuum degree is ≤5*10 ^-3 pa The rate of heating chemical material. When the temperature of the monitoring thermocouple at the seed crystal reaches 800°C, keep the temperature for 10 hours to fully remove the oxygen component in the raw material. Then continue to heat up at a rate of 50°C/h. By adjusting the heating power of the upper and lower heating elements 4 and 5, the temperature gradient in the temperature gradient area B is 30°C/cm. When the temperature of the monitoring thermocouple at the seed crystal position After reaching 1460-1480°C, the temperature is kept constant for 10 hours to ensure that the raw materials are fully melted and mixed, and then the crucible 13 is lowered at a speed of 1mm/h to start crystal growth. The water flow rate of the water-cooled rod 17 at the initial stage of crystal growth was set at 1.5m ³ /h, and the temperature was 15°C; during the process from the beginning of the shouldering to the end of the shouldering, the water flow rate of the water-cooling rod 17 gradually increased from 1.5m ³ /h As large as 4 m ³ /h, the cooling water temperature is gradually reduced from 15°C to 5°C. During the process from the end of shouldering to the end of equal-diameter growth, the water flow rate of the water-cooled rod 17 gradually increased from 4 m ³ /h to 6.5 m ³ /h, and the cooling water temperature gradually decreased from 5°C to 0°C. After the crystal growth is over, by adjusting the heating power of the upper and lower heating elements 4 and 5, the water flow rate of the water cooling rod 17 is gradually reduced, the temperature of the cooling water is increased, and the position of the crucible 13 is adjusted at the same time to reduce the temperature of the upper and lower ends of the crucible 13 Gradient, to achieve near-zero temperature gradient annealing.

The present invention can be embodied in various forms without departing from the essential characteristics of the present invention, so the embodiments in the present invention are for illustration rather than limitation, because the scope of the present invention is defined by the claims rather than by the specification , and all changes within the range defined in the claims, or within the range equivalent to the range defined in the claims, should be construed as being included in the claims.

Claims (10)

1. A thermally controlled Bridgman method single crystal growth device for fluoride single crystals, characterized in that it comprises: a body of furnace system, a heating and heat preservation system and a crucible lowering system; The furnace body system has a furnace cavity, a furnace bottom plate with an opening in the center, and a vacuum pipe communicating with the furnace cavity. The central opening of the furnace bottom plate communicates with the cavity of the furnace cavity. Both the cavity and the furnace bottom plate are of double-layer structure, and the middle interlayer is arranged with a cooling water channel; The heating and heat preservation system is arranged in the furnace cavity, and is equipped with a heat insulation board, heaters and heat preservation screens respectively located on the upper and lower sides of the heat insulation board, and an upper high temperature zone and a middle gradient zone are formed by the heat insulation board. and three temperature zones in the lower low temperature zone; The crucible lowering system includes a crucible water-cooling support column and a crucible lowering transmission device, the lower end of the crucible water-cooling support column is connected with the crucible lowering transmission device, and the upper end passes through the central opening of the furnace floor and extends into the The crucible bracket is supported inside the furnace cavity, and cooling water flows through the crucible water-cooled support column, and the flow rate and water temperature of the cooling water of the crucible water-cooled support column can be independently adjusted in real time. 2. The thermally controlled Bridgman method single crystal growth device according to claim 1, wherein the crucible water-cooled support column comprises a stainless steel water-cooled rod wrapped by a molybdenum tube, and the stainless steel water-cooled rod and all surrounding parts There is a gap of 2-4 mm between the molybdenum tubes. 3. The thermally controlled Bridgman method single crystal growth device according to claim 1 or 2, characterized in that the material of the furnace cavity is stainless steel, and the thickness of a single layer thereof is 6-10 mm. 4. The thermally controlled Bridgman method single crystal growth device according to any one of claims 1 to 3, wherein the material of the heat shield is graphite plate, molybdenum plate, tungsten plate or zirconia plate, the insulation screen includes graphite screen, molybdenum screen, tungsten screen or tungsten-molybdenum combination screen, and the heater includes a graphite heating body. 5 . The thermally controlled Bridgman method single crystal growth device according to any one of claims 1 to 4 , wherein the crucible bracket is used to fix the crucible and is a zirconia bracket. 6. The thermally controlled Bridgman method single crystal growth device according to any one of claims 1 to 5, wherein the cooling water of the crucible water-cooled support column is provided by a separate cooling water system, the The flow rate and water temperature of the cooling water provided by the cooling water system can be adjusted independently in real time; the control range of the flow rate of the cooling water is 1-8m ³ /h, the control range of the water temperature of the cooling water is -15-20°C, and the water temperature The fluctuation range is less than 0.2°C. 7. A method for preparing a fluoride single crystal using the thermal control Bridgman method single crystal growth device according to any one of claims 1 to 6, said method comprising: (1) Place the fluoride single crystal raw material in a crucible with a seed crystal at the bottom, and then fix the crucible on the crucible bracket on the crucible water-cooled support column inside the furnace cavity; (2) Raise the crucible to an appropriate position in the high temperature zone, close the furnace chamber and start vacuuming, and start heating up the chemical material when the vacuum degree is ≤5*10 ^-3 pa; (3) Adjust the heating power of the upper and lower heaters to establish a suitable temperature gradient area, and adjust the position of the crucible to melt the top part of the seed crystal, and lower the crucible to start crystal growth after constant temperature for 5-10 hours; (4) With the growth of the crystal, gradually increase the water flow rate of the water-cooled rod and reduce the temperature of the cooling water until the equal-diameter growth of the crystal ends; (5) After the crystal growth is completed, gradually reduce the water flow rate of the water-cooled rod, increase the temperature of the cooling water, and reduce the temperature of the upper and lower ends of the crucible by adjusting the position of the crucible and the heating power of the heater. Temperature gradient, to achieve near-zero temperature gradient annealing. 8. The method according to claim 7, wherein the crucible is a graphite crucible, and the crucible bracket is a zirconia bracket wrapped with tungsten or molybdenum sheets on the outside. 9 . The method according to claim 8 , characterized in that, the gradient in the temperature gradient zone is 20-40° C./cm, and the descending speed of the crucible is 0.5-1.5 mm/h. 10 . The method according to claim 9 , wherein, during the process from the shoulder growth of the crystal to the end of the equal diameter growth, the water flow rate of the water cooling rod is gradually increased while the temperature of the cooling water is decreased. 11 .