CN102560648B - Infrared non-linear optic crystalline material and preparation method thereof - Google Patents

Abstract

The invention discloses an infrared non-linear optic crystalline material, wherein the infrared non-linear optic crystalline material has a molecular formula of Cs2HgCl12I2 and a crystal space group of P21. The CsCl and the HgI2 are taken as initial reactants and a solid-phase tube-sealing method and an organic solvent method are respectively used for preparing the material. The infrared non-linear optic crystalline material has a strong phase-matched second-order non-linear optic effect, is provided with huge light-permeable windows in a visible light area and an infrared light area, and has the advantages of higher laser damage threshold, heat stability; and a synthesizing method is simple to operate, reaction time is short, experiment conditions are mild, and the product has high purity and can be widely applied to the optical field.

Description

A kind of infrared nonlinear optical crystal material and its preparation method

technical field

The invention relates to the preparation of a novel inorganic compound and its application as a nonlinear optical crystal material, which belongs to the field of inorganic chemistry, and also belongs to the field of material science and optics.

Background technique

Nonlinear optical effects originate from the interaction between laser and medium. When the laser propagates in a medium with non-zero second-order polarizability, nonlinear optical effects such as frequency doubling, sum frequency, difference frequency, and optical parametric amplification will occur. Using the second-order nonlinear optical effect of crystals, nonlinear optical devices such as second harmonic generators, frequency converters, and optical parametric oscillators can be made. In many fields, such as laser technology, atmospheric monitoring, national defense and military, etc., All have important application value. Inorganic nonlinear optical materials play a dominant role in the practical research of second-order nonlinear optical materials. According to the light transmission band and scope of application, inorganic nonlinear optical crystal materials can be divided into nonlinear optical materials in the ultraviolet region, nonlinear optical materials in the visible region and nonlinear optical materials in the infrared region. At present, the inorganic nonlinear optical materials that have been put into practical use in the ultraviolet and visible light regions include BBO (β-barium metaborate), LBO (lithium borate), KDP (potassium dihydrogen phosphate), KTP (potassium titanyl phosphate), etc., which can basically Meet most practical requirements. But for infrared nonlinear optical materials, there is still a gap from practicality. The reason is that the existing infrared nonlinear optical materials, such as AgGaS ₂ , AgGaSe _{2 ,} etc., have a large second-order nonlinear optical coefficient and a wide transmission range in the infrared region, but the synthesis conditions are harsh and it is not easy Growing large single crystals with high optical quality, especially with a low damage threshold, cannot meet the practical requirements of nonlinear optical crystal materials. Realizing the frequency conversion of infrared laser is of great value in the fields of national economy and national defense, such as realizing continuously adjustable molecular spectrum, realizing continuous laser spectrum in the 3-5 micron band, etc. Therefore, the research on infrared inorganic nonlinear optical materials has become an important topic in the field of nonlinear optical materials research. In the book "Nonlinear Optical Crystal Materials Science" published by Science Press in 2003, it was clearly stated that "in the entire spectral band of nonlinear optics, nonlinear optical crystals in the infrared band are a weak link. Therefore, in this band Research on new frequency conversion crystals needs to be strengthened."

Contents of the invention

The problem to be solved by the present invention is to provide an inorganic infrared nonlinear optical crystal material which is easy to prepare and has good stability and a preparation method thereof.

The technical scheme provided by the invention is:

An infrared nonlinear optical crystal material, the molecular formula is Cs ₂ HgCl ₂ I ₂ , and the crystal space group is P2 ₁ .

The frequency doubling effect of the above-mentioned infrared nonlinear optical crystal material powder is 1.0×KTP; phase matching is realized; the total transmission range is 0.5-25 microns; the laser damage threshold of the crystal is 70MW/cm ² ; the thermal weight loss temperature is 220°C.

The preparation method of the above-mentioned inorganic infrared nonlinear optical crystal material:

Weigh CsCl and _HgI2 in a molar ratio of 2:1, grind them evenly in an agate mortar, put them into an ampoule tube, vacuumize and seal the tube; then place it in a muffle furnace for reaction, heat up to 200-300°C and Keep the temperature constant for 10-24 hours, then lower the temperature to 100-200°C, keep the temperature constant for 5 hours, and then lower the temperature to room temperature. After the reaction, a yellow crystalline product is obtained. Rinse the reaction product with a small amount of absolute ethanol and filter it with suction to obtain a yellow product.

The rate of heating up to 200-300°C can be 1°C/min.

Another preparation method of the above-mentioned inorganic infrared nonlinear optical crystal material is:

Weigh CsCl and _HgI2 according to the molar ratio of 2:1 and dissolve them in an organic solvent, stir or heat at room temperature, react to obtain a light yellow clear solution, filter after standing, place the filtrate in a constant temperature water bath or volatilize at room temperature Cubic transparent light yellow crystals were obtained.

Above-mentioned organic solvent is acetone, ethanol, acetonitrile, tetrahydrofuran or ethyl acetate etc.

The following is the reaction equation for preparing the compound of the present invention:

2CsCl+HgI ₂ →Cs ₂ HgCl ₂ I ₂

The inorganic infrared nonlinear optical material Cs ₂ HgCl ₂ I ₂ disclosed in the present invention uses [HgCl ₂ I ₂ ] as an anion group, and the A-site cation is an alkali metal ion Cs ⁺ . Accompanying drawing 1 and Fig. 2 are the crystal packing figure of the infrared nonlinear optical crystal material (Cs ₂ HgCl ₂ I ₂ ) of the present invention, it can be seen that the anion group of this compound is a distorted [HgCl ₂ I ₂ ] tetrahedral structure type, and the direction of distortion is basically the same, which is conducive to the geometric superposition of microscopic second-order nonlinear optical effects. The space group of this crystal material is P2 ₁ , the unit cell parameter is a=8.0066(9), α=90°, β=108.152(1)°, γ=90°. This compound does not contain water of crystallization and has no absorption in the entire mid-infrared region; the measured value of the absorption edge in the visible region reaches 0.5 microns. It has strong nonlinear optical effect and laser damage threshold. In short, it has excellent comprehensive properties and can be used as a nonlinear optical crystal material.

This novel inorganic infrared nonlinear optical crystal material obtained by the present invention has the following characteristics:

1. It has a large frequency doubling effect (SHG), and the Kurtz powder frequency doubling test results show that its powder frequency doubling effect is equivalent to that of potassium titanyl phosphate (KTP);

2. The compound has a wide transmission range in the visible light region and infrared light region, and the complete transmission band is 0.5-25 microns;

3. Does not contain crystal water, is stable to air, does not deliquesce, and has good thermal stability;

4. Compounds can achieve phase matching;

5. It can be prepared by simple solvent evaporation method.

Description of drawings

Fig. 1 is the crystal packing _diagram of _Cs2HgCl2I2 of _the present invention;

Figure 2 is the distorted [HgCl ₂ I ₂ ] tetrahedral configuration in Cs ₂ HgCl ₂ I ₂ of the present invention;

Fig. 3 is the ultraviolet-visible- _near -infrared absorption spectrum of _Cs2HgCl2I2 of _the present invention;

Fig. 4 is _the infrared transmission spectrum of _Cs2HgCl2I2 of _the present invention, IR (2.5～25 microns) spectrum;

Fig. 5 is the thermal weight loss spectrum _{of Cs2HgCl2I2} of _the present invention;

Fig. 6 is a phase matching spectrum of Cs ₂ HgCl ₂ I ₂ of the present invention.

Detailed ways

The technical scheme of the present invention will be further described below in conjunction with specific implementation examples:

Embodiment 1: Preparation of Cs ₂ HgCl ₂ I ₂

Solid-phase sealed tube synthesis method: 1.6836 grams of cesium chloride (CsCl, 10mmol) and 2.2745 grams of mercury iodide (HgI ₂ , 5mmol) are ground evenly in an agate mortar, and then packed into thick-walled ampoule tubes; evacuated to Below 10 ^-2 Pa, seal the tube with an alcohol torch flame; then place it in a muffle furnace, slowly raise the temperature to 200-300°C at a rate of 1°C/min and keep the temperature constant for 10-24 hours, then cool down to 100-200°C, keep the temperature for 1 - After 10 hours, cool down to room temperature. After the reaction, a yellow crystalline product was obtained. The reaction product was rinsed with a small amount of absolute ethanol and then filtered to obtain a yellow product.

Embodiment 2: Preparation of Cs ₂ HgCl ₂ I ₂

Solution synthesis method: 1.6836 g (10 mmol) CsCl and 2.2745 g (5 mmol) _HgI2 were added to the flask, 20 ml of acetone was added, stirred rapidly at room temperature and heated for a few hours to obtain a light yellow clear solution. After standing still, filter and volatilize the filtrate in a constant temperature water bath at 20-50°C to obtain cubic transparent light yellow crystals.

Example 3: Crystal Growth of Cs ₂ HgCl ₂ I ₂

Dissolve CsCl and _HgI2 simultaneously in 20 ml of acetone, wherein the molar ratio of CsCl and _HgI2 is 2:1. Stir for about half an hour to obtain a yellow clear solution, filter, place the filtrate in a constant temperature tank at 20-50 degrees Celsius and evaporate for 5-30 days, and grow into a larger cube-shaped transparent light yellow single crystal, which is the required crystal material.

Example 4: Crystal Growth of Cs ₂ HgCl ₂ I ₂

Dissolve CsCl and HgI ₂ in 20 ml of tetrahydrofuran at the same time, wherein the molar ratio of CsCl and HgI ₂ is 2:1. Stir for 10-60 minutes to obtain a yellow clear solution, filter, place the filtrate in a constant temperature tank at 20-50 degrees Celsius and evaporate for 5-30 days, then grow into a larger cube-shaped transparent light yellow single crystal, which is the desired crystal material.

Example 5: Frequency doubling effect of Cs ₂ HgCl ₂ I ₂ powder

The frequency doubling performance of the material is obtained by the Kurtz powder frequency doubling test method. The specific operation steps are as follows:

The obtained second-order nonlinear optical crystal material is first ground into a powder with a particle size of about 100 microns, and then installed in a sample cell with glass windows on both sides, and then the sample cell is placed on the laser optical path, using Nd:YAG pulsed laser as the light source to generate The fundamental frequency light with a wavelength of 1064 nanometers is injected into the sample cell, and the KTP single crystal powder with a particle size of about 100 microns is used as a standard sample, and the signal is displayed on the oscilloscope through a photomultiplier tube.

Example 6: Cs ₂ HgCl ₂ I ₂ phase matching test

The obtained second-order nonlinear optical crystal material is first ground and sieved into powders of different particle size ranges (40-60, 60-80, 80-100, 100-125, 125-150, 150-200 microns), and then packed In the sample cell with glass windows on both sides, the sample cell is then placed on the laser optical path, using Nd:YAG pulsed laser as the light source to generate fundamental frequency light with a wavelength of 1064 nanometers into the sample cell, and KTP single crystal with a particle size of about 100 microns The powder is used as a standard sample, and the signal is displayed on the oscilloscope through a photomultiplier tube.

The obtained compound was determined by X-ray single crystal structure, and its crystal structure arrangement is shown in Fig. 1 . The product has undergone UV-visible-near-infrared spectroscopy, infrared spectroscopy, thermal analysis and phase matching test results, as shown in Figures 3, 4, 5 and 6. The absorption edge of the material in the visible light region reaches 0.5 microns; there is no absorption in the entire mid-infrared region, and it has a large light transmission range; the material begins to lose weight after 220 degrees Celsius, and has good thermal stability; it can be seen from Figure 6 It turns out that the materials are phase-matched.

The laser damage threshold test of Cs ₂ HgCl ₂ I ₂ crystal adopts Nd:YAG pulsed laser with Q-switching. The crystal is directly placed at the laser spot, and the same position of the crystal is continuously irradiated with 300 pulses to observe whether the crystal has visible color. , transparency, shape and other changes. Then adjust the size of the spot by changing the position of the lens in turn, observe the changes in the crystal caused by laser irradiation, and judge the laser damage threshold of the crystal. The wavelength of the laser light source is 1064nm, the half pulse width is 8ns, the average energy of each pulse is about 400mJ, and the initial spot diameter is 6mm (the spot area is 28.26mm ² , and the transmittance of the initial laser energy attenuation sheet is 77.1%) , the calculated average power density is 0.14GW/cm ² . Under the premise of the same laser pulse energy, the average power density of the laser is inversely proportional to the area of the spot. Therefore, when the area of the laser spot is twice the original area, the average power is 0.14×1/2GW/cm ² =0.07GW/cm ² =70MW/cm ² , and so on). When we adjusted the spot area to 4 times the initial spot area, the crystal did not undergo any significant changes; and then adjusted the spot area to 2 times the initial area, after irradiating 300 pulses, no obvious damage was observed on the crystal. At this time, the average power of the laser is 70MW/cm ² , and when the spot area is further adjusted to 1.5 times the initial area, after 300 pulses are irradiated, the crystal is obviously damaged. Therefore, we believe that the laser damage threshold of Cs ₂ HgCl ₂ I ₂ crystal is 70MW/cm ² . Accompanying drawing 1 and Fig. 2 are the crystal packing figure of the infrared nonlinear optical crystal material (Cs ₂ HgCl ₂ I ₂ ) of the present invention, it can be seen that the anion group of this compound is a distorted [HgCl ₂ I ₂ ] tetrahedral structure type, and the direction of distortion is basically the same, which is conducive to the geometric superposition of microscopic second-order nonlinear optical effects. The space group of this crystal material is P2 ₁ , the unit cell parameter is a=8.0066(9), α=90°, β=108.152(1)°, γ=90°. This compound does not contain water of crystallization and has no absorption in the entire mid-infrared region; the measured value of the absorption edge in the visible region reaches 0.5 microns.

Claims (3)

1. an infrared nonlinear optical crystal material, its molecular formula is Cs ₂hgCl ₂i ₂, crystal space group is P2 ₁, unit cell parameters is a=8.0066 (9) , α=90 °, β=108.152 (1) °, γ=90 °.

2. the preparation method of infrared nonlinear optical crystal material described in claim 1, is characterized in that:

By CsCl and HgI ₂by the molar ratio weighing of 2: 1, in agate mortar after grinding evenly, load in ampoul tube, vacuumize rear tube sealing; Then be placed in muffle furnace to react, be warming up to 200-300 DEG C and constant temperature 10-24 hour, then be cooled to 100-200 DEG C, constant temperature is cooled to room temperature after 5 hours again; Obtain yellow crystalline product after reaction terminates, reaction product is added suction filtration after dehydrated alcohol rinse, obtain yellow product.

3. preparation method according to claim 2, is characterized in that, the speed being warming up to 200-300 DEG C is 1 DEG C/min.