A preparation method and use of lithium niobium telluride compound and its nonlinear optical crystal

Abstract

The present invention relates to a preparation method and use of a lithium niobium telluride compound and a nonlinear optical crystal thereof, wherein the chemical formula of the lithium niobium telluride compound is LiNbTeO5. Specifically, the lithium niobium telluride compound is a polycrystalline powder or a nonlinear optical crystal, and the lithium niobium telluride nonlinear optical crystal has a wide transmission range, a strong frequency doubling effect, a high laser damage threshold, stable physical and chemical properties, is not easy to deliquesce, and is easy to cut, polish and store.

Description

Technical Field

[0001] The invention relates to the field of optoelectronic functional materials, and in particular to a preparation method and application of a lithium niobium telluride compound and a nonlinear optical crystal thereof. Background Art

[0002] Nonlinear optical crystals can expand the laser frequency range through frequency doubling, difference frequency, optical parametric oscillation and optical parametric amplification technologies. They are increasingly used in laser medicine, optical communications, signal processing and integrated optics, and play an indispensable role in all-solid-state lasers.

[0003] The nonlinear optical crystals that have been put into practical use, such as KH2PO4, KTiOPO4, β-BaB2O4, LiB3O5, ZnGeP2, AgGaS2 and AgGaSe2, have defects such as crystal deliquescence, two-photon absorption, low damage threshold, short transmission range, and difficulty in growing into bulk single crystals with uniform optical quality, which limits their application in fields such as all-solid-state lasers.

[0004] Nonlinear optical crystals with potential application value should meet the following conditions: (1) a sufficiently large nonlinear optical coefficient to obtain a relatively ideal frequency conversion efficiency; (2) a moderate birefringence to obtain phase matching conditions and effectively output coherent light; (3) a wide transmission range so that the crystal can be used in different wavelength ranges; (4) good chemical stability and a large laser damage threshold; and (5) easy to grow into centimeter-level optically uniform single crystals.

[0005] However, existing nonlinear optical crystals are difficult to meet the above conditions and are difficult to be applied in the field of all-solid-state lasers. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a lithium niobium telluride compound, whose chemical formula is LiNbTeO5.

[0007] According to the present invention, the lithium niobium telluride compound is a polycrystalline powder; specifically, it is a pure phase polycrystalline powder.

[0008] According to the present invention, the lithium niobium telluride compound is a nonlinear optical crystal.

[0009] According to the present invention, the lithium niobium telluride polycrystalline powder has the following characteristics: Figure 1 The XRD pattern described.

[0010] The present invention also provides a method for preparing the lithium niobium telluride compound. The method comprises the following steps: subjecting Nb2O5, a lithium compound and TeO2 to a solid phase reaction to prepare the lithium niobium telluride compound.

[0011] According to the present invention, the solid phase reaction is carried out under melting conditions.

[0012] According to the present invention, the solid phase reaction comprises mixing Nb2O5, a lithium compound and TeO2, reacting at a temperature of 600 to 700°C for 5 to 120 hours to obtain lithium niobium telluride polycrystalline powder.

[0013] Preferably, the temperature of the solid phase reaction is 620-680°C, more preferably 640-660°C, for example 600°C, 610°C, 630°C, 650°C, 670°C, or any point in the range formed by any two of these values.

[0014] Preferably, the solid phase reaction time is 10 to 100 h, more preferably 30 to 80 h, further preferably 40 to 60 h, for example 10 h, 20 h, 30 h, 50 h, 60 h, 70 h, 90 h or any point value in the range formed by any two values ​​thereof.

[0015] According to the present invention, the molar ratio of Nb2O5, lithium compound and TeO2, calculated as Nb, Li and Te, is 1:1:1.

[0016] According to the present invention, the solid phase reaction further comprises an exhaust operation.

[0017] According to the present invention, the lithium compound is at least one of Li2O, Li2CO3, LiNO3, LiOH, and LiOH·H2O.

[0018] According to the present invention, the lithium niobium telluride compound is a pure phase lithium niobium telluride polycrystalline powder.

[0019] According to the present invention, the pure phase lithium niobium telluride polycrystalline powder has the following characteristics: Figure 1 XRD pattern shown.

[0020] The present invention also provides a lithium niobium telluride nonlinear optical crystal. The molecular formula of the crystal is LiNbTeO5. The crystal is non-centrosymmetric and belongs to the monoclinic system. The polar space group of the crystal is P21.

[0021] In the present invention, lithium niobium telluride nonlinear optical crystal is abbreviated as LiNbTeO5 crystal.

[0022] According to the present invention, the unit cell parameters of LiNbTeO5 crystal are β=91.923(19)°.

[0023] According to the present invention, the unit cell volume of LiNbTeO5 crystal

[0024] According to the present invention, the number of molecules Z in the unit cell of the LiNbTeO5 crystal is 4.

[0025] According to the present invention, LiNbTeO5 crystals have the following characteristics: Figure 2 The crystal structure.

[0026] According to the present invention, LiNbTeO5 crystals have the following characteristics: Figure 3 The ultraviolet-visible-infrared transmission spectrum.

[0027] According to the present invention, the powder frequency doubling effect of LiNbTeO5 crystal is 2.3 times that of KTP.

[0028] The present invention also provides a method for preparing the above-mentioned lithium niobium telluride nonlinear optical crystal, which comprises the following steps: mixing Nb2O5, a lithium compound and TeO2, melting them until they are uniformly mixed, and then growing the crystal under cooling conditions to obtain the lithium niobium telluride nonlinear optical crystal.

[0029] According to the present invention, the preparation method comprises the following steps: subjecting Nb2O5, a lithium compound and TeO2 to a solid phase reaction to obtain lithium niobium telluride polycrystalline powder; mixing the lithium niobium telluride polycrystalline powder with a flux, melting the mixture until the mixture is uniform, and then growing the crystal under cooling conditions to obtain the lithium niobium telluride nonlinear optical crystal.

[0030] Preferably, the solid phase reaction comprises reacting at a temperature of 600 to 700° C. for 5 to 120 hours.

[0031] According to the present invention, before mixing with the flux, the method further comprises cooling and crushing the lithium niobium telluride polycrystalline powder.

[0032] According to the present invention, the lithium niobium telluride polycrystalline powder is mixed with a flux, for example, uniformly under grinding conditions.

[0033] According to the present invention, the flux is selected from one of the following:

[0034] TeO2 or TeO2-lithium compound mixed system, the molar ratio of TeO2 to the lithium compound is Te:Li: Te:Li=(1-6):(1-3), for example, 1:1, 1:2, 1:3, 2:1, 3:1, 4:1, 5:1, 6:1.

[0035] According to the present invention, the lithium compound in the TeO2-lithium compound mixed system is selected from at least one of Li2O, Li2CO3, LiNO3, LiOH, and LiOH·H2O.

[0036] According to the present invention, the molar ratio of the lithium niobium telluride polycrystalline powder to the flux TeO2 is 1:1.5 to 1:5.5, for example, 1:(2 to 5), for example, 1:(3 to 4), and for example, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5 or 1:5.5.

[0037] According to the present invention, the molar ratio of the lithium niobium telluride polycrystalline powder to the flux TeO2-lithium compound mixed system is 1:0.5 to 1:3.5, for example, 1:(1 to 3), for example, 1:(2 to 3), and for example, 1:1.5, 1:2, 1:2.5, 1:3 or 1:3.5;

[0038] In the flux TeO2-lithium compound mixed system, the molar ratio of TeO2 to lithium compound is (5:1):(1:1.5) calculated as Te:Li, for example (4.5~1.5):(1:1.3), for example (4.5~1.5):1.2, for example (4.5~1.5):1, and for example 3.5:1, 3:1, 2.5:1.

[0039] According to the present invention, in the lithium niobium telluride polycrystalline powder, the molar ratio of Nb2O5, lithium compound and TeO2, calculated as Nb, Li and Te, has the above-mentioned definition, which is 1:1:1.

[0040] According to the present invention, the mixing of Nb2O5, lithium compound and TeO2 may further include the following steps: uniformly mixing Nb2O5, lithium compound and TeO2 by direct mixing method.

[0041] According to the present invention, in the direct mixing method, TeO2 is used as a flux to uniformly mix Nb2O5, a lithium compound and TeO2, wherein, calculated as Nb:Li:Te, the molar ratio of the three is Nb:Li:Te=1:1:(2.5-6.5), exemplarily, Nb:Li:Te=1:1:(3-6), exemplarily, Nb:Li:Te=1:1:(3.5-5.5), more exemplarily, Nb:Li:Te=1:1:(4-5), for example, Nb:Li:Te=1:1:2.5, 1:1:3, 1:1:3.2, 1:1:3.8, 1:1:4.6, 1:1:5.2, 1:1:5.7, 1:1:6.3, 1:1:6.5.

[0042] According to the present invention, in the direct mixing method, a TeO2-lithium compound mixed system is used as a flux, and Nb2O5, a lithium compound and TeO2 are evenly mixed. Calculated by Nb:Li:Te, the molar ratio of the three is Nb:Li:Te=1:(2-4):(2-7), exemplarily, Nb:Li:Te=1:(2.5-3.5):(3.5-6.5), exemplarily, Nb:Li:Te=1:(2.8-3.2):(4-6), more exemplarily, Nb:Li:Te=1:(2.8-3.2):(4.5-5.5), for example, Nb:Li:Te=1:3:5.3, 1:3:5, 1:2.8:5.2, 1:2.8:5, 1:2.8:4.8.

[0043] According to the present invention, the direct mixing method comprises: uniformly mixing Nb2O5, a lithium compound and TeO2 under a melting condition.

[0044] According to the present invention, the melting is carried out at a temperature of 680-730°C. For example, the mixture is placed in a platinum crucible, put into a molten salt furnace, the molten salt furnace is installed, and the temperature is increased from room temperature to 680-730°C at a rate of 10-100°C / h, and the mixture is kept warm for 1-5 days to melt and mix evenly.

[0045] According to the present invention, the crystal growth under the cooling condition includes: cooling to near the melt saturation point, introducing a seed crystal, cooling to the crystal growth temperature and growing to obtain the nonlinear optical crystal.

[0046] According to the present invention, the introducing of seed crystals comprises preheating the seed crystals to 650-660° C. and then adding the seed crystals into the melt after the temperature has been reduced.

[0047] According to the present invention, the seed crystals are extracted from the melt during the cooling process, for example, a hanging platinum wire method is used to obtain small lithium niobium telluride crystals as seed crystals during the cooling process.

[0048] According to the present invention, the crystal growth parameters include: rotation speed 5-50 rpm, acceleration 1-10 s, operation 30-180 s, rest 5-50 s;

[0049] Exemplarily, the crystal growth parameters include: rotation speed 10-40 rpm, acceleration 1-8 s, operation 50-150 s, rest 10-40 s;

[0050] Exemplarily, the crystal growth parameters include: rotation speed of 20 to 30 rpm, acceleration of 2 to 6 s, operation of 50 to 100 s, and rest of 20 to 30 s.

[0051] According to the present invention, the growth temperature is 600-650°C; exemplarily, the growth temperature is 610-640°C; exemplarily, the growth temperature is 620-630°C, for example, the growth temperature is 600°C, 605°C, 610°C, 615°C, 620°C, 625°C, 630°C, 635°C, 640°C, 645°C, 650°C.

[0052] According to the present invention, the cooling rate is 0.01-5°C / h; exemplary, the cooling rate is 0.03-4°C / h; exemplary, the cooling rate is 0.05-3°C / h; exemplary, the cooling rate is 0.1-2°C / h; exemplary, the cooling rate is 0.5-1°C / h, for example, the cooling rate is 0.01-0.1°C / h, 0.01-0.3°C / h, 0.02-0.5°C / h, 0.03-0.6°C / h, 0.05-1°C / h, 1-3°C / h, 2-4°C / h, 3-5°C / h.

[0053] According to the present invention, the growth period of the crystal is 12 to 30 days; exemplarily, the growth period of the crystal is 15 to 28 days; exemplarily, the growth period of the crystal is 18 to 25 days, for example, 12 days, 14 days, 16 days, 18 days, 20 days, 23 days, 25 days, 28 days, and 30 days.

[0054] According to the present invention, after obtaining the nonlinear optical crystal, the step of extracting the nonlinear optical crystal is further included.

[0055] According to the present invention, extracting the nonlinear optical crystal includes lifting the crystal from the liquid surface, cooling the temperature to room temperature at a rate of 1-20°C / h and taking it out to obtain lithium niobium telluride crystal.

[0056] According to the present invention, the cooling rate of the crystal after being lifted from the liquid surface is 1 to 15°C / h; exemplarily, the cooling rate of the crystal after being lifted from the liquid surface is 1 to 10°C / h; exemplarily, the cooling rate of the crystal after being lifted from the liquid surface is 1 to 5°C / h, for example, the cooling rate of the crystal after being lifted from the liquid surface is 1 to 2°C / h, 1 to 3°C / h, 2 to 5°C / h, 3 to 7°C / h, 5 to 8°C / h, 6 to 10°C / h, 10 to 13°C / h, 12 to 15°C / h.

[0057] According to the present invention, after the crystal is lifted from the liquid surface, it is cooled in a molten salt furnace.

[0058] As an example, Nb2O5, lithium compound and TeO2 are weighed in a molar ratio of Nb:Li:Te=1:1:1, put into a mortar, mix and grind, put into a platinum crucible, put into a muffle furnace, slowly heat up to 650°C, keep the temperature constant for 24 hours, exhaust the gas as much as possible, take out of the crucible after cooling, put into a mortar, crush and grind to obtain pure phase lithium niobium telluride polycrystalline powder.

[0059] As an example, Nb2O5, lithium compound and TeO2 are weighed in a molar ratio of Nb:Li:Te=1:1:(2.5-6.5), mixed evenly and loaded into a platinum crucible.

[0060] According to the present invention, Nb2O5, lithium compound and TeO2 are weighed in a molar ratio of Nb:Li:Te=1:1:4, mixed evenly, loaded into a platinum crucible, placed in a molten salt furnace, slowly heated to 700°C, kept at a constant temperature for 24 hours, and then cooled. During the cooling period, a hanging platinum wire method is used to obtain small lithium niobium telluride crystals, and crystals can be obtained after cooling.

[0061] The present invention also provides the use of the above-mentioned lithium niobium telluride compound, such as lithium niobium telluride nonlinear optical crystal, which is used to prepare a frequency doubling generator, an up / down frequency converter, an optical parametric amplifier or an optical parametric oscillator.

[0062] The present invention also provides a lithium niobium telluride compound, such as the use of a lithium niobium telluride nonlinear optical crystal, which is used to prepare an electro-optic modulator, a deflector, a Q switch or a laser mode locking.

[0063] The present invention also provides an optical device, wherein the optical device contains the lithium niobium telluride nonlinear optical crystal.

[0064] According to the present invention, the optical device is a laser; illustratively, the laser is an all-solid-state laser.

[0065] Beneficial Effects

[0066] The lithium niobium telluride crystal prepared by the present invention has a wide transmission range (0.33-9.80 μm), a strong frequency doubling effect (2.3×KTP), a high laser damage threshold (178 MW / cm 2 ), stable physical and chemical properties, not easy to deliquesce, easy to cut, polish and preserve, etc., it has important applications in the preparation of frequency doubling generators, up and down frequency converters, optical parametric amplifiers, optical parametric oscillations, electro-optic modulators, deflectors, Q switches, laser mode locking, electric oscillators, and other devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 is the X-ray spectrum of the powder of the present invention;

[0068] Figure 2The crystal structure diagram of the present invention;

[0069] Figure 3 The ultraviolet-visible-infrared transmission spectrum of the crystal of the present invention;

[0070] Figure 4 This is a typical schematic diagram of the nonlinear optical effect of the lithium niobium telluride crystal prepared in Examples 1 to 5 of the present invention when used as a frequency doubling crystal.

[0071] In the figure: 1 is the laser, 2 is the incident light beam, 3 is the lithium niobium telluride crystal, 4 is the output light beam, and 5 is the filter. DETAILED DESCRIPTION

[0072] The following will be further described in detail with reference to specific examples of the compounds of the present invention and their preparation methods and applications. It should be understood that the following examples are only exemplary illustrations and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are included in the scope of protection that the present invention is intended to protect.

[0073] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0074] Embodiment 1:

[0075] Nb2O5, lithium compound and TeO2 are uniformly mixed in a molar ratio of 1:1:1 = Nb:Li:Te, and the temperature is raised from room temperature to 650°C at a rate of 50°C / h. The temperature is reacted for 60 hours to obtain lithium niobium telluride polycrystalline powder.

[0076] Subsequently, the obtained lithium niobium telluride polycrystalline powder is added to the flux TeO2, the molar ratio of the lithium niobium telluride polycrystalline powder to the flux is 1:3, the mixture is evenly mixed, and the mixture is loaded into a platinum crucible with a volume of Φ30mm×30mm, and the temperature is increased from room temperature to 700°C at a rate of 50°C / h, and the temperature is kept for 1 to 5 days to melt the raw materials and mix them evenly; the temperature is reduced to 630°C at a rate of 2°C / h, and small lithium niobium telluride crystals are obtained by using a hanging platinum wire method during this temperature period, with a growth cycle of 20 days. The small lithium niobium telluride crystals are lifted from the liquid surface, cooled to room temperature at a rate of 10°C / h, and crystals with good quality are picked as seed crystals.

[0077] The obtained seed crystal was structurally analyzed and its space group was found to be P21. Its powder X-ray pattern was consistent with the theoretical simulation, indicating that lithium niobium telluride crystal was obtained.

[0078] Embodiment 2:

[0079] The raw materials are prepared in a stoichiometric ratio to synthesize lithium niobium telluride polycrystalline powder: Nb2O5, lithium compound and TeO2 are mixed uniformly in a molar ratio of Nb:Li:Te=1:1:1, and the temperature is raised from room temperature to 650°C at a rate of 50°C / h, and the reaction is carried out for 60h at this temperature to obtain lithium niobium telluride polycrystalline powder.

[0080] Subsequently, the obtained lithium niobium telluride polycrystalline powder was added to a TeO2 flux, the molar ratio of the lithium niobium telluride polycrystalline powder to the flux being 1:3, the mixture was uniformly mixed, and the mixture was loaded into a platinum crucible with a volume of Φ60 mm×60 mm, and the temperature was increased to 700° C. at 50° C. / h, and the temperature was kept for 3 days to melt the raw materials and mix them uniformly; then the temperature was reduced to 650° C. at 2° C. / h, at which time the preheated seed crystal was put into the solution, the seed crystal being taken from the spontaneously crystallized lithium niobium telluride crystal in Example 1; the rotation speed parameters were set to: 20 rpm, acceleration for 5 s, operation for 60 s, rest for 10 s, and the temperature was reduced to 630° C. at a rate of 00.05° C. / h, the growth period was 20 days, the lithium niobium telluride crystal was lifted from the liquid surface, and the temperature was reduced to room temperature at 10° C. / h, and a bulk lithium niobium telluride single crystal was obtained.

[0081] Its powder X-ray image is consistent with the theoretical simulation, indicating that what is obtained is lithium niobium telluride crystal.

[0082] Embodiment 3:

[0083] Nb2O5, lithium compound and TeO2 are mixed uniformly in a molar ratio of Nb:Li:Te=1:1:1, and the temperature is raised from room temperature to 650°C at a rate of 50°C / h. The temperature is reacted for 60 hours to obtain lithium niobium telluride polycrystalline powder.

[0084] Subsequently, the obtained lithium niobium telluride polycrystalline powder is added to TeO2 and a lithium compound flux, the molar ratio of the lithium niobium telluride polycrystalline powder to the flux is 1:3, and the molar ratio of TeO2 to the lithium compound is Te:Li=2:1. The mixture is evenly mixed and loaded into a platinum crucible with a volume of Φ60mm×60mm, and the temperature is increased to 700°C at 10-100°C / h, and the raw materials are melted and mixed evenly for 3 days; then the temperature is reduced to 650°C at 2°C / h, and at this time, the preheated seed crystal is put into the solution, and the seed crystal is taken from the spontaneously crystallized lithium niobium telluride crystal in Example 1; the speed parameters are set to: 20rpm, acceleration for 5s, operation for 60s, rest for 10s, and cooling to 630°C at a rate of 0.05°C / h, and the growth period is 20 days. The lithium niobium telluride crystal is lifted from the liquid surface and cooled to room temperature at 10°C / h to obtain a bulk lithium niobium telluride single crystal.

[0085] Implementation 4:

[0086] Nb2O5, lithium compound and TeO2 are directly mixed at a molar ratio of Nb:Li:Te=1:1:4.5 (TeO2 is used as flux), and the mixture is uniformly loaded into a platinum crucible with a volume of Φ60mm×60mm. The mixture is heated from room temperature to 680°C at a rate of 40°C / h, and kept warm for 3 days to melt and mix the raw materials uniformly. The mixture is then cooled to 650°C at a rate of 1.5°C / h, and the preheated seed crystal is then placed into the solution. The seed crystal is taken from the spontaneously crystallized lithium niobium telluride crystal in Example 1. The rotation speed parameters are set to 20 rpm, acceleration for 5s, operation for 50s, rest for 15s, and cooling to 620°C at a rate of 0.05°C / h. The growth period is 20 days. The lithium niobium telluride crystal is lifted from the liquid surface and cooled to room temperature at a rate of 10°C / h to obtain a bulk lithium niobium telluride single crystal.

[0087] Embodiment 5:

[0088] Nb2O5, lithium compound and TeO2 are directly mixed uniformly in a molar ratio of Nb:Li:Te=1:2.5:6 (TeO2-lithium compound system is used as flux), and loaded into a platinum crucible with a volume of Φ60mm×60mm. The temperature is raised from room temperature to 680°C at a rate of 50°C / h, and the raw materials are melted and mixed uniformly for 4 days; then the temperature is lowered to 645°C at a rate of 1.5°C / h, and at this time, the preheated seed crystal is put into the solution, and the seed crystal is taken from the spontaneously crystallized lithium niobium telluride crystal in Example 1; the speed parameter is set to: 15rpm, acceleration for 5s, operation for 90s, rest for 10s, and cooling to 620°C at a rate of 0.03°C / h. The growth period is 22 days, and the lithium niobium telluride crystal is lifted from the liquid surface and cooled to room temperature at a rate of 10°C / h to obtain a bulk lithium niobium telluride single crystal.

[0089] Test Example 6:

[0090] The lithium niobium telluride crystals obtained in Examples 2 to 5 were processed in the phase matching direction. Figure 4 As shown, it is placed on the crystal accommodation position 3, using Nd:YAG laser as the light source, the laser 1 outputs an infrared incident laser beam 2 with a wavelength of 1064nm, which is incident on the single crystal 3, and outputs green doubled frequency light with a wavelength of 532nm. The output beam 4 contains infrared light with a wavelength of 1064nm and green light with a wavelength of 532nm. After being filtered out by the filter 5, a green laser with a wavelength of 532nm is obtained. The output intensity (powder doubled frequency effect) of the lithium niobium telluride crystal in Examples 2 to 5 of the specification is about 2.3 times that of KTP under the same conditions.

[0091] The above is an explanation of the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A lithium niobium telluride compound, characterized in that: Its chemical formula is LiNbTeO5; The lithium niobium telluride compound is a polycrystalline powder; the LiNbTeO5 crystal has a crystal structure as shown in FIG2 ; The lithium niobium telluride compound is a nonlinear optical crystal; The lithium niobium telluride polycrystalline powder has an XRD pattern as shown in FIG. 1 .

2. A method for preparing the lithium niobium telluride compound according to claim 1, characterized in that: The preparation method comprises the following steps: subjecting Nb2O5, a lithium compound and TeO2 to a solid phase reaction to obtain the lithium niobium telluride compound.

3. A lithium niobium telluride nonlinear optical crystal, characterized in that: The molecular formula of the crystal is LiNbTeO5. The crystal is non-centrosymmetric and belongs to the monoclinic system. The polar space group of the crystal is P21.

4. The lithium niobium telluride nonlinear optical crystal according to claim 3, characterized in that: The unit cell parameters of LiNbTeO5 crystal are a=5.122(6) Å, b=10.243(11) Å, c=7.814(9) Å, β=91.923(19)°.

5. The lithium niobium telluride nonlinear optical crystal according to claim 4, characterized in that: The unit cell volume of the LiNbTeO5 crystal is V = 409.73(80) Å 3 .

6. The lithium niobium telluride nonlinear optical crystal according to claim 4, characterized in that: The number of molecules in the unit cell of the LiNbTeO5 crystal is Z=4.

7. The lithium niobium telluride nonlinear optical crystal according to claim 4, characterized in that: The powder frequency-doubling effect of the LiNbTeO5 crystal is 2.3 times that of KTP.

8. A method for preparing the lithium niobium telluride nonlinear optical crystal according to any one of claims 3 to 7, characterized in that: The preparation method comprises the following steps: mixing Nb2O5, a lithium compound and TeO2, melting them until they are uniformly mixed, and growing crystals under cooling conditions to obtain the lithium niobium telluride nonlinear optical crystal.

9. The method for preparing lithium niobium telluride nonlinear optical crystal according to claim 8, characterized in that: The preparation method comprises the following steps: subjecting Nb2O5, a lithium compound and TeO2 to a solid phase reaction to obtain lithium niobium telluride polycrystalline powder; mixing the lithium niobium telluride polycrystalline powder with a flux, melting the mixture until the mixture is uniform, and then growing the crystal under cooling conditions to obtain the lithium niobium telluride nonlinear optical crystal.

10. The preparation method according to claim 9, characterized in that: The flux is TeO2 or a TeO2-lithium compound mixed system.

11. The preparation method according to claim 10, characterized in that: In the TeO2-lithium compound mixed system, the molar ratio of TeO2 to the lithium compound is Te:Li:Te:Li=(1~6):(1~3).

12. The preparation method according to claim 8, characterized in that: The method also includes the steps of cooling and crushing the lithium niobium telluride polycrystalline powder before mixing with the flux; and / or, the lithium niobium telluride polycrystalline powder is mixed with a flux and uniformly mixed under grinding conditions; And / or, the molar ratio of the lithium niobium telluride polycrystalline powder to the flux TeO2 is 1:1.5 to 1:5.5; And / or, the molar ratio of the lithium niobium telluride polycrystalline powder to the flux TeO2-lithium compound mixed system is 1:0.5~1:3.

5.

13. The method for preparing lithium niobium telluride nonlinear optical crystal according to claim 8, characterized in that: The mixing of Nb2O5, lithium compound and TeO2 comprises the following steps: The direct mixing method is used to uniformly mix Nb2O5, lithium compound and TeO2.

14. The preparation method according to claim 13, characterized in that: With TeO2 as flux, Nb2O5, lithium compound and TeO2 are uniformly mixed, wherein the molar ratio of Nb:Li:Te is 1:1: (2.5~6.5).

15. The preparation method according to claim 13, characterized in that: Using a mixed system of TeO2 and lithium compounds as flux, Nb2O5, lithium compounds and TeO2 are evenly mixed, and the molar ratio of Nb:Li:Te is Nb:Li:Te=1:(2~4): (2~7).

16. The method for preparing lithium niobium telluride nonlinear optical crystal according to claim 8 or 9, characterized in that: The melting is carried out at a temperature of 680-730°C.

17. The preparation method according to claim 16, characterized in that: The melting comprises: placing the mixture in a platinum crucible, placing the mixture in a molten salt furnace, installing the molten salt furnace, heating the mixture from room temperature to 680-730° C. at a rate of 10-100° C. / h, and keeping the temperature for 1-5 days to melt the mixture and mix it uniformly.

18. The preparation method according to claim 9, characterized in that: The crystal growth under the cooling condition includes: cooling to near the melt saturation point, introducing a seed crystal, cooling to the growth temperature of the crystal to grow until the nonlinear optical crystal is obtained.

19. The method for preparing lithium niobium telluride nonlinear optical crystal according to claim 8 or 9, characterized in that: After obtaining the nonlinear optical crystal, the method further includes the step of extracting the nonlinear optical crystal; Extracting the nonlinear optical crystal includes lifting the crystal from the liquid surface, cooling the temperature to room temperature at a rate of 1-20°C / h and taking it out to obtain lithium niobium telluride crystal.

20. The preparation method according to claim 19, characterized in that: After the crystal is lifted from the liquid surface, it is cooled in a molten salt furnace.

21. A use of the lithium niobium telluride nonlinear optical crystal according to any one of claims 3 to 7 for preparing a frequency doubling generator, an up / down frequency converter, an optical parametric amplifier or an optical parametric oscillator; Or used to prepare electro-optic modulators, deflectors or Q switches.

22. An optical device, comprising the lithium niobium tellurite nonlinear optical crystal according to any one of claims 3 to 7.

23. The optical device according to claim 22, characterized in that The optical device is a laser.

24. The optical device according to claim 23, characterized in that The laser is an all-solid-state laser.

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