Horizontal directional crystallization growth method of Nd, Ce: LuAG crystal

Abstract

The invention discloses a horizontal directional crystallization growth method of an Nd, Ce: LuAG crystal, which comprises the following steps: in a single crystal growth process, adopting a zone melting mode of three-phase coexistence of a single crystal, a melt and a pre-crystallized polycrystalline raw material, controlling a melting zone to be 20-25mm, and enabling the pre-crystallized polycrystalline raw material to form a narrow melting zone to obtain a solute non-conservative system so as to control components and realize a segregation coefficient k0lt; nd < 3 + > (k0 = 0.18-0.25) with the segregation coefficient of about 0.1 and Ce < 3 + > with the segregation coefficient of about 0.1 are uniformly doped in a LuAG matrix, and the growth rate is reasonably controlled, so that the Nd < 3 + > and Ce < 3 + > uniformly doped high-quality Nd, Ce: LuAG crystal is obtained. The crystal prepared through the method is high in quality and free of the defects of a core, a side core and the like, and the problem that high-quality Nd, Ce: LuAG crystals with uniform and controllable components are difficult to prepare through an existing crystal growth method is solved.

Description

Technical Field

[0001] The invention relates to the technical field of crystal growth, and in particular to a horizontal directional crystal growth method of a Nd, Ce:LuAG crystal. Background Art

[0002] In recent years, with the rapid development of science and technology, the demand for high-peak power laser output in high-tech fields such as long-range laser ranging, laser soft kill, and optoelectronic confrontation has been growing, and there is an urgent need to develop high-peak power and high-energy laser gain media.

[0003] As an emerging crystal material, Nd,Ce:LuAG (neodymium and cerium co-doped lutetium aluminum garnet) laser crystal has attracted much attention due to its unique properties. By adding Ce³⁺ ions to the LuAG matrix, energy can be effectively transferred to Nd³⁺ ions, thereby achieving effective sensitization of Nd³⁺ ions. This feature makes Nd,Ce:LuAG laser crystal perform well in increasing output energy and reducing oscillation threshold, becoming a high-performance double-doped lutetium aluminum garnet crystal material. In addition, the crystal also has the advantages of high fluorescence efficiency, good optical uniformity, and a large number of wide activated particle absorption bands. These characteristics make it have broad application prospects in high-peak power and high-energy lasers.

[0004] However, despite the many advantages of Nd, Ce: LuAG laser crystals, their preparation process faces many challenges. Currently, the Czochralski method is the most widely used method for growing Nd, Ce: LuAG crystals. However, the Czochralski method has defects such as long growth cycle, high cost, uneven concentration distribution of doped ions, high dislocation density, and the presence of core and side cores. These problems not only affect the quality of the crystal, but also limit the large-scale production of crystals, making it difficult to meet the needs of high-peak power and high-energy lasers for high-quality, large-size laser gain media.

[0005] Therefore, developing an efficient and low-cost Nd, Ce:LuAG crystal preparation technology to solve the problems existing in the existing technology and achieve stable production of high-quality, large-size crystals has become an important research topic for realizing high-peak power and high-energy lasers. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a method for horizontal directional crystal growth of Nd, Ce: LuAG crystals, so as to solve the problem that the existing crystal growth methods are difficult to efficiently prepare high-quality large-size Nd, Ce: LuAG crystals with uniform and controllable components and high cost.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows: A method for horizontal directional crystal growth of Nd, Ce: LuAG crystals, comprising the following steps: (1) According to Ce 3x Nd 3y Lu 3(1-y-x) Al 5 O 12 Weigh Al in the stoichiometric ratio 2 O 3 Powder, Lu 2 O 3 Powder, Ce 2 O 3 Powder and Nd 2 O 3 The powders are mixed evenly, then melted and cooled to obtain a pre-crystallized material; wherein x is 0.01~5at.%, and y is 0.01~5at.%; (2) The pre-crystallized material is crushed into small pieces and then spread flat in a boat-shaped crucible. Then, a seed crystal is inserted into a seed crystal groove at one end of the boat-shaped crucible near the shoulder angle. The boat-shaped crucible containing the pre-crystallized material and the seed crystal is placed in a working furnace, and the equal-width area of ​​the boat-shaped crucible is located in the heating area of ​​the working furnace. The furnace is closed. (3) Turn on the cooling system of the working furnace and keep the temperature of the cooling system at 25~35℃. Then evacuate the working furnace. When the vacuum degree is less than 1×10 -3 When the temperature is 0.0407°C, the heating power of the working furnace is turned on to heat the pre-crystallized material in the boat-shaped crucible in the heating area. By controlling the heating power, the pre-crystallized material in the heating area is melted to form a narrow melting zone with a length of 20-25 mm. (4) The formed narrow melting zone is kept warm for 0.5-1h. When the shape of the solid-liquid interface does not change significantly and tends to be a straight line, the heating power is kept unchanged, and the crucible boat is moved horizontally so that the heating zone is aligned with the end of the crucible boat containing the seed crystal for heating. At the same time, the seed crystal is ensured to be located at the edge of the heating zone. After keeping warm for 0.2-1h, the crucible boat is slowly moved toward the end of the crucible boat containing the seed crystal at a growth rate of 1-1.5mm / h. After seeding, shoulder release and equal width growth, all the pre-crystallization materials are melted and crystallized. After cooling and annealing, Nd, Ce:LuAG crystals are obtained. During the movement, the melt in the crucible boat that is gradually away from the heating zone produces supercooling, which serves as a driving force for crystallization and promotes the production of single crystals.

[0008] Furthermore, the crystal orientation of the seed crystal in step (2) is <100> or <110> direction.

[0009] Furthermore, the procedure of the cooling annealing in step (4) is: first cool to 22~24kW at a cooling rate of 10~30℃ / h, and keep warm at this power for 20~60h, and then cool to room temperature at 40~60℃ / h. In the cooling annealing process, although the cooling rate is too fast or the holding time is too short, the crystal growth cycle can be reduced. However, if the cooling rate is too fast and the holding time is too short, the degree of stress elimination during the annealing process will be weakened, and the risk of cracking will be increased. Therefore, the present invention adopts a segmented cooling method for annealing, first cooling at a smaller rate and keeping warm for 20~60h to achieve in-situ annealing, reduce the internal thermal stress of the crystal, and then cool to room temperature at a faster rate to improve the efficiency of crystal preparation.

[0010] Furthermore, the shoulder release angle in the shoulder release stage is 80~120º. The shoulder release angle should not be too large or too small. When the shoulder release angle is too small, the part of the crystal before the shoulder release cannot be reasonably utilized, and the crystal utilization rate is low; if it is too large, it will cause difficulty in shoulder collection. When the shoulder release angle is 90º, the entire crystal ingot can be used most reasonably, which well solves the problem of crystal ingot utilization rate. At the same time, shoulder collection is also easier. Therefore, the preferred shoulder release angle is 90º.

[0011] Furthermore, the boat-shaped crucible is a boat-shaped molybdenum crucible. The molybdenum crucible used in the present invention has a melting point of 2630°C, is easy to grow high-melting-point crystals, and during the growth process, the crucible has high stability, is not easy to leak, and has low cost.

[0012] Furthermore, the height of the boat-shaped crucible is 1 / 6 to 1 / 5 of the length of its equal diameter part.

[0013] When the present invention adopts the horizontal directional crystallization method to prepare Nd, Ce: LuAG crystal, during the single crystal growth process, the length of the melting zone is controlled to be 20-25 mm, and the growth rate is 1-1.5 mm / h to achieve the Nd 3+ and Ce 3+ The reason why the melting zone length is controlled at 20~25mm is to obtain a narrow melting zone, because for the zone melting method of the solute non-conservative system, the shorter the melting zone length, the more uniform the distribution of the grown crystals, so as to reduce the Nd 3+ and Ce 3+ The concentration of doping ions caused by the segregation effect gradually increases with the increase of crystal growth time, thereby achieving the purpose of controllable components. However, the length of the melting zone should not be too short, because if the melting zone is too short, it is easy to produce an undercooled melt or a partially undercooled melt, which is not conducive to the stability of the growth interface. If the interface is unstable, it is easy to produce dendrites or cellular structures, which is not conducive to obtaining high-quality crystals. At the same time, during the crystal growth process, a certain temperature is also required to maintain the fluidity of the melt. Too low a temperature (or too small a melting zone) will lead to poor melt fluidity, thereby affecting the growth of the crystal.

[0014] The inventors of the present invention have found through research that compared with the LuAG matrix, the single Nd 3+ , doping Nd with a segregation coefficient of 0.18-0.25 in the LuAG matrix 3+ and Ce with a segregation coefficient of about 0.1 3+ , a higher superheat is required to better achieve Nd 3+ and Ce 3+ This is because during the crystal growth process, the more the segregation coefficient of the doped ions deviates from 1 (too large or too small), the easier it is to produce component supercooling, which affects crystal growth and produces defects such as clouds. From the perspective of avoiding component supercooling, increasing the temperature gradient and reducing the growth rate can avoid component supercooling, but excessive temperature gradients can easily increase thermal stress, thereby increasing the risk of crystal cracking. Therefore, when the present invention increases the melting zone length to 20-25 mm, it can maximize the narrow melting zone and achieve Nd 3+ and Ce 3+ The uniform doping can increase the temperature gradient of the melt, avoid supercooling of the components, affect the quality of the crystal, produce defects such as clouding, and ensure that the melt has good fluidity. Reducing the growth rate to 1-1.5 mm / h can provide the melt with enough time to release latent heat evenly and reduce the local temperature and concentration fluctuations caused by excessively fast growth, thereby reducing the risk of supercooling of the components and avoiding the decrease in production efficiency and increase in cost due to too low a growth rate. Therefore, the present invention achieves Nd by reasonably controlling the length of the melting zone and the growth rate. 3+ and Ce 3+ The uniform doping of Nd in LuAG matrix resulted in 3+ and Ce 3+ Uniformly doped high quality Nd,Ce:LuAG crystal.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. The horizontal directional crystallization growth method of Nd, Ce: LuAG crystal of the present invention adopts a zone melting method in which single crystal, melt and pre-crystallized polycrystalline raw material coexist in the single crystal growth process, and controls the melting zone within a specific size range, so that the pre-crystallized polycrystalline raw material forms a narrow melting zone to obtain a solute non-conservative system, thereby controlling the composition (doping ion distribution) and achieving the segregation coefficient k 0 Nd < 1 3+ (k 0 =0.18-0.25) and Ce with a segregation coefficient of about 0.1 3+ The uniform doping in LuAG matrix and reasonable control of the growth rate have resulted in the Nd 3+ and Ce 3+Uniformly doped high-quality Nd, Ce: LuAG crystals. The crystals obtained by this method are of high quality and have no defects such as cores and side cores, which solves the problem that the existing crystal growth methods are difficult to prepare high-quality Nd, Ce: LuAG crystals with uniform and controllable components. The method is simple and easy to implement, and has high preparation efficiency.

[0016] 2. The boat-shaped molybdenum crucible used in the present invention has a low cost and a large free upper surface, which accounts for 35%-40% of the total contact area of ​​the melt. The grown crystal has a small dislocation density, and the height of the boat-shaped crucible is much smaller than its length, which creates favorable conditions for the evaporation of impurity components in the melt, facilitates the effective reduction of crystal scattering, and improves the transparency and optical properties of the crystal; and the present invention does not have a rotating operation, combined with a lower melt height, which makes the melt almost free of convection motion, increases the stability of the growth interface front, and the grown crystal has no core and side core, making it easy to obtain high-quality crystals. In addition, when preparing the crystal, in-situ annealing is used to reduce the stress inside the crystal and reduce the possibility of crystal cracking.

[0017] 3. Before the seeding growth, the present invention first heats the equal width area of ​​the boat-shaped crucible to melt the polycrystalline material to obtain a narrow melting zone, and then heats the end close to the seed crystal at the same power, and then slowly seeding the crystal. The reason for doing this is that the shape of the equal width area is a rectangular parallelepiped, which is convenient for observing the temperature and judging whether the solid-liquid interface is stable. The front end of the crucible where the seed crystal is located is a triangle, and the solid-liquid interface is very short. It is difficult to judge whether the solid-liquid interface is stable, and it is more difficult to control the power, which easily increases the risk of excessive melting of the seed crystal. The above method avoids the risk of excessive melting of the seed crystal, has lower operating difficulty, lower risk, and is easy to promote and apply.

[0018] 4. The method of the present invention is used to grow a large-sized lath-shaped Nd, Ce: LuAG laser crystal with a size of 200 mm × 100 mm × 25 mm. In actual production, the crucible size can be adjusted according to demand to change the crystal size. DETAILED DESCRIPTION

[0019] The specific implementation modes of the present invention are further described in detail below in conjunction with specific examples.

[0020] Example 1 This embodiment provides a method for horizontal directional crystal growth of Nd, Ce: LuAG crystal, comprising the following steps: (1) Ingredients: According to Ce 0.015 Nd 0.03 Lu 2.955 Al 5 O 12 Weigh 5N purity Al 2 O 3、Lu 2 O 3 、Ce 2 O 3 and Nd 2 O 3 A total of 1500g of powder is used as the raw material for polycrystalline materials; (2) Preparing a pre-crystallized material: the polycrystalline material raw materials in step (1) are mixed uniformly by a planetary ball mill, melted at high temperature and cooled to form a pre-crystallized material; (3) Charging the furnace: Place the pre-crystallized material into a pounding tube made of high-purity aluminum and crush it into small pieces of uniform size. Then spread it flat in a boat-shaped molybdenum crucible, and insert pure LuAG seed crystals into the seed crystal groove at one end of the boat-shaped molybdenum crucible near the shoulder corner. The seed crystal direction is <100> ; Then put the boat-shaped molybdenum crucible containing the pre-crystallization material and the seed crystal into the single crystal furnace, and make the equal width area of ​​the boat-shaped molybdenum crucible be located in the center of the annular resistance heater of the single crystal furnace, and then close the furnace; (4) Melting the pre-crystallized material: Turn on the water cooling circulation system and maintain the water temperature at 30±5℃. Then turn on the vacuum pump to draw vacuum. When the vacuum degree reaches 4×10 -4 Pa, turn on the heating power of the single crystal furnace, and make the annular resistance heater heat up at a uniform speed for 10 hours to reach the set power of 26kW. At this time, the narrow melting zone of the equal width area is about 20mm. After 30 minutes of heat preservation, there is no obvious change in the solid-liquid interface, and the shape of the solid-liquid interface is close to a straight line. Move the boat-shaped molybdenum crucible so that the end of the boat-shaped molybdenum crucible equipped with the seed crystal is located in the center of the annular resistance heater, and the seed crystal is located at the edge of the annular resistance heater; (5) Seeding, shoulder release, and equal-width growth: At the same power, keep warm for 1 hour, turn on the automatic movement program of the crucible, and move the boat-shaped molybdenum crucible toward the end containing the seed crystal at a growth rate of 1.5 mm / h. During the movement, the melt in the boat-shaped molybdenum crucible that is gradually away from the heating area produces supercooling, which serves as a driving force for crystallization and promotes the production of single crystals. Seeding, shoulder release, and equal-width growth are carried out in sequence until all the raw materials are crystallized; the shoulder release angle is 90°.

[0021] (6) Cooling annealing: After crystallization is completed, a three-stage in-situ annealing process is adopted. First, the temperature is cooled to 23kW at a cooling rate of 20 ℃ / h and kept at this temperature for 48 hours for in-situ annealing to reduce the internal thermal stress of the crystal. Then, the crystal is cooled to room temperature at a cooling rate of 40 ℃ / h to obtain large-sized, high-quality Nd, Ce:LuAG crystals.

[0022] The furnace was opened and the crystals were taken out. The macroscopic quality of the crystals was good, with high transparency, no cracks, no cloudiness and other defects. The size of the equal diameter part was 150×90×25mm.

[0023] Example 2 This embodiment provides a method for horizontal directional crystal growth of Nd, Ce: LuAG crystal, comprising the following steps: (1) Ingredients: According to Ce 0.009 Nd 0.03 Lu 2.961 Al 5 O 12 Weigh 5N purity Al 2 O 3 、Lu 2 O 3 、Ce 2 O 3 and Nd 2 O 3 A total of 1800g of powder was used as the raw material for polycrystalline materials; (2) Preparing a pre-crystallized material: the polycrystalline material raw materials in step (1) are mixed uniformly by a planetary ball mill, melted at high temperature and cooled to form a pre-crystallized material; (3) Charging the furnace: Place the pre-crystallized material into a pounding tube made of high-purity aluminum and crush it into small pieces of uniform size. Then spread it flat in a boat-shaped molybdenum crucible, and insert pure LuAG seed crystals into the seed crystal groove at one end of the boat-shaped molybdenum crucible near the shoulder corner. The seed crystal direction is <110> ; Then put the boat-shaped molybdenum crucible containing the pre-crystallization material and the seed crystal into the single crystal furnace, and make the equal width area of ​​the boat-shaped molybdenum crucible located in the center of the ring heater, and then close the furnace; (4) Melting pre-crystallized material: Turn on the water cooling circulation system and maintain the water temperature at 30±5℃. Then turn on the vacuum pump to draw vacuum. When the vacuum degree reaches 6×10 -4 Pa, turn on the heating power of the single crystal furnace, and make the annular resistance heater heat up at a uniform speed for 15 hours to reach the set power of 26.5kw. At this time, the length of the melting zone of the equal width area is 23mm. After keeping warm for 1 hour at this power, the shape of the solid-liquid interface has no obvious change and tends to be a straight line. Move the boat-shaped molybdenum crucible so that the end of the boat-shaped molybdenum crucible equipped with the seed crystal is located in the center of the annular resistance heater, and the seed crystal is located at the edge of the annular resistance heater; (5) Seeding, shoulder release, and equal-width growth: At the same power, keep warm for 20 min, turn on the automatic movement program of the crucible, and move the boat-shaped molybdenum crucible toward the end containing the seed crystal at a growth rate of 1.3 mm / h. During the movement, the melt in the boat-shaped molybdenum crucible that is gradually away from the heating area produces supercooling, which serves as a driving force for crystallization and promotes the production of single crystals. Seeding, shoulder release, and equal-width growth are carried out in sequence until all the raw materials are crystallized; the shoulder release angle is 90°.

[0024] (6) Cooling annealing: After crystallization is completed, a three-stage in-situ annealing process is adopted. First, the temperature is cooled to 23kW at a cooling rate of 20 ℃ / h and kept at this temperature for 48 hours for in-situ annealing to reduce the internal thermal stress of the crystal. Then, the crystal is cooled to room temperature at a cooling rate of 40 ℃ / h to obtain large-sized, high-quality Nd, Ce:LuAG crystals.

[0025] The furnace was opened and the crystals were taken out. The macroscopic quality of the crystals was good, with high transparency, no cracks, no cloudiness and other defects. The size of the equal diameter part was 140×85×25mm.

[0026] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the technical solution. Those skilled in the art should understand that those modifications or equivalent substitutions of the technical solution of the present invention that do not depart from the purpose and scope of the technical solution should be included in the scope of the claims of the present invention.

Claims

1. A method for horizontal directional crystal growth of Nd, Ce: LuAG crystals, characterized in that: The following steps are involved: (1) According to Ce 3x Nd 3y Lu 3(1-y-x) Al5O 12 Al2O3 powder, Lu2O3 powder, Ce2O3 powder and Nd2O3 powder are weighed and mixed evenly in a stoichiometric ratio, and then melted and cooled to obtain a pre-crystallized material; wherein, x is 0.01~5at.%, y is 0.01~5at.%; (2) The pre-crystallized material is crushed into small pieces and then spread flat in a boat-shaped crucible. Then, a seed crystal is inserted into a seed crystal groove at one end of the boat-shaped crucible near the shoulder angle. The boat-shaped crucible containing the pre-crystallized material and the seed crystal is placed in a working furnace, and the equal-width area of ​​the boat-shaped crucible is located in the heating area of ​​the working furnace. The furnace is closed. (3) Turn on the cooling system of the working furnace and keep the temperature of the cooling system at 25~35℃. Then evacuate the working furnace. When the vacuum degree is less than 1×10 -3 When the temperature is 0.0407°C, the heating power of the working furnace is turned on to heat the pre-crystallized material in the boat-shaped crucible in the heating area. By controlling the heating power, the pre-crystallized material in the heating area is melted to form a narrow melting zone with a length of 20-25 mm. (4) The formed narrow melting zone is kept warm for 0.5-1h. When the shape of the solid-liquid interface does not change significantly and tends to be a straight line, the heating power is kept unchanged, and the crucible boat is moved horizontally so that the heating zone is aligned with the end of the crucible boat containing the seed crystal for heating. At the same time, the seed crystal is ensured to be located at the edge of the heating zone. After keeping warm for 0.2-1h, the crucible boat is slowly moved toward the end of the crucible boat containing the seed crystal at a growth rate of 1-1.5mm / h. After seeding, shoulder release and equal width growth, all the pre-crystallization materials are melted and crystallized. After cooling and annealing, Nd, Ce:LuAG crystals are obtained. During the movement, the melt in the crucible boat that is gradually away from the heating zone produces supercooling, which serves as a driving force for crystallization and promotes the production of single crystals.

2. The method for horizontal directional crystal growth of Nd, Ce: LuAG crystal according to claim 1, characterized in that: The seed crystal in step (2) is <100> or <110> direction.

3. The method for horizontal directional crystal growth of Nd, Ce: LuAG crystal according to claim 1, characterized in that: The procedure of the cooling annealing in step (4) is as follows: first cool to 22-24 kW at a cooling rate of 10-30°C / h, keep at this power for 20-60 hours, and then cool to room temperature at 40-60°C / h.

4. The method for horizontal directional crystal growth of Nd, Ce: LuAG crystal according to claim 1, characterized in that: The shoulder release angle during the shoulder release phase is 80~120º.

5. The method for horizontal directional crystal growth of Nd, Ce: LuAG crystal according to claim 1, characterized in that: The boat-shaped crucible is a boat-shaped molybdenum crucible.

6. The method for horizontal directional crystal growth of Nd, Ce: LuAG crystal according to claim 1, characterized in that: The height of the boat-shaped crucible is 1 / 6 to 1 / 5 of the length of its equal diameter part.