A semi-organic imidazole phosphate nonlinear optical crystal material and its preparation and application

Abstract

The present invention relates to a semi-organic imidazole phosphate nonlinear optical crystal material, its preparation and application. The chemical formula is (C3H5N2)(H2PO4), belonging to the orthorhombic crystal system, with the space group Pna21. The unit cell parameters are #imgabs0##imgabs1#α = β = γ = 90°, Z = 4, and the unit cell volume is #imgabs2# The crystal (C3H5N2)(H2PO4) of the present invention has a birefringence of 0.15 at 546 nm, and the powder second harmonic generation effect under 1064 nm laser irradiation is about 0.1 times that of the KH2PO4 (KDP) crystal, and phase matching can be achieved. In addition, the optical band gap of this crystal material reaches 5.41 eV, showing broad application prospects in the solar-blind ultraviolet laser field.

Description

Technical Field

[0001] The invention belongs to the technical field of nonlinear optical crystal materials, and relates to a semi-organic imidazole phosphate nonlinear optical crystal material and a preparation method and application thereof. Background Art

[0002] Second-order nonlinear optical crystals are optoelectronic functional materials widely used in the field of lasers. They have important application value in laser frequency conversion, optoelectronic modulation, holographic storage of laser signals, laser communication, etc. At present, the second-order nonlinear optical materials that have been put into practical use include potassium dihydrogen phosphate (KH2PO4), potassium titanyl phosphate (KTiOPO4), L-arginine phosphate (LAP), deuterated L-arginine phosphate (DLAP), etc. Among them, the nonlinear optical materials used in the ultraviolet band are often constrained in practical applications due to their inherent defects. The above research and applications have put forward more and higher requirements for the physical and chemical properties of ultraviolet nonlinear optical materials, and also promoted the rapid development of ultraviolet nonlinear optical materials. In addition to having a non-centrosymmetric structure, an excellent ultraviolet nonlinear optical crystal material also needs to show strong frequency response, wide band gap, appropriate birefringence and stable physical and chemical properties. However, as two mutually opposing key optical properties, wide band gap and large birefringence are often difficult to achieve simultaneously in a nonlinear optical crystal.

[0003] In recent years, organic-inorganic hybrid nonlinear optical crystals have attracted more and more attention due to their unique ability to combine the structural diversity of the organic part with the high stability of the inorganic part. Among them, phosphates have attracted widespread attention in the field of inorganic nonlinear optical crystal materials due to their excellent properties, such as wide transmission band, high laser damage threshold and thermal stability, and are a type of nonlinear optical crystal material that is expected to be used in practical applications. Currently, the only commercial organic-inorganic hybrid nonlinear optical L-arginine phosphate (LAP) crystal was first explored and grown by Jiang Minhua's team at Shandong University in the 1980s. However, its ultraviolet absorption cutoff edge is 240nm, which limits its application in the short-wave ultraviolet region. At the same time, further development is needed in other aspects such as birefringence and powder frequency doubling effect. Summary of the invention

[0004] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a semi-organic imidazole phosphate nonlinear optical crystal material and its preparation and application. The birefringence at 546nm is 0.15, and the powder frequency doubling effect under 1064nm laser irradiation is about 0.1 times that of KH2PO4 (KDP) crystal, and phase matching can be achieved.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] In one aspect, the present invention provides a semi-organic imidazole phosphate nonlinear optical crystal material, whose chemical formula is (C3H5N2)(H2PO4), belongs to the orthorhombic system, whose space group is Pna21 (No.33), and whose unit cell parameters are α=β=γ=90°, Z=4, the unit cell volume is

[0007] The crystal structure of (C3H5N2)(H2PO4) of the present invention is as follows Figure 1 Each asymmetric unit contains one organic cation (C3H5N2) + and 1 inorganic anion (H2PO4) - , which are connected to each other through hydrogen bonds N2-H2···O1 ( Figure 1 a). (H2PO4) tetrahedron along c-axis through O2-H 2B ···O3 hydrogen bonds to form one-dimensional (1D) (H2PO4) ∞ chain( Figure 1 b). (C3H5N2) + The cations are bonded via hydrogen bonds (i.e. C1-H 1A ···O4,C2-H 2A ···O2 and N2-H2···O2) is (H2PO4) ∞ The chain is firmly fixed. The two-dimensional alternating intercalation structure is composed of (H2PO4) - Anion and (C3H5N2) + The cations are formed by hydrogen bonds on the bc plane ( Figure 1 b). The resulting 3D framework is a 2D intercalated structure formed by two different layered structures and two hydrogen bonds between the layers: N1-H1···O1 and O4-H4···O3 ( Figure 1 c).

[0008] Furthermore, the ultraviolet absorption cutoff wavelength of the nonlinear optical crystal material is 220-239 nm. Preferably, the ultraviolet absorption cutoff wavelength of the semi-organic imidazole phosphate (C3H5N2) (H2PO4) nonlinear optical crystal is 229 nm.

[0009] In the second aspect, the present invention provides a method for preparing a semi-organic imidazole phosphate nonlinear optical crystal material, wherein a mixed raw material of an organic source, a phosphorus source and water is placed in an open evaporation container and volatilized to obtain colorless transparent crystals, which are the target product.

[0010] Furthermore, the organic source is imidazole.

[0011] Furthermore, the phosphorus source is phosphoric acid.

[0012] Furthermore, the molar ratio of the organic source, the phosphorus source and water is (10-30):(10-30):(500-1250), preferably (10-20):(10-20):(700-1050). Specifically, the molar ratio of the organic source to the phosphorus source is

[0013] Furthermore, the volatilization temperature is 15°C to 45°C, preferably 20°C to 35°C.

[0014] Furthermore, the volatilization time is not less than one week, preferably 14 to 21 days.

[0015] In a third aspect, the present invention provides an application of a semi-organic imidazole phosphate nonlinear optical crystal material in a laser frequency converter, an optical parametric oscillator, an optical parametric amplifier and a photoelectric rectifier.

[0016] Furthermore, the nonlinear optical crystal material is used in a laser frequency converter, and outputs 532nm laser under 1064nm laser irradiation. Specifically, under 1064nm laser irradiation, its powder frequency doubling effect is about 0.1 times that of KH2PO4 (KDP) crystal, and phase matching can be achieved.

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

[0018] (1) The semi-organic imidazole phosphate nonlinear optical crystal material (C3H5N2) (H2PO4) provided by the present invention has a frequency doubling effect. Under 1064nm laser irradiation, its powder frequency doubling effect is about 0.1 times that of KH2PO4 (KDP) crystal, and phase matching can be achieved. In addition, the birefringence of the crystal material is 0.15, and its optical band gap reaches 5.41eV. The crystal material achieves an effective balance between wide band gap and birefringence, and has broad application prospects in the fields of day-blind ultraviolet laser frequency conversion, photoelectric modulation, laser signal holographic storage, etc.

[0019] (2) The present invention adopts a slow volatilization method to obtain a high-purity, high-crystallinity (C3H5N2)(H2PO4) nonlinear optical crystal material at 20°C to 45°C.

[0020] (3) The semi-organic imidazole phosphate nonlinear optical crystal material of the present invention has an ultraviolet absorption cutoff wavelength of 229nm, which greatly promotes the blue shift of ultraviolet wavelength. In addition, the birefringence of (C3H5N2)(H2PO4) crystal at 546nm is 0.15, which is twice the birefringence of LAP crystal (0.075@1064nm). BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1This is a schematic diagram of the crystal structure of (C3H5N2)(H2PO4); where (a) is the asymmetric unit; (b) is the two-dimensional network intercalation structure in the bc plane; and (c) is the structure in the ab plane.

[0022] Figure 2 The X-ray diffraction pattern of sample 1-1# obtained by fitting the crystal structure analyzed by single crystal X-ray diffraction is compared with the pattern obtained by X-ray diffraction test after sample 1-1# is ground into powder;

[0023] Figure 3 is the UV transmission spectrum of sample 1-1#;

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

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

[0026] Figure 6 It is the second harmonic signal diagram of sample 1-1# and standard KDP sample with sample size ranging from 105 to 150 μm;

[0027] Figure 7 This is the second harmonic phase matching diagram of sample 1-1# in the 1064nm band;

[0028] Figure 8 These are diagrams of birefringence tests, where (a) (C3H5N2) (H2PO4) has no extinction; (b) (C3H5N2) (H2PO4) has complete extinction; and (c) (C3H5N2) (H2PO4) has crystal thickness. DETAILED DESCRIPTION

[0029] The present invention is described in detail below in conjunction with 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.

[0030] Embodiment 1:

[0031] Preparation of samples 1# to 7#

[0032] An organic source (i.e., imidazole), a phosphorus source (i.e., phosphoric acid) and water are mixed in a certain proportion to form a raw material, placed in an open evaporating dish, and crystallized by slow evaporation at room temperature. After filtering and washing, colorless layered (C3H5N2)(H2PO4) crystals can be obtained.

[0033] The relationship between the type and ratio of raw materials in the initial mixture, crystallization temperature, crystallization time and sample number 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 7#

[0037] The structures of samples 1-1# to 1-7# were analyzed using single crystal X-ray diffraction and powder X-ray diffraction methods.

[0038] The single crystal X-ray diffraction was performed on a D8 VENTURE CMOS X-ray single crystal diffractometer from Bruker, Germany. The data collection temperature was 293K, 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 analysis was completed using the SHELXTL-2017 program package; the positions of heavy atoms were determined using the direct method, and the coordinates of the remaining atoms were obtained using the difference Fourier synthesis method; the F-based 2 The full-matrix least-squares method was used to refine the coordinates of all atoms and the anisotropic thermal parameters.

[0039] Powder X-ray diffraction 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 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 5 to 70°, and the scanning step is 0.02°.

[0040] Among them, the single crystal X-ray diffraction results show that samples 1-1#~1-7# have the same chemical formula and crystal structure, the chemical formula is (C3H5N2)(H2PO4), the molecular weight is 166.08, it belongs to the orthorhombic crystal system, its space group is Pna21 (No.33), and the unit cell parameters are α=β=γ=90°, Z=4, the unit cell volume is

[0041] Take sample 1-1# as a typical representative, its crystal structure data is α=β=γ=90°, Z=4, the unit cell volume is Its crystal structure is Figure 1 shown.

[0042] Take sample 1-1# as a typical example. Figure 2As shown, according to the crystal structure analyzed by single crystal X-ray diffraction, the fitted X-ray diffraction pattern is consistent with the pattern obtained by X-ray diffraction test after sample 1-1# is ground into powder, and the peak position and peak intensity are consistent, indicating that the obtained samples are of high purity.

[0043] UV transmittance spectrum test

[0044] The UV transmission spectrum test of sample 1-1# was conducted on a Carry 5000 UV-visible-near infrared spectrophotometer produced by Agilent Technologies, Inc., USA. Figure 3 As shown by Figure 3 It can be seen that the ultraviolet absorption cutoff edge of the compound is 229nm and the optical band gap is 5.41eV.

[0045] Infrared spectrum test

[0046] The infrared spectrum test of sample 1-1# was conducted on a Nicolet iS10 Fourier infrared spectrometer from Thermo Fisher Scientific Inc., USA. The results are as follows Figure 4 As shown by Figure 4 It can be seen that the vibration absorption frequency of this compound is 500-550cm -1 OPO bending vibration at 949cm -1 PO asymmetric stretching vibration at 1088cm -1 PO symmetric stretching vibration at 3135 cm -1 The OH stretching vibrations at the positions are respectively attributed to the anion group (H2PO4) - The characteristic frequency.

[0047] Thermogravimetric testing

[0048] Thermogravimetric test of sample 1-1# was conducted on TGA / DSC1 / 1100SF thermogravimetric analyzer of Mettler-Toledo International Trading (Shanghai) Co., Ltd. The results are shown in Figure 5 As shown, the compound is stable up to 68°C.

[0049] Frequency doubling test experiment and results

[0050] The frequency doubling test experiment of sample 1-1# is as follows: a Q-switched Nd:YAG solid laser is used to generate a wavelength of 1064nm as the fundamental frequency light to irradiate the tested crystal powder, a photomultiplier tube is used to detect the generated second harmonic, and an oscilloscope is used to display the harmonic intensity. The crystal sample and the standard sample KDP crystal are ground separately, and crystals of different particle sizes are sieved out with a standard sieve, and the particle size ranges are less than 50-74, 74-105, 105-150, 150-200, and 200-280μm, respectively. Observe the change trend of the frequency doubling signal with the particle size to determine whether it can achieve phase matching. Under the same test conditions, the second harmonic intensity generated by the sample and the reference crystal KDP under 1064nm wavelength laser irradiation is compared to obtain the relative size of the sample frequency doubling effect.

[0051] The test results show that the compound (C3H5N2)(H2PO4) crystal has a frequency doubling effect. At a wavelength of 546nm, the frequency doubling signal intensity is 0.1 times that of the KDP crystal (e.g. Figure 6 ).like Figure 7 As shown, the crystal material can achieve phase matching in the 1064nm laser band.

[0052] Birefringence experiment and results

[0053] The birefringence test experiment of sample 1-1# is as follows:

[0054] The birefringence of (C3H5N2)(H2PO4) was evaluated using a ZEISS Axio Scope 5 polarizing microscope equipped with a Berek compensator under a 546 nm light source. e -N o |×T=Δn×T determines the birefringence, the optical path difference is ΔR, the measured birefringence is Δn, and the crystal thickness is T. The thickness of the crystalline sample (C3H5N2)(H2PO4) was measured on a Bruker D8 VENTURE diffractometer.

[0055] The test results show that Figure 8 In a, (C3H5N2)(H2PO4) is not extinguished. Figure 8 In b, (C3H5N2)(H2PO4) is completely extinguished, and its optical path difference is 1.98μm. The crystal thickness of (C3H5N2)(H2PO4) is 13.6μm ( Figure 8 c). According to the formula ΔR = Δn × T, the birefringence of (C3H5N2)(H2PO4) is 0.15.

[0056] In the above embodiments, if there is no special description of materials or processing techniques, they are all conventional commercial products or conventional techniques in the art.

[0057] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and 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 semi-organic imidazole phosphate nonlinear optical crystal material, characterized in that: Its chemical formula is (C3H5N2)(H2PO4), it belongs to the orthorhombic system, and its space group is Pn 21, the unit cell parameters are a = 8.12~8.54 Å, b = 17.33~17.71Å, c = 4.56~4.93 Å, α = β = γ = 90°, Z = 4, the unit cell volume is V = 667.86~708.45 Å 3 ; The crystalline material is prepared by the following method: The mixed raw material of organic source, phosphorus source and water is placed in an open evaporation container and evaporated to obtain colorless transparent crystals; The organic source is imidazole; The phosphorus source is phosphoric acid; The molar ratio of the organic source, the phosphorus source and the water is (10-30): (10-30): (500-1250); The volatile temperature is 15~45℃; The volatilization time is not less than one week.

2. The semi-organic imidazole phosphate nonlinear optical crystal material according to claim 1, characterized in that: Its ultraviolet absorption cut-off wavelength is 220~239nm.

3. The method for preparing a semi-organic imidazole phosphate nonlinear optical crystal material according to claim 1 or 2, characterized in that: Place the mixed raw material of organic source, phosphorus source and water in an open evaporation container and volatilize to obtain colorless transparent crystals, which are the target product; The organic source is imidazole; The phosphorus source is phosphoric acid; The molar ratio of the organic source, the phosphorus source and the water is (10-30): (10-30): (500-1250); The volatile temperature is 15~45℃; The volatilization time is not less than one week.

4. Use of a semi-organic imidazole phosphate nonlinear optical crystal material as claimed in claim 1 or 2 in a laser frequency converter, an optical parametric oscillator, an optical parametric amplifier and a photoelectric rectifier.

5. The use of a semi-organic imidazole phosphate nonlinear optical crystal material according to claim 4, characterized in that: This nonlinear optical crystal material is used in laser frequency converters and outputs 532 nm laser under 1064 nm laser irradiation.

Images