A formamidine thiosulfate second-order nonlinear optical crystal and its preparation and application

Abstract

The present invention relates to a second-order nonlinear optical crystal of formamidine thiosulfate, and its preparation and application. The crystal material has a chemical formula of [CH(NH2)2]2SO3S, a molecular weight of 203.27, belongs to the orthorhombic crystal system, has a space group of P212121, unit cell parameters of α=β=γ=90°, Z=4, and a unit cell volume of . The formamidine thiosulfate crystal material of the present invention has excellent optical properties. Under 1064nm laser irradiation, the powder frequency harmonic intensity is approximately twice that of potassium dihydrogen phosphate crystal, and phase matching can be achieved. In addition, the crystal material has a wide light transmission band, an ultraviolet absorption cutoff edge of 253nm, an optical band gap of 4.90eV, and is easy to grow. Optical frequency conversion technologies such as second harmonic generation and optical parametric amplification can be used to expand the wavelength range of coherent light sources. Therefore, the crystal material has important application value in fields such as laser frequency conversion and optoelectronic information storage.

Description

Technical Field

[0001] The invention belongs to the technical field of nonlinear optical crystal materials and relates to a formamidine thiosulfate second-order nonlinear optical crystal and its preparation and application. Background Art

[0002] Nonlinear optical (NLO) materials have a wide range of applications in laser frequency doubling, electro-optical modulation, optical storage, optical limiting, and optical switching, and are an important material foundation for the realization of modern information technology centered on optoelectronics. Among them, ultraviolet solar blind (210-280nm) second-order nonlinear optical materials have important applications in secure communication networks, fire monitoring systems, and food sterilization. [PO4] 3- and [SO4] 2- Non-π conjugated groups such as [SO4] have a wide energy gap and have attracted widespread attention. However, traditional phosphates / sulfates often have difficulty in achieving strong second harmonic generation (SHG) response and large birefringence. 2- Group, polar tetrahedron [S2O3] 2- There are significant improvements in both polarizability anisotropy and first-order hyperpolarizability, while maintaining a wide energy gap. The introduction of organic planar π-conjugated units can synergistically improve the polarizability anisotropy of the compound. However, there are large dipole interactions between organic nonlinear units, which makes it difficult to crystallize in non-centrosymmetric space groups (non-centrosymmetric structures are a prerequisite for materials to generate second harmonics). From the perspective of optical performance, ultraviolet second-order nonlinear optical crystal materials often find it difficult to have both a strong powder frequency-harmonic effect and a moderate birefringence. Therefore, the development of ultraviolet second-order nonlinear optical crystal materials with non-centrosymmetric crystal structures is a hot topic and difficulty in current research. Summary of the Invention

[0003] The purpose of the present invention is to provide a second-order nonlinear optical crystal of formamidine thiosulfate and its preparation and application, wherein the heterocoordinate tetrahedron [SO3S] 2- The group greatly enhances the nonlinear optical properties of formamidine thiosulfate, and the organic cationic group [CH(NH2)2] + The π-conjugated molecular orbital gives the crystal material a large birefringence (0.13@546nm), a strong frequency-doubling effect (2×KH2PO4(KDP)@1064nm), and a wide optical band gap (4.9eV).

[0004] The purpose of the present invention can be achieved by the following technical solutions:

[0005] In one aspect, the present invention provides a second-order nonlinear optical crystal of formamidine thiosulfate, whose chemical formula is [CH(NH2)2]2SO3S, molecular weight is 203.27, belongs to the orthorhombic crystal system, its space group is P212121, and unit cell parameters are α=β=γ=90°,Z=4,the unit cell volume is

[0006] Furthermore, the unit cell parameters of the optical crystal are α=β=γ=90°,Z=4。 Further preferably, the unit cell parameters are α=β=γ=90°,Z=4。 Most preferably, the unit cell parameters are α=β=γ=90°, Z=4.

[0007] The crystal structure of formamidine thiosulfate of the present invention is as follows Figure 1 As shown. Each [SO3S] 2- The tetrahedron is formed by one central S atom coordinated with three O atoms and one S atom, and the SO bond length is The S=S bond length is [CH(NH2)2] + and [SO3S] 2- Tetrahedra are connected to each other by NH··O hydrogen bonds. Heterocoordinate tetrahedron [SO3S] 2- The group greatly enhances the nonlinear optical properties of formamidine thiosulfate, and the organic cationic group [CH(NH2)2] + The π-conjugated molecular orbitals make the crystal exhibit a large birefringence.

[0008] In the second aspect, the present invention provides a method for preparing thiosulfate formamidine second-order nonlinear optical crystals, which comprises mixing a N source, an S source and water and continuously stirring until a clear and transparent solution is obtained, and then naturally evaporating the solvent to finally obtain colorless and transparent flaky crystals, which are the target product.

[0009] Furthermore, the added amounts of the S source and the N source satisfy the following molar ratio of the S element to the N element: (1-10): (2-20).

[0010] Furthermore, the S source is at least one of sodium thiosulfate, potassium thiosulfate, and ammonium thiosulfate. Preferably, the S source is sodium thiosulfate.

[0011] Furthermore, the nitrogen source is at least one of formamidine hydrochloride and formamidine. Preferably, the nitrogen source is formamidine hydrochloride.

[0012] Furthermore, the temperature at which the solvent evaporates is 25 to 55°C.

[0013] Furthermore, the solvent volatilization time is not less than one week.

[0014] In a third aspect, the present invention provides an application of a formamidine thiosulfate second-order nonlinear optical crystal in a laser frequency converter, an optical parametric oscillator, an optical parametric amplifier, and a photoelectric rectifier.

[0015] Furthermore, when the formamidine thiosulfate second-order nonlinear optical crystal material is used in a laser frequency converter, it can output 532nm green light under 1064nm laser irradiation.

[0016] The present invention utilizes the strategy of element substitution to replace the heterocoordinate tetrahedron of O atom in sulfuric acid with S element [SO3S] 2- As a functional unit, and with the π conjugated group [CH(NH2)2] + The reaction successfully synthesized [CH(NH2)2]2SO3S. Heterocoordinate tetrahedron [SO3S] 2- The group greatly enhances the nonlinear optical properties of formamidine thiosulfate, and the organic cationic group [CH(NH2)2] + The π-conjugated molecular orbital makes the crystal material exhibit a large birefringence (0.13@546nm), while formamidine thiosulfate exhibits a strong frequency response (2×KDP) and a short ultraviolet absorption cutoff edge (253nm).

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] (1) This application provides a new second-order nonlinear optical crystal, [CH(NH2)2]2SO3S. This crystal material has a large frequency-doubled effect, approximately twice the frequency-doubled intensity of a KDP crystal under 1064nm laser irradiation, and is capable of phase matching. Furthermore, this crystal material has high transmittance in the 253-800nm ​​spectral range, with an ultraviolet absorption cutoff wavelength of 253nm. Therefore, this crystal material has broad application prospects in the field of nonlinear optics.

[0019] (2) This application provides a method for preparing the nonlinear optical crystal [CH(NH2)2]2SO3S, using a solution evaporation method to grow colorless, flaky [CH(NH2)2]2SO3S crystals. The method is simple, employs mild conditions, and readily grows single crystals of high optical quality and purity, facilitating large-scale industrial production.

[0020] (3) The formamidine thiosulfate crystal material of the present invention can be applied to a laser frequency converter, and can be used to output a laser beam as a second harmonic. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the crystal structure of formamidine thiosulfate;

[0022] Figure 2 The following are comparisons of X-ray diffraction patterns; (a) is the X-ray diffraction pattern obtained by analyzing and simulating the single crystal X-ray diffraction data of sample 1#; (b) is the pattern obtained by X-ray diffraction testing after grinding sample 1# into powder;

[0023] Figure 3 is the UV-visible-near-infrared absorption spectrum of sample 1#;

[0024] Figure 4 is the infrared spectrum of sample 1#;

[0025] Figure 5 This is the thermogravimetric analysis spectrum of sample 1#;

[0026] Figure 6 This is the second harmonic signal diagram of sample 1# and KDP sample with size ranging from 200 to 280 μm;

[0027] Figure 7 This is the second harmonic phase matching diagram of sample 1# at a wavelength of 1.064μm. DETAILED DESCRIPTION

[0028] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0029] In the following examples, unless otherwise specified, raw materials or processing techniques are conventional commercially available raw materials or conventional processing techniques in the art.

[0030] Example 1:

[0031] Preparation of samples 1# to 8#

[0032] A mixture of a sulfur source, a nitrogen source, and water in a certain ratio is placed in a polytetrafluoroethylene-lined container and stirred continuously until a clear, transparent solution is obtained. The solvent is then slowly evaporated at room temperature, ultimately yielding colorless, transparent, flaky [CH(NH2)2]2SO3S crystals.

[0033] The relationship between the types and ratios of raw materials in the initial mixture, volatilization temperature, volatilization time and sample numbers is shown in Table 1.

[0034] Table 1 Correspondence between samples, raw materials and synthesis conditions

[0035]

[0036] Crystal structure analysis of samples 1# to 8#

[0037] Single crystal X-ray diffraction and powder X-ray diffraction techniques were used to perform structural analysis and phase analysis on samples 1# to 8#, respectively.

[0038] Single crystal X-ray diffraction measurements were performed on a Bruker D8 VENTURE CMOS X-ray single crystal diffractometer from Germany. The data collection temperature was 298.15 K, and the diffraction light source was graphite monochromatized Mo Kα rays. The scanning mode was ω; the data were processed for absorption correction using the Multi-Scan method. The structure was solved using the Olex2 program package; the positions of heavy atoms were determined by direct method, and the coordinates of the remaining atoms were obtained by difference Fourier synthesis method; the F-based 2 The coordinates of all atoms and anisotropic thermal parameters were refined using the full-matrix least-squares method.

[0039] Single crystal X-ray diffraction results show that samples 1# to 8# have the same chemical formula and crystal structure, the chemical formula is [CH(NH2)2]2SO3S, the molecular weight is 203.27, and they belong to the orthorhombic system. Their space group is P212121, and the unit cell parameters are α=β=γ=90°, Z=4.

[0040] Taking sample 1# as a typical representative, its crystal structure data is α=β=γ=90°,Z=4. The crystal structure of [CH(NH2)2]2SO3S is as follows Figure 1 shown.

[0041] The powder X-ray diffraction test was carried out on a Bruker D8 X-ray powder diffractometer from Bruker, Germany. The test conditions were a fixed target monochromatic light source Cu Kα, a wavelength of The voltage and current are 40 kV / 20 A, the slits DivSlit / RecSlit / SctSlit are 2.00 deg / 0.3 mm / 2.00 deg respectively, the scanning range is 10-70°, and the scanning step is 0.02°.

[0042] The powder X-ray diffraction test results show that in the XRD spectra of samples 1# to 8#, the peak positions of each sample are basically the same, but the peak intensities are slightly different.

[0043] Take sample 1# as a typical example. Figure 2 As shown in the figure, the peak positions of the fitted X-ray diffraction pattern obtained based on the crystal structure analyzed by single crystal X-ray diffraction are consistent with the pattern obtained by X-ray diffraction testing of sample 1 after grinding into powder. This indicates that the obtained sample has a high purity.

[0044] UV-visible absorption spectrum test

[0045] The diffuse reflectance absorption spectrum of sample 1# was tested on a Cary 5000 UV-visible-near infrared spectrophotometer from Agilent Technologies, USA. Figure 3 As shown, the compound has no absorption in the range of 253 to 800 nm and an optical band gap of 4.9 eV.

[0046] Infrared spectrum test

[0047] The infrared spectrum test of sample 1# was conducted on a Nicolet iS10 Fourier infrared spectrometer from Thermo Fisher Scientific Inc., USA. Figure 4 As shown, 704cm -1 、1062cm -1 The characteristic absorption peak at confirms the presence of [SO3S] 2- The presence of groups, 1644 cm -1 、1713cm -1 、3035cm -1 and 3173cm -1 The characteristic absorption peak at confirms that [CH(NH2)2] - The presence of groups.

[0048] Thermogravimetric testing

[0049] The thermogravimetric test of sample 1# was carried out on a Netzsch STA 409PC thermogravimetric analyzer manufactured by Netzsch Equipment Manufacturing Co., Ltd., Germany. Figure 5 As shown, the thermal decomposition temperature of this compound is 170°C.

[0050] Frequency doubling test experiment and results

[0051] The SHG test experiment for sample 1# was conducted as follows: a Q-switched Nd:YAG solid-state laser with a wavelength of 1064 nm was used as the fundamental frequency to illuminate the crystal powder under test. The generated second harmonics were detected using a spectrometer, and the harmonic intensity was displayed using an oscilloscope. The crystal sample and a control KDP crystal were ground separately and sieved using a standard sieve to produce crystals of varying particle sizes: 26-50, 50-105, 105-150, 150-200, and 200-280 μm, respectively. The SHG signal intensity was observed as a function of particle size to determine whether phase matching was achieved. Under the same test conditions, the second harmonic intensities generated by the sample and the KDP sample were compared to determine the relative magnitude of the SHG effect.

[0052] The test results show that the compound formamidine thiosulfate crystal has a large frequency-doubled effect. Under 1064nm wavelength laser irradiation, the frequency-doubled signal intensity is twice that of the control sample KDP crystal (such as Figure 6 ), phase matching can be achieved (such as Figure 7 ).

[0053] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A formamidine thiosulfate second-order nonlinear optical crystal, characterized in that: Its chemical formula is [CH(NH2)2]2SO3S, its molecular weight is 203.27, it belongs to the orthorhombic crystal system, its space group is P212121, and its unit cell parameters are α=β=γ=90°,Z=4,the unit cell volume is 2. The formamidine thiosulfate second-order nonlinear optical crystal according to claim 1, characterized in that: The unit cell parameters of the optical crystal are α=β=γ=90°, Z=4.

3. The method for preparing a formamidine thiosulfate second-order nonlinear optical crystal according to claim 1 or 2, characterized in that: Mix the N source, S source and water and stir continuously until a clear and transparent solution is obtained. Then the solvent is naturally evaporated to finally obtain colorless and transparent flaky crystals, which are the target product.

4. The method for preparing formamidine thiosulfate second-order nonlinear optical crystal according to claim 3, characterized in that: The added amounts of the S source and the N source satisfy the following requirements: the molar ratio of the S element to the N element is (1-10):(2-20).

5. The method for preparing formamidine thiosulfate second-order nonlinear optical crystal according to claim 3, characterized in that: The S source is at least one of sodium thiosulfate, potassium thiosulfate, and ammonium thiosulfate.

6. The method for preparing formamidine thiosulfate second-order nonlinear optical crystal according to claim 3, characterized in that: The nitrogen source is at least one of formamidine hydrochloride and formamidine.

7. The method for preparing formamidine thiosulfate second-order nonlinear optical crystal according to claim 3, characterized in that: The temperature at which the solvent evaporates is 25 to 55°C.

8. The method for preparing formamidine thiosulfate second-order nonlinear optical crystal according to claim 3, characterized in that: The solvent should evaporate for at least one week.

9. Use of the formamidine thiosulfate second-order nonlinear optical crystal according to claim 1 or 2 in a laser frequency converter, an optical parametric oscillator, an optical parametric amplifier and a photoelectric rectifier.

10. The use of a formamidine thiosulfate second-order nonlinear optical crystal according to claim 9, characterized in that: When the second-order nonlinear optical crystal material of formamidine thiosulfate is used in a laser frequency converter, it can output 532nm green light under 1064nm laser irradiation.

Images