Alkali metal niobium tantalum oxyfluoride second-order nonlinear optical crystalline material, preparation and application thereof

Abstract

This invention relates to an alkali metal niobium tantalum oxyfluoride second-order nonlinear optical crystalline material, its preparation, and its applications. The chemical formula of the material is A5(NbOF4)(TaF7)2, where A = K, Rb, or Cs. This crystalline material belongs to the tetragonal crystal system with a space group of I4cm and cell parameters α = β = γ = 90° and Z = 2. Under 1064nm laser irradiation, the powder frequency doubling effect of the nonlinear optical crystals K5(NbOF4)(TaF7)2, Rb5(NbOF4)(TaF7)2, and Cs5(NbOF4)(TaF7)2 of this invention can reach 3.8 times, 3.6 times, and 3.3 times that of KH2PO4 (KDP), respectively. Under 532nm laser irradiation, the powder frequency doubling effect of the crystalline material is 0.38 times, 0.36 times, and 0.33 times that of β-BaB2O4 (BBO), respectively, and phase matching can be achieved in all cases. Furthermore, the ultraviolet absorption cutoff edges of this series of crystalline materials are all less than 195 nm, and they exhibit moderate birefringence (0.103@546 nm, 0.099@546 nm, and 0.093@546 nm). The crystalline materials provided by this invention have significant application value in optoelectronic conversion fields such as solid-state lasers, stereolithography, and optical communication.

Description

Technical Field

[0001] This invention belongs to the field of nonlinear optical crystalline materials technology, and relates to an alkali metal niobium tantalum oxyfluoride second-order nonlinear optical crystalline material and its preparation and application. Background Technology

[0002] Nonlinear optical crystalline materials, as a type of optoelectronic functional material, are widely used in various fields such as laser frequency conversion, laser communication, optoelectronic modulation, laser ranging, medical treatment, and national defense. With social development and the continuous expansion of application areas, existing commercially available frequency-doubling crystals are insufficient to fully meet the needs of production and research. Developing novel nonlinear optical materials with superior performance and suitable for the ultraviolet wavelength range is one of the important tasks and challenges facing modern researchers. Currently, utilizing the excellent transmittance of perfluorinated / fluorinated oxides in the ultraviolet band to develop nonlinear optical materials is an effective strategy, and crystals such as BaMgF4, SrAlF5, and KBa2BO3F2 (KBBF) have been successfully prepared. However, the inherent shortcomings of these materials (such as the poor frequency doubling response of BaMgF4 and SrAlF5 crystals, and the layered growth tendency of KBBF crystals) limit their practical applications. Therefore, the development of novel high-performance second-order nonlinear optical crystalline materials is an important research direction in the field of optoelectronic functional materials. Summary of the Invention

[0003] The purpose of this invention is to provide a class of alkali metal niobium tantalum oxyfluoride second-order nonlinear optical crystalline materials, their preparation, and applications. The general chemical formula of this series of materials is A5(NbOF4)(TaF7)2 (A = K, Rb, or Cs). The crystalline materials belong to the tetragonal crystal system with a space group of I4cm, and their structure contains strongly distorted d... 0 Transition metal oxyfluorine polyhedra, as nonlinear optically active building blocks, can generate high microscopic second-order polarizability and significant optical anisotropy, thus endowing the materials with excellent frequency doubling performance and optical anisotropy. Experiments show that the powder frequency doubling effect of K5(NbOF4)(TaF7)2, Rb5(NbOF4)(TaF7)2, and Cs5(NbOF4)(TaF7)2 under 1064 nm laser irradiation is 3.8 times, 3.6 times, and 3.3 times that of KH2PO4(KDP) crystal, respectively. The powder frequency doubling effect under 532 nm laser irradiation is approximately 0.38 times, 0.36 times, and 0.33 times that of β-BaB2O4(BBO) crystal, respectively, and all can achieve phase matching. In addition, this series of crystalline materials has an ultraviolet absorption cutoff edge of less than 195 nm and moderate birefringence (0.103@546nm, 0.099@546nm and 0.093@546nm), and has important application potential in optoelectronic conversion devices such as solid-state lasers, stereolithography, and optical communication.

[0004] The objective of this invention can be achieved through the following technical solutions:

[0005] One of the technical solutions of this invention provides an alkali metal niobium tantalum oxyfluoride second-order nonlinear optical crystalline material with the general chemical formula A5(NbOF4)(TaF7)2, where A = K, Rb, or Cs. The crystalline material belongs to the tetragonal crystal system with a space group of I4cm, and its unit cell parameters are as follows: α=β=γ=90°, Z=2.

[0006] Furthermore, the chemical formula of this crystalline material is K5(NbOF4)(TaF7)2, which belongs to the tetragonal crystal system, has a space group of I4cm, and a unit cell parameter of... α = β = γ = 90°, Z = 2. More preferably, the cell parameters are: α = β = γ = 90°, Z = 2. More preferably, the unit cell parameters are: α = β = γ = 90°, Z = 2. Most preferably, the cell parameters are... α=β=γ=90°, Z=2.

[0007] The crystal structure of the inorganic crystalline material K5(NbOF4)(TaF7)2 described in this invention is as follows: Figure 1 As shown, each niobium atom coordinates with two oxygen atoms and four fluorine atoms to form a [NbO₂F₄] octahedron. These [NbO₂F₄] octahedrons are interconnected through shared Nb-O bonds, forming a one-dimensional chain along the c-axis, resulting in a significant net dipole moment. Each tantalum atom coordinates with seven fluorine atoms to form a [TaF₇] polyhedron. Potassium atoms are connected to fluorine atoms through ionic bonds, serving as structural fillers linking the [TaF₇] polyhedra and the [NbO₂F₄] chains.

[0008] Furthermore, the chemical formula of this crystalline material is Rb5(NbOF4)(TaF7)2, which belongs to the tetragonal crystal system, has a space group of I4cm, and a unit cell parameter of [missing information]. α = β = γ = 90°, Z = 2. More preferably, the cell parameters are: α = β = γ = 90°, Z = 2. More preferably, the unit cell parameters are: α = β = γ = 90°, Z = 2. Most preferably, the cell parameters are... α=β=γ=90°, Z=2.

[0009] The crystal structure of the inorganic crystalline material Rb5(NbOF4)(TaF7)2 described in this invention is as follows: Figure 2 As shown, each niobium atom coordinates with two oxygen atoms and four fluorine atoms to form a [NbO₂F₄] octahedron. These [NbO₂F₄] octahedrons are interconnected through shared Nb-O bonds, forming a one-dimensional chain along the c-axis, resulting in a significant net dipole moment. Each tantalum atom coordinates with seven fluorine atoms to form a [TaF₇] polyhedron. Rubidium atoms are connected to fluorine atoms through ionic bonds, serving as structural fillers linking the [TaF₇] polyhedra and the [NbO₂F₄] chains.

[0010] Furthermore, the chemical formula of this crystalline material is Cs5(NbOF4)(TaF7)2, which belongs to the tetragonal crystal system, with a space group of I4cm and unit cell parameters of [missing information]. α = β = γ = 90°, Z = 2. More preferably, the cell parameters are: α = β = γ = 90°, Z = 2. More preferably, the unit cell parameters are: α = β = γ = 90°, Z = 2. Most preferably, the cell parameters are... α=β=γ=90°, Z=2.

[0011] The crystal structure of the inorganic crystalline material Cs5(NbOF4)(TaF7)2 of the present invention is as follows: Figure 3 As shown, each niobium atom coordinates with two oxygen atoms and four fluorine atoms to form a [NbO₂F₄] octahedron. These [NbO₂F₄] octahedrons are interconnected through shared Nb-O bonds, forming a one-dimensional chain along the c-axis, resulting in a significant net dipole moment. Each tantalum atom coordinates with seven fluorine atoms to form a [TaF₇] polyhedron. Cesium atoms are connected to fluorine atoms through ionic bonds, serving as structural fillers linking the [TaF₇] polyhedra and the [NbO₂F₄] chains.

[0012] The second technical solution of this invention provides a method for preparing second-order nonlinear optical crystalline materials of alkali metal niobium tantalum oxyfluoride. The A5(NbOF4)(TaF7)2 (A=K, Rb, or Cs) crystalline material is prepared using a two-step hydrothermal method.

[0013] Step 1: Synthesis of precursor A2TaF7 (A = K, Rb, or Cs). An alkali metal source, a tantalum source, a fluorine source, and water are mixed and placed in a reaction vessel. After being heated at a constant temperature, the mixture is slowly cooled to room temperature to obtain colorless and transparent A2TaF7 (A = K, Rb, or Cs) crystals.

[0014] Furthermore, in the first step reaction, the alkali metal source is selected from one or more of the corresponding alkali metal carbonates, nitrates, sulfates, or hydrochlorides; the tantalum source is selected from tantalum pentoxide or tantalum pentachloride; and the fluorine source is a 40% hydrofluoric acid aqueous solution.

[0015] Furthermore, in the first step of the reaction, the molar ratio of alkali metal element to tantalum element is (1.8-2.2):(0.9-1.1), and the volume ratio of fluorine source to water is (1-3):(1-3).

[0016] Furthermore, in the first step of the reaction, the heating temperature is 200°C and the time is not less than 48 hours.

[0017] Step 2: Mix the A2TaF7 obtained in Step 1 with niobium source, fluorine source and water, place it in a reaction vessel, heat it to react and then slowly cool it to room temperature to obtain colorless and transparent A5(NbOF4)(TaF7)2 (A=K, Rb or Cs) crystals.

[0018] Furthermore, in the second step of the reaction, the niobium source is selected from niobium pentoxide or niobium pentachloride; the fluorine source is a 40% hydrofluoric acid aqueous solution.

[0019] Furthermore, in the second step of the reaction, the molar ratio of the A2TaF7 precursor to niobium is (1.8–2.5):(0.8–1.2), and the volume ratio of the fluorine source to water is (1–3):(1–3).

[0020] Furthermore, in the second step of the reaction, the heating temperature is 200–220°C, and the time is no less than 72 hours.

[0021] The third technical solution of the present invention provides the application of alkali metal niobium tantalum oxyfluoride second-order nonlinear optical crystalline materials in laser frequency converters, optical parametric oscillators, optical parametric amplifiers and photoelectric rectifiers.

[0022] Furthermore, this material is used in laser frequency converters to output 532nm laser light under 1064nm laser irradiation.

[0023] Furthermore, this material is used in laser frequency converters to output 266nm laser light under 532nm laser irradiation.

[0024] Specifically, K5(NbOF4)(TaF7)2 crystal, as a second-order nonlinear optical crystalline material, outputs a strong 532nm laser under 1064nm laser irradiation, with its powder frequency doubling intensity being 3.8 times that of KDP crystal. Under 532nm laser irradiation, it outputs a strong 266nm laser, with its powder frequency doubling intensity being 0.38 times that of BBO crystal, and both can achieve phase matching.

[0025] Specifically, Rb5(NbOF4)(TaF7)2 crystal, as a second-order nonlinear optical crystalline material, outputs a strong 532nm laser under 1064nm laser irradiation, with its powder frequency doubling intensity being 3.6 times that of KDP crystal. Under 532nm laser irradiation, it outputs a strong 266nm laser, with its powder frequency doubling intensity being 0.36 times that of BBO crystal, and both can achieve phase matching.

[0026] Specifically, Cs5(NbOF4)(TaF7)2 crystal, as a second-order nonlinear optical crystalline material, outputs a strong 532nm laser under 1064nm laser irradiation, with its powder frequency doubling intensity being 3.3 times that of KDP crystal. Under 532nm laser irradiation, it outputs a strong 266nm laser, with its powder frequency doubling intensity being 0.33 times that of BBO crystal, and both can achieve phase matching.

[0027] This invention introduces d into alkali metal perfluorides 0 Transition metal oxyfluorine polyhedra were prepared, including a class containing two types of d-type polyhedra. 0 A second-order nonlinear optical crystal of transition metal, A5(NbOF4)(TaF7)2 (A = K, Rb, or Cs). This crystalline material possesses uniformly arranged one-dimensional chain-like metal-oxy-fluorine polyhedral nonlinear optical functional units. These units are conducive to generating large microscopic second-order polarizability and strong optical anisotropy. This results in strong powder frequency doubling (3.8 × KDP, 3.6 × KDP, and 3.3 × KDP) under 1064 nm laser irradiation, and the material can output 266 nm ultraviolet light (0.38 × BBO, 0.36 × BBO, and 0.33 × BBO) under 532 nm laser irradiation. The material also possesses moderate birefringence (0.103@546 nm, 0.099@546 nm, and 0.093@546 nm) and a short ultraviolet absorption cutoff edge (<195 nm).

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] (1) This application provides a novel second-order nonlinear optical crystal, K5(NbOF4)(TaF7)2, which exhibits a significant frequency doubling effect. Under 1064 nm laser irradiation, its frequency doubling intensity is 3.8 times that of KDP crystal, and under 532 nm laser irradiation, it outputs a strong 266 nm laser, with a powder frequency doubling intensity 0.38 times that of BBO crystal, both achieving phase matching. Furthermore, the ultraviolet absorption cutoff edge of this crystalline material is less than 195 nm, and its birefringence is 0.103@546 nm. This crystalline material has broad application prospects in the field of nonlinear optics.

[0030] (2) This application also provides a method for preparing the second-order nonlinear optical crystal K5(NbOF4)(TaF7)2, which uses a two-step hydrothermal method to prepare colorless and transparent K5(NbOF4)(TaF7)2 crystals. The synthesis method is simple, the synthesis conditions are mild, the yield is high, and it is easy to obtain high-quality millimeter-scale single crystals.

[0031] (3) This application provides a novel second-order nonlinear optical crystal, Rb5(NbOF4)(TaF7)2, which exhibits a significant frequency doubling effect. Under 1064 nm laser irradiation, its frequency doubling intensity is 3.6 times that of a KDP crystal. Under 532 nm laser irradiation, it outputs a strong 266 nm laser, with a powder frequency doubling intensity 0.36 times that of a BBO crystal, and it can achieve phase matching. Furthermore, the ultraviolet absorption cutoff edge of this crystalline material is less than 195 nm, and its birefringence is 0.099@546 nm. This crystalline material has broad application prospects in the field of nonlinear optics.

[0032] (4) This application also provides a method for preparing the second-order nonlinear optical crystal Rb5(NbOF4)(TaF7)2, which uses a two-step hydrothermal method to prepare colorless and transparent Rb5(NbOF4)(TaF7)2 crystals. The synthesis method is simple, the synthesis conditions are mild, the yield is high, and it is easy to obtain high-quality millimeter-scale single crystals.

[0033] (5) This application provides a novel second-order nonlinear optical crystal, Cs5(NbOF4)(TaF7)2, which exhibits a significant frequency doubling effect. Under 1064 nm laser irradiation, its frequency doubling intensity is 3.3 times that of the KDP crystal. Under 532 nm laser irradiation, it outputs a strong 266 nm laser, with a powder frequency doubling intensity 0.33 times that of the BBO crystal, and both exhibit phase matching. Furthermore, the ultraviolet absorption cutoff edge of this crystalline material is less than 195 nm, and its birefringence is 0.093@546 nm. This crystalline material has broad application prospects in the field of nonlinear optics.

[0034] (6) This application also provides a method for preparing the second-order nonlinear optical crystal Cs5(NbOF4)(TaF7)2, which uses a two-step hydrothermal method to prepare colorless and transparent Cs5(NbOF4)(TaF7)2 crystals. The synthesis method is simple, the synthesis conditions are mild, the yield is high, and it is easy to obtain high-quality millimeter-scale single crystals. Attached Figure Description

[0035] Figure 1 , 2 Figure 3 is a schematic diagram of the crystal structure of A5(NbOF4)(TaF7)2 (A = K, Rb or Cs);

[0036] Figure 4The X-ray diffraction pattern of sample 1-1# obtained by fitting the crystal structure resolved by single-crystal X-ray diffraction is compared with the X-ray diffraction pattern obtained by grinding sample 1-1# into powder.

[0037] Figure 5 The X-ray diffraction pattern of sample 2-1# obtained by fitting the crystal structure resolved by single-crystal X-ray diffraction is compared with the X-ray diffraction pattern obtained by grinding sample 2-1# into powder.

[0038] Figure 6 The X-ray diffraction pattern of sample 3-1# obtained by fitting the crystal structure resolved by single-crystal X-ray diffraction is compared with the X-ray diffraction pattern obtained by grinding sample 3-1# into powder.

[0039] Figure 7 These are the ultraviolet-visible-near-infrared transmission spectra of samples 1-1#, 2-1#, and 3-1#.

[0040] Figure 8 This is the infrared spectrum of sample 1-1#;

[0041] Figure 9 This is the infrared spectrum of sample 2-1#;

[0042] Figure 10 This is the infrared spectrum of sample 3-1#;

[0043] Figure 11 These are the second harmonic phase matching diagrams of samples 1-1#, 2-1#, 3-1# and the standard KDP sample size in the 1064nm band;

[0044] Figure 12 These are the second harmonic phase matching diagrams of samples 1-1#, 2-1#, 3-1# and the standard KDP sample size in the 532nm band;

[0045] Figure 13 This is the birefringence test chart for sample 1-1#;

[0046] Figure 14 This is the birefringence test chart for sample 2-1#;

[0047] Figure 15 This is the birefringence test chart for sample 3-1#. Detailed Implementation

[0048] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0049] Example:

[0050] In the following embodiments, unless otherwise specified, the raw materials or processing techniques are conventional commercially available raw materials or conventional processing techniques in the art.

[0051] Example 1:

[0052] Preparation of samples 1# to 8#

[0053] Niobium source, K2TaF7 and fluorine source are mixed with water and added to a high-pressure autoclave lined with polytetrafluoroethylene. After heating in an oven and cooling to room temperature, colorless and transparent K5(NbOF4)(TaF7)2 crystals can be obtained.

[0054] The relationship between the types and proportions of raw materials, constant temperature, constant temperature time and sample number in the initial mixture is shown in Table 1.

[0055] Table 1. Correspondence between samples and raw materials and synthesis conditions.

[0056]

[0057] Crystal structure analysis of samples 1-1# to 1-8#

[0058] The structures of samples 1-1# to 1-8# were analyzed using single-crystal X-ray diffraction and powder X-ray diffraction (XRD).

[0059] Single-crystal X-ray diffraction measurements were performed on a Bruker D8 VENTURE CMOS X-ray single-crystal diffractometer (Germany). Data was collected at 100 K, and the diffraction source was graphite-monochromatic Mo-Kα rays. The scanning mode was ω; the data underwent absorption correction processing using the Multi-Scan method. Structural analysis was performed using the SHELXTL-2018 package; the positions of heavy atoms were determined using a direct method, and the coordinates of the remaining atoms were obtained using difference Fourier synthesis; F-based... 2 The full matrix least squares method is used to refine the coordinates and anisotropic thermal parameters of all atoms.

[0060] Powder X-ray diffraction tests were performed on a Bruker D8 X-ray powder diffractometer from Bruker GmbH, Germany. The test conditions were a fixed target, a monochromatic Cu-Kα light source, and a wavelength of [missing information]. The voltage and current are 40kV / 20A, the slits DivSlit / RecSlit / SctSlit are 2.00deg / 0.3mm / 2.00deg respectively, the scanning range is 5~70°, and the scanning step size is 0.02°.

[0061] The single-crystal X-ray diffraction results show that samples 1-1# to 1-8# have the same chemical formula and crystal structure, with the chemical formula K5(NbOF4)(TaF7)2, belonging to the tetragonal crystal system, space group I4cm, and cell parameters of [missing information]. α=β=γ=90°, Z=2. Taking sample 1-1# as a typical example, its crystal structure data are as follows: α = β = γ = 90°, Z = 2. Its crystal structure is as follows: Figure 1 As shown.

[0062] The powder X-ray diffraction test results show that on the XRD patterns of samples 1-1# to 1-8#, the diffraction peaks of the samples are in the same positions as the diffraction peaks fitted by the single crystal data, but the peak intensities are slightly different.

[0063] Taking sample 1-1# as a typical example, such as Figure 4 As shown, the X-ray diffraction pattern obtained by fitting the crystal structure obtained by single-crystal X-ray diffraction analysis is consistent with the X-ray diffraction pattern obtained by grinding sample 1-1# into powder. The peak positions are consistent, indicating that the obtained sample has high purity.

[0064] Ultraviolet-Visible-NearInfrared Transmission Spectroscopy Test

[0065] The UV-Vis-NIR transmission spectroscopy of samples 1-1# was measured using an Agilent Technologies Carry 5000 UV-Vis-NIR spectrophotometer. The results are as follows: Figure 7 As shown, by Figure 7 It can be seen that the ultraviolet absorption cutoff edge of this compound is less than 195 nm.

[0066] Infrared spectroscopy test

[0067] Infrared spectroscopy measurements of samples 1-1# were performed using a Nicoleti S10 Fourier transform infrared spectrometer from Thermo Fisher Scientific, Inc., USA. The results are as follows: Figure 8 As shown, the characteristic absorption peaks in the infrared spectrum confirm the presence of metal-oxygen-fluorine bonds in the crystal structure.

[0068] Frequency doubling test experiment and results

[0069] The frequency doubling test experiment for sample 1-1# is as follows: A Q-switched Nd:YAG solid-state laser with a wavelength of 1064nm was used as the fundamental frequency light to irradiate the test crystal powder. The intensity of the generated second harmonic was detected using an Ocean Optics Maya2000 Pro spectrometer. The crystal sample and the standard sample KDP crystal were ground separately, and crystals of different sizes were separated using a standard sieve, with particle sizes ranging from 26–50, 50–74, 74–105, 105–150, and 150–200 μm. The variation of the frequency doubling signal with particle size was observed to determine whether phase matching could be achieved. Under the same test conditions, the intensity of the second harmonic generated by the sample and the standard sample KDP was compared to obtain the relative magnitude of the frequency doubling effect of the sample. Using the same test method, the test crystal powder was irradiated with a fundamental frequency light with a wavelength of 532nm, and the intensity of the generated second harmonic was detected using an Ocean Optics Maya2000 Pro spectrometer. The variation of the frequency doubling signal with particle size was observed to determine whether phase matching could be achieved. Under the same test conditions, the intensity of the second harmonic generated by the sample and the standard sample BBO is compared to obtain the relative magnitude of the frequency doubling effect of the sample.

[0070] Test results show that compound K5(NbOF4)(TaF7)2 exhibits a large powder frequency doubling effect; under 1064 nm laser irradiation, the frequency doubling signal intensity is 3.8 times that of KDP crystal. This crystalline material can achieve phase matching (e.g., ...) under 1064 nm laser irradiation. Figure 11 Under 532nm laser irradiation, the frequency doubling signal intensity is 0.38 times that of the BBO crystal. This crystalline material can achieve phase matching under 532nm laser irradiation (e.g., ...). Figure 12 ).

[0071] Birefringence test

[0072] Birefringence tests on samples 1-1# were performed on a Zeiss AXIO Scope 5 polarizing microscope equipped with a Berek compensator, using a light source with a wavelength of 546 nm. The experimental results are as follows: Figure 13 As shown, the optical path difference ΔR and crystal thickness T were measured. The test results show that the birefringence of sample 1-1# at 546 nm is 0.103.

[0073] Example 2

[0074] Preparation of samples 1# to 8#

[0075] Niobium source, Rb2TaF7 and fluorine source are mixed with water and added to a high-pressure autoclave lined with polytetrafluoroethylene. After heating in an oven and cooling to room temperature, colorless and transparent Rb5(NbOF4)(TaF7)2 crystals can be obtained.

[0076] The relationship between the types and proportions of raw materials, constant temperature, constant temperature time and sample number in the initial mixture is shown in Table 2.

[0077] Table 2. Correspondence between samples and raw materials and synthesis conditions.

[0078]

[0079]

[0080] Crystal structure analysis of samples 2-1# to 2-8#

[0081] The structures of samples 2-1# to 2-8# were analyzed using single-crystal X-ray diffraction and powder X-ray diffraction methods.

[0082] Single-crystal X-ray diffraction measurements were performed on a Bruker D8 VENTURE CMOS X-ray single-crystal diffractometer (Germany). Data was collected at 100 K, and the diffraction source was graphite-monochromatic Mo-Kα rays. The scanning mode was ω; the data underwent absorption correction processing using the Multi-Scan method. Structural analysis was performed using the SHELXTL-2018 package; the positions of heavy atoms were determined using a direct method, and the coordinates of the remaining atoms were obtained using difference Fourier synthesis; F-based... 2 The full matrix least squares method is used to refine the coordinates and anisotropic thermal parameters of all atoms.

[0083] Powder X-ray diffraction tests were performed on a Bruker D8 X-ray powder diffractometer from Bruker GmbH, Germany. The test conditions were a fixed target, a monochromatic Cu-Kα light source, and a wavelength of [missing information]. The voltage and current are 40kV / 20A, the slits DivSlit / RecSlit / SctSlit are 2.00deg / 0.3mm / 2.00deg respectively, the scanning range is 5~70°, and the scanning step size is 0.02°.

[0084] The single-crystal X-ray diffraction results show that samples 2-1# to 2-8# have the same chemical formula and crystal structure, with the chemical formula Rb5(NbOF4)(TaF7)2, belonging to the tetragonal crystal system, space group I4cm, and cell parameters of [missing information]. α=β=γ=90°, Z=2. Taking sample 2-1# as a typical example, its crystal structure data is as follows: α = β = γ = 90°, Z = 2. Its crystal structure is as follows: Figure 2 As shown.

[0085] The powder X-ray diffraction test results show that on the XRD patterns of samples 2-1# to 2-8#, the diffraction peaks of the samples and the diffraction peaks fitted by the single crystal data are in the same position, but the peak intensities are slightly different.

[0086] Taking sample 2-1# as a typical example, such as Figure 5 As shown, the X-ray diffraction pattern obtained by fitting the crystal structure obtained by single-crystal X-ray diffraction analysis is consistent with the X-ray diffraction pattern obtained by grinding sample 2-1# into powder. The peak positions are consistent, indicating that the obtained sample has high purity.

[0087] Ultraviolet-Visible-NearInfrared Transmission Spectroscopy Test

[0088] The UV-Vis-NIR transmission spectrum of sample 2-1# was measured using an Agilent Technologies Carry 5000 UV-Vis-NIR spectrophotometer. The results are as follows: Figure 7 As shown, by Figure 7 It can be seen that the ultraviolet absorption cutoff edge of this compound is less than 195 nm.

[0089] Infrared spectroscopy test

[0090] The infrared spectra of sample 2-1# were measured using a Nicoleti S10 Fourier transform infrared spectrometer from Thermo Fisher Scientific, Inc., USA. The results are as follows: Figure 9 As shown, the characteristic absorption peaks in the infrared spectrum confirm the presence of metal-oxygen-fluorine bonds in the crystal structure.

[0091] Frequency doubling test experiment and results

[0092] The frequency doubling test experiment for sample 2-1# is as follows: A Q-switched Nd:YAG solid-state laser with a wavelength of 1064 nm was used as the fundamental frequency light to irradiate the test crystal powder. The intensity of the generated second harmonic was detected using an Ocean Optics Maya2000 Pro spectrometer. The crystal sample and the standard sample KDP crystal were ground separately, and crystals of different sizes were separated using a standard sieve, with particle sizes ranging from 26–50, 50–74, 74–105, 105–150, and 150–200 μm. The variation of the frequency doubling signal with particle size was observed to determine whether phase matching could be achieved. Under the same test conditions, the intensity of the second harmonic generated by the sample and the standard sample KDP was compared to obtain the relative magnitude of the frequency doubling effect of the sample. Using the same test method, the test crystal powder was irradiated with a fundamental frequency light with a wavelength of 532 nm, and the intensity of the generated second harmonic was detected using an Ocean Optics Maya2000 Pro spectrometer. The variation of the frequency doubling signal with particle size was observed to determine whether phase matching could be achieved. Under the same test conditions, the intensity of the second harmonic generated by the sample and the standard sample BBO is compared to obtain the relative magnitude of the frequency doubling effect of the sample.

[0093] Test results show that the compound Rb5(NbOF4)(TaF7)2 exhibits a large powder frequency doubling effect, with a frequency doubling signal intensity 3.6 times that of KDP crystal under 1064 nm laser irradiation. This crystalline material can achieve phase matching (e.g., ...) under 1064 nm laser irradiation. Figure 11 Under 532nm laser irradiation, the frequency doubling signal intensity is 0.36 times that of the BBO crystal. This crystalline material can achieve phase matching under 532nm laser irradiation (e.g., ...). Figure 12 ).

[0094] Birefringence test

[0095] Birefringence tests on sample 2-1# were performed on a Zeiss AXIO Scope 5 polarizing microscope equipped with a Berek compensator, using a light source with a wavelength of 546 nm. The experimental results are as follows: Figure 14 As shown, the optical path difference ΔR and crystal thickness T were measured. The test results show that the birefringence of sample 2-1# at 546nm is 0.099.

[0096] Example 3

[0097] Preparation of samples 1# to 8#

[0098] Niobium source, Cs2TaF7 and fluorine source are mixed with water and added to a high-pressure autoclave lined with polytetrafluoroethylene. After heating in an oven and cooling to room temperature, colorless and transparent Cs5(NbOF4)(TaF7)2 crystals can be obtained.

[0099] The relationship between the types and proportions of raw materials, constant temperature, constant temperature time and sample number in the initial mixture is shown in Table 3.

[0100] Table 3. Correspondence between samples and raw materials and synthesis conditions.

[0101]

[0102]

[0103] Crystal structure analysis of samples 3-1# to 3-8#

[0104] The structures of samples 3-1# to 3-8# were analyzed using single-crystal X-ray diffraction and powder X-ray diffraction methods.

[0105] Single-crystal X-ray diffraction measurements were performed on a Bruker D8 VENTURE CMOS X-ray single-crystal diffractometer (Germany). Data was collected at 100 K, and the diffraction source was graphite-monochromatic Mo-Kα rays. The scanning mode was ω; the data underwent absorption correction processing using the Multi-Scan method. Structural analysis was performed using the SHELXTL-2018 package; the positions of heavy atoms were determined using a direct method, and the coordinates of the remaining atoms were obtained using difference Fourier synthesis; F-based... 2 The full matrix least squares method is used to refine the coordinates and anisotropic thermal parameters of all atoms.

[0106] Powder X-ray diffraction tests were performed on a Bruker D8 X-ray powder diffractometer from Bruker GmbH, Germany. The test conditions were a fixed target, a monochromatic Cu-Kα light source, and a wavelength of [missing information]. The voltage and current are 40kV / 20A, the slits DivSlit / RecSlit / SctSlit are 2.00deg / 0.3mm / 2.00deg respectively, the scanning range is 5~70°, and the scanning step size is 0.02°.

[0107] The single-crystal X-ray diffraction results showed that samples 3-1# to 3-8# had the same chemical formula and crystal structure, with the chemical formula Cs5(NbOF4)(TaF7)2, belonging to the tetragonal crystal system, space group I4cm, and cell parameters of [missing information]. α=β=γ=90°, Z=2. Taking sample 3-1# as a typical example, its crystal structure data is as follows: α = β = γ = 90°, Z = 2. Its crystal structure is as follows: Figure 3 As shown.

[0108] The powder X-ray diffraction test results show that on the XRD patterns of samples 3-1# to 3-8#, the diffraction peaks of the samples and the diffraction peaks fitted by the single crystal data are in the same position, but the peak intensities are slightly different.

[0109] Taking sample 3-1# as a typical example, such as Figure 6 As shown, the X-ray diffraction pattern obtained by fitting the crystal structure obtained by single-crystal X-ray diffraction analysis is consistent with the X-ray diffraction pattern obtained by grinding sample 3-1# into powder. The peak positions are consistent, indicating that the obtained sample has high purity.

[0110] Ultraviolet-Visible-NearInfrared Transmission Spectroscopy Test

[0111] The UV-Vis-NIR transmission spectrum of sample 3-1# was measured using an Agilent Technologies Carry 5000 UV-Vis-NIR spectrophotometer. The results are as follows: Figure 7 As shown, by Figure 7 It can be seen that the ultraviolet absorption cutoff edge of this compound is less than 195 nm.

[0112] Infrared spectroscopy test

[0113] The infrared spectra of sample 3-1# were measured using a Nicoleti S10 Fourier transform infrared spectrometer from Thermo Fisher Scientific, Inc., USA. The results are as follows: Figure 10 As shown, the characteristic absorption peaks in the infrared spectrum confirm the presence of metal-oxygen-fluorine bonds in the crystal.

[0114] Frequency doubling test experiment and results

[0115] The frequency doubling test experiment for sample 3-1# is as follows: A Q-switched Nd:YAG solid-state laser with a wavelength of 1064 nm was used as the fundamental frequency light to irradiate the test crystal powder. The intensity of the generated second harmonic was detected using an Ocean Optics Maya2000 Pro spectrometer. The crystal sample and the standard sample KDP crystal were ground separately, and crystals of different sizes were separated using a standard sieve, with particle sizes ranging from 26–50, 50–74, 74–105, 105–150, and 150–200 μm. The variation of the frequency doubling signal with particle size was observed to determine whether phase matching could be achieved. Under the same test conditions, the intensity of the second harmonic generated by the sample and the standard sample KDP was compared to obtain the relative magnitude of the frequency doubling effect of the sample. Using the same test method, the test crystal powder was irradiated with a fundamental frequency light with a wavelength of 532 nm, and the intensity of the generated second harmonic was detected using an Ocean Optics Maya2000 Pro spectrometer. The variation of the frequency doubling signal with particle size was observed to determine whether phase matching could be achieved. Under the same test conditions, the intensity of the second harmonic generated by the sample and the standard sample BBO is compared to obtain the relative magnitude of the frequency doubling effect of the sample.

[0116] Test results show that the compound Cs5(NbOF4)(TaF7)2 exhibits a large powder frequency doubling effect, with a frequency doubling signal intensity 3.3 times that of KDP crystal under 1064 nm laser irradiation. This crystalline material can achieve phase matching (e.g., ...) under 1064 nm laser irradiation. Figure 11 Under 532nm laser irradiation, the frequency doubling signal intensity is 0.33 times that of the BBO crystal. This crystalline material can achieve phase matching under 532nm laser irradiation (e.g., ...). Figure 12 ).

[0117] Birefringence test

[0118] The birefringence test of sample 3-1# was performed on a Zeiss AXIO Scope 5 polarizing microscope equipped with a Berek compensator, with a wavelength of 546 nm as the experimental light source. The experimental results are as follows: Figure 15 As shown, the optical path difference ΔR and crystal thickness T were measured. The test results show that the birefringence of sample 3-1# at 546 nm is 0.093.

[0119] Example 4

[0120] Preparation of A2TaF7 (A = K, Rb or Cs) precursor.

[0121] An alkali metal source, a tantalum source, and a fluorine source are mixed with water and added to a high-pressure autoclave lined with polytetrafluoroethylene. After heating in an oven and cooling to room temperature, colorless and transparent A2TaF7 (A = K, Rb, or Cs) crystals can be obtained.

[0122] The relationship between the types and proportions of raw materials, constant temperature, constant temperature time and sample number in the initial mixture is shown in Table 4.

[0123] Table 4. Correspondence between samples and raw materials and synthesis conditions.

[0124]

[0125]

[0126] The description of the above embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any 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 invention should be within the protection scope of the present invention.

Claims

1. A second-order nonlinear optical crystalline material of alkali metal niobium tantalum oxyfluorate, characterized in that, The general chemical formula is A5(NbOF4)(TaF7)2, where A = K, Rb, or Cs. The crystalline material belongs to the tetragonal crystal system with space group I4cm. The cell parameters satisfy a = 14.0~17.0 Å, b = 14.0~17.0 Å, c = 7.0~8.0 Å, and the cell volume V = 1680~2200 Å. 3 , α= β = γ = 90°, Z = 2.

2. The alkali metal niobium tantalum oxyfluorate second-order nonlinear optical crystalline material according to claim 1, characterized in that, The A is K, with the chemical formula K5(NbOF4)(TaF7)2, belonging to the tetragonal crystal system, space group I4cm, and cell parameters a = 14.0~15.0 Å, b = 14.0~15.0 Å, c = 7.0~8.0 Å, V = 1650~1700 Å. 3 , α = β = γ = 90°, Z =2; Alternatively, A may be Rb, with the chemical formula Rb5(NbOF4)(TaF7)2, belonging to the tetragonal crystal system, space group I4cm, and cell parameters a = 15.0~16.0 Å, b = 15.0~16.0 Å, c = 7.0~8.0 Å, V = 1800~1900 Å. 3 , α = β = γ =90°, Z = 2; Alternatively, A may be Cs, with the chemical formula Cs5(NbOF4)(TaF7)2, belonging to the tetragonal crystal system, space group I4cm, and cell parameters a = 16.0~17.0 Å, b = 16.0~17.0 Å, c = 7.0~8.0 Å, V = 2000~2200 Å. 3 , α = β = γ =90°, Z = 2.

3. The method for preparing the second-order nonlinear optical crystalline material of alkali metal niobium tantalum oxyfluorate according to claim 1 or 2, characterized in that, The method is a two-step hydrothermal method used to prepare the crystalline material with millimeter-scale dimensions.

4. The method for preparing the second-order nonlinear optical crystalline material of alkali metal niobium tantalum oxyfluorate according to claim 3, characterized in that, The first step includes: Using alkali metal sources, tantalum sources, and fluorine sources as raw materials, they are mixed with water in a certain proportion and subjected to a hydrothermal reaction. After constant temperature heating and cooling processes, an alkali metal fluorotantalate precursor with the chemical formula A2TaF7 (A = K, Rb, or Cs) is obtained.

5. The method for preparing the second-order nonlinear optical crystalline material of alkali metal niobium tantalum oxyfluorate according to claim 4, characterized in that, The alkali metal source is selected from one or more of the corresponding alkali metal carbonates, nitrates, sulfates, or hydrochlorides; the tantalum source is selected from tantalum pentoxide or tantalum pentachloride; and the fluorine source is a 40% hydrofluoric acid aqueous solution.

6. The method for preparing the second-order nonlinear optical crystalline material of alkali metal niobium tantalum oxyfluorate according to claim 4, characterized in that, The molar ratio of the alkali metal element to tantalum element is (1.8~2.2): (0.9~1.1), and the volume ratio of the fluorine source to water is (1~3): (1~3).

7. The method for preparing the second-order nonlinear optical crystalline material of alkali metal niobium tantalum oxyfluorate according to claim 4, characterized in that, The heating temperature for the first step of the hydrothermal reaction is 200 ℃, and the reaction time is not less than 48 hours.

8. The method for preparing the second-order nonlinear optical crystalline material of alkali metal niobium tantalum oxyfluorate according to claim 3, characterized in that, The second step includes: mixing the A2TaF7 precursor obtained in claim 4 with a niobium source, a fluorine source and water in a certain proportion, carrying out a hydrothermal reaction, and obtaining the colorless and transparent alkali metal niobium tantalum oxyfluorate crystals through a constant temperature heating and cooling process.

9. The method for preparing the second-order nonlinear optical crystalline material of alkali metal niobium tantalum oxyfluorate according to claim 8, characterized in that, The niobium source is selected from niobium pentoxide or niobium pentachloride; the fluorine source is a 40% hydrofluoric acid aqueous solution.

10. The method for preparing the second-order nonlinear optical crystalline material of alkali metal niobium tantalum oxyfluorate according to claim 8, characterized in that, The molar ratio of A2TaF7 precursor to niobium is (1.8~2.5): (0.8~1.2), and the volume ratio of fluorine source to water is (1~3): (1~3).

11. The method for preparing the second-order nonlinear optical crystalline material of alkali metal niobium tantalum oxyfluorate according to claim 8, characterized in that, The second step of the hydrothermal reaction is heated at a temperature of 200~220 ℃ for a time of not less than 72 hours.

12. The application of the alkali metal niobium tantalum oxyfluoride second-order nonlinear optical crystalline material according to claim 1 or 2 in laser frequency converters, optical parametric oscillators, optical parametric amplifiers and photoelectric rectifiers.

13. The application of the alkali metal niobium tantalum oxyfluorate second-order nonlinear optical crystalline material according to claim 12, characterized in that, The material is used in a laser frequency converter to achieve the output of 532 nm laser under 1064 nm laser irradiation, and to output 266 nm laser under 532 nm laser irradiation.

Images