A germanium-based chiral perovskite second-order nonlinear optical crystal material, preparation and application thereof

Abstract

This invention relates to a germanium-based chiral perovskite second-order nonlinear optical crystalline material, its preparation and application, wherein the chemical formula of the material is ( R -C7H 10 NO)GeI3 and ( S -C7H 10 NO)GeI3, where R -C7H 10 NO is a (R)-2-(1-hydroxyethyl)pyridine cation. S -C7H 10 NO is a (S)-2-(1-hydroxyethyl)pyridine cation. This crystal belongs to the hexagonal crystal system, space group [space group number missing]. P 63, cell parameters a =17.0~18.0 Å, b =17.0~18.0 Å, c =7.0~8.0 Å, unit cell volume V =2000~2200 Å 3 , α = β =90°, gamma =120° Z= 2. Under 1200 nm laser irradiation, the nonlinear optical crystal of the present invention ( R -C7H 10 NO)GeI3 and ( S -C7H 10 The frequency doubling effect of GeI3 powder is 15 times that of KH2PO4; under 2000 nm laser irradiation, the frequency doubling effect of the crystalline material powder is 1.0 times that of KTiOPO4, and both can achieve phase matching. The crystalline material also has a large birefringence, wherein ( R -C7H 10 NO)GeI3 is 0.518 @ 546 nm, ( S -C7H 10 The NO)GeI3 has a wavelength of 0.529 nm at 546 nm and a moderate optical band gap (2.68 eV). The crystalline material of this invention shows significant engineering application value in nonlinear optical applications such as near-infrared laser frequency conversion, optical parametric amplification, and electro-optic signal processing.

Description

Technical Field

[0001] This invention belongs to the field of nonlinear optical crystal materials technology, specifically relating to a germanium-based chiral perovskite second-order nonlinear optical crystal material and its preparation and application. Background Technology

[0002] Nonlinear optical materials are a core foundation of modern optoelectronic technology, widely used in laser frequency conversion, electro-optic modulation, optical signal processing, and optical communication. Organic-inorganic hybrid perovskite crystals, with their rich structural diversity and excellent photophysical properties, have become a research hotspot in the field of second-order nonlinear optical materials in recent years. Organic-inorganic hybrid perovskites use organic cations and inorganic metal halide polyhedra as basic building blocks. These polyhedra assemble into a three-dimensional framework through corner sharing or face sharing. By modulating the organic / inorganic composition, the connection mode and dimensions of the framework can be flexibly controlled, thus obtaining perovskite systems with rich structures. Among them, the main group metal Ge, containing lone pairs of electrons, is prone to strong distortion in its coordination polyhedra, which is beneficial for generating significant second harmonic effects. To achieve non-centrosymmetric structures, chiral aliphatic amine cations are often used as structural guiding templates, but their contribution to macroscopic nonlinear optical properties is limited. In contrast, aromatic cations, due to their large π-conjugated system and greater steric hindrance, not only promote the formation of low-dimensional structures, but their stronger hyperpolarizability and polarizability anisotropy also provide a more favorable structural basis for improving nonlinear and linear optical performance. Therefore, developing novel perovskite nonlinear optical crystals with both high birefringence and strong frequency doubling effect using aromatic amine cations with π-conjugated structures has become a key direction and research frontier in the field of optoelectronic materials that urgently needs breakthroughs. Summary of the Invention

[0003] This invention provides a chemical formula of ( R -C7H 10 NO)GeI3 and ( S -C7H 10 A second-order nonlinear optical crystal based on germanium (NO)GeI3, comprising its preparation method and applications. This material incorporates (R)-2-(1-hydroxyethyl)pyridine and (S)-2-(1-hydroxyethyl)pyridine cations with chiral centers. Utilizing their strong π-conjugated electronic structure and high hyperpolarizability, a hydrogen bonding network is constructed within the lattice, guiding the inorganic [GeI6] octahedron to exhibit a face-sharing one-dimensional infinite chain. The inorganic framework contains Ge... 2+ 4s 2The strong stereochemical activity of lone pair electrons induces a strong distortion of the [GeI6] octahedron. This high degree of distortion in the inorganic framework, combined with the spatial arrangement of chiral aromatic organic cations, successfully breaks the central symmetry of the lattice, preserving a significant net dipole moment and extremely strong optical anisotropy on a macroscopic scale. Experiments show that both crystal materials exhibit a large powder frequency doubling effect; under 1200 nm laser irradiation, their intensity reaches 15 times that of KH2PO4 (KDP) and phase matching is achieved; under 2000 nm laser irradiation, their intensity reaches 1.0 times that of KTiOPO4 (KTP) and phase matching is also achieved. Simultaneously, both crystals exhibit strong optical anisotropy. R -C7H 10 The birefringence of NO)GeI3 is 0.518 @ 546 nm. S -C7H 10 The birefringence of NO (GeI3) is 0.529 @ 546 nm, and its optical bandgap is 2.68 eV. This material is readily grown into high-quality millimeter-scale single crystals via hydrothermal methods, and the thermal decomposition temperature of the crystal material is not lower than 380 K. The crystal material of this invention exhibits significant engineering application value in nonlinear optical applications such as near-infrared laser frequency conversion, optical parametric amplification, and electro-optic signal processing.

[0004] The objective of this invention can be achieved through the following technical solutions: One of the technical solutions of this invention provides a germanium-based chiral perovskite second-order nonlinear optical crystal material, the chemical formula of which is ( R -C7H 10 NO)GeI3 and ( S -C7H 10 NO)GeI3, where R -C7H 10 NO is a (R)-2-(1-hydroxyethyl)pyridine cation. S -C7H 10 NO is a (S)-2-(1-hydroxyethyl)pyridine cation. This crystalline material belongs to the hexagonal crystal system, space group [space group number missing]. P 63, the cell parameters satisfy a = 17.0~18.0 Å, b = 17.0~18.0 Å, c = 7.0~8.0 Å, unit cell volume V = 2000~2200Å 3 , α = β = 90°, γ = 120°, Z = 2.

[0005] Furthermore, the chemical formula of this crystalline material is ( R -C7H 10 NO)GeI3, which belongs to the hexagonal crystal system and has space group . P 63, cell parameters are a = 17.0~18.0 Å, b = 17.0~18.0 Å, c = 7.0~8.0 Å, unit cell volume V = 2000~2200 Å 3 , α = β = 90°, γ = 120°, Z = 2. More preferably, the cell parameter is: a = 17.5~18.0Å, b = 17.5~18.0 Å, c = 7.5~8.0 Å, unit cell volume V = 2000~2200 Å 3 , α = β = 90°, γ =120° Z = 2. Most preferably, the cell parameter is... a = 17.73 Å, b = 17.73 Å, c = 7.60 Å, unit cell volume V = 2069.9 Å 3 , α = β = 90°, γ = 120°, Z = 2.

[0006] The present invention ( R -C7H 10 The crystal structure of NO)GeI3 is as follows: Figure 1 As shown, this material possesses a one-dimensional perovskite structure. The inorganic framework consists of one-dimensional infinite chains of face-shared [GeI6] octahedra, with (R)-2-(1-hydroxyethyl)pyridine cations located between adjacent [GeI6] one-dimensional chains. The (R)-2-(1-hydroxyethyl)pyridine cations interact with the inorganic framework through N–H···I and O–H···I hydrogen bonds, retaining a significant net macroscopic dipole moment in the unit cell. The high polarizability anisotropy and hyperpolarizability of the organic π-conjugated cations, in conjunction with the strong distortion of the inorganic framework, jointly induce a strong overtone response.

[0007] Furthermore, the chemical formula of this crystalline material is ( S -C7H 10 NO)GeI3, which belongs to the hexagonal crystal system and has space group . P 63, cell parameters are a = 17.0~18.0 Å, b = 17.0~18.0 Å, c = 7.0~8.0 Å, unit cell volume V = 2000~2200 Å 3 , α = β = 90°, γ = 120°, Z = 2. More preferably, the cell parameter is: a = 17.5~18.0Å, b = 17.5~18.0 Å, c = 7.5~8.0 Å, unit cell volume V = 2000~2200 Å 3 , α = β = 90°, γ =120° Z = 2. Most preferably, the cell parameter is... a = 17.75 Å, b = 17.75 Å, c = 7.60 Å, unit cell volume V = 2074.04 Å 3 , α = β = 90°, γ = 120°, Z = 2.

[0008] The present invention ( S -C7H 10 The crystal structure of NO)GeI3 is as follows: Figure 2 As shown, this material possesses a one-dimensional perovskite structure. The inorganic framework consists of one-dimensional infinite chains of face-shared [GeI6] octahedra, with (S)-2-(1-hydroxyethyl)pyridine cations located between adjacent [GeI6] one-dimensional chains. The (S)-2-(1-hydroxyethyl)pyridine cations interact with the inorganic framework through N–H···I and O–H···I hydrogen bonds, retaining a significant net macroscopic dipole moment in the unit cell. The high polarizability anisotropy and hyperpolarizability of the organic π-conjugated cations, in conjunction with the strong distortion of the inorganic framework, jointly induce a strong overtone response.

[0009] The second technical solution of the present invention provides a method for preparing a germanium-based chiral perovskite second-order nonlinear optical crystal material, characterized in that a germanium source, (R)-2-(1-hydroxyethyl)pyridine or (S)-2-(1-hydroxyethyl)pyridine and a mixed solvent are mixed and added to a reaction vessel, heated to a constant temperature and reacted for a period of time, and then cooled to crystallize to obtain yellow rod-shaped crystals, which are the target products.

[0010] Furthermore, the molar ratio of the germanium source to (R)-2-(1-hydroxyethyl)pyridine or (S)-2-(1-hydroxyethyl)pyridine is (1.5~2.5):(1.5~2.5).

[0011] Furthermore, the mixed solvent is a mixed solution of hydroiodic acid and hypophosphite in a volume ratio of (1~2): (1~2).

[0012] Furthermore, the germanium source is germanium oxide.

[0013] Furthermore, the constant temperature reaction time at 110~130 ℃ shall not be less than 120 h, and the temperature shall be lowered to room temperature for a period of not less than 60 h thereafter.

[0014] The third technical solution of the present invention provides an application of germanium-based chiral perovskite second-order nonlinear optical crystal material in laser frequency converters, optical parametric oscillators, optical parametric amplifiers, and photoelectric rectifiers.

[0015] Furthermore, this material is used in laser frequency converters to output 600 nm laser light under 1200 nm laser irradiation.

[0016] Specifically, ( R -C7H 10 NO)GeI3 and ( S -C7H 10 As a nonlinear optical crystal material, NO)GeI3 crystal outputs a strong 600 nm laser under 1200 nm laser irradiation. Its powder frequency doubling intensity is 15 times that of KDP crystal, and it can achieve phase matching.

[0017] Furthermore, this material is used in laser frequency converters, which can output 1000nm laser light even under 2000nm laser irradiation.

[0018] Specifically, ( R -C7H 10 NO)GeI3 and ( S -C7H 10NO)GeI3 crystal, as a nonlinear optical crystal material, outputs a strong 1000 nm laser under 2000 nm laser irradiation. Its powder frequency doubling intensity is 1.0 times that of KTP crystal, and it can achieve phase matching.

[0019] This invention combines organic cations with a large π-conjugated structure with an inorganic germanium iodide framework to successfully prepare a germanium-based chiral perovskite second-order nonlinear optical crystal. R -C7H 10 NO)GeI3 and ( S -C7H 10 NO)GeI3. This invention breaks crystal symmetry with a chiral (R)- / (S)-2-(1-hydroxyethyl)pyridine cation and utilizes Ge in a one-dimensional [GeI6] framework. 2+ Lone-pair electron-induced octahedral distortion, through the synergistic coupling of organic cation polarizability anisotropy and inorganic framework distortion, successfully yielded a crystal material exhibiting both excellent linear and nonlinear optical responses. This material achieved powder frequency doubling effects of 15 × KDP and 1.0 × KTP under 1200 nm and 2000 nm laser irradiation, respectively, while also possessing a large birefringence (0.518–0.529 @ 546 nm) and a band gap of 2.68 eV.

[0020] Compared with the prior art, the present invention has the following advantages: (1) This application provides a novel type of second-order nonlinear optical crystal ( R -C7H 10 NO)GeI3 and ( S -C7H 10 NO)GeI3, this crystal material exhibits a significant frequency doubling effect. Under 1200 nm laser irradiation, its frequency doubling intensity is 15 times that of KDP crystal, and under 2000 nm laser irradiation, its powder frequency doubling intensity is 1.0 times that of KTP crystal, with phase matching achieved in both cases. Furthermore, the material also possesses a large birefringence, wherein ( R -C7H 10 NO)GeI3 is 0.518 @ 546 nm, ( S -C7H 10 NO)GeI3 has a wavelength of 0.529 nm at 546 nm and an optical band gap of 2.68 eV. This crystal material has broad application prospects in the field of nonlinear optics.

[0021] (2) This application also provides the second-order nonlinear optical crystal ( R -C7H 10 NO)GeI3 and ( S -C7H 10The preparation method of NO)GeI3 was carried out by hydrothermal method. R -C7H 10 NO)GeI3 and ( S -C7H 10 NO)GeI3 crystals. The synthesis method is simple, the synthesis conditions are mild, the yield is high, and it is easy to obtain high-quality millimeter-sized single crystals. Attached Figure Description

[0022] Figure 1 yes( R -C7H 10 Schematic diagram of the crystal structure of NO)GeI3; Figure 2 yes( S -C7H 10 Schematic diagram of the crystal structure of NO)GeI3; Figure 3 The 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. Figure 4 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. Figure 5 These are the UV-Vis absorption spectra of samples 1-1# and 2-1#; Figure 6 This is the infrared spectrum of sample 1-1#; Figure 7 This is the infrared spectrum of sample 2-1#; Figure 8 This is the thermogravimetric analysis chromatogram of sample 1-1#; Figure 9 This is the thermogravimetric analysis chromatogram of sample 2-1#; Figure 10 These are the second harmonic phase matching diagrams of samples 1-1# and 2-1# in the 1200 nm band; Figure 11 This is the second harmonic phase matching diagram of samples 1-1# and 2-1# in the 2000 nm band; Figure 12 This is a birefringence test result of sample 1-1# at a wavelength of 546 nm. Figure 13 This is a birefringence test result of sample 2-1# at a wavelength of 546 nm. Detailed Implementation

[0023] 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.

[0024] Example:

[0025] 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.

[0026] Example 1: Preparation of samples 1-1#~1-8# A germanium source, (R)-2-(1-hydroxyethyl)pyridine, and a mixed solvent were mixed and added to a reaction vessel. The mixture was heated to a constant temperature and reacted for a period of time. Then, the mixture was cooled and crystallized to obtain ( R -C7H 10 NO)GeI3 yellow rod-shaped crystals.

[0027] The relationship between the types and proportions of raw materials, isothermal temperature, isothermal time and sample number in the initial mixture is shown in Table 1.

[0028] Table 1. Correspondence between samples and raw materials and synthesis conditions.

[0029] Crystal structure analysis of samples 1-1#~1-8# The structures of samples 1-1# to 1-8# were analyzed using single-crystal X-ray diffraction and powder X-ray diffraction methods.

[0030] Single-crystal X-ray diffraction measurements were performed on a Bruker D8 VENTURE CMOS X-ray single-crystal diffractometer (Germany). Data collection was conducted at 150 K, using a graphite-monochromatic Mo-K diffractometer as the source. α X-rays (λ = 0.71073 Å), scanning method: ω Data underwent absorption correction 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; [Further details about the method and its application are needed for accurate translation.] The full matrix least squares method is used to refine the coordinates and anisotropic thermal parameters of all atoms.

[0031] Powder X-ray diffraction tests were performed on a Bruker D8 X-ray powder diffractometer from Bruker GmbH, Germany, under the following conditions: fixed target, monochromatic light source, Cu-K. αThe wavelength is 1.540598 Å, the voltage and current are 40 kV / 20 mA, the slit widths (DivSlit / RecSlit / SctSlit) are 2.00 deg / 0.3 mm / 2.00 deg, the scanning range is 5~70°, and the scanning step size is... .

[0032] Among them, single-crystal X-ray diffraction results showed that samples 1-1# to 1-8# had the same chemical structural formula and crystal structure, with the chemical formula being ( R -C7H 10 NO)GeI3, belongs to the hexagonal crystal system, space group 1. P 63, cell parameters are a = 17.5~18.0 Å, b = 17.5~18.0 Å, c = 7.5~8.0 Å, unit cell volume V = 2000~2200 Å 3 , α = β = 90°, γ = 120°, Z = 2.

[0033] Taking sample 1-1# as a typical example, its crystal structure data is as follows: a = 17.73 Å, b = 17.73 Å, c = 7.60 Å, unit cell volume V = 2069.9 Å 3 , α = β = 90°, γ = 120°, Z = 2. Its crystal structure is as follows: Figure 1 As shown.

[0034] 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 and the diffraction peaks fitted by the single crystal data are in the same position, but the peak intensities are slightly different.

[0035] Taking sample 1-1# as a typical example, such as Figure 3 As shown, the X-ray diffraction pattern obtained by fitting the crystal structure determined by single-crystal X-ray diffraction is consistent with the X-ray diffraction pattern obtained after grinding sample 1-1# into powder. The peak positions are consistent, indicating that the obtained sample has high purity.

[0036] Ultraviolet-Visible Absorption Spectroscopy Test The UV-Vis absorption spectra of samples 1-1# were measured using an Agilent Technologies Cary 5000 UV-Vis-NIR spectrophotometer. The results are as follows: Figure 5 As shown, the band gap of this compound is 2.68 eV.

[0037] Infrared spectroscopy test Infrared spectroscopy measurements of samples 1-1# were performed using a Nicolet iS10 Fourier transform infrared spectrometer from Thermo Fisher Scientific, Inc., USA. The results are as follows: Figure 6 As shown, in the infrared spectrum (1516 cm⁻¹) –1 1369 cm –1 3167 cm –1 1600cm –1 The characteristic absorption peaks of [C7H] confirmed the presence of these peaks in the crystal. 10 NO] + The presence of functional groups.

[0038] Thermogravimetric test Thermogravimetric analysis (TGA) of samples 1-1# was performed on a Netzsch STA 409PC thermogravimetric analyzer from Netzsch GmbH, Germany. The results are as follows: Figure 8 As shown, by Figure 8 It can be seen that this compound is stable up to 380 K.

[0039] Frequency doubling test experiment and results The frequency doubling test experiment for sample 1-1# is as follows: A Q-switched Nd:YAG solid-state laser combined with an optical parametric oscillator was used to generate lasers with wavelengths of 1200 nm and 2000 nm, respectively. These were used as the fundamental frequency light to irradiate the crystal powder under test, and the generated second harmonic intensity was detected by an Ocean Optics Maya2000 Pro spectrometer. The crystal sample and the standard sample KDP crystal or KTP crystal were ground separately, and crystals of different particle sizes were separated using a standard sieve, with particle size ranges of 50~74, 74~105, 105~150, 150~200, and 200~280 μm. The variation of the frequency doubling signal with particle size was observed to determine whether phase matching could be achieved. Under irradiation conditions of 1200 nm or 2000 nm laser, the second harmonic intensity generated by the sample and the standard sample KDP crystal or KTP crystal were compared to obtain the relative magnitude of the frequency doubling effect of the sample.

[0040] Test results show that compound ( R -C7H 10 NO)GeI3 exhibits a powder frequency doubling effect, which is approximately 15 times that of KDP crystal under 1200 nm laser irradiation (e.g., Figure 10It can achieve phase matching; the powder frequency doubling effect under 2000 nm laser irradiation is about 1.0 times that of KTP crystal (e.g., Figure 11 Similarly, phase matching can also be achieved.

[0041] Crystal birefringence test The birefringence properties of crystal sample 1-1# were measured using a ZEISS AXIO Scope 5 polarizing microscope equipped with a Berek compensator. The light source wavelength was 546 nm. The birefringence was calculated using the following formula:

[0042] In the formula Δ R For optical path difference, Δ n It is birefringent. T For crystal thickness. Compensated positive and negative rotations provide a relative delay.

[0043] The results are as follows Figure 12 As shown, this illustrates the effect of achieving complete extinction using the Berek compensator. R -C7H 10 NO)GeI3 crystal. Optical path difference ( R The measured single crystal thickness was 13.533 μm. T The diameter is 26.126 μm. Single-crystal XRD analysis identified the crystal plane as (010). The calculated value is (...). R -C7H 10 The refractive index difference of the (010) crystal plane of NO)GeI3 crystal at 546 nm is 0.518.

[0044] Example 2: Preparation of samples 2-1#~2-8# A germanium source, (S)-2-(1-hydroxyethyl)pyridine, and a mixed solvent were mixed and added to a reaction vessel. The mixture was heated to a constant temperature and reacted for a period of time. Then, the mixture was cooled and crystallized to obtain ( S -C7H 10 NO)GeI3 yellow rod-shaped crystals.

[0045] 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.

[0046] Table 2. Correspondence between samples and raw materials and synthesis conditions.

[0047] Crystal structure analysis of samples 2-1#~2-8# The structures of samples 2-1# to 2-8# were analyzed using single-crystal X-ray diffraction and powder X-ray diffraction methods.

[0048] Single-crystal X-ray diffraction measurements were performed on a Bruker D8 VENTURE CMOS X-ray single-crystal diffractometer (Germany). Data collection was conducted at 150 K, using a graphite-monochromatic Mo-K diffractometer as the source. α X-rays (λ = 0.71073 Å), scanning method: ω Data underwent absorption correction 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; [Further details about the method and its application are needed for accurate translation.] The full matrix least squares method is used to refine the coordinates and anisotropic thermal parameters of all atoms.

[0049] Powder X-ray diffraction tests were performed on a Bruker D8 X-ray powder diffractometer from Bruker GmbH, Germany, under the following conditions: fixed target, monochromatic light source, Cu-K. α The wavelength is 1.540598 Å, the voltage and current are 40 kV / 20 mA, the slit widths (DivSlit / RecSlit / SctSlit) are 2.00 deg / 0.3 mm / 2.00 deg, the scanning range is 5~70°, and the scanning step size is... .

[0050] Among them, single-crystal X-ray diffraction results showed that samples 2-1#~2-8# had the same chemical structural formula ( S -C7H 10 NO)GeI3, belongs to the hexagonal crystal system, space group 1. P 63, cell parameters are a = 17.5~18.0 Å, b = 17.5~18.0Å, c = 7.5~8.0 Å, unit cell volume V = 2000~2200 Å 3 , α = β = 90°, γ = 120°, Z = 2.

[0051] Taking sample 2-1# as a typical example, its crystal structure data is as follows: a = 17.75 Å, b = 17.75 Å, c = 7.60 Å, unit cell volume V = 2074.04 Å 3 , α = β= 90°, γ = 120°, Z = 2. Its crystal structure is as follows: Figure 2 As shown.

[0052] The powder X-ray diffraction test results show that on the XRD patterns of samples 2-1#~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.

[0053] Taking sample 2-1# as a typical example, such as Figure 4 As shown, the X-ray diffraction pattern obtained by fitting the crystal structure determined by single-crystal X-ray diffraction is consistent with the X-ray diffraction pattern obtained after grinding sample 2-1# into powder. The peak positions are consistent, indicating that the obtained sample has high purity.

[0054] Ultraviolet-Visible Absorption Spectroscopy Test The UV-Vis absorption spectrum of sample 2-1# was measured using an Agilent Technologies Cary 5000 UV-Vis-NIR spectrophotometer. The results are as follows: Figure 5 As shown, the band gap of this compound is 2.68 eV.

[0055] Infrared spectroscopy test The infrared spectra of sample 2-1# were measured using a Nicolet iS10 Fourier transform infrared spectrometer from Thermo Fisher Scientific, Inc., USA. The results are as follows: Figure 7 As shown, in the infrared spectrum (1516 cm⁻¹) –1 1446 cm –1 3161 cm –1 1599cm –1 The characteristic absorption peaks of [C7H] confirmed the presence of these peaks in the crystal. 10 NO] + The presence of functional groups.

[0056] Thermogravimetric test Thermogravimetric analysis (TGA) of sample 2-1# was performed on a Netzsch STA 409PC thermogravimetric analyzer from Netzsch GmbH, Germany. The results are as follows: Figure 9 As shown, by Figure 9 It can be seen that this compound is stable up to 380 K.

[0057] Frequency doubling test experiment and results The frequency doubling test experiment for sample 2-1# is as follows: A Q-switched Nd:YAG solid-state laser combined with an optical parametric oscillator was used to generate lasers with wavelengths of 1200 nm and 2000 nm, respectively. These were used as the fundamental frequency light to irradiate the crystal powder under test, and the generated second harmonic intensity was detected by an Ocean Optics Maya2000 Pro spectrometer. The crystal sample and the standard KDP or KTP crystal were ground separately, and crystals of different particle sizes were separated using a standard sieve, with particle size ranges of 50~74, 74~105, 105~150, 150~200, and 200~280 μm. The variation of the frequency doubling signal with particle size was observed to determine whether phase matching could be achieved. Under irradiation conditions of 1200 nm or 2000 nm laser, the second harmonic intensity generated by the sample and the standard KDP or KTP crystal was compared to obtain the relative magnitude of the frequency doubling effect of the sample.

[0058] Test results show that compound ( S -C7H 10 NO)GeI3 exhibits a powder frequency doubling effect, which is approximately 15 times that of KDP crystal under 1200 nm laser irradiation (e.g., Figure 10 It can achieve phase matching; the powder frequency doubling effect under 2000 nm laser irradiation is about 1.0 times that of KTP crystal (e.g., Figure 11 Similarly, phase matching can also be achieved.

[0059] Crystal birefringence test The birefringence properties of crystal sample 2-1# were measured using a ZEISS AXIO Scope 5 polarizing microscope equipped with a Berek compensator. The light source wavelength was 546 nm. The birefringence was calculated using the following formula:

[0060] In the formula Δ R For optical path difference, Δ n It is birefringent. T For crystal thickness. Compensated positive and negative rotations provide a relative delay.

[0061] The results are as follows Figure 13 As shown, this illustrates the effect of achieving complete extinction using the Berek compensator. S -C7H 10 NO)GeI3 crystal. Optical path difference ( R The measured single crystal thickness was 8.568 μm. T The diameter is 16.196 μm. Single-crystal XRD analysis identified the crystal plane as (010). The calculated value is (...). S -C7H 10The refractive index difference of the (010) crystal plane of NO)GeI3 at 546 nm is 0.529.

[0062] The above description of the 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 germanium-based chiral perovskite second-order nonlinear optical crystal material, characterized in that, Its chemical formula is ( R -C7H 10 NO)GeI3 and ( S -C7H 10 NO)GeI3, where R -C7H 10 NO is a (R)-2-(1-hydroxyethyl)pyridine cation. S -C7H 10 NO is a (S)-2-(1-hydroxyethyl)pyridine cation; the crystalline material belongs to the hexagonal crystal system, space group [missing information]. P 63, the cell parameters satisfy a = 17.0~18.0 Å, b = 17.0~18.0 Å, c = 7.0~8.0 Å, unit cell volume V = 2000~2200 Å 3 , α = β = 90°, γ = 120°, Z = 2.

2. The method for preparing a germanium-based chiral perovskite second-order nonlinear optical crystal material as described in claim 1, characterized in that, First, the germanium source, (R)-2-(1-hydroxyethyl)pyridine or (S)-2-(1-hydroxyethyl)pyridine are mixed with a mixed solvent and placed in a reaction vessel. After heating to a constant temperature and reacting for a period of time, the mixture is cooled and crystallized to obtain yellow rod-shaped crystals, which are the target products.

3. The method for preparing a germanium-based chiral perovskite second-order nonlinear optical crystal material according to claim 2, characterized in that, The molar ratio of germanium source to (R)-2-(1-hydroxyethyl)pyridine or (S)-2-(1-hydroxyethyl)pyridine is (1.5~2.5): (1.5~2.5).

4. The method for preparing a germanium-based chiral perovskite second-order nonlinear optical crystal material according to claim 2, characterized in that, The mixed solvent is a solution of hydroiodic acid and hypophosphoric acid mixed in a volume ratio of (1~2): (1~2).

5. The method for preparing a germanium-based chiral perovskite second-order nonlinear optical crystal material according to claim 2, characterized in that, The germanium source is germanium oxide.

6. The method for preparing a germanium-based chiral perovskite second-order nonlinear optical crystal material according to claim 2, characterized in that, The reaction is carried out at a constant temperature of 110~130 ℃ for no less than 120 h, and then the temperature is lowered to room temperature for no less than 60 h.

7. The application of the germanium-based chiral perovskite second-order nonlinear optical crystal material as described in claim 1 in laser frequency converters, optical parametric oscillators, optical parametric amplifiers, and photoelectric rectifiers.

8. The application of the germanium-based chiral perovskite second-order nonlinear optical crystal material according to claim 7, characterized in that, The material is used in a laser frequency converter to achieve the output of 600 nm laser under 1200 nm laser irradiation and 1000 nm laser under 2000 nm laser irradiation.

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