CN107723794B - Nonlinear optical crystal lithium fluorotellurite, preparation method and use thereof - Google Patents

Abstract

α＝β＝90°，γ＝120°，Z＝2。该无机化合物采用高温固相法制备，是含孤对电子基团和四面体单元的紫外‑可见非线性光学晶体，表现出强的倍频效应，宽的透光范围以及较高的热稳定性，可作为非线性光学晶体材料用于激光变频领域。The invention provides an inorganic compound, a preparation method and application thereof. The chemical formula of the inorganic compound is Li ₇ Te ₃ O ₉ F, which belongs to the hexagonal crystal system, the space group is P6 ₃ , and the unit cell parameter is

α=β=90°, γ=120°, Z=2. The inorganic compound is prepared by a high-temperature solid-phase method. It is a UV-visible nonlinear optical crystal containing lone pair electron groups and tetrahedral units. It exhibits strong frequency doubling effect, wide light transmission range and high thermal stability. , can be used as nonlinear optical crystal material in the field of laser frequency conversion.

Description

Nonlinear optical crystal lithium fluorotellurite, preparation method and use thereof

technical field

The invention relates to a novel nonlinear optical crystal fluorine-containing lithium tellurite, a preparation method thereof and its use as a nonlinear optical crystal, and belongs to the technical field of nonlinear optical materials.

Background technique

Non-linear optics (NLO) crystals are important functional materials for optoelectronic information. They are widely used in laser frequency conversion, telecommunication, non-invasive medical diagnosis, environmental monitoring, and laser guidance. They have become an indispensable key material for high-tech. It has always been a difficult and hot spot in the field of NLO to deeply understand and develop nonlinear optical (IR-NLO) crystal materials from the perspective of structure-property relationship. According to the theory of anionic groups, the macroscopic nonlinear effects mainly come from the effective superposition of microscopic nonlinear groups. These nonlinear units include Te ⁴⁺ , Se ⁴⁺ , I ^{5+ plasmons} containing lone pairs of electrons, and π-conjugated BO ₃ , NO ₃ , CO ₃ planar triangular unit, distorted MO ₆ (M=Mo ⁶⁺ , V ⁵⁺ , Ti ⁴⁺ etc.) octahedron, and PO ₄ , LiO ₄ and other tetrahedral units. The nonlinear performance can be effectively improved by utilizing the coordinated polarization effect of different structural units, such as combining lone pair electrons and octahedral units to obtain β-BaTeMo ₂ O ₉ (600×α-SiO ₂ ), Na ₂ TeW ₂ O ₉ ( 500×α-SiO ₂ ), Cs ₂ TeW ₃ O ₁₂ (400×α-SiO ₂ ), A ₂ (MoO ₃ ) ₃ (SeO ₃ )(A=Tl,NH ₄ )(400×α-SiO ₂ ) Wait. However, such compounds have small band gaps and are difficult to apply in the ultraviolet-visible light field. In order to solve this problem, researchers in the field of materials science have been innovating for a long time, in order to prepare a new type of wide band gap and nonlinear nonlinearity with large frequency doubling effect. optical crystal.

SUMMARY OF THE INVENTION

In view of the deficiencies of the prior art, the object of the present invention is to provide a novel compound, which is an ultraviolet-visible nonlinear optical crystal containing a lone pair electron group and a tetrahedral unit containing fluorine lithium tellurite, and the crystal exhibits Strong frequency doubling effect, wide light transmission range and high thermal stability, it is a new type of nonlinear optical crystal material with application value. This crystalline material has not been reported so far.

In order to achieve the purpose of the present invention, the inventor has made unremitting exploration through a large number of experimental studies, and finally obtained the following technical solution: an inorganic compound, which is lithium fluorotellurite and whose chemical formula is Li ₇ Te ₃ O ₉ F.

α＝β＝90°，γ＝120°，Z＝2。优选地，所述晶胞参数为

α＝β＝90°，γ＝120°，Z＝2。Further preferably, the inorganic compound belongs to the hexagonal crystal system, the space group is P6 ₃ , and the unit cell parameter is

α=β=90°, γ=120°, Z=2. Preferably, the unit cell parameter is

α=β=90°, γ=120°, Z=2.

Z＝2。As a specific embodiment, the inorganic compound described in the present invention has a molecular formula of Li ₇ (TeO ₃ ) ₃ F, a molecular weight of 546.81(7), a hexagonal crystal system, and a space group of P6 ₃ , (No.173) , the unit cell parameter is

Z=2.

It should be noted that the crystal structure of the inorganic compound Li ₇ (TeO ₃ ) ₃ F according to the present invention is shown in FIG. 1 . Three Li(1)O ₃ F share F atoms to form [Li ₃ O ₉ F] ¹⁶ -trimer, which links three Li(2)O ₄ tetrahedra to form [Li ₆ O ₁₅ F] [Li ₇ O ₁₆ F] ^{26 -} layer _A , which is rotated 60 degrees along the c-axis to form layer B. These layers are stacked along the c-axis in an ABAB... manner to form a three-dimensional framework [Li ₇ O ₉ F] ^12- containing 12-membered channels, and Te ⁴⁺ ions are filled in the channels.

On the other hand, the present invention also provides a method for preparing the above-mentioned inorganic compound Li ₇ (TeO ₃ ) ₃ F by adopting a relatively low temperature. The preparation method has a simple process and can obtain the inorganic compound Li ₇ with high purity and high crystallinity. (TeO ₃ ) ₃ F crystal material.

Specifically, the above-mentioned preparation method of the inorganic compound is prepared by a high-temperature solid-phase method, and the raw material mixture containing lithium element, tellurium element and fluorine element is crystallized at a crystallization temperature of 530-850 °C to obtain;

In the raw material mixture, the molar ratio of lithium element, tellurium element, oxygen element and fluorine element is:

Li:Te:O:F=(1～20):3:(6～80):(1～12).

In the method described in this application, the amount of fluorine in the raw material mixture is sensitive, and the amount of fluorine is not less than the stoichiometric ratio. Therefore, further preferably, the raw material mixture of lithium element, tellurium element, oxygen element and fluorine element in the raw material mixture:

Li:Te:O:F=(5～8):3:(8～14):(1～3).

Preferably, the crystallization temperature is 630-750° C., and the crystallization time is not less than 6 hours. Further preferably, the crystallization temperature is 600-720° C., and the crystallization time is 30-240 hours.

As an embodiment, after the crystallization is completed, the temperature is lowered to room temperature at a rate of not more than 30° C./h, and the inorganic compound can be obtained after filtration, washing and drying. Preferably, after the crystallization is completed, the temperature is lowered to room temperature at a rate of 0.5°C/h to 3°C/h.

Preferably, the lithium element in the raw material mixture comes from lithium carbonate and/or lithium element; the tellurium element comes from tellurite oxide and/or lithium tellurite and/or elemental tellurium; the fluorine element comes from lithium fluoride; the oxygen element comes from the atmosphere, Or at least one of the raw materials. Further preferably, the raw material mixture is obtained by mixing lithium carbonate, tellurium dioxide and lithium fluoride.

In yet another aspect, the present invention also provides the use of the above-mentioned inorganic compound and the inorganic compound Li ₇ (TeO ₃ ) ₃ F prepared according to any of the above-mentioned methods as nonlinear optical crystal materials. The powder frequency doubling test was carried out using the laser with a wavelength of 1064 nm output from a Q-switched Nd:YAG laser as the fundamental frequency light, and it was shown that the compound Li ₇ (TeO ₃ ) ₃ F crystal has a large frequency doubling effect, which is KH ₂ PO ₄ ( KDP) crystal 3.0 times, and can achieve phase matching.

In another aspect, the present invention also provides a laser frequency converter, which comprises the inorganic compound Li ₇ (TeO ₃ ) ₃ F and/or the inorganic compound Li ₇ (TeO ₃ ) ₃ F prepared by any of the above methods .

Compared with the prior art, the beneficial effects of the technical solutions of the present invention include but are not limited to:

(1) The present application provides a new inorganic compound crystal Li ₇ (TeO ₃ ) ₃ F, which has a large frequency doubling effect, 3.0 times that of KH ₂ PO ₄ (KDP) crystal, and can achieve phase matching . Commercial lone pair electron system nonlinear crystals have small band gaps and low laser loss thresholds. Therefore, Li ₇ (TeO ₃ ) ₃ F crystals have potential advantages as UV-Vis nonlinear optical materials.

(2) The inorganic compound crystal Li ₇ (TeO ₃ ) ₃ F provided by the present invention has high transmittance in the spectral range of 0.24-12.8 μm, and its ultraviolet absorption cut-off edge is about 240 nm.

(3) The inorganic compound crystal Li ₇ (TeO ₃ ) ₃ F provided by the present invention has high thermal stability and can be stable to 680°C.

(4) The present invention also provides a method for preparing the inorganic compound crystal Li ₇ (TeO ₃ ) ₃ F, using a high temperature solid phase method to grow a colorless Li ₇ (TeO ₃ ) ₃ F crystal. The process of the method is simple, and high-purity, high-crystallinity inorganic compound Li ₇ (TeO ₃ ) ₃ F crystal material can be obtained.

(5) The inorganic compound crystal Li ₇ (TeO ₃ ) ₃ F provided by the present invention has a light transmission range covering the ultraviolet-mid-infrared band, and has a strong nonlinear optical effect, which can be used as an ultraviolet-visible nonlinear optical crystal, and has a wide range of Used in the field of laser frequency conversion.

It should be understood that, within the scope of the disclosed technical solutions, the above-mentioned technical features of the present invention and the technical features specifically described in the following (such as the embodiments) can be combined with each other, thereby forming new or preferred technologies Program. Due to space limitations, it is not repeated here.

According to the technical solution disclosed in the present invention, those skilled in the art have the motivation to select the types of lithium source, tellurium source, fluorine source and oxygen source according to actual production needs; achieve the desired technical effect.

Unless otherwise defined, all professional and scientific terms used herein have the same meanings as those familiar to those skilled in the art. In addition, any methods and materials similar or equivalent to those described can be used in the methods of the present invention. Methods and materials for preferred embodiments described herein are provided for illustrative purposes only.

Description of drawings

Fig. 1 is a schematic diagram of the crystal structure of the inorganic compound Li ₇ (TeO ₃ ) ₃ F; wherein, (a) is the coordination environment of Li and Te atoms; (b) [Li ₆ O ₁₅ F] ^25- secondary structure construction unit; (c) [Li ₇ O ₁₆ F] ^26- projection along the c-axis; (d) three-dimensional framework [Li ₇ O ₉ F] ^12- projection along the a-axis; (e) Li ₇ Projection of the crystal structure of (TeO ₃ ) ₃ F along the c-axis.

Fig. 2 is the X-ray diffraction pattern of sample 1#; wherein, (a) is the pattern obtained by X-ray diffraction test after sample 1# is ground into powder; (b) is the crystal structure fitting based on single crystal X-ray diffraction analysis The obtained X-ray diffraction pattern.

Figure 3 is the UV-Vis-NIR diffuse reflectance spectrum of Sample 1#.

Figure 4 is a comprehensive thermogram of sample 1#.

Detailed ways

The technical solutions of the present invention will be further clearly and completely described below with reference to the embodiments and the accompanying drawings. The following embodiments are only used to illustrate the present invention and should not be regarded as limiting the protection scope of the present invention. In addition, if the specific technical operation steps or conditions are not indicated in the examples, they are all carried out according to the general techniques or conditions described in the literature in this field or according to the product specification. The reagents or instruments used without the manufacturer's indication are conventional products that can be obtained from the market.

Example 1: Synthesis of Inorganic Compound Li ₇ (TeO ₃ ) ₃ F Crystal by Vacuum High Temperature Solid Phase Method

The raw material mixture obtained by mixing the raw materials according to a certain proportion is put into a platinum crucible with a diameter of 10.0mm, and the crucible is placed in a high-temperature tube furnace with _N2 atmosphere. , washed and dried to obtain colorless and transparent Li ₇ (TeO ₃ ) ₃ F crystals. Table 1 shows the relationship between the types of raw materials contained in the raw material mixture, the ratio of each raw material, the crystallization temperature, the crystallization time and the sample number.

Table 1 Relationship between Li ₇ (TeO ₃ ) ₃ F synthesis conditions and sample numbers

Example 2: Crystal Structure Analysis of Inorganic Compound Li ₇ (TeO ₃ ) ₃ F

The structures of samples 1# to 5# were analyzed by single crystal X-ray diffraction and powder X-ray diffraction methods.

数据采用Multi-Scan方法进行吸收校正处理。结构解析采用SHELXTL-97程序包完成；用直接法确定重原子的位置，用差傅立叶合成法得到其余原子坐标；用基于F²的全矩阵最小二乘法精修所有原子的坐标及各向异性热参数。Among them, single crystal X-ray diffraction was performed on an Agilent SuperNova Dual Wavelength CCD type X-ray single crystal diffractometer. The crystal size is 0.06×0.13×0.09mm ³ ; the data collection temperature is 295K, and the diffraction light source is monochromatic Mo-Kα rays

The data were processed by the Multi-Scan method for absorption correction. Structural analysis was completed using the SHELXTL-97 package; the positions of heavy atoms were determined by the direct method, and the coordinates of the remaining atoms were obtained by the differential Fourier synthesis method; the coordinates and anisotropic heat of all atoms were refined by the full-matrix least squares method based on F ² parameter.

电压电流为30kV/15A，扫描范围10-70°，扫描步长0.02°。Powder X-ray diffraction was carried out on a Miniflex II X-ray powder diffractometer of Japan RIGAKU company, and the test conditions were a fixed target monochromatic light source Cu-Kα, wavelength

The voltage and current were 30kV/15A, the scanning range was 10-70°, and the scanning step was 0.02°.

Among them, the single crystal X-ray diffraction results show that the chemical formulas of samples 1#-5# are all Li ₇ (TeO ₃ ) ₃ F, belonging to the hexagonal crystal system, the space group is P6 ₃ , and the unit cell parameters are α=β=90°, γ=120°, Z=2. Its crystal structure is shown in Figure 1.

Z＝2。样品1#各原子坐标如表2所示:Taking sample 1# as a typical representative, its crystal structure data is

Z=2. The atomic coordinates of sample 1# are shown in Table 2:

Table 2 Atomic coordinates, equivalent thermal parameters and occupancy rates in sample 1#

The powder X-ray diffraction results show that the peak positions of samples 1# to 5# are basically the same on the XRD spectrum, and the peak intensity of each sample is slightly different.

Taking sample 1# as a typical representative, the X-ray diffraction pattern obtained by fitting the crystal structure analyzed by its single crystal X-ray diffraction was compared with the pattern obtained by X-ray diffraction test after sample 1# was ground into powder. The peak positions and peaks The intensities are consistent, indicating that the obtained samples have high purity.

Example 3: Frequency doubling test experiment and results

The frequency doubling test experiment of sample 1# is as follows: The laser with a wavelength of 1064 nm generated by a Q-switched Nd:YAG solid-state laser with a frequency converter is used as the fundamental frequency light to irradiate the tested crystal powder, and the photomultiplier tube is used to detect the generated The second harmonic of the oscilloscope can be used to display the harmonic intensity. Grind the crystal samples to be tested and the KDP crystals of the standard sample respectively, and screen out crystals of different particle sizes with a standard sieve. 212μm, 210-270μm. Observe the change trend of the frequency multiplied signal with the particle size, and judge whether it can achieve phase matching. Under the same test conditions, compare the intensity of the second harmonic generated by the sample to be tested with that generated by the reference crystal KDP, so as to obtain the relative magnitude of the frequency doubling effect of the sample.

The test results show that the compound Li ₇ (TeO ₃ ) ₃ F crystal has a great frequency doubling effect, which is about 3.0 times that of the KDP crystal, and can achieve phase matching.

Example 4: Diffuse Reflectance Absorption Spectroscopy Test

The diffuse reflection absorption spectrum test of sample 1# was carried out on a Lambda-950 UV-Vis-NIR spectrophotometer of Perkin-Elmer Company in the United States. The crystalline samples _were ground to powder with BaSO4 as the reference substrate. The test results are shown in Figure 3, indicating that the compound Li ₇ (TeO ₃ ) ₃ F has a wide transmittance range, a high transmittance in the spectral range of 240-2500nm, and an absorption cut-off edge of about 240nm.

Example 5: Thermogravimetric testing

The thermogravimetric analysis of sample 1# was carried out on a STA 449F3 thermogravimetric analyzer from NETZSCH, Germany, and the results are shown in Figure 4. It can be seen from the figure that the Li ₇ (TeO ₃ ) ₃ F crystal has high thermal stability and can be stable to 680°C.

The above are only a few embodiments of the present application, and are not intended to limit the present application in any form. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Without departing from the scope of the technical solution of the present application, any changes or modifications made by using the technical content disclosed above are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims (10)

1. an inorganic compound crystal, it is characterised in that the inorganic compound is lithium fluorotellurite, the chemical formula is Li ₇ Te ₃ O ₉ F, the crystal is a hexagonal crystal system, the space group is P6 ₃ , the crystal The cellular parameters are a = b = 11.3~11.5 Å, c = 4.7~4.9 Å, α = β = 90°, γ = 120°, Z = 2. 2. The inorganic compound crystal according to claim 1, wherein the unit cell parameters are a=b=11.416~11.419 Å, c=4.842~4.845 Å, α=β=90°, γ=120° , Z = 2. 3. A method for preparing inorganic compound crystals as claimed in claim 1, characterized in that: preparing by a high temperature solid phase method, the raw material mixture containing lithium element, tellurium element and fluorine element is crystallization temperature at 530～850℃ obtained by lower crystallization; In the raw material mixture, the molar ratio of lithium element, tellurium element, oxygen element and fluorine element is: Li:Te:O:F=(1~20):3:(6~80):(1~12). 4. the preparation method of inorganic compound crystal according to claim 3, is characterized in that, in described raw material mixture, the molar ratio of lithium element, tellurium element, oxygen element and fluorine element is: Li:Te:O:F=(5~8):3:(8~14):(1~3). 5 . The method for preparing inorganic compound crystals according to claim 3 , wherein the crystallization temperature is 600-700° C., and the crystallization time is not less than 6 hours. 6 . 6 . The method for preparing inorganic compound crystals according to claim 5 , wherein the crystallization temperature is 650-690° C., and the crystallization time is 10-240 hours. 7 . 7. according to the preparation method of the described inorganic compound crystal of claim 3, it is characterized in that, in described raw material mixture, lithium element comes from lithium oxide and/or lithium element and/or lithium carbonate, and tellurium element comes from tellurium oxide and/or sub-oxide Lithium tellurate and/or elemental tellurium, fluorine comes from lithium fluoride, and oxygen comes from at least one of oxide raw materials or air. 8. The method for preparing an inorganic compound crystal according to any one of claims 3-6, wherein after the crystallization is completed, the temperature is lowered to room temperature at a rate of 0.5°C/h to 10°C/h, and filtered , washing and drying to obtain the inorganic compound crystals. 9. Use of at least one of the inorganic compound crystals of claim 1 or 2 as a nonlinear optical crystal material. 10 . A laser frequency converter comprising one of the inorganic compound crystals according to claim 1 or 2 . 11 .

Images