Na5Tb9F32 magneto-optical crystal and preparation method and application thereof

Abstract

The invention discloses a Na5Tb9F32 magneto-optical crystal and a preparation method and application thereof, the chemical formula of the Na5Tb9F32 magneto-optical crystal is Na5Tb9F32, the crystal is of a cubic structure, the space group structure is Fm-3m, and birefringence does not exist; the order of magnitude of the thermo-optical coefficient of the material reaches 10 <-6 > K <-1 >, and the Vierdet constant is 33-34 Rad.m <-1 >. T <-1 > at 1064nm; the uniform melt crystallization characteristic is realized. The Na5Tb9F32 magneto-optical crystal is of a cubic structure, and birefringence does not exist; the thermo-optical coefficient is small, and the system is suitable for a high-power and high-stability optical system; the crystals have consistent melt crystallization characteristics, and large-size crystals are easy to grow. The Na5Tb9F32 magneto-optical crystal can be prepared by adopting a well-known crystal growth method, is a novel magneto-optical material with great potential, and is very suitable for being used as a crystal element of a high-power and high-stability magneto-optical device.

Description

Technical Field

[0001] This application belongs to the technical field of optical crystals, and specifically relates to a Na5Tb9F 32 magneto-optical crystal and its preparation method, and also relates to the application of this Na5Tb9F 32 magneto-optical crystal in magneto-optical devices. Background Technique

[0002] Typical magneto-optical devices, such as Faraday isolators, are based on the Faraday effect of magneto-optical crystals. Under the action of an external magnetic field, the polarization direction of the incident light is rotated unidirectionally to achieve the unidirectional propagation of light. It is widely used in laser systems and optical communications, can effectively isolate the reflected light, prevent damage to the pre-stage laser, and improve the system stability. Magneto-optical crystals are a type of crystal material that can change the polarization state of light under the action of an external magnetic field. Its core principle is based on the Faraday magneto-optical effect. As a key crystal component in magneto-optical devices, its performance directly affects the performance of magneto-optical devices.

[0003] Currently, the most widely used magneto-optical crystal is terbium gallium garnet (TGG). It has a cubic structure, is easy to process and has no birefringence. It is a commercially available magneto-optical material for making Faraday rotators and isolators; however, the TGG crystal has a high absorption coefficient and a large thermo-optic coefficient, and is prone to thermal lens effect and beam depolarization under high-power lasers, which limits its application in higher-power laser systems.

[0004] Fluoride magneto-optical crystals have become important candidate materials for the next generation of high-power magneto-optical devices due to their lower optical loss and thermo-optic coefficient. Currently, the developed fluoride magneto-optical crystals include KTb3F 10 magneto-optical crystals, LiTbF4, CeF3 crystals, etc. Among them, KTb3F 10 has the advantages of low absorption coefficient, small thermo-optic coefficient, high laser damage threshold, etc., and can effectively suppress the thermal lens effect and beam depolarization under high-power lasers, showing excellent optical performance and thermal stability. It is a very promising magneto-optical material in high-power laser systems; however, KTb3F 10 crystals have non-uniform melting characteristics, resulting in greater difficulty in crystal growth, prone to peritectic reactions and impurity phases, affecting the purity and optical quality of the crystals; in addition, the KF raw material has strong hygroscopicity and is very likely to cause water and oxygen pollution of KTb3F 10 crystals during the preparation process. These preparation difficulties limit the large-size and high-quality KTb3F 10The stable production of magneto-optical crystals increases the preparation cost and difficulty of the materials. LiTbF4 and CeF3 crystals also have the advantages of low absorption coefficient, small thermo-optical coefficient, high laser damage threshold, large Verdet constant, etc. However, LiTbF4 and CeF3 are in tetragonal and trigonal structures respectively, with natural birefringence. During their use, crystal orientation deviation is likely to occur, resulting in the inconsistent direction of light propagation and the crystal optical axis, thus causing polarization state change and beam quality degradation, which limits their application in high-power laser systems.

[0005] Although fluoride magneto-optical crystal materials have great advantages in aspects such as absorption loss, thermo-optical coefficient, and laser damage threshold, due to the above various problems existing in the prior art, it is very necessary to develop and study new fluoride magneto-optical crystals. Summary of the Invention

[0006] In view of this, the primary object of this application is to provide a Na5Tb9F 32 magneto-optical crystal, which has a cubic structure and no birefringence; has a small thermo-optical coefficient and is suitable for high-power and high-stability optical systems; the crystal has congruent melting crystallization characteristics and is easy to grow large-sized crystals.

[0007] To achieve the above object, this application adopts the following technical solutions:

[0008] One aspect of this application provides a Na5Tb9F 32 magneto-optical crystal, whose chemical formula is Na5Tb9F 32 , this crystal has a cubic structure, the space group structure is Fm-3m, and there is no birefringence; the order of magnitude of its thermo-optical coefficient reaches 10 -6 K -1 , the Verdet constant is 33 - 34 Rad·m -1 ·T -1 @1064nm; it has congruent melting crystallization characteristics.

[0009] Another aspect of this application provides a preparation method of the above-mentioned Na5Tb9F 32 magneto-optical crystal, using NaF and TbF3 as raw materials, and growing and preparing it by the Bridgman method or the Czochralski method.

[0010] Another aspect of this application provides the use of the above-mentioned Na5Tb9F 32 magneto-optical crystal or the Na5Tb9F 32 magneto-optical crystal prepared by the above-mentioned preparation method as a crystal element in magneto-optical devices.

[0011] Another aspect of this application provides a magneto-optical device containing the above-mentioned Na5Tb9F 32Magneto-optical crystal or Na5Tb9F prepared by the described preparation method 32 magneto-optical crystal.

[0012] Advantages of this application:

[0013] The Na5Tb9F 32 magneto-optical crystal provided by this application has a cubic structure, where Na + and F - form a co-edge NaF 16 tetrahedral structure, and Tb 3+ is bonded to eight F - atoms in an 8-coordination manner to jointly form a three-dimensional cubic structure. The space group structure is Fm-3m(225), and the unit cell constant The unit cell volume is There is no birefringence; the order of magnitude of the thermo-optical coefficient of this crystal reaches 10 -6 K -1 The Verdet constant is 33 - 34 Rad·m -1 ·T -1 @1064 nm, which is very suitable for high-power and high-stability optical systems. In addition, this crystal has congruent melting crystallization characteristics and is easy to grow large-sized single crystals. Description of the drawings

[0014] Figure 1 is a photo of the Na5Tb9F 32 magneto-optical crystal prepared by the Bridgman method in Example 1 of this application.

[0015] Figure 2 is the XRD powder diffraction pattern of the Na5Tb9F 32 magneto-optical crystal prepared in Example 1 of this application.

[0016] Figure 3 is the transmittance spectrum of the Na5Tb9F 32 magneto-optical crystal prepared in Example 1 of this application in the range of 250 - 2500 nm. Detailed implementation manners

[0017] The implementation manners of this application will be clearly and completely described below. The technical solutions in the following described implementation manners are exemplary and only possible technical implementations of this application, not all possible implementations. Those skilled in the art can fully combine the implementation manners of this application and obtain other implementation manners without creative labor, and these implementation manners are also within the protection scope of this application.

[0018] The first aspect of this application discloses a Na5Tb9F 32 magneto-optical crystal, and its chemical formula is Na5Tb9F 32, the crystal has a cubic structure, the space group structure is Fm-3m(225), and the unit cell constant The unit cell volume is There is no birefringence, and the order of magnitude of the thermo-optic coefficient reaches 10 -6 K -1 , and the Verdet constant is 33 - 34 Rad·m -1 ·T -1 @1064 nm; the melting point is between 1065 - 1072 °C, and the crystal has congruent melting and crystallization characteristics.

[0019] Compared with the existing fluoride magneto-optical crystals, the Na5Tb9F in this application 32 The magneto-optical crystal has a cubic structure (space group: Fm-3m, 225), no birefringence effect, and is an ideal high-power magneto-optical crystal; the order of magnitude of its thermo-optic coefficient reaches ×10 -6 K -1 , and is suitable for high-power and high-stability optical systems. Its Verdet constant is 33 - 34 Rad·m -1 ·T -1 @1064 nm, slightly lower than that of the KTb3F 10 crystal (35 Rad·m -1 ·T -1 ), but because the crystal has congruent melting and crystallization characteristics and is easy to grow large-sized crystals, therefore, the Verdet constant can be compensated by increasing the crystal length.

[0020] The second aspect of this application discloses a method for preparing a Na5Tb9F 32 magneto-optical crystal. The preparation of the Na5Tb9F 32 magneto-optical crystal in this application can adopt the crystal growth methods well-known to those skilled in the art, such as the Bridgman method or the Czochralski method.

[0021] In some examples, the Na5Tb9F 32 magneto-optical crystal is prepared by the Bridgman method, and specifically includes the following steps:

[0022] S1. Under the condition of isolating water and oxygen, according to the chemical formula of the Na5Tb9F 32 magneto-optical crystal, provide the raw materials NaF and TbF3, place the raw materials in a platinum crucible, and evacuate and seal the platinum crucible;

[0023] S2. Install the sealed platinum crucible into the furnace chamber of a two-temperature-zone horizontal rocking furnace. After evacuating, synchronously heat the two temperature zones to 1090 °C; after keeping the temperature constant for more than 500 min, rock the furnace body; then synchronously cool the two temperature zones to room temperature, and take out the platinum crucible;

[0024] S3. Place the platinum crucible in a double-temperature vertical single crystal furnace, adjust the position of the platinum crucible so that the bottom end of the platinum crucible is located at the middle position of the adiabatic zone of the single crystal furnace, and place a temperature measuring thermocouple at the bottom end of the crucible; after evacuating the furnace chamber, fill it with a protective gas at 95-105 Pa and keep the pressure constant; heat the upper temperature zone and the lower temperature zone of the double-temperature vertical single crystal furnace to 1250 °C and 900 °C respectively within 600 min, and keep the temperature constant for 45-50 h. At this time, the temperature gradient in the adiabatic zone reaches 40 °C / cm, and the temperature of the temperature measuring thermocouple is 1075 °C; then, lower the platinum crucible at a rate of 1-3 mm / h by 120 mm, and cool the upper temperature zone and the lower temperature zone of the double-temperature vertical single crystal furnace to room temperature within 1000 min, and take out the crystal.

[0025] In the present application, in step S1, the condition of isolating water and oxygen can be achieved by a glove box commonly used in the art, but is not limited thereto.

[0026] Further, the sealing of the platinum crucible is achieved by evacuating and then, under vacuum conditions, welding and sealing the platinum crucible with a laser.

[0027] Further, 1 wt% NaF is additionally added to the raw materials to supplement the volatilization loss of NaF.

[0028] In the present application, in step S2, the evacuation means that the vacuum degree reaches below 10 Pa, preferably below 4 Pa.

[0029] Further, the time for keeping the temperature constant and shaking the furnace body can be adjusted or optimized as needed. In some examples, the temperature-keeping time is above 500 min, preferably 500-600 min; the time for shaking the furnace body is 180-220 min, preferably 200 min.

[0030] Further, the heating rate and the cooling rate of the two temperature zones can adopt the rates commonly used in the art. The heating rate is 1-10 °C / min, and the cooling rate is 1-10 °C / min. In some examples, the heating rate is 2 °C / min and the cooling rate is 5 °C / min.

[0031] In the present application, in step S3, the evacuation means that the order of magnitude of the vacuum degree reaches 10 -3 Pa, preferably 5×10 -3 Pa; wherein, the protective gas filled is high-purity argon or high-purity helium with a purity of 99.999%.

[0032] In some other examples, the Na5Tb9F 32 magneto-optical crystal is prepared by the Czochralski method, and the Czochralski method includes the following steps:

[0033] S1. According to Na5Tb9F32 The chemical formula of the magneto-optical crystal. Provide raw materials NaF and TbF3, place the raw materials in a crucible, and transfer the charged crucible into a Czochralski furnace;

[0034] S2. Evacuate the Czochralski furnace and raise the temperature to melt the raw materials;

[0035] S3. Use a pre-prepared <111>-oriented Na5Tb9F 32 crystal as a seed crystal, immerse it in the platinum crucible melt, and control the temperature and pulling speed to grow the crystal;

[0036] S4. After the crystal growth is completed, lower the temperature and take out the crystal;

[0037] In this application, in step S1, 2-5 wt% of NaF is additionally added to the raw materials to supplement the volatilization loss of NaF.

[0038] In this application, the step of melting the raw materials in step S2 is specifically as follows: Evacuate to below 1×10 -6 Pa, then raise the temperature of the Czochralski furnace at a rate of 2-10 °C / min to 300 °C; keep the temperature constant for 500-600 min, then fill with a protective gas, and the air pressure is kept constant at 1×10 5 ~1.2×10 5 Pa; then, raise the temperature at a rate of 1-10 °C / min to 1100-1140 °C, and keep the temperature constant for 500-600 min;

[0039] In step S3 of this application, the growth of the crystal successively includes the steps of seeding, shoulder formation, equal-diameter growth, and finishing. Those skilled in the art can adjust various parameters such as temperature and pulling speed according to the needs such as the size of the crystal to obtain a suitable crystal. Those skilled in the art have such an ability, so there is no special limitation.

[0040] In some specific examples, the processes of seeding, shoulder formation, equal-diameter growth, and finishing are as follows:

[0041] Seeding: Slowly immerse the pre-prepared <111>-oriented Na5Tb9F 32 crystal seed into the platinum crucible melt to partially melt it to ensure good bonding. Subsequently, precisely control the temperature and pulling speed to gradually solidify the melt on the seed crystal and form an initial crystal nucleus. At the same time, apply appropriate rotation to promote the uniform distribution of the melt and stabilize the crystal growth.

[0042] Shoulder formation: Adopt the automatic shoulder formation program of the single crystal Czochralski furnace to slowly expand the diameter of the seed crystal to form a conical shoulder.

[0043] Equal-diameter growth: After shoulder formation, the equal-diameter growth stage begins. An automated weighing feedback program of a single crystal pulling furnace is used to control the power of the power supply and the pulling rate, so that the crystal diameter remains unchanged, achieving the purpose of equal-diameter control. The equal-diameter growth controls the crystal length. During this period, the rotation rate of the seed crystal remains unchanged.

[0044] Tail end: Gradually increase the melt temperature and at the same time increase the pulling speed, so that the crystal diameter gradually decreases, forming a conical tail, and pulling out of the melt surface.

[0045] In step S4 of the present application, the rate of temperature reduction is 1 to 10 °C / min, preferably 1 °C / min.

[0046] In some examples, the preparation method further includes a step of crystal processing. The crystal processing adopts a common crystal cutting and processing method in the art. In some preferred examples, a single crystal orientation instrument is used to orient the grown Na5Tb9F 32 magneto-optical crystal, marking the (111) direction; cutting and processing a crystal element of the required size, ensuring that the two light-transmitting surfaces are perpendicular to the (111) direction; then, performing fine processing on the two light-transmitting surfaces, with flatness ≤ λ / 10@633nm and parallelism ≤ 10″.

[0047] The third aspect of the present application discloses the use of the Na5Tb9F 32 magneto-optical crystal or the Na5Tb9F 32 magneto-optical crystal prepared by the preparation method as a crystal element in a magneto-optical device.

[0048] In the present application, the magneto-optical device is a Faraday isolator.

[0049] The fourth aspect of the present application discloses a magneto-optical device containing the Na5Tb9F 32 magneto-optical crystal or the Na5Tb9F 32 magneto-optical crystal prepared by the preparation method described above.

[0050] The following are specific examples of the present application. It should be noted that the following specific examples are only for illustrative purposes and do not limit the scope of the present application in any way.

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs. The terms used in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0052] In addition, unless otherwise specified, the methods without specific conditions or steps recorded are conventional methods, and the reagents and materials used can be obtained from commercial sources.

[0053] Example 1

[0054] In this example, a method for preparing a Na5Tb9F 32 magneto - optical crystal is provided. It is prepared by the Bridgman method, and the specific steps are as follows:

[0055] (1) Weighing the materials and sealing the crucible: Inside the glove box, weigh the materials according to the molar ratio of NaF:TbF3 = 5:9, and add 1 wt% of NaF by mass to supplement its volatilization loss; put the weighed NaF and TbF3 into a platinum crucible, and under vacuum conditions, use a laser to perform vacuum welding and sealing on the platinum crucible.

[0056] (2) Synthesis of raw materials: Put the sealed platinum crucible into the furnace chamber of a two - temperature - zone horizontal shaking furnace. After pumping the vacuum to below 4 Pa, the two temperature zones are synchronously heated to 1090 °C at a rate of 2 °C / min; after maintaining the temperature for 600 min, the furnace body shakes for 200 min; then, the two temperature zones are synchronously cooled to room temperature at a rate of 5 °C / min, and the platinum crucible is taken out.

[0057] (3) Single - crystal growth: Put the platinum crucible into a two - temperature - zone vertical single - crystal furnace, adjust the position of the crucible so that the bottom end of the platinum crucible is located at the middle position of the adiabatic zone of the single - crystal furnace, and place a thermocouple for temperature measurement at the bottom end of the platinum crucible; after pumping the furnace chamber to a vacuum of 5×10 -3 Pa, fill it with 100 Pa of high - purity argon and maintain a constant pressure; heat the upper and lower temperature zones of the two - temperature - zone vertical single - crystal furnace to 1250 °C and 900 °C respectively within 600 min, and maintain the temperature for 48 h. At this time, the temperature gradient in the adiabatic zone reaches 40 °C / cm, and the temperature measured by the thermocouple is 1075 °C; then, lower the crucible at a rate of 2 mm / h by 120 mm, and cool the upper and lower temperature zones of the two - temperature - zone vertical single - crystal furnace to room temperature within 1000 min, and take out the crystal. The physical appearance of the crystal is as Figure 1 shown in.

[0058] (4) Crystal processing: Use a single - crystal orientator to orient the grown Na5Tb9F 32 crystal and mark the (111) direction; use a general crystal processing method to cut and process a crystal element with the required size, ensuring that the two light - passing surfaces are perpendicular to the (111) direction; then, perform fine processing on the two light - passing surfaces so that their flatness ≤ λ / 10@633 nm and parallelism ≤ 10″.

[0059] (5) Crystal property testing:

[0060] Use an X - ray powder diffractometer to test the phase structure of the Na5Tb9F 32 crystal. Figure 2 For Na5Tb9F 32The XRD powder diffraction pattern of the crystal shows good agreement with the standard powder diffraction database (PDF#00-027-0808), indicating that the crystal prepared in this example has the correct structure.

[0061] The transmittance of the Na5Tb9F 32 crystal was measured using a spectrophotometer. Figure 3 For the Na5Tb9F 32 crystal, the transmittance spectrum in the wavelength range of 250 - 2500 nm shows that the transmittance in the light-transmitting band is close to 94%; the absorptions at 370 nm, 378 nm, and 488 nm correspond to the 3+ energy level transitions of 7 F6→ 5 L0, 7 F6→ 5 D4, 7 F6→ 5 D3 of Tb.

[0062] After testing, its thermo-optic coefficient is 1×10 -6 K -1 , and the Verdet constant is 33 Rad·m -1 ·T -1 @1064 nm, and the melting point is between 1065 - 1072 °C.

[0063] Example 2

[0064] In this example, a preparation method of a Na5Tb9F 32 magneto-optical crystal was provided. The Czochralski method was used for preparation, and the specific steps are as follows:

[0065] (1) Weighing and loading the furnace: Inside the glove box, weigh the materials according to the molar ratio of NaF:TbF3 = 5:9, and add 2 - 5 wt% of NaF by mass to supplement its volatilization loss; put the weighed NaF and TbF3 into a platinum crucible, and transfer the platinum crucible with the loaded materials into the Czochralski furnace and place it in the middle position of the graphite heater.

[0066] (2) Melting of raw materials: Close the furnace door of the Czochralski furnace, evacuate to below 1×10 -6 Pa, then heat the Czochralski furnace at a rate of 2 - 10 °C / min to 300 °C; after holding at a constant temperature for 600 min, fill it with Ar or He protective gas, and keep the gas pressure constant at 1 - 1.2×10 5 Pa; then, heat it at a rate of 5 °C / min to 1100 - 1140 °C and hold at a constant temperature for 600 min.

[0067] (3) Seeding: Use the pre-prepared <111>-oriented Na5Tb9F 32The crystal seed is slowly immersed in the melt of the platinum crucible to partially melt it to ensure good bonding. Subsequently, by precisely controlling the temperature and pulling rate, the melt gradually solidifies on the seed crystal to form an initial crystal nucleus. At the same time, an appropriate rotation is applied to promote the uniform distribution of the melt and stabilize crystal growth.

[0068] (4) Shoulder formation: Using the automatic shoulder formation program of the single crystal pulling furnace, the 6-mm-diameter seed crystal is slowly expanded to 50 mm to form a conical shoulder.

[0069] (5) Equal-diameter growth: After shoulder formation, it enters the equal-diameter growth stage. Using the automatic weighing feedback program of the single crystal pulling furnace, the power of the power supply and the pulling rate are controlled so that the crystal diameter remains unchanged to achieve the purpose of equal-diameter control. The length of the equal-diameter grown crystal is controlled within 80 - 100 mm. During this period, the rotation rate of the seed crystal remains unchanged.

[0070] (6) Ending: Gradually increase the temperature of the melt and at the same time increase the pulling rate to gradually reduce the crystal diameter to form a conical tail and pull it out of the melt surface.

[0071] (7) Cooling and removing the crystal: After crystal growth is completed, the pulling furnace is cooled to room temperature at a rate of 1 °C / min or less, and the crystal is removed.

[0072] (8) Crystal processing: Use a single crystal orientator to orient the grown Na5Tb9F 32 crystal and mark the (111) direction; use a general crystal processing method to cut and process the crystal element with the required size to ensure that the two light-transmitting surfaces are perpendicular to the (111) direction; then, perform fine processing on the two light-transmitting surfaces so that their flatness ≤ λ / 10 @ 633 nm and parallelism ≤ 10″.

[0073] After testing, the order of magnitude of its thermo-optic coefficient reaches 10 -6 K -1 , and the Verdet constant is 34 Rad·m -1 ·T -1 @1064 nm, and the melting point is between 1065 - 1072 °C.

[0074] It should be noted that this application is not limited to the above embodiments. The above embodiments are only examples, and embodiments having the same composition and the same function and effect as the technical idea within the scope of the technical solution of this application are all included in the technical scope of this application. In addition, within the scope of not departing from the gist of this application, various deformations that can be thought of by those skilled in the art are applied to the embodiments, and other ways constructed by combining some constituent elements of the embodiments are also included in the scope of this application.

Claims

1. A Na5Tb9F 32 magneto-optical crystal, characterized in that Its chemical formula is Na5Tb9F 32 , and this crystal has a cubic structure with a space group structure of Fm-3m and no birefringence; The order of magnitude of its thermo-optic coefficient reaches 10 -6 K -1 , and the Verdet constant is 33 - 34 Rad·m -1 ·T -1 @1064 nm; it has congruent melting and crystallization characteristics.

2. The Na5Tb9F as described in claim 1 32 magneto - optical crystal, characterized in that Its unit cell constant The unit cell volume is 3. The Na5Tb9F as claimed in claim 1 32 magneto-optical crystal, characterized in that Its melting point is 1065 - 1072 °C.

4. A method for preparing a Na5Tb9F 32 magneto-optical crystal as claimed in any one of claims 1-3, characterized in that It is prepared by the Bridgman method or the Czochralski method using NaF and TbF3 as raw materials.

5. The preparation method according to claim 4, characterized in that, The Na5Tb9F 32 The magneto-optical crystal is prepared by the Bridgman method, and the Bridgman method includes the following steps: S1. Under the condition of isolating water and oxygen, according to the chemical formula of the 32 magneto-optical crystal, provide raw materials NaF and TbF3, place the raw materials in a platinum crucible, and evacuate and seal the platinum crucible; S2. Place the sealed platinum crucible into the furnace chamber of a two-zone horizontal rocking furnace. After evacuating the air, heat the two zones synchronously to 1090 °C; keep the temperature constant for more than 500 min and then rock the furnace body; subsequently, cool the two zones synchronously to room temperature and take out the platinum crucible. S3. Place the platinum crucible into a two-zone vertical single crystal furnace, adjust the position of the platinum crucible so that the bottom end of the platinum crucible is located in the middle of the adiabatic zone of the single crystal furnace, and place a temperature-measuring thermocouple at the bottom end of the crucible; evacuate the furnace chamber and then fill it with a protective gas at 95 - 105 Pa and keep the pressure constant; heat the upper and lower zones of the two-zone vertical single crystal furnace to 1250 °C and 900 °C respectively within 600 min, keep the temperature constant for 45 - 50 h. At this time, the temperature gradient in the adiabatic zone reaches 40 °C / cm and the temperature of the temperature-measuring thermocouple is 1075 °C; then, lower the platinum crucible at a rate of 1 - 3 mm / h by 120 mm, and cool the upper and lower zones of the two-zone vertical single crystal furnace to room temperature within 1000 min and take out the crystal. Preferably, in step S1, the sealing of the platinum crucible is achieved by evacuating the air and then, under vacuum conditions, welding and sealing the platinum crucible with a laser. Preferably, in step S1, 1 wt% NaF is additionally added to the raw materials. Preferably, in step S2, the evacuation refers to a vacuum degree below 10 Pa. Preferably, in step S2, the time for keeping the temperature constant is 500 - 600 min, and the time for rocking the furnace body is 180 - 220 min. Preferably, in step S2, the heating rate of the two zones is 1 - 10 °C / min, and the cooling rate is 1 - 10 °C / min. Preferably, in step S3, the evacuation means that the order of magnitude of the vacuum degree reaches 10 -3 Pa; Preferably, in step S3, the protective gas is high-purity argon or high-purity helium with a purity of 99.999%.

6. The preparation method according to claim 4, characterized in that, The Na5Tb9F 32 The magneto-optical crystal is prepared by the Czochralski method, and the Czochralski method includes the following steps: S1. According to the chemical formula of the magneto-optical crystal Na5Tb9F 32 provide raw materials NaF and TbF3, place the raw materials in a crucible, and transfer the charged crucible into a Czochralski furnace; S2. Evacuate the Czochralski furnace and heat it up to melt the raw materials. S3. Using the pre-prepared <111>-oriented Na5Tb9F 32 crystal as a seed crystal, immersing it in the platinum crucible melt, and growing the crystal by controlling the temperature and pulling speed; S4. After crystal growth is completed, cool down and take out the crystal. Preferably, in step S1, 2 - 5 wt% NaF is additionally added to the raw materials. Preferably, step S2 is specifically as follows: After evacuating to below 1×10 -6 Pa, heat the lifting furnace to 300°C at a rate of 2-10°C / min; after maintaining the temperature for 500-600 min, fill in a protective gas, and keep the air pressure constant at 1×10 5 ~1.2×10 5 Pa; then, heat it to 1100-1140°C at a rate of 1-10°C / min and maintain the temperature for 500-600 min; Preferably, in step S3, the crystal growth sequentially includes the steps of seeding, shoulder formation, and equal-diameter growth. Preferably, in step S4, the cooling rate is 1 - 10 °C / min.

7. The preparation method according to any one of claims 4-6, characterized in that, The preparation method further includes the step of crystal processing. Preferably, the crystal processing technology includes: Use a single crystal orientation instrument to orient the grown Na5Tb9F 32 crystal, and mark the (111) direction; cut and process the crystal components into the required sizes, ensuring that the two light-transmitting surfaces are perpendicular to the (111) direction; then, perform finish machining on the two light-transmitting surfaces, with flatness ≤ λ / 10 @ 633 nm and parallelism ≤ 10″.

8. The Na5Tb9F 32 magneto-optical crystal as claimed in any one of claims 1 to 3 or the Na5Tb9F 32 magneto-optical crystal prepared by the preparation method as claimed in any one of claims 4 to 7, as an application of a crystal component in a magneto-optical device; Preferably, the magneto-optical device is a Faraday isolator.

9. A magneto-optical device, characterized in that, Containing the Na5Tb9F described in any one of claims 1-3 32 magneto-optical crystal or the Na5Tb9F magneto-optical crystal prepared by the preparation method described in any one of claims 4-7 32 magneto-optical crystal.

10. The magneto-optical device according to claim 9, characterized in that, The magneto-optical device is a Faraday isolator.

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