CN108070906A - Non-linear optical crystal of iodic acid germanium lithium and its preparation method and application - Google Patents

Abstract

The invention provides a nonlinear optical crystal lithium germanium iodate, a preparation method thereof, and an application thereof as a nonlinear optical crystal material. The molecular formula of lithium germanium iodate is Li ₂ Ge(IO ₃ ) ₆ , which belongs to the hexagonal crystal system, and the crystal space group is P6 ₃ . The preparation method is as follows: add lithium-containing raw materials, GeO ₂ and HIO ₃ with a molar ratio of 3-6:1:8-15 into a hydrothermal reaction kettle, add distilled water; seal the reaction kettle and raise it to 220-230°C, and At this temperature, the reaction was carried out at a constant temperature. After the reaction was completed, the mixture was allowed to stand slowly to room temperature, filtered, washed, and dried to obtain the inorganic crystal compound Li ₂ Ge(IO ₃ ) ₆ . The method is simple to operate and the experimental conditions are mild; the prepared lithium germanium iodate crystal has excellent growth habit, has a strong second-order nonlinear optical effect, and can realize phase matching; High transparency; large band gap and good thermal stability; the lithium germanium iodate crystal can be widely used as a nonlinear crystal material in the fields of optics and the like.

Description

Nonlinear optical crystal lithium germanium iodate and its preparation method and application

technical field

The invention belongs to the field of inorganic crystal optical materials, and in particular relates to a nonlinear optical crystal germanium lithium iodate compound, a preparation method of the compound, and its application as a nonlinear optical crystal material.

technical background

Nonlinear optical crystal materials are a new class of materials based on the application of laser technology, which play an irreplaceable role in solid-state laser equipment. Using nonlinear optical effects such as frequency doubling, sum frequency, difference frequency and optical parametric amplification produced when laser propagates in nonlinear optical crystal materials, second harmonic generators, frequency converters, optical parametric oscillators and Nonlinear optical devices such as optical parametric amplifiers, so as to obtain continuous laser spectra that cannot be directly generated by laser light sources. Lasers with different wavelengths have extremely important application values in many fields such as medical treatment, information, communication, and national defense.

In the process of practical development of second-order nonlinear optical crystal materials, inorganic nonlinear optical crystal materials still occupy a dominant position due to their better comprehensive performance. According to the light transmittance and application of crystal materials in different wavelength ranges, inorganic second-order nonlinear optical crystal materials can be divided into ultraviolet region nonlinear optical materials, visible-near infrared region nonlinear optical materials and infrared region nonlinear optical materials. Linear Optical Materials. So far, β-barium metaborate (BBO), lithium triborate (LBO), potassium beryllium fluoroborate (KBBF) in the ultraviolet region, and potassium dihydrogen phosphate (KDP) and titanyl phosphate in the visible-near-infrared region Inorganic nonlinear optical crystal materials such as potassium (KTP) and lithium niobate (LN) can basically meet most of the practical needs of these two bands. As far as infrared nonlinear optical crystal materials are concerned, although AgGaS ₂ , AgGaSe ₂ and ZnGeP ₂ crystals that have been applied so far have large second-order nonlinear optical coefficients, their synthesis conditions are harsh, and it is difficult to grow them with optical quality. High large single crystals, especially their low laser damage threshold, severely restrict the practical development of second-order nonlinear optical crystal materials in the infrared band in the field of high-intensity lasers.

Infrared nonlinear optical crystal materials with high laser damage threshold have important application value in the fields of national economy, national defense and military affairs. Excellent mid-infrared nonlinear optical crystal materials with comprehensive properties such as thermal stability and crystal growth habit have become an important topic in the field of nonlinear optical materials research.

Contents of the invention

The present invention aims to provide a crystalline compound germanium lithium iodate with large second-order nonlinear optical coefficient, phase matching, wide optical bandgap, wide light transmission band range, simple preparation and good stability and its preparation method, and the application of the crystal compound as a second-order nonlinear optical crystal material.

In order to achieve the above object, the present invention adopts the following scheme:

<Nonlinear optical crystal lithium germanium iodate>

The invention provides a nonlinear optical crystal lithium germanium iodate, which is characterized in that the molecular formula is Li ₂ Ge(IO ₃ ) ₆ , belongs to the hexagonal crystal system, and the crystal space group is P6 ₃ .

Further, the nonlinear optical crystal lithium germanium iodate provided by the present invention can also have the following characteristics: the unit cell parameter is: α=90°, β=90°, γ=120°.

Furthermore, the nonlinear optical crystal lithium germanium iodate provided by the present invention may also have the following characteristics: the thermogravity temperature is 380° C., the optical band gap is 3.65 eV, and the infrared absorption cut-off edge is 11 microns.

<Preparation method>

The present invention also provides a preparation method of nonlinear optical crystal lithium germanium iodate, which is characterized in that it comprises the following steps: adding lithium-containing raw materials, GeO ₂ and HIO ₃ with a molar ratio of 3-6:1:8-15 Then add distilled water into the hydrothermal reaction kettle; seal the hydrothermal reaction kettle and slowly raise it to 220-230°C, and react at a constant temperature at this temperature. That is, the inorganic crystal compound Li ₂ Ge(IO ₃ ) ₆ is obtained.

Furthermore, the preparation method of the nonlinear optical crystal lithium germanium iodate provided by the present invention may also have the following characteristics: the optimal molar ratio of the lithium-containing raw material, GeO ₂ and HIO ₃ is 4:1:10.

Furthermore, the preparation method of the nonlinear optical crystal lithium germanium iodate provided by the present invention may also have the following characteristics: the lithium-containing raw material is preferably any one of LiOH, LiCl, and LiNO ₃ .

Furthermore, the preparation method of the nonlinear optical crystal lithium germanium iodate provided by the present invention may also have the following characteristics: the concentration of HIO ₃ after adding distilled water into the hydrothermal reaction kettle is preferably 2-5 mol/L.

Further, the preparation method of the nonlinear optical crystal lithium germanium iodate provided by the present invention can also have the following characteristics: the lithium-containing raw material is LiCl, and the concentration of _HIO3 after adding distilled water is 4mol/L, so the effect is the best.

Furthermore, the preparation method of the nonlinear optical crystal lithium germanium iodate provided by the present invention may also have the following characteristics: the hydrothermal reaction time is preferably more than 4 days, and the cooling rate is preferably 0.5-8°C/h after the hydrothermal reaction is completed Bring to room temperature.

Further, the preparation method of the nonlinear optical crystal lithium germanium iodate provided by the present invention may also have the following characteristics: After the hydrothermal reaction kettle is sealed, the temperature is raised to 230°C within 3 hours, and the temperature drops to 230°C at a cooling rate of 0.5°C/h after the reaction ends Room temperature works best.

<application>

The present invention also provides the application of the above-mentioned nonlinear optical crystal lithium germanium iodate as a nonlinear optical crystal material.

Function and Effect of Invention

1, the lithium germanium iodate crystal compound provided by the present invention has larger frequency doubling effect (SHG), and the Kurtz powder frequency doubling test result shows that its powder frequency doubling effect is 20 times that of potassium dihydrogen phosphate under 1064 nanometer laser; 1.95 times that of potassium titanyl phosphate under 1950nm laser;

2. The lithium germanium iodate crystal compound provided by the present invention can realize phase matching;

3. The lithium germanium iodate crystal compound provided by the present invention has a wide transmission range in the visible light region and the mid-infrared light region, and has high transparency in the wavelength range of 0.34 to 11 microns, and the transmittance is close to 100%;

4. The lithium germanium iodate crystal compound provided by the present invention does not contain crystal water, is stable to air, does not deliquesce, and has good thermal stability, with a thermal decomposition temperature of 380°C;

5. The present invention utilizes a hydrothermal preparation method, which has the advantages of simple operation, high utilization rate of raw materials, mild experimental conditions and high product purity.

Description of drawings

Fig. 1 is the crystal structure diagram of Li ₂ Ge (IO ₃ ) ₆ along the a-axis direction in the embodiment;

Fig. 2 is a crystal structure diagram of Li ₂ Ge(IO ₃ ) ₆ along the c-axis direction in the embodiment;

Fig. 3 is the structural diagram of the anionic group [Ge(IO ₃ ) ₆ ] of Li ₂ Ge(IO ₃ ) ₆ in the embodiment;

Fig. 4 is the UV-Vis-NIR absorption spectrum of the solid powder of Li ₂ Ge (IO ₃ ) ₆ in the embodiment;

Fig. 5 is the transmission spectrum of the solid powder of Li ₂ Ge(IO ₃ ) ₆ in the embodiment in the range of 0.2-14 microns;

Fig. 6 is the thermal weight loss spectrum of Li ₂ Ge (IO ₃ ) ₆ in the embodiment;

Fig. 7 is a graph showing the relationship between frequency doubling effect intensity and particle size of Li ₂ Ge(IO ₃ ) ₆ under 1064 nm laser in the embodiment;

Fig. 8 is a graph showing the relationship between frequency doubling effect intensity and particle size of Li ₂ Ge(IO ₃ ) ₆ under 1950nm laser light in the embodiment.

Detailed ways

The specific embodiments of the nonlinear optical crystal lithium germanium iodate Li ₂ Ge(IO ₃ ) ₆ , its preparation method and application according to the present invention will be described in detail below with reference to the accompanying drawings. In the following examples, the inner lining of the hydrothermal reaction kettle is polytetrafluoroethylene with excellent airtightness.

<Example 1>

Add 3mmol LiCl, 1mmol GeO ₂ and 8mmol HIO ₃ into a hydrothermal reactor with a volume of 23mL, and then add 4mL of distilled water to make the final concentration of HIO ₃ 2mol/L; seal the hydrothermal reactor and put it into the muffle furnace , heated to 220°C for 0.5h, reacted at constant temperature for 4 days, and then cooled to room temperature at a cooling rate of 8°C/h; after the reaction, the product was suction-filtered and the obtained solid was washed with deionized water and ethanol in sequence, and dried to obtain Inorganic crystal Li ₂ Ge(IO ₃ ) ₆ with an average particle size of 0.1 mm.

<Example 2>

Add 6mmol LiNO ₃ , 1mmol GeO ₂ and 15mmol HIO ₃ into a hydrothermal reaction kettle with a volume of 23mL, and then add 3mL distilled water to make the final concentration of HIO ₃ 5mol/L; seal the hydrothermal reaction kettle and put it into the muffle furnace Within 5 hours, it was heated to 230°C, reacted at constant temperature for 6 days, and then cooled to room temperature at a cooling rate of 1°C/h; after the reaction, the product was suction-filtered and the obtained solid was washed with deionized water and ethanol in sequence, and dried to obtain Inorganic crystal Li ₂ Ge(IO ₃ ) ₆ with an average particle size of 0.6 mm.

<Example Three>

Add 4mmol LiCl, 1mmol GeO ₂ and 10mmol HIO ₃ into a hydrothermal reactor with a volume of 23mL, and then add 2.5mL distilled water to make the final concentration of HIO ₃ 4mol/L; seal the hydrothermal reactor and put it into the muffle furnace Within 3 hours, it was heated to 230°C, and then reacted at constant temperature for 4 days, and then cooled to room temperature at a cooling rate of 0.5°C/h; Inorganic crystal Li ₂ Ge(IO ₃ ) ₆ with an average particle size of 1.4 mm.

The frequency doubling performance and phase matching test of the inorganic crystal compound Li ₂ Ge(IO ₃ ) ₆ prepared in the above-mentioned examples were obtained by Kurtz powder frequency doubling test method. The specific operation steps are as follows: the obtained inorganic crystal compound is firstly ground and sieved into powders of different particle size ranges (20～40, 40～60, 60～80, 80～100, 100～125, 125～150, 150～200 , 200 to 300, 300 to 400 microns), and then loaded into a sample cell with glass windows on both sides, and then placed the sample cell in the laser light path of a Nd:YAG pulsed laser as a light source, using lasers with wavelengths of 1064 nm and 1950 nm respectively The fundamental frequency light irradiates the sample cell, and the double frequency signal is displayed on the oscilloscope through the photomultiplier tube. The frequency doubling effect is plotted against the particle size. If the intensity increases first and then tends to a plateau as the particle size increases, it indicates phase matching; if the intensity increases first and then decreases as the particle size increases, it indicates phase matching. Mismatch. KDP single crystal powder or KTP single crystal powder with the same particle size is used as a standard sample, and the particle size sample after the frequency doubling effect reaches a plateau is compared with the frequency doubling signal intensity measured by KDP or KTP to obtain the relative frequency doubling effect. size.

The obtained inorganic crystal compound Li ₂ Ge(IO ₃ ) ₆ is determined by single crystal X-ray diffraction structure analysis, and belongs to the hexagonal crystal system, the crystal space group is P6 ₃ , and the unit cell parameters are: α=90°, β=90°, γ=120°. The arrangement and distribution of the crystal structure are shown in Figures 1 and 2. The crystal has a one-dimensional chain structure. The [GeO ₆ ] octahedra form [GeO ₆ ] _∞ chains through coplanarity in the c-axis direction, and the [GeO ₆ ] _∞ chains The iodate ion groups are connected to the surrounding by sharing O atoms, forming [Ge(IO ₃ ) ₆ ] _∞ chains, and the gaps between the chains are filled with Li ⁺ ions; the distribution of Ti-O bonds in the crystal structure The arrangement distribution of and (IO ₃ ) ^-groups is shown in Fig. 3 . The UV-Vis-NIR absorption spectrum and diffuse reflectance spectrum of this compound are shown in Figure 4, the ultraviolet absorption edge of this inorganic crystal compound is 339 nanometers, and the corresponding optical band gap is about 3.65eV; The UV of this inorganic compound powder The /Vis/IR transmission spectrum is shown in Figure 5. The infrared absorption cut-off edge of this inorganic crystal compound can reach 11 microns, and the light transmission performance is excellent in the wavelength range of 0.34 to 11 microns; its thermal weight loss spectrum is shown in Figure 6 As shown, the inorganic crystalline compound begins to lose weight at 380°C, and its thermal stability is very good; the relationship curve between the frequency doubling effect (SHG) intensity and the particle size of the sample under 1064 nm laser is shown in Figure 7, at 1950 nm The relationship between the SHG intensity and the particle size of the sample under the laser is shown in Figure 8. The inorganic crystal compound can achieve phase matching no matter under the laser of 1064 nm or 1950 nm, and has a frequency doubling effect of about 20 times KDP under the laser of 1064 nm. , has a frequency doubling effect of about 1.95 times KTP at 1950 nm laser.

In the crystal structure of the inorganic crystalline compound Li ₂ Ge(IO ₃ ) ₆ , its unit cell contains two Li atoms, one Ge atom, six I atoms and 18 O atoms. Among them, Ge atom and six O atoms are bonded to form [GeO ₆ ] distorted octahedron; each I atom is connected with three O atoms to form (IO ₃ ⁾ -ion group, which has a lone pair of electrons; ( IO ₃ ) ^-groups and [GeO ₆ ] octahedra form [Ge(IO ₃ ) ₆ ] _∞ one-dimensional chains by sharing O atoms, and the [Ge(IO ₃ ) ₆ ] _∞ chains are filled with Li ⁺ ions, forming The crystal structure of the whole Li ₂ Ge(IO ₃ ) ₆ is obtained. In the inorganic crystal structure, (IO ₃ ) ^-groups with lone pairs of electrons have very large structural distortions, they are regularly arranged in the structure, and the microscopic dipole moments overlap each other in the c-axis direction; at the same time, due to the bond length distribution Inhomogeneous, [GeO ₆ ] also has a large structural distortion, and the dipole moments are also superimposed on each other in the c-axis direction. The synergistic effect of (IO ₃ ) ^- and [GeO ₆ ] groups superimposing dipole moments on the c-axis direction directly leads to a larger dipole moment on the c-axis direction of the structure, so that Li ₂ Ge(IO ₃ ) ₆ crystals exhibit very strong nonlinear optical effects on the macroscopic scale.

In summary, the inorganic crystal compound Li ₂ Ge(IO ₃ ) ₆ provided in the above examples has excellent comprehensive properties and can be used as a second-order nonlinear optical crystal material.

The above embodiments are merely illustrations for the technical solution of the present invention. The nonlinear optical crystal lithium germanium iodate and its preparation method and application involved in the present invention are not limited to the contents described in the above embodiments, but are subject to the scope defined in the claims. Any modifications, supplements or equivalent replacements made by those skilled in the art of the present invention on the basis of the embodiments are within the protection scope of the claims of the present invention.

Claims (10)

1. a nonlinear optical crystal lithium germanium iodate, characterized in that: The molecular formula is Li ₂ Ge(IO ₃ ) ₆ , which belongs to the hexagonal crystal system, and the crystal space group is P6 ₃ . 2. nonlinear optical crystal lithium iodate germanium according to claim 1, is characterized in that: The unit cell parameters are: α=90°, β=90°, γ=120°. 3. nonlinear optical crystal germanium iodate lithium lithium according to claim 1, is characterized in that: The thermal weight loss temperature is 380°C, the optical band gap is 3.65eV, and the infrared absorption cut-off edge is 11 microns. 4. a preparation method of nonlinear optical crystal germanium lithium iodate, is characterized in that, comprises the following steps: Add lithium-containing raw materials, GeO ₂ and HIO ₃ with a molar ratio of 3-6:1:8-15 into the hydrothermal reaction kettle, and then add distilled water; seal the hydrothermal reaction kettle and raise it to 220-230°C, and At this temperature, the reaction was performed at a constant temperature. After the reaction was completed, the mixture was allowed to stand slowly to room temperature, filtered, washed, and dried to obtain the inorganic crystal compound Li ₂ Ge(IO ₃ ) ₆ . 5. the preparation method of nonlinear optical crystal germanium iodate lithium according to claim 4 is characterized in that: Among them, the molar ratio of Li-containing raw material, _GeO2 and _HIO3 is 4:1:10. 6. the preparation method of nonlinear optical crystal germanium iodate lithium according to claim 4 is characterized in that: Wherein, the lithium-containing raw material is any one of LiOH, LiCl, and LiNO ₃ . 7. the preparation method of nonlinear optical crystal germanium iodate lithium according to claim 4 is characterized in that: Wherein, the concentration of HIO ₃ after adding distilled water in the hydrothermal reaction kettle is 2-5 mol/L. 8. the preparation method of nonlinear optical crystal germanium iodate lithium according to claim 7, is characterized in that: Wherein, the lithium-containing raw material is LiCl, and the concentration of _HIO after adding distilled water is 4mol/L. 9. the preparation method of nonlinear optical crystal germanium iodate lithium according to claim 4, is characterized in that: Wherein, after the completion of the hydrothermal reaction, the temperature is lowered to room temperature at a cooling rate of 0.5-8° C./h. 10. The application of the nonlinear optical crystal germanium lithium iodate as claimed in claim 1 as a nonlinear optical crystal material.