Preparation method of pure LuAG-Nd: LuAG continuous heat dissipation crystal

Abstract

The invention discloses a preparation method of a pure LuAG-Nd: LuAG continuous heat dissipation crystal, during crystal preparation, a horizontal directional crystallization method is adopted, and the length of a melting zone is reasonably controlled, so that permanent and interface-free uniform combination of an undoped crystal (LuAG) and a doped crystal (Nd: LuAG) of which the segregation coefficient of the same matrix is less than 1 (the segregation coefficient of Nd < 3 + > ions is 0.18-0.25) is realized; the high-quality large-size lath-shaped pure LuAG-Nd: LuAG continuous heat dissipation crystal is obtained by reasonably controlling the growth rate, the internal defect density of the crystal is low, the physical performance is excellent, the continuous heat dissipation crystal can effectively solve the problems of oscillation and non-uniform heat distribution caused by ASE, and the problem of an interface between crystals does not exist. The method is simple in process, easy to implement and convenient to popularize and apply.

Description

Technical Field

[0001] The invention relates to the technical field of crystal growth, and in particular to a method for preparing a pure LuAG-Nd:LuAG continuous heat dissipation crystal. Background Art

[0002] With the rapid development of laser science and technology, the field of laser materials has ushered in unprecedented innovation and breakthroughs. Among them, Nd:LuAG (neodymium-doped lutetium aluminum garnet), as a new generation of high-performance laser gain medium, has shown great application potential in the field of solid-state lasers due to its unique high gain coefficient, excellent thermal properties and excellent optical properties. The introduction of this material not only improves the performance of the laser, but also provides a new direction for the research and development of high-power and large-size lasers.

[0003] However, the single-structure Nd:LuAG crystal gain medium is not perfect in practical applications. When the laser system is running, this type of crystal is prone to amplified spontaneous emission (ASE), which often leads to parasitic oscillation and a series of serious thermal effect problems, such as thermal stress, thermally induced birefringence and thermal lens effect. These problems not only affect the stability and output quality of the laser, but also greatly limit the application scope of Nd:LuAG crystals in large-size and high-power lasers.

[0004] In order to overcome these challenges, researchers began to explore the preparation technology of Nd:LuAG composite crystals. At present, the preparation methods of composite crystals include hot bonding, pulling, guided mold, hydrothermal and liquid phase epitaxy. Among these methods, only the hot bonding method has been commercialized, while the other methods have not yet been commercialized because it is difficult to prepare high-quality and large-sized composite crystals. The hot bonding method can effectively reduce thermal effects and parasitic oscillations by permanently combining undoped crystals (LuAG) with the same matrix-doped crystals (Nd:LuAG), thereby alleviating the limitations of single crystals. Although this method can balance thermal effects and improve beam quality to a certain extent, it has extremely high process requirements and it is difficult to completely eliminate the problems of oscillation and uneven heat distribution caused by ASE, especially under extreme working conditions. Interface problems between crystals may further affect the optimization of laser performance.

[0005] Therefore, developing a continuous crystal preparation technology that can simply and efficiently prepare large-size, high-quality composite crystals has become a frontier issue that needs to be urgently addressed in the current field of laser materials. 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 preparing pure LuAG-Nd:LuAG continuous heat dissipation crystals, so as to solve the problems of the existing composite crystal preparation technology, such as difficulty in preparing high-quality large-size composite crystals, extremely high process requirements, and difficulty in completely solving the oscillation and uneven heat distribution caused by ASE and the interface problems between crystals.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows: A method for preparing a pure LuAG-Nd:LuAG continuous heat dissipation crystal comprises the following steps: (1) Charging the furnace: lay small blocks of pure LuAG pre-crystallization material evenly and evenly on one end of the boat-shaped crucible near the shoulder angle, then lay Nd:LuAG pre-crystallization material evenly and evenly in the remaining space of the boat-shaped crucible except the seed crystal groove, and insert pure LuAG seed crystal into the seed crystal groove near the shoulder angle of the boat-shaped crucible, and then place them together in the working furnace, and make the pure LuAG pre-crystallization material located in the heater, and then seal the furnace; (2) Crystal melting: After sealing the furnace, turn on the water cooling circulation system to keep the water temperature at 25-45°C, then turn on the high vacuum system. When the vacuum degree is less than 1×10 -3 When the temperature reaches 0.0400 Pa, the heating system is turned on to heat the pure LuAG pre-crystallized material in the heater. The pure LuAG pre-crystallized material is partially melted by adjusting the heating power, and the length of the melting zone reaches 10-30 mm. (3) Seeding, shouldering and equal-width growth: When the solid-liquid interface is stable and the seed crystal is slightly melted or the seed crystal neither melts nor grows, the crucible boat is slowly moved toward the end of the crucible boat containing the seed crystal at a speed of 1-1.5 mm / h to perform seeding and shouldering growth in turn; after shouldering, the crucible boat is continued to move toward the end of the crucible boat containing the seed crystal at a rate of 1.5-2 mm / h to perform equal-width growth until all pre-crystallized materials are crystallized; during the movement, the melt in the crucible boat that gradually moves away from the heater produces supercooling, which serves as a driving force for crystallization and promotes the production of single crystals; after crystallization, the temperature is reduced and annealed to obtain pure LuAG-Nd:LuAG continuous heat dissipation crystals; during the crystallization growth process, the heating power is adjusted to keep the length of the melting zone unchanged.

[0008] Furthermore, in the Nd:LuAG pre-crystallization material in step (1), Nd 3+ The doping concentration is 1~2at.%. Too low a concentration of doping ions is not conducive to achieving a high gain effect, while too high a concentration of doping ions is not conducive to ensuring the integrity of the crystal due to the segregation effect of doping ions in the LuAG matrix. 3+ The doping concentration in this range can meet most commercial purposes.

[0009] Further, in step (1), the seed crystal is <111> , <100> or <110> Direction. LuAG belongs to the cubic crystal system and generally adopts these three directions.

[0010] Further, in step (3), the procedure of cooling annealing is: first, the furnace temperature is reduced to 1600-1750°C at a cooling rate of 10-30°C / h, and the temperature is kept for 30-60h, and in-situ annealing is performed to reduce the internal thermal stress of the crystal, and then cooled to room temperature at a cooling rate of 30-60°C / h. Although a cooling rate that is too fast or a holding time that is too short can reduce the crystal growth cycle, a cooling rate that is too fast or a holding time that is too short will weaken the degree of stress elimination during the annealing process and increase the risk of cracking. Therefore, the present invention adopts a segmented cooling method for annealing, first cooling at a smaller rate and keeping it warm for 30-60h 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.

[0011] 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.

[0012] 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.

[0013] Furthermore, in step (1), the preparation method of the pre-crystallized material is: according to the chemical formula Lu 3(1-x) Nd 3x Al 5 O 12 Weigh Al in the stoichiometric ratio 2 O 3 Polycrystalline, Lu 2 O 3 Powder and Nd 2 O 3 The powder raw materials are then mixed evenly, melted and cooled to obtain a solid solution, and then the solid solution is broken into small pieces as a pre-crystallized material; wherein x is Nd 3+ The doping concentration is 0at.% when preparing pure LuAG pre-crystallization material; when preparing Nd:LuAG pre-crystallization material, its value is 1~2at.%.

[0014] Furthermore, in step (1), the heater is a split heater composed of multiple groups of independent heating units, and the heating power of each independent unit decreases symmetrically and slowly from the middle to both sides.

[0015] Furthermore, in step (2), the method for adjusting the heating power is: when the heating power is increased to the melting point of the pure LuAG pre-crystallized material, the power is increased at a rate of 0.1-0.5 kW / h until the melting zone length of the pure LuAG pre-crystallized material reaches 10-30 mm.

[0016] The method for preparing pure LuAG-Nd:LuAG continuous heat dissipation crystals of the present invention adopts a horizontal directional crystallization method when preparing the crystals, and controls the melting zone length to be 10-30 mm, thereby achieving a segregation coefficient of less than 1 between the undoped crystal (LuAG) and the same matrix (Nd 3+ The doped crystals (Nd:LuAG) with a segregation coefficient of ions of 0.18-0.25) are permanently and uniformly combined without interfaces, and by reasonably controlling the growth rate, high-quality, large-size lath-shaped pure LuAG-Nd:LuAG continuous heat dissipation crystals are obtained.

[0017] The present invention controls the melting zone length to 10-30 mm because, if the melting zone length is too long, the chance of pure LuAG pre-crystallization material and Nd:LuAG pre-crystallization material mixing with each other after being heated and melted will be increased, which is not conducive to obtaining pure LuAG crystals at the front end of the crystal. When the melting zone length is controlled within 30 mm, after obtaining pure LuAG crystals at the front end of the crystal, the LuAG pre-crystallization material and part of the Nd:LuAG pre-crystallization material in the remaining area are heated and melted, and the doping ion concentration after the two are mixed is not high. In addition, Nd 3+ Due to the segregation effect, the doping ion concentration is very low at the beginning after the mixture crystallizes, which makes the transition between LuAG crystal and Nd:LuAG crystal very good, thus realizing the permanent and interface-free uniform combination of pure LuAG crystal and Nd:LuAG crystal. The length of the melting zone should not be too short, because if the melting zone is too short, it is easy to produce supercooled melt or partially supercooled melt, which is not conducive to the stability of the growth interface. If the interface is unstable, dendrites or cellular structures are easy to be produced, which is not conducive to obtaining high-quality crystals. At the same time, a certain temperature is also required to maintain the fluidity of the melt during the crystal growth process. Too low temperature (or too small melting zone) will lead to poor melt fluidity, thus affecting the growth of the crystal. As for the growth rate, the seeding growth is carried out at a lower growth rate of 1-1.5mm / h at the beginning, in order to stabilize the seeding and shouldering as much as possible, to ensure the smooth growth of the crystal at the beginning. When entering the equal width zone, the growth rate is appropriately increased to 1.5-2mm / h after the crystal grows relatively stably, which can improve the growth efficiency of the crystal.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. The method for preparing pure LuAG-Nd:LuAG continuous heat dissipation crystals of the present invention adopts a horizontal directional crystallization method during crystal preparation, and controls the melting zone length to be 10-30 mm, thereby achieving a segregation coefficient of less than 1 between the undoped crystal (LuAG) and the same matrix (Nd 3+ The doped crystal (Nd:LuAG) with a segregation coefficient of ions of 0.18-0.25) is permanently and uniformly combined without interface, and by reasonably controlling the growth rate, high-quality large-size lath-shaped pure LuAG-Nd:LuAG continuous heat dissipation crystals are obtained. The obtained crystal has low internal defect density and excellent physical properties. The continuous heat dissipation crystal can effectively solve the problems of oscillation and uneven heat distribution caused by ASE, and there is no interface problem between crystals. The method is simple in process, easy to implement, and easy to promote and apply.

[0019] 2. The molybdenum crucible used in the present invention has a melting point of 2630°C, which is easy to grow high-melting-point crystals. During the growth process, the crucible has high stability, is not easy to leak, and has low cost. In the single crystal growth process, there is no melt rotation operation, which avoids the generation of core, side core and cloud defects, and is easy to obtain high-quality crystals with less processing allowance, thereby increasing production efficiency. In addition, during the single crystal cooling process, the present invention adopts an in-situ annealing process to reduce the stress inside the crystal and reduce the possibility of crystal cracking, thereby improving the yield rate of the crystal. DETAILED DESCRIPTION

[0020] The specific implementation modes of the present invention are further described in detail below in conjunction with specific examples.

[0021] Example 1 This embodiment provides a method for preparing a pure LuAG-Nd:LuAG continuous heat dissipation crystal, comprising the following steps: (1) Furnace loading: according to the chemical formula Lu 3(1-x) Nd 3x Al 5 O 12 Weighing Al 2 O 3 Polycrystalline, Lu 2 O 3 Powder and Nd 2 O 3 The powder raw materials are then mixed evenly, melted and cooled to obtain a solid solution, and then the solid solution is broken into small pieces as pre-crystallization materials. Where x is the concentration of doped neodymium ions. When preparing pure LuAG pre-crystallization materials, its value is 0at.%; when preparing Nd:LuAG pre-crystallization materials, its value is 1at.%. 800g of pure LuAG pre-crystallization materials are evenly laid on one end of the boat-shaped molybdenum crucible near the shoulder angle, and then 1200g of Nd 3+The Nd:LuAG pre-crystallization material with a doping concentration of 1 at.% is evenly and evenly laid in the remaining space of the boat-shaped molybdenum crucible except the seed crystal groove, and the pure LuAG seed crystal with a crystal orientation of

[100] is inserted into the seed crystal groove at one end of the boat-shaped molybdenum crucible near the shoulder angle, and then placed in a horizontal single crystal furnace together, and the pure LuAG pre-crystallization material is located in the heater, and then the furnace is sealed; in specific implementation, the loading positions of the pure LuAG pre-crystallization material and the Nd:LuAG pre-crystallization material cannot be exchanged, because if they are exchanged, due to the Nd 3+ Segregation effect of doping, Nd 3+ It will gather at the tail of the crystal, which is not conducive to obtaining pure LuAG crystals.

[0022] (2) Crystal melting: Turn on the water cooling circulation system and high vacuum system until the water temperature and vacuum degree are maintained at 32°C and 6.6×10 -4 Pa, turn on the heating system and heat the heater. When the heater power reaches 29kW, observe the solid-liquid interface shape of the pre-crystallized material in the heater, and obvious liquid streamlines appear. Observe the liquid streamlines every 20 minutes. After 1 hour, it is found that the curvature of the liquid streamlines is still large. Adjust the power appropriately (0.3kW / h). After 1 hour, the liquid streamlines are basically stable, and the length of the melting zone reaches 18mm. At this time, the melt contacts the seed crystal, and the seed crystal is slightly melted. (3) Seeding, shouldering and equal-width growth: Move the boat-shaped molybdenum crucible slowly toward the end of the boat-shaped molybdenum crucible with the seed crystal at a speed of 1.5 mm / h to start seeding and shouldering growth. After 40 hours, it enters the equal-width growth stage, and continues to move toward the end of the boat-shaped molybdenum crucible with the seed crystal at a rate of 1.8 mm / h to continue crystal growth until the crystal growth is completed. During the movement, the melt in the boat-shaped crucible that gradually moves away from the heater produces supercooling, which serves as a driving force for crystallization and promotes the production of single crystals. During the entire movement of the boat-shaped molybdenum crucible, the heating power is adjusted by a heating and cooling rate of 0.1 kW / h to keep the length of the melting zone unchanged. This is because Nd 3+ The doping of Nd:LuAG will reduce the melting point of the LuAG matrix. When obtaining the same melt length, the power required for pure LuAG and Nd:LuAG will be different. Therefore, the power is adjusted appropriately to avoid excessively high or low temperatures, thereby ensuring the stable growth of LuAG-Nd:LuAG continuous crystals.

[0023] (4) Cooling annealing: After the crystal growth is completed, it enters the cooling stage. First, the furnace temperature is lowered to 1750℃ at a cooling rate of 20℃ / h. The annealing time is 50h, and then it is cooled to room temperature at a cooling rate of 40℃ / h. The furnace is opened and the crystal is taken out to obtain a pure LuAG-Nd:LuAG continuous heat dissipation crystal.

[0024] After testing, the pure LuAG-Nd (1at.%):LuAG continuous crystal grown by this process has no bubbles, clouds and cracks visible to the naked eye, and is of good quality. The crystal size is 140mm×85mm×20mm.

[0025] Example 2 This embodiment provides a method for preparing a pure LuAG-Nd:LuAG continuous heat dissipation crystal, comprising the following steps: (1) Furnace loading: according to the chemical formula Lu 3(1-x) Nd 3x Al 5 O 12 Weighing Al 2 O 3 Polycrystalline, Lu 2 O 3 Powder and Nd 2 O 3 Powder raw materials, then mix the raw materials evenly, melt and cool to obtain a solid solution, and then break the solid solution into small pieces as pre-crystallization materials. Wherein x is the concentration of doped neodymium ions, and when preparing pure LuAG pre-crystallization materials, its value is 0at.%; when preparing Nd:LuAG pre-crystallization materials, its value is 2at.%. 500g of pure LuAG pre-crystallization materials are evenly and evenly laid on one end of the boat-shaped molybdenum crucible near the shoulder angle, and then 1500g of Nd:LuAG pre-crystallization materials with a Nd doping concentration of 2at.% are evenly and evenly laid in the remaining space of the boat-shaped molybdenum crucible except the seed crystal groove, and a pure LuAG seed crystal with a crystal direction of

[111] is inserted into the seed crystal groove at one end of the boat-shaped molybdenum crucible near the shoulder angle, and then placed together in a horizontal single crystal furnace, and the pure LuAG pre-crystallization material is located in the heater, and then the furnace is sealed; (2) Crystal melting: Turn on the water cooling circulation system and high vacuum system until the water temperature and vacuum degree are maintained at 32°C and 3×10 -4 Pa, turn on the heating system and heat the heater. When the heater power reaches 29kW, observe the solid-liquid interface shape of the pre-crystallized material in the heater, and obvious liquid streamlines appear. The liquid streamlines are observed every 20 minutes. After 1 hour, it is found that the liquid streamlines of the melting zone length are still unstable. The power is fine-tuned appropriately (0.2kW / h). After 2 hours, the liquid streamlines have basically no tendency to expand forward, and the curvature is small. The melting zone length reaches about 10mm. The melt contacts the seed crystal, and the seed crystal neither melts nor grows. (3) Seeding, shouldering and equal-width growth: The molybdenum boat crucible is slowly moved toward the end of the molybdenum boat crucible with the seed crystal at a speed of 1.2 mm / h for 40 hours to carry out seeding and shouldering growth. Then the molybdenum boat crucible continues to move toward the end of the molybdenum boat crucible with the seed crystal at a speed of 1.5 mm / h to carry out equal-width growth until the crystal growth is completed; during the movement, the melt in the boat crucible that gradually moves away from the heater produces supercooling, which serves as a driving force for crystallization and promotes the production of single crystals. During the entire movement of the molybdenum boat crucible, the heating power is adjusted by a heating and cooling rate of 0.2 kW / h to keep the length of the melting zone unchanged.

[0026] (4) Cooling annealing: After the crystal growth is completed, it enters the cooling stage. First, the furnace temperature is lowered to 1600℃ at a cooling rate of 10℃ / h. The annealing time is 45h, and then it is cooled to room temperature at a cooling rate of 35℃ / h. The furnace is opened and the crystal is taken out to obtain a pure LuAG-Nd:LuAG continuous heat dissipation crystal.

[0027] After testing, the pure LuAG-Nd (2at.%):LuAG continuous crystals grown by this process have no bubbles, clouds and cracks visible to the naked eye, are of good quality, and the crystal size is 130mm×85mm×20mm.

[0028] 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 preparing pure LuAG-Nd:LuAG continuous heat dissipation crystal, characterized in that: The following steps are involved: (1) Charging the furnace: lay small blocks of pure LuAG pre-crystallization material evenly and evenly on one end of the boat-shaped crucible near the shoulder angle, then lay Nd:LuAG pre-crystallization material evenly and evenly in the remaining space of the boat-shaped crucible except the seed crystal groove, and insert pure LuAG seed crystal into the seed crystal groove near the shoulder angle of the boat-shaped crucible, and then place them together in the working furnace, and make the pure LuAG pre-crystallization material located in the heater, and then seal the furnace; (2) Crystal melting: After sealing the furnace, turn on the water cooling circulation system to keep the water temperature at 25-45°C, then turn on the high vacuum system. When the vacuum degree is less than 1×10 -3 Pa, the heating system is turned on to heat the pure LuAG pre-crystallized material in the heater, and the pure LuAG pre-crystallized material is partially melted by adjusting the heating power, and the length of the melting zone reaches 10-30 mm; (3) Seeding, shouldering and equal-width growth: When the solid-liquid interface is stable and the seed crystal is slightly melted or the seed crystal neither melts nor grows, the crucible boat is slowly moved toward the end of the crucible boat containing the seed crystal at a speed of 1-1.5 mm / h to perform seeding and shouldering growth in turn; after shouldering, the crucible boat is continued to move toward the end of the crucible boat containing the seed crystal at a rate of 1.5-2 mm / h to perform equal-width growth until all pre-crystallized materials are crystallized; during the movement, the melt in the crucible boat that gradually moves away from the heater produces supercooling, which serves as a driving force for crystallization and promotes the production of single crystals; after crystallization, the temperature is reduced and annealed to obtain pure LuAG-Nd:LuAG continuous heat dissipation crystals; during the crystallization growth process, the heating power is adjusted to keep the length of the melting zone unchanged.

2. The method for preparing the pure LuAG-Nd:LuAG continuous heat dissipation crystal according to claim 1, characterized in that: In step (1), Nd:LuAG pre-crystallization material 3+ The doping concentration is 1~2at.%.

3. The method for preparing the pure LuAG-Nd:LuAG continuous heat dissipation crystal according to claim 1, characterized in that: In step (1), the seed crystal is <111> , <100> or <110> direction.

4. The method for preparing the pure LuAG-Nd:LuAG continuous heat dissipation crystal according to claim 1, characterized in that: In step (3), the cooling annealing procedure is as follows: first, the furnace temperature is lowered to 1600-1750°C at a cooling rate of 10-30°C / h, kept at this temperature for 30-60h, and in-situ annealing is performed to reduce the internal thermal stress of the crystal, and then cooled to room temperature at a cooling rate of 30-60°C / h.

5. The method for preparing the pure LuAG-Nd:LuAG continuous heat dissipation crystal according to claim 1, characterized in that: The shoulder release angle during the shoulder release phase is 80~120º.

6. The method for preparing the pure LuAG-Nd:LuAG continuous heat dissipation crystal according to claim 1, characterized in that: The boat-shaped crucible is a boat-shaped molybdenum crucible.

7. The method for preparing the pure LuAG-Nd:LuAG continuous heat dissipation crystal according to claim 1, characterized in that: In step (1), the preparation method of the pre-crystallized material is: according to the chemical formula Lu 3(1-x) Nd 3x Al5O 12 Al2O3 polycrystalline material, Lu2O3 powder and Nd2O3 powder raw materials are weighed in a stoichiometric ratio, and then the raw materials are mixed evenly, melted and cooled to obtain a solid solution, and then the solid solution is broken into small pieces as a pre-crystallization material; wherein x is Nd 3+ The doping concentration is 0at.% when preparing pure LuAG pre-crystallization material; when preparing Nd:LuAG pre-crystallization material, its value is 1~2at.%.

8. The method for preparing the pure LuAG-Nd:LuAG continuous heat dissipation crystal according to claim 1, characterized in that: In step (1), the heater is a split heater composed of multiple groups of independent heating units, and the heating power of each independent unit decreases symmetrically and slowly from the middle to both sides.

9. The method for preparing the pure LuAG-Nd:LuAG continuous heat dissipation crystal according to claim 1, characterized in that: In step (2), the method for adjusting the heating power is: when the heating power is increased to the melting point of the pure LuAG pre-crystallized material, the power is increased at a rate of 0.1-0.5 kW / h until the melting zone length of the pure LuAG pre-crystallized material reaches 10-30 mm.