A lithium barium terbium fluoroborate magneto-optical crystal, its preparation method and application

Abstract

This invention discloses a lithium barium terbium fluoroborate magneto-optical crystal, wherein the chemical formula of the lithium barium terbium fluoroborate magneto-optical crystal is LiBa. 0.5 Tb 2.5 (BO3)3F 0.5 The lithium barium terbium fluoroborate magneto-optical crystal is a single crystal belonging to the cubic crystal system, with space group F d⁻³m(227), unit cell parameters α=β=γ=90°, Z=16. This crystal has the highest symmetry and a high terbium ion concentration (10.52×10⁻³ m). 21 ion / cm 3 Furthermore, its transmittance is greater than 80% in the infrared wavelength range. Therefore, it can be used as a magneto-optical crystal in the visible-infrared wavelength range and has good application potential in the fabrication of magneto-optical isolators, magneto-optical switches, magneto-optical sensors, magneto-optical storage, and magneto-optical modulators. At the same time, this crystal can also be used as a phosphor matrix for applications in optical lighting and optical communication.

Description

Technical Field

[0001] This invention relates to the field of magneto-optical crystal fabrication technology. More specifically, it relates to a lithium barium terbium fluoroborate magneto-optical crystal, its fabrication method, and its applications. Background Technology

[0002] Under the influence of a magnetic field, the polarization direction of light in a magneto-optical crystal undergoes an irreversible unidirectional rotation. Therefore, it can be used in conjunction with polarization devices to construct optical isolators, enabling unidirectional laser transmission and limiting or completely eliminating back reflections along the beam's propagation path, thus achieving optical isolation. Under a constant external magnetic field, the Verdet coefficient of a material is directly proportional to its effective length. Since a longer light path within the material increases the likelihood of light loss, exploring magneto-optical materials with high Verdet constants is of great significance for developing novel magneto-optical isolators.

[0003] Tb3Ga5O 12 Ga₂O₃ (TGG), due to its high symmetry (cubic structure), high terbium content, low-temperature paramagnetism, and low absorption coefficient, has become the most commonly used magneto-optical material in magneto-optical isolators. However, TGG crystals require high-temperature growth, and the significant volatilization of Ga₂O₃ during growth alters the melt composition, increasing crystal defects. It typically exhibits absorption in the visible light region, making it difficult to obtain high-optical-quality TGG crystals. Overcoming the shortcomings of TGG magneto-optical crystals and discovering new and better magneto-optical crystals applicable to different wavelengths (infrared, visible, and ultraviolet) remains a challenge for crystal researchers.

[0004] Inorganic borate materials have long been a focus of research in the modern laser field due to their high transmittance in the ultraviolet-visible range, rich structures, high laser damage threshold, and numerous potential applications. Several compounds have been discovered among rare-earth borates, which can serve as nonlinear optical materials, luminescent materials, birefringent materials, and thermal neutron detectors. Because magneto-optical crystals require high symmetry, only Sr3Tb(BO3)3 has been reported as a magneto-optical crystal so far. However, due to its low terbium content, its magneto-optical performance is poor, significantly lagging behind commercially available TGG.

[0005] Generally, the Verdet coefficient of magneto-optical crystals is approximately proportional to the terbium ion concentration. Among the existing rare-earth borate systems, terbium borate (TbBO3) has the highest terbium ion concentration. However, existing research results on terbium borate indicate that it undergoes a phase transition at around 1000℃, changing from a hexagonal high-temperature phase to a triclinic low-temperature phase. Therefore, it cannot be used as a magneto-optical crystal.

[0006] Patent ZL201510179899.2 discloses a high terbium content alkaline earth borate, LiMTb2(BO3)3, belonging to the trigonal crystal system, equivalent to 1 / 3 LiMBO3 + 2 / 3 TbBO3 (M = Sr, Ba); Patent ZL201510570794X discloses a high terbium concentration borate, LiCaTb5(BO3)6, equivalent to 1 / 6 LiCaBO3 + 5 / 6 TbBO3, belonging to the hexagonal crystal system. Both have terbium ion contents very close to TbBO3 (reaching 83.3%), and crystal structure analysis results show a terbium ion concentration of 13.5 × 10⁻⁶. 21 ion / cm 3 This exceeds the terbium ion concentration in TGG (12.8 × 10⁻⁶). 21 ion / cm 3 ).

[0007] On the other hand, magneto-optical materials must avoid thermo-optical effects, so the material must meet the requirement of high symmetry, requiring the magneto-optical crystal to be a uniaxial or cubic crystal. The cubic crystal system has the highest symmetry among all crystal systems, making it a key focus in the search for highly symmetric magneto-optical crystals.

[0008] Therefore, there is a need for a cubic crystal with high terbium ion concentration, large Verdet coefficient, and high symmetry. Summary of the Invention

[0009] One object of the present invention is to provide a lithium barium terbium borate magneto-optical crystal, the chemical formula of which is LiBa 0.5 Tb 2.5 (BO3)3F 0.5 It has a high terbium ion content; at the same time, the crystal belongs to the cubic crystal system, has high symmetry, and high magneto-optical effect.

[0010] Another object of the present invention is to provide a method for preparing a lithium barium terbium fluoroborate magneto-optical crystal.

[0011] Another object of the present invention is to provide an application of lithium barium terbium fluoroborate magneto-optical crystal.

[0012] To achieve the above objectives, the present invention adopts the following technical solution:

[0013] A lithium barium terbium fluoroborate magneto-optical crystal, wherein the chemical formula of the lithium barium terbium fluoroborate magneto-optical crystal is LiBa. 0.5 Tb 2.5 (BO3)3F 0.5 The lithium barium terbium fluoroborate magneto-optical crystal is a single crystal, belonging to the cubic crystal system, with space group F d⁻³m(227), and unit cell parameters of . α=β=γ=90°, Z=16,

[0014] The lithium barium terbium fluoroborate magneto-optical crystal of this invention belongs to the cubic crystal system. Its cell parameters, including the three axial lengths and three axial angles, are all equal, exhibiting the highest symmetry. When used as a magneto-optical material, it can effectively avoid thermo-optical effects. Furthermore, crystal structure analysis shows that its terbium ion concentration is 10.52 × 10⁻⁶. 21 ion / cm 3 The terbium ion concentration is close to that in TGG, which is beneficial to improving the magneto-optical effect. Its magneto-optical Verdet coefficient is expected to be 110 rad / mT at 633 nm and 36 rad / mT at 1064 nm.

[0015] Furthermore, this crystal has high transmittance in the wavelength range of 600nm to 1500nm, making it a magneto-optical crystal material with excellent application prospects in the visible infrared field.

[0016] A method for preparing lithium barium terbium fluoroborate magneto-optical crystals includes a flux method and a melt pulling method. The resulting crystals have high transparency, large size, and few structural defects, making them particularly suitable for fabricating magneto-optical isolators.

[0017] The flux-based crystal growth method includes the following steps:

[0018] The raw materials are mixed with flux to obtain crystal growth material; the crystal growth material is heated to 1000-1100℃ and stirred at a constant temperature; the temperature is lowered to 4-5℃ above the melt saturation point temperature and a seed crystal rod is placed in it; the temperature is lowered at a rate of 0.01-1.5℃ / day, while the crystal is rotated at a rate of 15-30r / min; after the crystal growth is completed, the crystal is lifted off the liquid surface and then annealed to room temperature at a cooling rate of no more than 10℃ / h.

[0019] The raw material contains a mixture of Tb compounds, Ba compounds, B compounds, Li compounds, and F compounds, or is a polycrystalline pure-phase powder LiBa. 0.5 Tb 2.5 (BO3)3F 0.5 .

[0020] In the specific preparation process, a platinum crucible is preferably used for crystal growth. When the crystal growth material is heated to 1000–1100°C, it completely melts. During crystal growth, the melt temperature decreases. The crystal growth rate is relatively fast in the temperature range of 870–930°C. After a growth cycle of 25–50 days, single crystals with dimensions in the millimeter range can be obtained. For example, lithium barium terbium fluoroborate (LiBa) prepared by the flux method is shown. 0.5 Tb 2.5 (BO3)3F 0.5The size of a single crystal is (12-15)mm×(12-15)mm×(7-10)mm, such as 12mm×12mm×8mm, etc.

[0021] Preferably, the molar ratio of Tb, Ba, B, Li, F elements and cosolvent in the Tb-containing compound, Ba-containing compound, B-containing compound, Li-containing compound, and F-containing compound is 2-3:0.3-0.9:2-4:0.7-1.2:0.4-0.9:0.4-0.7;

[0022] It should be noted that when considering the relative proportions of Tb, Ba, B, Li, and F elements in this invention, if a compound contains at least two of these elements, then the compound can simultaneously provide at least two of these elements, and the compound must be considered when calculating the molar amounts of the contained elements. However, if the fluxing compound also contains Tb, Ba, B, Li, or F elements, then the fluxing compound must not be considered when calculating the amount of Tb, Ba, B, Li, or F elements.

[0023] Preferably, the polycrystalline pure-phase powder LiBa 0.5 Tb 2.5 (BO3)3F 0.5 The molar ratio of flux to flux is 0.7-1.2:2.3-5.

[0024] Preferably, the co-solvent is LiBO2·8H2O.

[0025] The melt pulling method for crystal growth includes the following steps:

[0026] polycrystalline pure phase powder LiBa 0.5 Tb 2.5 (BO3)3F 0.5 The crystal is placed in a Czochralski furnace and heated to melt under N2 environment with constant temperature stirring. The temperature is then lowered to 2-3°C above the saturation point, and a seed crystal is introduced using a seed crystal rod. After holding the temperature for 70-90 minutes, the temperature is lowered to the saturation point, and the seed crystal rod is rotated at a rate of 15-25 r / min while the temperature is lowered at a rate of 1.5-2°C / day. The crystal is then pulled at a pulling speed of 0.03-0.4 mm / h. After the crystal growth is complete, the crystal is lifted off the liquid surface and then annealed to room temperature at a cooling rate of no more than 6-14°C / h.

[0027] In the specific melt pulling process, an iridium crucible is preferably used for crystal growth. When introducing a seed crystal using a seed rod, the end of the seed rod is fitted with the seed crystal and is either in contact with the melt surface or extends into the melt. Preferably, the crystal growth rate is faster in the temperature range of 1100–1150°C, and millimeter-sized lithium barium terbium fluoroborate (LiBa) can be obtained after 25–50 days of growth. 0.5 Tb 2.5 (BO3)3F 0.5 Single crystal, exemplarily, lithium barium terbium fluoroborate (LiBa) prepared by melt pulling method. 0.5 Tb 2.5 (BO3)3F 0.5 The size of a single crystal is (12-15)mm×(12-15)mm×(7-10)mm, such as 12mm×12mm×8mm.

[0028] Preferably, the polycrystalline pure-phase powder LiBa 0.5 Tb 2.5 (BO3)3F 0.5 The preparation method includes the following steps:

[0029] The compounds containing Tb, Ba, B, Li, and F are ground, heated to 400-500℃ and held for 12 hours, then heated to 650-700℃ and held for 12 hours, and then cooled to obtain the final product.

[0030] The molar ratio of Tb, Ba, B, Li, and F in the Tb-containing, Ba-containing, B-containing, Li-containing, and F-containing compounds is 22-3:0.3-0.9:2-4:0.7-1.2:0.4-0.9:0.4-0.7.

[0031] Preparation of polycrystalline pure-phase powder LiBa 0.5 Tb 2.5 (BO3)3F 0.5 During the process, the temperature is raised to 400-500℃ at a uniform rate of 50℃ / h. This process is called pre-calcination. The uniform heating rate ensures that the composition of the raw materials does not change significantly during dehydration or carbon dioxide removal. At the same time, multiple grinding processes are performed during the preparation process to ensure thorough mixing of the materials, which is beneficial for obtaining pure-phase polycrystalline powder.

[0032] In the preparation of lithium barium terbium fluoroborate magneto-optical crystals LiBa 0.5 Tb 2.5 (BO3)3F 0.5 Polycrystalline pure phase powder LiBa 0.5 Tb 2.5 (BO3)3F 0.5 During the process,

[0033] Preferably, the Tb-containing compound is one of an oxide, nitrate, or sulfate containing the element Tb;

[0034] Preferably, the Ba-containing compound is one of a Ba-containing carbonate, nitrate, or hydroxide;

[0035] Preferably, the B-containing compound is boric acid or boron oxide;

[0036] Preferably, the Li-containing compound is one of an oxide, hydride, or nitrate containing the element Li.

[0037] Preferably, the F-containing compound is one of the fluorides containing the F element.

[0038] Of course, those skilled in the art can select other suitable compounds containing Tb, Ba, B, Li and F elements according to actual needs, but this will not have a substantial impact on the crystal preparation process and the crystals obtained, and is within the protection scope of this invention.

[0039] The present invention also provides applications of the aforementioned lithium barium terbium fluoroborate magneto-optical crystal. These applications include the use of the lithium barium terbium borate magneto-optical crystal as a phosphor matrix, and its use in the fabrication of magneto-optical isolators.

[0040] The lithium barium terbium fluoroborate magneto-optical crystal described in this invention is a cubic crystal with the highest level of symmetry, effectively avoiding the thermo-optical effect; and its terbium ion concentration is very high, which is beneficial to improving the magneto-optical effect. It is an excellent magneto-optical crystal that can be used to make magneto-optical isolators, magneto-optical switches, magneto-optical sensors, magneto-optical storage, and magneto-optical modulators.

[0041] The beneficial effects of the present invention are as follows:

[0042] The lithium barium terbium fluoroborate magneto-optical crystal provided by this invention is a single crystal, belonging to the cubic crystal system, and possesses the highest symmetry; moreover, the concentration of terbium ions in this crystal compound is as high as 10.52 × 10⁻⁶. 21 ion / cm 3 The light transmittance is greater than 80% in the wavelength range of 600nm to 1500nm. Therefore, the magneto-optical Verdet coefficient of this crystal can be expected to be 110 rad / mT at 633nm and 36 rad / mT at 1064nm. At the same time, it can avoid the thermo-optical effect and can be used as a magneto-optical crystal in the visible-infrared wavelength range. It has good application potential in the fabrication of magneto-optical isolators, magneto-optical switches, magneto-optical sensors, magneto-optical storage, and magneto-optical modulators. In addition, this crystal can also be used as a phosphor matrix, which has important economic and scientific research value in optical lighting and optical communication. Attached Figure Description

[0043] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0044] Figure 1 This illustrates the polycrystalline pure-phase powder lithium barium terbium fluoroborate (LiBa) prepared in Example 1. 0.5 Tb 2.5 (BO3)3F 0.5 The X-ray diffraction pattern (PXRD) of the sample.

[0045] Figure 2 This illustrates the polycrystalline pure-phase powder lithium barium terbium fluoroborate (LiBa) prepared in Example 1. 0.5 Tb 2.5 (BO3)3F 0.5 The ultraviolet-visible-near-infrared transmission spectrum.

[0046] Figure 3 This illustrates the polycrystalline pure-phase powder lithium barium terbium fluoroborate (LiBa) prepared in Example 1. 0.5 Tb 2.5 (BO3)3F 0.5 The fluorescence spectrum.

[0047] Figure 4 This illustrates the polycrystalline pure-phase powder lithium barium terbium fluoroborate (LiBa) prepared in Example 1. 0.5 Tb 2.5 (BO3)3F 0.5 The infrared spectrum.

[0048] Figure 5 This invention demonstrates the presence of lithium barium terbium fluoroborate (LiBa). 0.5 Tb 2.5 (BO3)3F 0.5 A schematic diagram of the crystal structure.

[0049] Figure 6 This invention demonstrates the presence of lithium barium terbium fluoroborate (LiBa). 0.5 Tb 2.5 (BO3)3F 0.5 A schematic diagram of the optical path when a crystal is used in a magneto-optical isolator. Detailed Implementation

[0050] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments and accompanying drawings, further clarifies the invention. Similar components in the drawings are indicated by the same reference numerals. Those skilled in the art should understand that the specific description below is illustrative rather than restrictive and should not be construed as limiting the scope of protection of the present invention.

[0051] Example 1

[0052] Preparation of polycrystalline pure phase powder lithium barium terbium fluoroborate (LiBa)0.5 Tb 2.5 (BO3)3F 0.5

[0053] Li₂CO₃ (0.071 g), BaCO₃ (0.378 g), Tb₄O₇ (1.791 g), H₃BO₃ (0.711 g), and LiF (0.050 g) were mixed in a mortar and ground thoroughly. The mixture was then placed in a platinum crucible and placed in a muffle furnace. The temperature was increased to 500 °C at a rate of 50 °C / h, held for 12 h, and then cooled. After cooling, the sample was removed and ground again until homogeneous. The mixture was then placed in a muffle furnace and heated to 720 °C at the same rate and held for 12 h. After cooling, lithium barium terbium fluoroborate (LiBa) was obtained. 0.5 Tb 2.5 (BO3)3F 0.5 Polycrystalline pure-phase powder. The X-ray diffraction pattern of this polycrystalline pure-phase powder is as follows: Figure 1 As shown, the polycrystalline pure phase powder is LiBa. 0.5 Tb 2.5 (BO3)3F 0.5 Pure phase, with no other impurities present; the ultraviolet-visible-near-infrared transmission spectrum of this polycrystalline pure phase powder is as follows: Figure 2 As shown, the results indicate that the lithium barium terbium borate (LiBa) of the present invention... 0.5 Tb 2.5 (BO3)3F 0.5 The polycrystalline pure-phase powder exhibits good transmittance (above 80%) in the 500-1500 nm range, making it highly valuable for practical applications. The fluorescence spectrum of this polycrystalline pure-phase powder is as follows: Figure 3 As shown, this invention illustrates the lithium barium terbium fluoroborate (LiBa) 0.5 Tb 2.5 (BO3)3F 0.5 The polycrystalline pure phase powder emits effective green fluorescence at 530-560 nm, indicating that it can be used as a phosphor.

[0054] Example 2

[0055] Flux method for growing lithium barium terbium fluoroborate (LiBa) 0.5 Tb 2.5 (BO3)3F 0.5 crystal

[0056] LiBO2·8H2O was selected as the flux to melt LiBa 0.5 Tb 2.5 (BO3)3F 0.5 The polycrystalline pure phase powder (430.22g) and flux LiBO2·8H2O (264.65g) were mixed in a mortar and ground thoroughly. The mixture was then added in batches. The material is melted in a platinum crucible and cooled to obtain a mixed growth material. The crucible containing the mixed growth material is placed in a crystal growth furnace and heated to 1030℃. It is stirred at a constant temperature for 24 hours to melt and mix the material evenly. The temperature is then lowered to 5℃ above the melt saturation point, and a platinum wire (seed crystal rod) is lowered into the melt. The temperature is then lowered to 920℃ at a rate of 0.5℃ / d, while the seed crystal rod is rotated at a speed of 20 rad / min. After the crystal growth is complete (growth cycle of 30 days), the seed crystal rod is lifted to remove the crystal from the liquid surface. The crystal is then cooled to room temperature at a rate of 8℃ / h to obtain a 11mm×10mm×7mm millimeter-sized crystal.

[0057] X-ray single-crystal diffraction was employed, with single-crystal X-ray diffraction performed on a Rigaku Oxford X-ray single-crystal diffractometer. Monochromatic Mo-Kα rays were used as the diffraction source, and absorption correction was performed using the Multi-Scan method. Structural analysis was performed using the SHELXL-2018 software package; the positions of heavy atoms were determined using a direct method, and the coordinates of the remaining atoms were obtained using difference Fourier synthesis; and the structure was analyzed using an F-based method. 2 The coordinates and anisotropic thermal parameters of all atoms were refined using matrix least squares. The final crystal structure parameters obtained in Example 2 are shown in Table 1.

[0058] Table 1. Lithium barium terbium fluoroborate crystal (LiBa) 0.5 Tb 2.5 (BO3)3F 0.5 Crystal structure data

[0059]

[0060] Example 3

[0061] Flux method for growing lithium barium terbium fluoroborate (LiBa) 0.5 Tb 2.5 (BO3)3F 0.5 crystal

[0062] Weigh out Li2CO3 (19.38g), BaCO3 (103.19g), Tb4O7 (488.94g), H3BO3 (194.10g), LiF (13.65g) and flux LiBO2·8H2O (240.31g), mix and grind them in a mortar, and melt them in batches in a φ60mm×60mm platinum crucible to obtain a mixed melt. After the melting is completed, cool it to room temperature to obtain crystal growth material.

[0063] A crucible containing the mixed melt was placed in a crystal growth furnace and heated to 1030℃. The mixture was stirred at this constant temperature for 24 hours until completely melted. The temperature was then lowered to 4℃ above the saturation temperature of the mixed melt, and a platinum wire (i.e., a seed crystal rod) was inserted into the melt. The temperature was lowered at a rate of 0.2℃ / day, while the seed crystal rod was rotated at a speed of 30 rd / min. The crystal growth was observed. Once the crystal growth was complete (growth cycle 40 days), the seed crystal rod was lifted, and the crystal was removed from the liquid surface. The crystal was then cooled to room temperature at a rate of 8℃ / h, yielding a lithium barium terbium fluoroborate (LiBa) crystal with dimensions of 11mm × 11mm × 9mm. 0.5 Tb 2.5 (BO3)3F 0.5 crystal.

[0064] Example 4

[0065] Melt-pulley growth of lithium barium terbium fluoroborate (LiBa) 0.5 Tb 2.5 (BO3)3F 0.5 crystal

[0066] After weighing Li₂CO₃ (33.8g), LiF (23.75g), BaCO₃ (180.75g), Tb₄O₇ (342.5g), and H₃BO₃ (170g), they were mixed and ground in a mortar, and then loaded into a container. The platinum crucible was placed in a muffle furnace and heated to 450°C for 12 hours, then the temperature was increased to 700°C to obtain polycrystalline pure-phase powder. The polycrystalline pure-phase powder was then loaded into... An iridium crucible is placed in a Czochralski furnace and protected with high-purity N2. The mixture is heated until completely melted and stirred for 24 hours. When the melt temperature is 2°C above the saturation point, a seed crystal is added. The seed crystal is fixed to the end of a seed crystal rod, which is then lowered from the growth furnace, either into contact with the melt surface or extending into the melt. One hour after adding the seed crystal, the temperature is lowered to the saturation point while the seed crystal rod is rotated at a rate of 24 revolutions per minute. The temperature is then reduced at a rate of 1.5°C per day, and the crystal is pulled at a rate of 0.04 mm per hour. The crystal gradually grows until it reaches a certain size. The crystal is then lifted from the liquid surface and cooled to room temperature at a rate of 10°C per hour, yielding a crystal measuring 20 mm × 18 mm × 14 mm.

[0067] Example 5

[0068] Lithium barium terbium fluoroborate (LiBa) 0.5 Tb 2.5 (BO3)3F 0.5 The crystal is used as a magneto-optical crystal to fabricate magneto-optical isolator devices, including the following steps:

[0069] The lithium barium terbium fluoroborate (LiBa) obtained in Example 2 0.5Tb 2.5 (BO3)3F 0.5 The crystal is cut according to requirements to obtain a crystal device with a certain cross-sectional size and light transmission direction length; the light transmission surfaces at both ends of the crystal device are precision polished and coated. Figure 6 The diagram shows the working principle. When light from a light source such as a laser enters the polarizer, it becomes linearly polarized light. After the linearly polarized light passes through the Faraday deflector, the polarization direction of the linearly polarized light changes.

[0070] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A lithium barium terbium fluoroborate magneto-optical crystal, characterized in that, The chemical formula of the lithium barium terbium fluoroborate magneto-optical crystal is LiBa. 0.5 Tb 2.5 (BO3)3F 0.5 The lithium barium terbium fluoroborate magneto-optical crystal is a single crystal, belonging to the cubic crystal system, with space group 1. F d- 3m (227)， The unit cell parameters are a=b=c=14.9536(3)Å, α=β=γ=90 o Z=16, V=3343.78(12)Å 3 .

2. A method for preparing the lithium barium terbium fluoroborate magneto-optical crystal as described in claim 1, characterized in that, Crystals are grown using either the flux method or the melt pulling method.

3. The preparation method according to claim 2, characterized in that, The flux-based crystal growth method includes the following steps: The raw materials are mixed with flux to obtain crystal growth material; the crystal growth material is heated to 1000~1100℃ and stirred at a constant temperature; the temperature is lowered to 4~5℃ above the melt saturation point temperature and a seed crystal rod is placed in it; the temperature is lowered at a rate of 0.01~1.5℃ / day, while the crystal is rotated at a rate of 15-30r / min; after the crystal growth is completed, the crystal is lifted off the liquid surface and then annealed to room temperature at a cooling rate of no more than 10℃ / h. The raw material is a mixture containing Tb compounds, Ba compounds, B compounds, Li compounds, and F compounds, or a polycrystalline pure-phase powder LiBa. 0.5 Tb 2.5 (BO3)3F 0.5 .

4. The preparation method according to claim 3, characterized in that, The molar ratio of Tb, Ba, B, Li, F elements and flux in the mixture containing Tb, Ba, B, Li, and F is 2-3:0.3-0.9:2-4:0.7-1.2:0.4-0.9:0.4-0.

7.

5. The preparation method according to claim 3, characterized in that, The polycrystalline pure phase powder LiBa 0.5 Tb 2.5 (BO3)3F 0.5 The molar ratio of flux to flux is 0.7-1.2:2.3-5.

6. The preparation method according to claim 3, characterized in that, The flux is LiBO2·8H2O.

7. The preparation method according to claim 2, characterized in that, The melt-pulling method for crystal growth includes the following steps: polycrystalline pure phase powder LiBa 0.5 Tb 2.5 (BO3)3F 0.5 Place the crystal in a Czochralski furnace and heat it to melt under N2 environment, stirring at a constant temperature. Cool it down to 2-3°C above the saturation point temperature and introduce a seed crystal using a seed crystal rod. After holding the temperature for 70-90 minutes, cool it down to the saturation point temperature and rotate the seed crystal rod at a rate of 15-25 r / min while cooling it down at a rate of 1.5-2°C / day. Pull the crystal at a pulling speed of 0.03-0.4 mm / h. After the crystal growth is complete, lift the crystal off the liquid surface and anneal it to room temperature at a cooling rate of no more than 6-14°C / h.

8. The preparation method according to any one of claims 3-6, characterized in that, The polycrystalline pure phase powder LiBa 0.5 Tb 2.5 (BO3)3F 0.5 The preparation method includes the following steps: The compounds containing Tb, Ba, B, Li, and F are ground, heated to 400-500℃ and held for 12 hours, then heated to 650-750℃ and held for 12 hours, and then cooled to obtain the final product. The molar ratio of Tb, Ba, B, Li, and F in compounds containing Tb, Ba, B, Li, and F is 2-3:0.3-0.9:2-4:0.7-1.2:0.4-0.

9.

9. The preparation method according to any one of claims 3-6, characterized in that, The Tb-containing compound is one of the following: an oxide, a nitrate, or a sulfate containing the element Tb; The Ba-containing compound is one of the following: a carbonate, a nitrate, or a hydroxide containing the element Ba; The B-containing compound is boric acid or boron oxide; The Li-containing compound is one of the following: an oxide, a hydride, or a nitrate containing the element Li. The F-containing compound is one of the fluorides containing the F element.

10. The application of the lithium barium terbium fluoroborate magneto-optical crystal as described in claim 1 as a fluorescent matrix.

11. The application of the lithium barium terbium fluoroborate magneto-optical crystal as described in claim 1 in the fabrication of magneto-optical isolators, magneto-optical switches, magneto-optical sensors, magneto-optical storage, and magneto-optical modulators.

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