Mixed bonded isothiocyanate nonlinear optical crystal and preparation method thereof

Abstract

The invention relates to the field of nonlinear optical materials, and discloses a mixed bonded isothiocyanate nonlinear optical crystal and a preparation method thereof.The preparation method comprises the following steps that a zinc source is dissolved in deionized water to obtain a zinc source solution, and a sulfur source is dissolved in deionized water to obtain a sulfur source solution; mixing the solutions, heating and stirring to form a [SZn4] covalent core precursor suspension; sequentially adding 1, 2, 4-triazole, thiocyanate and triethanolamine into the suspension liquid, and uniformly stirring; and placing the obtained mixture in a reaction kettle for temperature programming reaction and constant-temperature reaction, then performing temperature programming cooling to room temperature, and filtering, washing and drying to obtain the crystal. By constructing a stable [SZn4] covalent core and regulating and controlling directional arrangement of NCS-and C2H2N3 ligands, effective superposition of microscopic nonlinear polarizability is realized, so that the material obtains higher second harmonic response, the thermal stability of the crystal is improved, and the optical band gap is widened.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of nonlinear optical materials, in particular to a mixed-bonding isothiocyanate nonlinear optical crystal and a preparation method thereof. BACKGROUND

[0002] Nonlinear optical crystals are indispensable functional materials in the field of laser technology and optoelectronics. At present, in the field of commercialized deep ultraviolet nonlinear optical crystals, beta-BaB2O4 (BBO) and LiB3O5 (LBO) of borate system occupy a dominant position. However, this kind of high-temperature melting growth method generally faces challenges such as high energy consumption and complex temperature control equipment.

[0003] In terms of material performance, an ideal nonlinear optical crystal needs to have a wide optical band gap to ensure a high laser damage threshold, a high second harmonic response efficiency and excellent thermal stability. However, the existing material system generally has challenges in optimizing the above multiple performance indicators at the same time. For example, when pursuing high second harmonic response efficiency, it is often difficult to ensure a wide optical band gap or excellent thermal stability at the same time.

[0004] In the exploration of new nonlinear optical materials, metal sulfide or thiocyanate complex systems have attracted much attention due to their structural diversity. However, such complex materials generally have the problem of insufficient thermal stability and are prone to decomposition at relatively low temperatures, thereby limiting their application tolerance in a laser environment. In addition, in the design of crystal structure, how to effectively regulate the arrangement direction of the microstructure unit so that it presents a non-centrosymmetric structure macroscopically to generate a second harmonic response and at the same time has a large birefringence that meets the phase matching requirement is still a key challenge faced by synthesis technology. The existing synthesis strategy cannot accurately control the ordered assembly of polar groups, which limits the nonlinear optical efficiency and phase matching ability of the material.

[0005] In summary, the existing nonlinear optical material technology has deficiencies in the control of energy consumption in the preparation process, and the balance of the comprehensive performance of material thermal stability, optical band gap, second harmonic response and birefringence. Therefore, it is a problem to be solved in the field to develop a crystal material with mild preparation conditions and high thermal stability, wide band gap and high nonlinear optical performance. SUMMARY

[0006] The purpose of the present application is to provide a mixed-bonding isothiocyanate nonlinear optical crystal and a preparation method thereof to solve the problems raised in the background art.

[0007] To solve the above problems, the present application provides the following technical solutions: The present application provides a mixed-bonding isothiocyanate nonlinear optical crystal, which adopts the following technical solutions: A mixed-bonded isothiocyanate nonlinear optical crystal is prepared by reacting raw materials comprising the following weight parts under hydrothermal conditions: 0.55-0.86 parts of a zinc source; 0.24-0.36 parts of a sulfur source; 0.34-0.92 parts of 1,2,4-triazole; 0.38-0.69 parts of isothiocyanate; 0.03-0.7 parts of triethanolamine; and the balance is deionized water.

[0008] By adopting the technical scheme, the application successfully constructs a new non-centrosymmetric crystal material Zn4S(C2H2N3)3(NCS)3. The crystal realizes the synergistic integration of a wide-bandgap sulfide core and a high-polarizability organic ligand through the key technical point of co-ligand assembly. The preparation process of the crystal avoids high-temperature and high-pressure melting growth conditions, while still obtaining a high-performance crystal.

[0009] The key technical point of the application lies in the following structure design and reaction process control: Pre-assembly of [SZn4] covalent core and band gap characteristics: In the S3 step, the zinc source and the sulfur source are pre-reacted in deionized water to form a [SZn4] covalent core precursor suspension with a tetrahedral structure. The electronic state distribution characteristics of the core help to widen the optical band gap of the material, so that the crystal has an ultraviolet cutoff edge shorter than 230 nm and has a higher laser damage resistance potential.

[0010] Directional coordination of nonlinear active groups: The NCS - (thiocyanate) and C2H2N3 (triazole) ligands in the system have high microscopic superpolarizability. The application uses triethanolamine as a structure regulator and a pH buffer to accurately regulate the coordination between the [SZn4] core and the organic / inorganic ligands. This regulation drives the NCS - and C2H2N3 - ligands with high nonlinear activity to be directionally connected to the [SZn4] core in a non-centrosymmetric manner. This directional arrangement realizes the effective superposition of microscopic nonlinear polarizability on a macroscopic scale, so that the crystal has a strong second harmonic response.

[0011] Realization of large birefringence: In the crystal structure, the high-anisotropy ligands (NCS - and C2H2N3 -The spatial orientation arrangement of the [SZn4] core unit is close to parallel. The arrangement macroscopically causes a large difference in polarizability, and gives the crystal a high birefringence, thereby satisfying the necessary condition of phase matching.

[0012] Preferably, the weight parts of the raw materials are as follows: 0.67 parts of a zinc source; 0.29 parts of a sulfur source; 0.51 parts of 1,2,4-triazole; 0.46 parts of a thiocyanate; and 0.25 parts of triethanolamine.

[0013] By adopting the technical scheme, a block crystal with high optical quality can be obtained. Preferably, the zinc source is specifically ZnCl2; the sulfur source is specifically Na2S·9H2O; and the thiocyanate is specifically NH4SCN.

[0014] The application further provides a preparation method of a mixed-bonded thiocyanate nonlinear optical crystal. The preparation method of the mixed-bonded thiocyanate nonlinear optical crystal comprises the following steps: S1. Accurately weighing a zinc source and dissolving the zinc source in deionized water to obtain a zinc source solution; S2. Accurately weighing a sulfur source and dissolving the sulfur source in deionized water to obtain a sulfur source solution; S3. Mixing the zinc source solution and the sulfur source solution, and heating and stirring to obtain a [SZn4] covalent core precursor suspension; S4. Adding 1,2,4-triazole, thiocyanate and triethanolamine into the precursor suspension in sequence, and stirring uniformly to obtain a mixed material; S5. Placing the mixed material in a reaction kettle to perform a programmed temperature rising reaction and a constant temperature reaction; S6. After the temperature rising reaction and the constant temperature reaction are completed, the temperature is programmed to cool to room temperature, and the crystal is obtained after filtration, washing and drying.

[0015] By adopting the technical scheme, the mild hydrothermal co-ligand assembly method is adopted, and the preparation difficulty, energy consumption and cost are effectively reduced. By controlling the heating and stirring temperature to be 60-80℃ and the heating time to be 1-2 hours, the controllable self-assembly of the [SZn4] core unit is realized, and the pre-assembly is the basis for the accurate orientation of subsequent coordination.

[0016] The material system is accurately controlled by slow programmed temperature rising at a speed of 1-3℃ / hour, and after the temperature is raised to 160-200℃, the constant temperature reaction is performed for 3-5 days. The programmed temperature control guarantees the stable growth of the crystal in thermodynamics and kinetics, and helps to obtain a functional single crystal with high optical quality. In the S5 step, the filling degree of the mixed material in the reaction kettle is controlled to be in the range of 65-75%.

[0017] Preferably, in the S6 step, the rate of the programmed cooling is 5-10℃ / h, which ensures slow cooling of the crystal and avoids internal stress cracking.

[0018] Preferably, the molar ratio of the raw materials is as follows: the molar ratio of the zinc source to the sulfur source is 4.0-4.2:1; the molar ratio of 1,2,4-triazole to the sulfur source is 4.0-7.2:1; the molar ratio of thiocyanate to the sulfur source is 5.0-6.0:1. In addition, in the S4 step, the molar ratio of the triethanolamine to the sulfur source is 0.2-3.5:1.

[0019] By the above preferred ratio and process parameters, the growth environment of the crystal is precisely controlled. The optimization of the molar ratio reasonably matches the concentrations of the reactants, and especially when the molar ratio of the zinc source to the sulfur source is controlled in the range of 4.0-4.2:1, the formation efficiency and purity of the [SZn4] core can be maximized. When the molar ratio of the triethanolamine to the sulfur source is controlled in the range of 0.2-3.5:1, the pH value of the reaction system can be effectively buffered, and the activation state and coordination ability of the coordination atoms can be precisely controlled. This fine control ensures the selective generation of the target product in the multi-ligand system and inhibits the generation of impurities, which is a key technical means to ensure the uniformity of the product purity and optical performance.

[0020] Compared with the prior art, the present application has the following beneficial effects: 1. The present application constructs a stable [SZn4] covalent core by a two-step precursor thermal pre-assembly strategy, and uses the coordination geometry of the core to promote the directional arrangement of NCS - and C2H2N3 ligands in a non-centrosymmetric manner, effectively superimposes the microscopic nonlinear polarizability, and makes the powder second harmonic response intensity of the obtained crystal material Zn4S(C2H2N3)3(NCS)3 reach 5.3 times that of KDP, thereby obtaining a high nonlinear optical efficiency.

[0021] 2. The present application uses C2H2N3 and NCS - ligands to bridge the [SZn4] covalent core into a three-dimensional framework structure, so that the material has an initial decomposition temperature of 415℃, and has a high thermal stability; at the same time, the valence band top in the structure is mainly contributed by the p orbitals of S atoms and N atoms, and the conduction band bottom is mainly formed by the s orbitals of Zn atoms, which widens the optical band gap, so that the optical band gap of the material reaches 4.72eV, and has the potential of high laser damage threshold.

[0022] 3. The present application uses a preparation process comprising thermal pre-reaction, programmed temperature rise and programmed cooling to control NCS -The high polarizability anisotropic groups are arranged approximately parallel in space, thereby giving the crystal a large macroscopic birefringence, which satisfies the condition of phase matching in the deep ultraviolet waveband. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The figure is a powder X-ray diffraction (PXRD) spectrum of Zn4S(C2H2N3)3(NCS)3 of the application, and the simulated spectrum is obtained from SCXRD data. Figure 2 The figure is a thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) curve of Zn4S(C2H2N3)3(NCS)3 of the application. Figure 3 The figure is an infrared spectrum of Zn4S(C2H2N3)3(NCS)3 of the application. Figure 4 The figure is an optical band gap diagram of the ultraviolet-visible-near infrared reflectance spectrum of Zn4S(C2H2N3)3(NCS)3 of the application. Figure 5 The figure is a comparison of the geometry, polarizability anisotropy, hyperpolarizability, and Eg value of the conventional functional group and NCS - and C2H2N3 - groups of the application DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the application will be described clearly and completely below in combination with the drawings, examples, comparative examples, and test examples of the application. Obviously, the described embodiments are only some of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the application.

[0025] Examples 1-3: Example 1: The embodiment provides a mixed-bonding isothiocyanate nonlinear optical crystal preparation method, and the specific steps are as follows: S1, accurately weigh 0.86 g (6.30 mmol) of ZnCl2, dissolve it in 20 mL of deionized water to obtain a zinc source solution.

[0026] S2, accurately weigh 0.36 g (1.50 mmol) of Na2S·9H2O, dissolve it in 15 mL of deionized water to obtain a sulfur source solution.

[0027] S3, the sulfur source solution was slowly added dropwise into the zinc source solution under continuous stirring to obtain a white suspension. The suspension was heated at 80°C and stirred for 2 hours, and then cooled to room temperature to obtain a [SZn4] covalent core precursor suspension.

[0028] S4, 0.92 g (10.80 mmol) of 1,2,4-triazole, 0.69 g (9.00 mmol) of NH4SCN, and finally 0.7 mL of triethanolamine were sequentially added into the precursor suspension obtained in the previous step, and stirred uniformly.

[0029] S5, the uniformly mixed material was transferred into a polytetrafluoroethylene-lined stainless steel reaction kettle with a volume of 50 mL, and the filling degree was about 75%. The reaction kettle was sealed, placed in a program-controlled oven, and heated to 200°C at a rate of 3°C / hour, and reacted at this temperature for 5 days.

[0030] S6, after the reaction was completed, it was cooled to room temperature at a rate of 10°C / hour. The obtained crystals were collected by filtration, and sequentially washed with deionized water and anhydrous ethanol for 3 times. After drying in a vacuum oven at 60°C for 12 hours, colorless transparent block crystals were obtained.

[0031] Example 2: The embodiment provides a mixed-bonded isothiocyanate nonlinear optical crystal preparation method, and the specific steps are as follows: S1, 0.67 g (4.92 mmol) of ZnCl2 was accurately weighed and dissolved in 15 mL of deionized water to obtain a zinc source solution.

[0032] S2, 0.29 g (1.20 mmol) of Na2S·9H2O was accurately weighed and dissolved in 10 mL of deionized water to obtain a sulfur source solution.

[0033] S3, the sulfur source solution was slowly added dropwise into the zinc source solution under continuous stirring to obtain a white suspension. The suspension was heated at 70°C and stirred for 1.5 hours, and then cooled to room temperature to obtain a [SZn4] covalent core precursor suspension.

[0034] S4, 0.51 g (6.00 mmol) of 1,2,4-triazole, 0.46 g (6.00 mmol) of NH4SCN, and finally 0.25 mL of triethanolamine were sequentially added into the precursor suspension obtained in the previous step, and stirred uniformly.

[0035] S5, the mixed material after uniform transfer to the volume of 50 mL of polytetrafluoroethylene lining stainless steel reactor, filling degree is about 70%. Seal the reactor, it is placed in the program temperature oven, with the rate of 2 ℃ / h to 180 ℃, and constant temperature reaction 4 days at this temperature.

[0036] S6, after the reaction, with the rate of 8 ℃ / h to room temperature. Filter collection of the resulting crystals, in turn with deionized water and anhydrous ethanol each wash 3 times. In 60 ℃ vacuum oven drying 8 hours, can get colorless transparent block crystal.

[0037] Example 3: The embodiment provides a mixed bonding isothiocyanate nonlinear optical crystal preparation method, and the specific steps are as follows: S1, accurately weigh 0.55g (4.00mmol) of ZnCl2, dissolve it in 10 mL of deionized water to obtain a zinc source solution.

[0038] S2, accurately weigh 0.24g (1.00mmol) of Na2S·9H2O, dissolve it in 5 mL of deionized water to obtain a sulfur source solution.

[0039] S3, under continuous stirring, slowly add the sulfur source solution to the zinc source solution to obtain a white suspension. The suspension is heated at 60 ℃ and stirred for 1 hour, and then cooled to room temperature to obtain a [SZn4] covalent core precursor suspension.

[0040] S4, to the precursor suspension obtained in the previous step, add 0.34g (4.00mmol) of 1,2,4-triazole, 0.38g (5.00mmol) of NH4SCN, and finally add 0.03 mL of triethanolamine, and stir uniformly.

[0041] S5, the mixed material after uniform transfer to the volume of 50 mL of polytetrafluoroethylene lining stainless steel reactor, filling degree is about 65%. Seal the reactor, it is placed in the program temperature oven, with the rate of 1 ℃ / h to 160 ℃, and constant temperature reaction 3 days at this temperature.

[0042] S6, after the reaction, with the rate of 5 ℃ / h to room temperature. Filter collection of the resulting crystals, in turn with deionized water and anhydrous ethanol each wash 3 times. In 60 ℃ vacuum oven drying 6 hours, can get colorless transparent block crystal.

[0043] Comparative examples 1-4: Comparative Example 1: Compared with Example 2, the difference is that in S3, after the sulfur source solution is added dropwise to the zinc source solution, no pre-reaction step of heating and stirring at 70°C for 1.5 hours is performed, but directly enters the S4 step after stirring at room temperature for 1.5 hours, and the rest is the same.

[0044] Comparative Example 2: Compared with Example 2, the difference is that in S4, 0.25 mL of triethanolamine is not added, and the rest is the same.

[0045] Comparative Example 3: Compared with Example 2, the difference is that in S5, the 2°C / hour programmed heating rate is not used, but the reaction kettle is directly placed in a 180°C oven for constant temperature reaction, and the rest is the same.

[0046] Comparative Example 4: Compared with Example 2, the difference is that in S6, after the reaction is completed, the 8°C / hour programmed cooling rate is not used, but the reaction kettle is immediately taken out and quickly cooled in room temperature air, and the rest is the same.

[0047] Test Examples 1-7: Test Example 1: Phase purity and precursor preparation strategy verification (PXRD) Purpose: To verify that the product prepared by Example 2 is the target phase pure crystal, and to compare the influence of the precursor thermal pre-reaction step on the formation of the target crystal phase.

[0048] Experimental Description: Sample Preparation: Sample A (Example 2): Take the block-shaped crystal obtained according to the complete steps of Example 2, and grind it into fine powder.

[0049] Sample B (Comparative Example 1): Take the solid product obtained according to Comparative Example 1, and grind it into fine powder.

[0050] Test Method: Use an X-ray diffractometer equipped with a CuKα radiation source, wavelength λ = 1.5418 Å; Perform a continuous scan in the 2θ range of 5° to 60°; Record the diffraction data. Compare the experimental pattern with the simulated powder diffraction pattern calculated based on the single crystal structure data of Zn4S(C2H2N3)3(NCS)3.

[0051] Test Data: Table 1: Comparison of powder X-ray diffraction data of products of Example 2 and Comparative Example 1 (partial) ; Note: "-" indicates that the diffraction peak does not belong to the crystal structure of the target product Zn4S(C2H2N3)3(NCS)3, so the crystal plane index cannot be assigned, but it comes from the impurity phase component in Comparative Example 1.

[0052] in conclusion: Appendix Figure 1 The figure shows a comparison between the measured PXRD pattern of Example 2 and the simulated pattern based on single-crystal data. Here, "Experimental" refers to experimental data, "Simulated" refers to simulated data, and "Intensity" is the intensity in au. Referring to this figure, the 2θ positions and relative intensities of all characteristic diffraction peaks of the product of Example 2 are in high agreement with the simulated pattern derived from the analytical data of the Zn4S(C2H2N3)3(NCS)3 single-crystal structure. This consistency between experimental and theoretical simulation values ​​confirms that the bulk powder sample prepared in Example 2 has the same crystal structure as the single-crystal analytical results, and no impurity phases were detected, confirming it as a single pure phase.

[0053] In contrast, the product spectrum of Comparative Example 1 shows a difference. While Comparative Example 1 retains the characteristic diffraction peaks of the target phase in the low-angle range, such as 8.91° and 14.89°, several additional diffraction peaks with higher intensity appear in the region from 22° to 36°, such as the main peaks at 24.35° and 28.50° in Table 1. These additional diffraction signals cannot be attributed to the target Zn4S(C2H2N3)3(NCS)3 phase, indicating that the product is a multiphase mixture, with impurities including simple sulfides lacking complete ligand coordination, such as ZnS, or zinc-thiocyanate complexes.

[0054] The key technical point of this invention lies in its two-step precursor thermal pre-assembly strategy. In Zn 2+ With S 2- In step S3 of the reaction, a heat treatment at 70°C for 1.5 h provides the activation energy and kinetic conditions required to form a stable [SZn4] covalent core precursor. This precursor is the structural building block for constructing the final complex three-dimensional framework. Comparative Example 1 omitted this thermal pre-assembly process and carried out only at room temperature, resulting in incomplete or inhomogeneous precursor formation. Subsequent addition of ligands and hydrothermal treatment led to insufficiently formed intermediates thermodynamically or kinetically more prone to generating simpler, non-target crystalline phase byproducts, resulting in reduced purity of the final product phase. Therefore, the thermal pre-reaction step in S3 is a critical process control point for ensuring the purity of the final product phase.

[0055] Test Example 2: Thermal Stability Test (TGA) Objective: To determine the thermal decomposition temperature and thermal stability range of the product of Example 2.

[0056] Experimental description: Instrument: A simultaneous thermal analyzer was used.

[0057] Sample preparation: Several intact crystals, weighing approximately 5.0 to 10.0 mg in total, were selected from the product obtained in Example 2 and placed in an Al2O3 crucible.

[0058] Test conditions: Atmosphere: High-purity N2 (nitrogen) protective atmosphere; Gas flow rate: 50 mL / min; Temperature program: Temperature increased from 30 °C to 900 °C at a heating rate of 10 °C / min.

[0059] Data recording: Simultaneously record the change in sample mass with temperature (TGA curve) and its first derivative (DTG curve).

[0060] Test data: Table 2: Key data points from thermogravimetric analysis of the product (ZSTN) in Example 2 ; Note: "-" corresponds to the mass of the final inorganic residue. DTG has no peak value.

[0061] in conclusion: See attached document Figure 2 Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) curves were used, where Weight is the mass percentage (%), Temperature is the temperature (°C), and Deriv.Weight is the mass derivative with respect to time (%) / °C. The product ZSTN in Example 2 exhibited high thermal stability under N2 atmosphere. The TGA curves showed that the material experienced no mass loss before 410°C, and its initial decomposition temperature was approximately 415°C.

[0062] Thermal stability data are shown in Table 2. This invention constructs a [SZn4] covalent core through a thermal pre-assembly strategy and utilizes C2H2N3 and NCS. - The two ligands bridge it into a stable three-dimensional framework structure, which is the basis for achieving high thermal stability.

[0063] Unlike crystalline materials that rely on weak interactions or unsaturated coordination bonds, the product of this invention is a fully connected covalent framework. The thermal decomposition of the material corresponds to the high energy input required to break these strong chemical bonds, such as S-Zn bonds or CN and CS bonds within the ligands themselves. The multi-stage decomposition process shown in Table 2 has two DTG peaks at 475°C and 610°C, corresponding to the gradual pyrolysis of different components in the lattice and the final collapse of the framework.

[0064] For applications such as nonlinear optics, the material is subjected to thermal loads during operation, such as high-power laser irradiation. The decomposition temperature of 415℃ ensures sufficient structural stability for this material in most high-power laser applications, preventing thermal degradation, which is a prerequisite for its practical application.

[0065] Test Example 3: Functional Group Introduction Verification (FT-IR) Objective: To confirm that 1,2,4-triazole (C2H2N3) and thiocyanate (NCS) have been successfully introduced into the crystals of Example 2. - Two functional ligands.

[0066] Experimental description: Instrument: Fourier transform infrared spectrometer.

[0067] Sample preparation: A small amount of the crystal sample obtained in Example 2 was taken and thoroughly mixed and ground with spectroscopically pure KBr (potassium bromide) powder (mass ratio approximately 1:100) in an agate mortar. The mixed powder was transferred to a tableting mold and pressed into uniform and transparent sheets under a pressure of approximately 10 MPa.

[0068] Test conditions: Scan range: 4000cm -1 Up to 400cm -1 Resolution: 4cm -1 Number of scans: 32 in total.

[0069] Data was collected after removing the blank KBr background.

[0070] Test result data: Table 3: Assignment of characteristic infrared peaks of the product (ZSTN) from Example 2 (partial) ; Note: s = strong peak, m = medium peak, w = weak peak.

[0071] in conclusion: See attached document Figure 3 The infrared spectrum, where Transmittance is the transmittance in %, and Wavenumbers are the number of peaks in cm⁻¹. -1 In the FT-IR spectrum of the product in Example 2, at 2102 cm⁻¹... -1 A strong absorption peak was observed at [location], as shown in Table 3. This peak is attributed to NCS. - The characteristic stretching vibration of the C≡N bond in the ligand, its position relative to the free NCS - Ions (approximately 2050 cm⁻¹) -1 A blue shift occurred, indicating that NCS - The ligand has been coordinated with the Zn(II) center through the N-terminus, forming a bridge.

[0072] At the same time, at 3119cm -1 A moderate-intensity absorption peak was observed at [value missing], attributed to the stretching vibration of the NH bond in the 1,2,4-triazole ligand. [Value missing] at 1528 cm⁻¹ in the fingerprint region. -1 and 1445cm -1Vibrational absorption attributed to the C=N and C-N bonds of the triazolate ring skeleton was also observed.

[0073] The key technical point of the present application is that in the S4 step, C2H2N3 and NCS are simultaneously introduced into the [SZn4] core precursor system - Two ligands. The FT-IR test results provide direct vibrational spectral evidence that both of the two different organic and inorganic ligands have been successfully bonded into the crystal lattice of the final product. The simultaneous appearance of the C≡N vibration peak and the N-H vibration peak confirms that the product is the target co-ligand material Zn4S(C2H2N3)3(NCS)3, verifying the feasibility of the co-ligand assembly strategy described in the present application.

[0074] Test Example 4: Comparison test of nonlinear optical performance (SHG) Objective: To comparatively evaluate the powder second harmonic (SHG) response intensity of the products obtained by the complete process (Example 2) and the missing key process steps (Comparative Examples 1-4) of the present application.

[0075] Experimental description: Instrument: Modified Kurtz-Perry powder method test system was used.

[0076] A Q-switched Nd:YAG pulse laser with a wavelength of 1064 nm, a pulse width of 10 ns, and a repetition frequency of 10 Hz was used.

[0077] Sample preparation: The products of Example 2 and Comparative Examples 1-4 (if solid) were ground respectively; Standard screen was used for screening, and powder sample pieces with a particle size of 150-210 μm were collected; Potassium dihydrogen phosphate (KDP) powder with the same particle size was prepared in the same way as a reference.

[0078] Test method: The sample to be tested and the KDP reference sample were respectively loaded into a quartz cuvette with a thickness of 0.5 mm and compacted.

[0079] The 1064 nm fundamental frequency light beam was focused on the surface of the sample.

[0080] The outgoing light passed through a filter (to filter out the 1064 nm fundamental frequency light) and a monochromator.

[0081] The photomultiplier tube (PMT) was used to detect the frequency-doubled light signal intensity at 532 nm, and the peak voltage was read by an oscilloscope.

[0082] Test result data: Table 4: Comparison of powder SHG response of products of Example 2 and Comparative Examples 1-4 ; Conclusions: The powder SHG results are shown in Table 4. The product of Example 2 (ZSTN) shows a SHG response 5.3 times stronger than the KDP reference under 1064 nm laser irradiation, and has phase-matching behavior, indicating that the material is a highly efficient nonlinear optical crystal.

[0083] In contrast, the SHG responses of all the comparative product are weak or close to zero. This set of comparative data reveals the necessity of various process control points in the present application: Comparative Example 1: The product of Test Example 1 has been confirmed to be a heterogeneous mixture. The SHG effect depends on the specific non-centrosymmetric crystal structure, and the presence of heterogeneous phases destroys the periodicity and symmetry of the crystal lattice, resulting in almost complete quenching of the SHG signal.

[0084] Comparative Examples 2 and 3: These two processes result in explosive nucleation, and the product is a fine powder or microcrystal. The strength of the powder SHG effect is related to the particle size, and the tiny crystals cannot achieve effective phase matching, and the generated second harmonic light is incoherently superimposed between the grains, resulting in a weak macroscopic response.

[0085] Comparative Example 4: The product of this process has internal stress and cracking. The crystal cracking forms a large number of scattering interfaces inside, which destroys the coherence of the fundamental light and the second harmonic light, and the light path is blocked, and also cannot achieve effective phase matching, resulting in a decrease in SHG efficiency.

[0086] In summary, the SHG performance test shows that the key technical points of the present application, including the thermal pre-reaction of S3, the regulating agent and programmed heating and cooling of S5, are a complete technical solution for obtaining large-size, high-quality, high-SHG-effect crystal materials. The absence of any step will result in the failure or degradation of the nonlinear optical function of the product.

[0087] Test Example 5: Measurement of Key Optical Parameters Purpose: To measure the ultraviolet cutoff edge, optical band gap (Eg) and birefringence (Δn) of the product of Example 2 (ZSTN), and to evaluate its basic performance as an optical material.

[0088] Experimental Description: Ultraviolet-visible spectrum test (cutoff edge and band gap): Instrument: UV-Vis-NIR spectrophotometer.

[0089] Cutoff edge measurement: Select a high-quality ZSTN single crystal with a thickness of about 1.0 mm prepared in Example 2, and polish both sides. Scan its transmission spectrum in the wavelength range of 1100 nm to 190 nm. The position where the transmittance sharply decreases to near zero is defined as the ultraviolet cutoff edge.

[0090] Bandgap measurement (diffuse reflectance method): The product of Example 2 was ground into fine powder and tested by UV-Vis diffuse reflectance spectroscopy (DRS) with BaS04(reference). After data collection, the Kubelka-Munk function was used to convert the data and the optical bandgap Egof the material was calculated by Tauc plot extrapolation method ((ahv) 2 Vshv).

[0091] Birefringence measurement (Δn): Instrument: polarizing microscope equipped with Berek compensator.

[0092] Sample: polished wafer of ZSTN from the above transmittance test.

[0093] Method: under crossed polarized light, the wafer was rotated to the maximum extinction position. The optical path difference (R) of the wafer at a specific wavelength (e.g. 546 nm) was measured using the Berek compensator. The thickness of the wafer at this point (d) was accurately measured. The birefringence was calculated by the formula Δn = R / d.

[0094] Test result data: Table 5: Key optical parameters of the product of Example 2 (ZSTN) ; Conclusion: Referring to the data in Figure 4 Table 5, it can be seen that the product of Example 2 (ZSTN) has a short ultraviolet cutoff edge of 225 nm, corresponding to a wide optical bandgap of 4.72 eV. This characteristic makes the material have high transmittance in the ultraviolet band, and the wide bandgap structure makes it have the potential of high laser damage threshold, which is the basis for its application as a nonlinear optical material. Figure 4 At the same time, the birefringence Δn of the material measured at 546 nm reaches 0.321. This is a large birefringence value, which is a prerequisite for realizing nonlinear optical phase matching, especially deep ultraviolet phase matching.

[0095] The key technical point of the present application is that through the complete process of S3-S5, a millimeter-level, high-optical-quality crystal can be stably grown. The conclusion of Test Example 4 shows that the absence of any step cannot obtain a functional crystal. This test example further confirms that the crystal prepared by the complete process has the physical conditions (size and quality) required for precise optical parameter measurement.

[0096]

[0097] ​The optical parameters are realized due to the designed co-ligand structure of Zn4S(C2H2N3)3(NCS)3. The function groups with high anisotropy of polarizability (such as NCS - ) are orderly arranged under the guidance of the [SZn4] core, which constructs high anisotropy at the micro level and reflects as large birefringence at the macro level. The preparation method of the application successfully converts the molecular design into block crystal material with practical optical parameters.

[0098] Test Example 6: Theoretical analysis of design principle Objective: Based on the first principle calculation, the electronic band structure of the product (ZSTN) of Example 2 is clarified, and the micro contribution of each structural unit to the macro nonlinear optical coefficient (SHG) and birefringence is quantitatively analyzed, and the physical origin of the material performance is revealed.

[0099] Experimental description: Calculation software and method: The CASTEP software package based on the density functional theory (DFT) is used to calculate the electronic structure and optical properties.

[0100] Parameter setting: The exchange correlation functional is selected as PBE functional (GGA-PBE) under generalized gradient approximation.

[0101] The ion-electron interaction is described by the norm-conserving pseudo-potential.

[0102] The plane wave cutoff energy is set to 830 eV.

[0103] The Monkhorst-Pack scheme is used for Brillion zone integration, and the k-point grid density is set to 3x3x2.

[0104] The single crystal structure model (Zn4S(C2H2N3)3(NCS)3) obtained by analyzing Example 2 is geometrically optimized, and the convergence standard is that the single atom energy change is less than 1.0x10-5 eV / atom.

[0105] Calculation content: The band structure and partial density of states (PDOS) are calculated.

[0106] The complex dielectric function is calculated, and then the second harmonic coefficient tensor is derived.

[0107] The first-order hyperpolarizability (β) and the anisotropy of polarizability (δ) of the independent structural units ([SZn4] cluster, NCS - group, C2H2N3 - group) are calculated.

[0108] Test result data: Table 6: Calculated values ​​of first-order hyperpolarizability and bandgap contribution of each structural unit in ZSTN crystal ; Note: "-" indicates that the parameter is calculated for isolated units and is not applicable to the entire unit cell.

[0109] in conclusion: See attached document Figure 5 Based on the data in Table 6, the sources of optical performance of ZSTN are analyzed as follows, where, Figure 5 In this context, Polarizability anisotropy represents polarizability, Hyperpolarizability represents hyperpolarizability, and the HOMO-LUMO gap represents the energy difference between the highest occupied molecular orbital and the lowest unoccupied molecular orbital. Band structure and partial density of states (PDOS) analysis revealed that the valence band top (VBM) of ZSTN is mainly contributed by the 3p orbitals of S atoms and the 2p orbitals of N atoms, while the conduction band bottom (CBM) is mainly formed by the hybridization of the 4s orbitals of Zn atoms, the 2p orbitals of C atoms, and some 3p orbitals of S atoms. This electronic state distribution indicates that charge transfer within the material mainly occurs between the [SZn4] inorganic core and the organic ligands. This covalent interaction is beneficial for widening the optical band gap, which is consistent with the wide band gap of 4.72 eV measured in Test Example 5.

[0110] Regarding the origin of SHG, Table 6 data shows that although the [SZn4] core provides structural support, its microscopic hyperpolarizability βmax is low (1.26 × 10⁻⁶). -30 esu). The main contributor to the SHG response of the material is NCS. - The functional group contributes approximately 65.8% of the total, and its microscopic hyperpolarizability reaches as high as 19.34 × 10⁻⁶. -30 esu. This is attributed to NCS. - The group possesses a highly delocalized π-electron conjugated system. C2H2N3 - The functional group provides a secondary contribution. The chemical design strategy of this invention, utilizing [SZn4] as an anchoring center, forces NCSs with high β values... - and C2H2N3 - The ligands are oriented in a non-centrosymmetric manner, which enables the effective superposition of microscopic nonlinear polarizability on a macroscopic scale, thereby generating the strong SHG signal observed in Test Example 4.

[0111] Regarding birefringence, NCS in Table 6 - The functional groups exhibit anisotropic polarizability (δ = 56.2 au). This is due to NCS. -As linear molecules, the electron cloud deformation ability of the molecules is quite different between axial and vertical directions. The present application controls the preparation process to keep the high anisotropic groups in a nearly parallel arrangement in space, thereby giving the crystal a large macroscopic birefringence (Δn ≈ 0.32) to meet the phase matching conditions in the deep ultraviolet waveband.

[0112] In summary, the theoretical calculation confirms the structural design of the present application: by means of precursor thermal pre-assembly to construct the [SZn4] core, and by means of the unique coordination geometry of the core to directionally assemble high-activity organic / inorganic ligands, the synergistic optimization of wide band gap, large frequency doubling effect and large birefringence is achieved at the micro level. This theoretical result is mutually confirmed with all the aforementioned macro experimental test data (test examples 2, 4, 5), forming a complete evidence chain of structure-activity relationship.

[0113] Test Example 7: Comprehensive Performance Benchmarking Objective: Benchmark the key functional indicators of the product (ZSTN) of Example 2 with the currently known excellent nonlinear optical (NLO) materials to determine the performance advantages of the material of the present application.

[0114] Experimental Description: This test example is a comprehensive comparative analysis and does not involve new single experimental steps. The data are all from literature reports or completed test examples (test examples 2, 4, 5).

[0115] Materials to be compared: Three representative commercial or research hotspot NLO crystals are selected as reference benchmarks: KDP (potassium dihydrogen phosphate): commercial standard reference.

[0116] BBO (beta-BaB2O4): representative of deep ultraviolet NLO crystals.

[0117] LBO (LiB3O5): representative of high-performance NLO crystals.

[0118] Comparison parameters: four key parameters that determine the practical value of NLO crystals are selected for comparison: Ultraviolet cutoff edge: determines the short-wave application range.

[0119] Optical band gap (Eg): reflects the potential of laser damage threshold.

[0120] Second harmonic (SHG) response intensity: reflects NLO efficiency (usually relative to KDP).

[0121] Decomposition temperature (Tdec): reflects thermal stability.

[0122] Data sources: The data of Example 2 are from test example 2, test example 4, and test example 5. The data of the comparison materials are from authoritative literature in the relevant field.

[0123] Test result data: Table 7: Comparison of the comprehensive performance of the product of Example 2 with typical nonlinear optical crystals ; Conclusion: The data in Table 7 show that the product ZSTN of Example 2 has good comprehensive performance in key performance parameters.

[0124] The ultraviolet cutoff edge of ZSTN is 225 nm, which is not as good as BBO or LBO, but still covers the commonly used harmonic output wave bands of 355 nm, 266 nm, etc. The optical band gap of 4.72 eV and the decomposition temperature of 415℃ make the thermal stability and laser damage resistance potential of ZSTN better than the commercial reference KDP. The SHG response strength of ZSTN reaches 5.3 times KDP, which is at a similar level to the response strength of high-performance BBO (6.0 times KDP), but the preparation cost and process complexity are lower than those of borate systems (such as BBO and LBO) grown by high-temperature melting method.

[0125] The present application adopts a mild hydrothermal co-ligand assembly strategy, especially the thermal pre-reaction of S3, to avoid the high-temperature and high-pressure melt environment required by the borate system, thereby reducing the preparation difficulty and energy consumption. This strategy successfully integrates the wide band gap characteristics of the inorganic sulfide core [SZn4], the high nonlinear polarizability of the NCS - ligand, and the structure-directing property of the C2H2N3 ligand into the same crystal structure. The comparison results confirm that the zinc-based thiocyanate framework material prepared by low-temperature and hydrothermal method is highly competitive in performance with traditional high-temperature borate NLO crystals, proving the innovation value and technical feasibility of the present application in exploring new preparation paths for NLO materials.

Claims

1. A hybrid bonded isothiocyanate nonlinear optical crystal, characterized in that, It is produced by reacting the following raw materials in parts by weight under hydrothermal conditions: Zinc source 0.55-0.86 parts; Sulfur source: 0.24-0.36 parts; 0.34-0.92 parts of 1,2,4-triazole; Thiocyanate 0.38-0.69 parts; Triethanolamine 0.03-0.7 parts; The remainder is deionized water.

2. The hybrid-bonded isothiocyanate nonlinear optical crystal according to claim 1, characterized in that, The weight parts of the raw materials are: 0.67 parts of zinc source; 0.29 parts of sulfur source; 0.51 parts of 1,2,4-triazole; 0.46 parts of thiocyanate; 0.25 parts of triethanolamine.

3. The hybrid-bonded isothiocyanate nonlinear optical crystal according to claim 2, characterized in that, The zinc source is specifically ZnCl2; the sulfur source is specifically Na2S·9H2O; and the thiocyanate is specifically NH4SCN.

4. A method for preparing a mixed-bonded isothiocyanate nonlinear optical crystal as described in any one of claims 1-3, characterized in that, Includes the following steps: S1. Weigh the zinc source and dissolve it in deionized water to obtain a zinc source solution; S2. Weigh the sulfur source and dissolve it in deionized water to obtain a sulfur source solution; S3. Mix the zinc source solution and the sulfur source solution, heat and stir to obtain a [SZn4] covalent core precursor suspension; S4. Add 1,2,4-triazole, thiocyanate and triethanolamine to the [SZn4] covalent core precursor suspension in sequence, and stir evenly to obtain a mixture. S5. Place the mixture in a reaction vessel and carry out a programmed temperature rise reaction and a constant temperature reaction; S6. After the heating reaction and the isothermal reaction are completed, the mixture is cooled to room temperature, and then filtered, washed and dried to obtain the crystal.

5. The method for preparing a mixed-bonded isothiocyanate nonlinear optical crystal according to claim 4, characterized in that, In step S3, the heating and stirring temperature is 60-80℃, and the heating time is 1-2 hours.

6. The method for preparing a mixed-bonded isothiocyanate nonlinear optical crystal according to claim 4, characterized in that, In step S5, the programmed heating rate is 1-3℃ / hour, the temperature is increased to 160-200℃, and the isothermal reaction time is 3-5 days.

7. The method for preparing a mixed-bonded isothiocyanate nonlinear optical crystal according to claim 4, characterized in that, In step S6, the cooling rate of the process is 5-10°C / hour.

8. The method for preparing a mixed-bonded isothiocyanate nonlinear optical crystal according to claim 4, characterized in that, The raw materials include: The molar ratio of the zinc source to the sulfur source is 4.0-4.2:1; The molar ratio of the 1,2,4-triazole to the sulfur source is 4.0-7.2:1; The molar ratio of the thiocyanate to the sulfur source is 5.0-6.0:

1.

9. The method for preparing a mixed-bonded isothiocyanate nonlinear optical crystal according to claim 8, characterized in that, In step S4, the molar ratio of triethanolamine to the sulfur source is 0.2-3.5:

1.

10. The method for preparing a mixed-bonded isothiocyanate nonlinear optical crystal according to claim 4, characterized in that, In step S5, the filling degree of the mixture in the reactor is 65-75%.

Images