An ultraviolet nonlinear optical crystal material, a preparation method and application thereof

Abstract

The application belongs to the field of nonlinear optical materials, and relates to a kind of ultraviolet nonlinear optical crystal material and its preparation method and application.The crystal chemical formula of the ultraviolet nonlinear optical crystal material is Zn (C5H4NO) 2, C5H4NO represents 4-hydroxy pyridine, 4-hydroxy pyridine is combined with Zn 2+ Form [ZnN2O2] tetrahedron by coordination bond;The crystal belongs to the orthorhombic system, and the space group is Fdd2.The band gap of the ultraviolet nonlinear optical crystal material is 4.40eV, the second harmonic generation is as high as 13.6xKDP, the birefringence Δn at 532nm wavelength is 0.073, the birefringence Δn at 1064nm wavelength is 0.074, and it shows photoluminescence characteristics, has phosphorescence with a lifetime of 558ms under the excitation light with a wavelength of 330-420nm, and blue afterglow with a naked eye visible and a duration of 5s.In addition, the ultraviolet nonlinear optical crystal material has strong water resistance, thermal stability and environmental stability, and has good application prospect in the field of nonlinear optical materials.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nonlinear optical materials, in particular to an ultraviolet nonlinear optical crystal material and a preparation method and application thereof. BACKGROUND

[0002] The ultraviolet nonlinear optical crystal material is a kind of material with nonlinear optical effect in the ultraviolet region, which plays an important role in the field of optoelectronic information function. The ultraviolet nonlinear optical crystal material requires nonlinear optical effect greater than 1 times of potassium dihydrogen phosphate crystal (1xKDP), band gap exceeding 4.2eV and moderate birefringence (Δn) for phase matching. In the prior art, the ultraviolet nonlinear optical crystal material has poor environmental stability, poor thermal stability and poor water resistance, which limits its development in the field of laser technology. SUMMARY

[0003] The present application provides an ultraviolet nonlinear optical crystal material and a preparation method and application thereof, to solve the problems of poor environmental stability, poor thermal stability and poor water resistance of the ultraviolet nonlinear optical crystal material in the related art.

[0004] The technical scheme provided by the present application is as follows:

[0005] In a first aspect, the present application provides an ultraviolet nonlinear optical crystal material, the crystal chemical formula of which is Zn(C5H4NO)2, C5H4NO represents 4-hydroxypyridine, and 4-hydroxypyridine and Zn 2+ form a [ZnN2O2] tetrahedron through coordination bond combination; the crystal belongs to the orthorhombic system, and the space group is Fdd2.

[0006] 4-hydroxypyridine and Zn 2+ combine according to the following structural formula:

[0007]

[0008] In combination with the first aspect of the present application, in some embodiments, the ultraviolet nonlinear optical crystal material has a regular lattice-like two-dimensional layer structure, the [ZnN2O2] tetrahedron has consistent atomic arrangement on the same two-dimensional layer and consistent atomic arrangement on different two-dimensional layers.

[0009] In combination with the first aspect of the present application, in some embodiments, the unit cell parameters of the crystal are as follows: α=90°, β=90°, γ=90°, Z=8.

[0010] In combination with the first aspect of the present application, in some embodiments, the band gap of Zn(C5H4NO)2 is 4.40eV.

[0011] In combination with the first aspect of the present application, in some embodiments, the birefringence of Zn(C5H4NO)2 is Δn=0.073 at a wavelength of 532 nm, and Δn=0.074 at a wavelength of 1064 nm.

[0012] In combination with the first aspect of the present application, in some embodiments, the ultraviolet nonlinear optical crystal material has phosphorescence and blue afterglow under excitation light with a wavelength of 330-420 nm.

[0013] In the second aspect, the present application provides a preparation method of the ultraviolet nonlinear optical crystal material, comprising the following steps: uniformly mixing 4-hydroxypyridine and a zinc source according to a molar ratio of 4:1-2, and keeping the mixture at a temperature of 155-200 ℃ for at least 72 hours. 2+ After cooling, the unreacted substances are washed away to obtain the ultraviolet nonlinear optical crystal material.

[0014] In combination with the second aspect of the present application, in some embodiments, the molar ratio of 4-hydroxypyridine to the zinc source is 5:1-2; and / or, the zinc source is ZnF2; and / or, the keeping temperature is 180 ℃±10 ℃; and / or, the unreacted substances are washed away by alcohol and / or water. 2+

[0015] In the third aspect, the present application provides an application of the above ultraviolet nonlinear optical crystal material in the field of nonlinear optics.

[0016] In combination with the third aspect of the present application, in some embodiments, the application comprises the application in deep ultraviolet laser lithography, semiconductor chip defect detection, short-wave communication, high-density storage, biological tissue imaging, laser micro-processing, military confrontation, and environmental monitoring.

[0017] Compared with the prior art, the above technical solutions provided by the embodiments of the present application have the following advantages:

[0018] 1. The present application first increases the second harmonic generation response of the zinc-based metal organic complex ultraviolet nonlinear optical crystal material to 13.6×KDP, which is much higher than that of other zinc-based metal organic complex ultraviolet nonlinear optical crystal materials.

[0019] 2. The ultraviolet nonlinear optical crystal material provided by the present application has a room temperature phosphorescence lifetime of up to 558 ms, which is much longer than that of existing metal-based phosphorescent materials. In addition, the ultraviolet nonlinear optical crystal material also has a persistent blue afterglow of up to 5 s, which can be observed by the naked eye.

[0020] 3. The ultraviolet nonlinear optical crystal material provided by the present application has a band gap of 4.40 eV, good thermal stability, environmental stability and water resistance, and exhibits stable application potential. BRIEF DESCRIPTION OF DRAWINGS

[0021] ​In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort based on these drawings.

[0022] Figure 1 (a) 0kl plane diffraction pattern, (b) h0l plane diffraction pattern, (c) hk0 plane diffraction pattern, and (d) unit cell structure of Zn(C5H4NO)2.

[0023] Figure 2 Crystal structure of Zn(C5H4NO)2: (a) local coordination environment of Zn; (b) two-dimensional plane structure (100) view; (c) (010) structure view. The polarization alignment of each Zn(C5H4NO)2 tetrahedron is indicated by blue arrows.

[0024] Figure 3 Evolution of different coordination modes and alignment of each tetrahedral dipole moment in Zn(C5H4NO)2 (a) (Example 1) and Zn(C5H5NO)2Cl2 (b) (Comparative Example 1).

[0025] Figure 4 Optical properties of Zn(C5H5NO)2Cl2 and Zn(C5H4NO)2: (a) band gap values of Zn(C5H5NO)2Cl2 and Zn(C5H4NO)2 obtained by Kubelka-Munk method; (b) SHG intensity of Zn(C5H4NO)2 and KDP as a function of particle size at 1064 nm laser wavelength (the SHG intensity comparison of samples and KDP in the 280-450 nm particle size range is shown); (c) SHG intensity of Zn(C6H8N)2SO4, Zn(C5H9NO2)2Cl2, [Zn(H-ntb)] n , Zn2(bpp)(pht)2, [Zn(bct)(H2O)2], Zn(C6H4NO2)2, Zn(S,S)C 14 H 14 N2O6, Zn(R,R)C 14 H 14 N2O6 and Zn(C5H4NO)2.

[0026] Figure 5 (a) electron density difference map of Zn(C5H4NO)2; (b) theoretical SHG coefficient of Zn(C5H4NO)2; SHG weighted density of (c) imaginary electron occupancy density map and (d) imaginary hole occupancy density map in Zn(C5H4NO)2.

[0027] Figure 6 Experimental and simulated XRD patterns of Zn(C5H4NO)2.

[0028] Figure 7 Experimental and simulated XRD patterns of Zn(C5H5NO)2Cl2.

[0029] Figure 8 Infrared spectra of Zn(C5H4NO)2.

[0030] Figure 9 Infrared spectra of Zn(C5H5NO)2Cl2.

[0031] Figure 10 Refractive index of Zn(C5H4NO)2.

[0032] Figure 11 Relative stability between Zn(C5H5NO)2Cl2and Zn(C5H4NO)2: (a) thermal stability, and (b) resistance to water.

[0033] Figure 12 Comparison of resistance to water of Zn(C5H5NO)2Cl2(a) and Zn(C5H4NO)2(b).

[0034] Figure 13 Comparison of SHG intensity of Zn(C5H4NO)2before and after soaking in water (particle size: 280-450 μm).

[0035] Figure 14 Fluorescence spectra of Zn(C5H4NO)2(excitation wavelength 330-420 nm).

[0036] Figure 15 Phosphorescence spectra of Zn(C5H4NO)2(excitation wavelength 330-420 nm).

[0037] Figure 16 Decay curves of Zn(C5H5NO)2Cl2(λ ex = 365 nm, λ em = 450 nm).

[0038] Figure 17 Photoluminescence tests of Zn(C5H4NO)2: (a) Normalized emission spectrum of Zn(C5H4NO)2; (b) Phosphorescence spectrum and afterglow photo of Zn(C5H4NO)2at 365 nm; (c) λ ex = 365 nm and λ em=420nm when the luminescence decay of Zn(C5H4NO)2; (d) temperature dependence test of Zn(C5H4NO)2; (e) afterglow photo of Zn(C5H4NO)2. DETAILED DESCRIPTION

[0039] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0040] Unless otherwise specifically defined, the terms used herein are understood as having the meanings commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meanings as generally understood by a person of ordinary skill in the art to which the present application belongs. If there is a conflict, the present specification takes precedence.

[0041] Zinc-based metal organic complex nonlinear optical materials have important application potential in the field of nonlinear optics, especially in the aspects of optical limiting, optical switching and ultrafast laser technology, etc., but the phosphorescent lifetime, thermal stability, environmental stability and water resistance of the existing zinc-based metal organic complex nonlinear optical materials are not ideal.

[0042] In order to solve the above problems, the present application provides a kind of ultraviolet nonlinear optical crystal material, its crystal chemical formula is Zn(C5H4NO)2, C5H4NO represents 4-hydroxy pyridine, 4-hydroxy pyridine is combined with Zn 2+ Form [ZnN2O2] tetrahedron by coordination bond combination;The crystal belongs to orthorhombic system, and the space group is Fdd2.

[0043] 4-hydroxy pyridine is combined with Zn 2+ According to the following structural formula:

[0044]

[0045] The ultraviolet nonlinear optical crystal material is referred to as the ultraviolet nonlinear optical crystal material with the crystal chemical formula Zn(C5H4NO)2 below.

[0046] As shown in Figure 2 The ultraviolet nonlinear optical crystal material has a regular lattice-like two-dimensional layer structure, the [ZnN2O2] tetrahedron has a consistent atomic arrangement on the same two-dimensional layer, and the atomic arrangement is consistent on different two-dimensional layers.

[0047] The unit cell parameters of Zn(C5H4NO)2 are as follows: a = 90°, β = 90°, γ = 90°, Z = 8.

[0048] The band gap of Zn(C5H4NO)2 is 4.40 eV, and the birefringence Δn is 0.073 at 532 nm and 0.074 at 1064 nm. Zn(C5H4NO)2 exhibits photoluminescence properties, with phosphorescence under excitation light of 330-420 nm with a lifetime of up to 558 ms and a rare, visually perceptible, blue afterglow with a duration of up to 5 s, the phosphorescence lifetime being significantly longer than that of existing metal-based phosphorescent materials (see Table 5).

[0049] In addition, the SHG of Zn(C5H4NO)2 can reach 13.6xKDP, which is the highest among all zinc-based metal-organic complex nonlinear optical materials, and the reason is that, as shown in its structural formula, Zn(C5H4NO)2 has a coordination mode different from that of the traditional 4-hydroxypyridine ligand. The strong coordination interaction between Zn 2+ and the 4-hydroxypyridine ligand forces the polarization of the [ZnO2N2] tetrahedral building unit to align uniformly, which produces very strong SHG, reaching 13.6xKDP.

[0050] In addition, Zn(C5H4NO)2 has a high thermal stability of up to 300°C, excellent environmental stability and strong water resistance.

[0051] As shown in Figure 1 , the non-centrosymmetric (NCS) Zn(C5H4NO)2 crystallizes in the orthorhombic system Fdd2 (no. 43), and each Zn 2+ is coordinated by four monodentate 4-hydroxypyridine ligands to form a distorted [ZnN2O2] tetrahedron Figure 2 a), in which the Zn-N bond length is the Zn-O bond length is within the normal bond length range. At the same time, according to the charge difference density map Figure 5 a), the zinc atom in the [ZnN2O2] unit is positively charged, while the oxygen atom is negatively charged, so that the [ZnN2O2] unit is polarized. Notably, the (C5H4NO) - group acts as a monodentate ligand, with the pyridine nitrogen atom and the deprotonated hydroxyl oxygen atom both coordinating to zinc. This is quite unusual, similar to the inorganic monodentate ligand thiocyanate (SCN - ). Zn(C5H4NO)2 forms highly oriented two-dimensional layers in the bc plane of the coordinate system Figure 2 b), and is tightly stacked along the a axis through edge-to-face π-π interactions. These layers stack without inverting and maintain the same orientation Figure 2c), which results in all organic ring ligands (C5H4NO) - (0→N direction along the c-axis) of the same direction. In addition, the organic ring ligand (C5H4NO) - has rigidity due to the planar π-conjugation effect, resulting in the formation of a regular lattice-like two-dimensional layer structure having a [ZnN2O2] tetrahedron.

[0052] By calculating the dipole moment of these compounds, it is found that although the [ZnN2O2] tetrahedron of different planes is deflected by a certain angle, the rotation axis of this deflection coincides with the direction of the dipole moment of the [ZnN2O2] tetrahedron, which results in that this deflection does not affect the size or direction of the dipole moment of the [ZnN2O2] tetrahedron (along the c-axis direction) (Table 3, Figure 3 ). This unique NCS structure produces a strong SHG effect.

[0053] Preparation method:

[0054] The present application provides a preparation method of a UV nonlinear optical crystal material, comprising the following steps: uniformly mixing 4-hydroxypyridine and a zinc source according to a molar ratio greater than 2, and keeping the mixture at 155-200°C for at least 72 hours, and then washing away the unreacted substances after cooling to obtain the UV nonlinear optical crystal material. 2+

[0055]

[0056] The present application controls the molar ratio of 4-hydroxypyridine and Zn 2+ to be greater than 2, which can ensure that 4-hydroxypyridine is in excess and can react with Zn 2 + to form Zn(C5H4NO)2. In some embodiments of the present application, the molar ratio of 4-hydroxypyridine and ZnF2 is 5:1-2. The zinc source is preferably ZnF2, and the unreacted 4-hydroxypyridine is removed by washing with water or ethanol after the reaction.

[0057] The present application controls the reaction temperature in the range of 155-200°C, which can ensure that 4-hydroxypyridine is melted but not carbonized and decomposed, and after 4-hydroxypyridine is melted, it reacts with ZnF2 to form the complex structure 1.

[0058] The Zn(C5H4NO)2 provided by the present application is synthesized by a low-temperature solid-phase method according to formula (1), and the yield is 83.5% (calculated based on zinc). During the reaction process, the raw material 4-hydroxypyridine (compound 3) loses the hydroxyl hydrogen at high temperature, generates the intermediate 4 and HF under the action of zinc fluoride, and then the intermediate 4 has two active sites to react with Zn 2+ ​The coordination forms a complex structure 1, namely Zn(C5H4NO)2. The complex structure 1 is well resolved by advanced three-dimensional precision electron diffraction tomography (Table 1). By analyzing the diffraction patterns of 0kl, h0l and hk0 planes and the reconstructed dynamic refinement pattern, the positions of all C, H, O, N, Zn atoms are determined, and finally the structure is well determined Figure 1 ). The powder X-ray diffraction data confirm the consistency and purity of the phase, and the fully specified experimental observation PXRD pattern also confirms the accuracy of the 3D ED structure refinement.

[0059] Application:

[0060] The ultraviolet nonlinear optical crystal material Zn(C5H4NO)2 provided by the application has good thermal stability at 300°C, excellent environmental stability and strong water resistance, and has good application prospects in the field of nonlinear optics. For example, in the applications of deep ultraviolet laser lithography, semiconductor chip defect detection, short wave communication, high density storage, biological tissue imaging, laser micro machining, military confrontation and environmental monitoring.

[0061] Embodiment:

[0062] The ultraviolet nonlinear optical crystal material and the preparation method thereof provided by the application are described in detail through specific embodiments as follows:

[0063] In order to compare the structure and performance, Zn(C5H4NO)2 is synthesized by a low-temperature solid-phase method in Example 1 of the application, and the reaction formula is shown as formula (1). The center-symmetric compound Zn(C5H5NO)2Cl2 is synthesized by a hydrothermal method in Comparative Example 1. The main difference between the two is that the coordination atoms around Zn are different. It is found that Zn(C5H5NO)2Cl2 and Zn(C5H4NO)2 also use 4-hydroxypyridine as a ligand, but exhibit completely different structures and properties. The applicant finds that in the synthesis of Zn(C5H5NO)2Cl2, 4-hydroxypyridine (compound 3) first removes H + from the hydroxyl group to obtain intermediate 4, and then the N atom in intermediate 4 reacts with water in the system to obtain a protonated compound, and the protonated compound undergoes structural intercalation to form Zn(C5H5NO)2Cl2. Since Zn(C5H5NO)2Cl2 has only one active site, it is formed with ZnCl2, and its structure is completely different from that of Zn(C5H4NO)2 Figure 3 ). In Zn(C5H5NO)2Cl2 (C2 / c, no. 15), Zn 2+ forms a [ZnO2Cl2] tetrahedron, and the main Zn-O, C-O and C-N bond lengths are consistent with those of Zn(C5H4NO)2.

[0064] The band gap of Zn(C5H5NO)2Cl2 and Zn(C5H4NO)2 was calculated using the Kubelka-Munk method to explore its potential application in the ultraviolet range, as Figure 4 As shown in a, the band gap of Zn(C5H4NO)2 is 4.40 eV, which is greater than the band gap of Zn(C5H4NO)2Cl2 of 4.11 eV, indicating that it has a wide range of light transmission in the ultraviolet range, indicating its potential application potential in the ultraviolet range.

[0065] The linear and nonlinear optical properties of Zn(C5H4NO)2 were calculated, and it was found that the Δn cal of Zn(C5H4NO)2 is 0.073@532 nm and Δn cal. = 0.074@1064 nm, which is moderate and meets the phase matching condition of ultraviolet nonlinear optical materials. Figure 10

[0066] The SHG intensity of Zn(C5H4NO)2 was measured at 1064 nm by using the Kurtz-Perry powder SHG test method, using the reference KDP material as a reference. Figure 4 As shown in b, the SHG intensity increases with the increase of particle size and reaches a plateau in the range of 280-450 μm, indicating that it can achieve phase matching.

[0067] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or prepared by existing methods. The zinc fluoride (ZnF2, 99%, Macklin), zinc chloride (ZnCl2, 99%, Macklin), and 4-hydroxy pyridine (C5H5NO, 99%, Macklin) used in the examples of the present application were not further purified and were used directly.

[0068] The following is the characterization method of the material:

[0069] (1) Electron diffraction tomography (PEDT) 3D ED:

[0070] Grind the Zn(C5H5NO)2 polycrystalline sample, then transfer it to a test tube, ultrasonic treatment in anhydrous ethanol for 5 minutes, then drop on a carbon film coated copper mesh and dry in air for 5 min. PEDT 3D ED data were collected on a FEI Tecnai G2F20 transmission electron microscope (200 kV) equipped with a Gatan 832 camera. The processing speed was 100 Hz, and the exposure time of each frame was 2 s. The data reduction was processed using the PETS2.0 program. The structure was determined from scratch using the charge flipping algorithm in the Superflip program. Dynamic refinement of PEDT data was completed in the program. ​

[0071] (2) Single crystal X-ray diffraction:

[0072] Single crystal X-ray diffraction (SC-XRD) data of Zn(C5H5NO)2Cl2sample was collected on an XtaLAB Synergy R equipped with a graphite monochromator, using Mo Kα radiation Carried out at 298 K. The crystal structure was solved by direct methods with Olex2 and refined by least-squares techniques on anisotropic displacement parameters for all atoms.

[0073] (3) Powder X-ray diffraction (PXRD):

[0074] Powder X-ray diffraction data were recorded on an Advance diffractometer at a temperature of 40 kV, 100 mA, Cu Kα1 radiation (Bruker D8, radiation wavenumber 1.5406 A) with a scan speed of 10° / min and a scan angle range of 10-70°. The phase purity was determined by powder X-ray diffraction.

[0075] (4) Infrared spectroscopy

[0076] Infrared spectra were collected on a Nicolet iS5 Fourier transform infrared spectrometer at room temperature in the wavelength range of 4000-400 cm -1 -1. The sample and dry KBr were mixed in a weight ratio of 1 : 100 and ground into a tablet for measurement.

[0077] (5) UV-Vis diffuse reflectance spectroscopy

[0078] UV-Vis diffuse reflectance spectroscopy was obtained using a Varian Cary 5000 spectrophotometer at room temperature with a scan range of 200-800 nm. The spectrum of pure barium sulfate was chosen as a reference (100% reflectance) and a ground powder sample was coated on its surface for testing.

[0079] (6) Phosphorescence spectroscopy

[0080] Phosphorescence excitation spectra and luminescence emission decay of the samples were obtained using a Hitachi F-4700 spectrofluorometer.

[0081] (7) Thermal analysis

[0082] Thermogravimetric analysis (TGA) was performed using a Netzsch STA449F5 analyzer. The specific method is to weigh about 0.8 mg of sample, put it into a platinum crucible, and heat it from room temperature to 800°C at a rate of 10 K·min -1 under N2 gas atmosphere.

[0083] (8) Second harmonic generation measurement

[0084] Second-order nonlinear optical measurements were performed on the powder samples at room temperature and the SHG effect of the powder samples was measured using the modified Kurtz and Perry method using a Q-switched 1064 nm Nd:YAG laser. The polycrystalline sample of the compound was sieved into different particle sizes (35-50, 50-74, 74-100, 100-154, 154-180, 180-280 and 280-450 pm) to investigate whether its SHG response can be phase matched. The reference material KH2PO4 (KDP) was chosen for comparison with the sample's SHG efficiency to evaluate the second-order NLO effect of the measured sample.

[0085] (9) Calculation method

[0086] The first-principle calculation of Zn(C5H4NO)2 was based on the CASTEP module of the Materials Studio software package and was performed by systematic geometry optimization through density functional theory. The exchange-correlation functional was described by the generalized gradient approximation Heyd-Scuseria-Ernzerhof (HSE06), the cutoff energy was set to 550 eV, and a Monkhorst-Pack k-point grid of 3x3x3 was selected in the first Brillouin zone to ensure the accuracy of the calculation results. The self-consistent iteration convergence (SCF) was 5.0x10 -7 eV / atom, and the maximum displacement convergence was The internal stress was 0.1 GPa, and the force on the atom was The energy was converged within 2.0x10 -6 eV / atom. The ion-electron interaction of all atoms was through the ultra-soft pseudo-potential model, and the atomic electron configuration was: C (2s 2 2p 2 ), H (1s 1 ), N (2s 2 2p 3 ), O (2s 2 2p 4 ), Zn (3d 10 4s 2 ).

[0087] Example 1: Synthesis of compound Zn(C5H4NO)2 by low-temperature solid-phase method:

[0088] ZnF2 (1 mmol, 0.103 g) and 4-hydroxypyridine (crystal chemical formula C5H5NO, 5 mmol, 0.475 g) were ground together in a marble mortar for 5 min to mix homogeneously, and then the mixture was transferred to a polytetrafluoroethylene-lined reactor. The reactor was heated to 180 °C in an oven for 72 h, and then slowly cooled to 30 °C at a rate of 3 °C / h. The resulting product was repeatedly ultrasonicated with deionized water and anhydrous ethanol to obtain Zn(C5H4NO)2crystals in the form of white powder (yield of 83.5% based on Zn).

[0089] Comparative Example 1: Synthesis of compound Zn(C5H5NO)2Cl2 by simple hydrothermal method

[0090] In order to compare the structure and properties of Zn(C5H4NO)2, this comparative example prepared a centrosymmetric compound Zn(C5H5NO)2Cl2 closely related to Zn(C5H4NO)2:

[0091] ZnCl2 (1 mmol, 0.136 g), 4-hydroxypyridine (2 mmol 0.172 g) and 3 mL of deionized water were added to a hydrothermal reactor, which was raised from room temperature to 150 °C for 24 h, and then slowly cooled to room temperature at a rate of 5 °C / h to obtain Zn(C5H5NO)2Cl2crystals in the form of colorless blocks (yield of 75.5% based on Zn).

[0092] Characterization and results:

[0093] The samples obtained in Example 1 and Comparative Example 1 were characterized, and the results are as follows:

[0094] Table 1 Crystallographic data of the sample prepared in Example 1

[0095]

[0096]

[0097] As can be seen from Table 1, the crystal chemical formula of the sample prepared in Example 1 can be expressed as Zn(C5H4NO)2, the crystal structure is orthorhombic, the space group is Fdd2 (no. 43), and the unit cell parameters are: α = 90°, β = 90°, γ = 90°, Z = 8.

[0098] Table 2 Atomic coordinates, equivalent isotropic displacement parameters and occupancy of Zn(C5H4NO)2 prepared in Example 1

[0099]

[0100] Table 3Zn(C5H4NO)2, Zn(C5H5NO)2Cl2, C5H5NO, C5H4NO - 、C5H5NO calculated dipole moment component

[0101]

[0102]

[0103] Table 4 Crystal data and structure refinement of Zn(C5H5NO)2Cl2 of the sample prepared in Comparative Example 1

[0104]

[0105] As shown in Table 4, the crystal chemical formula of the sample prepared in Comparative Example 1 of the present invention can be expressed as Zn(C5H5NO)2Cl2. Furthermore, the crystal data show that the Zn(C5H4NO)2 prepared in Example 1 and the Zn(C5H5NO)2Cl2 prepared in Comparative Example 1 both use 4-hydroxypyridine as a ligand, yet exhibit completely different structures and properties.

[0106] Table 5 Comparison of phosphorescence lifetime of Zn(C5H4NO)2 and reported metal-based phosphorescent materials

[0107]

[0108] As can be seen from Table 5, the phosphorescence lifetime of Zn(C5H4NO)2 prepared by the present invention far exceeds that of reported metal-based phosphorescent materials. Due to the long emission lifetime of phosphorescent materials, they can continue to emit light after the excitation stops, which can eliminate the interference of short-lived fluorescence, so that they can still be clearly displayed in an environment with strong background light or fluorescence interference, providing a higher signal-to-noise ratio, which is particularly important for applications requiring high contrast and clarity, such as bioimaging and information encryption. In addition, this performance is also very useful in anti-counterfeiting and security applications, and can be used in advanced anti-counterfeiting and encryption fields. Since the long life can provide a more stable light source, Zn(C5H4NO)2 also has application potential in LED lighting and laser technology. Compared with traditional metal-based phosphorescent materials, the Zn(C5H4NO)2 provided by the present invention has the characteristics of low toxicity, low cost and high flexibility, which makes them show great application prospects in many fields.

[0109] like Figure 4As shown in Figure 2b, the SHG intensity of Zn(C5H4NO)2 increases with increasing particle size and reaches a plateau in the particle size range of 280-450μm, meeting the phase matching condition. Specifically, the maximum SHG intensity of Zn(C5H4NO)2 is 13.6 times that of KH2PO4, which is the strongest among the recently reported zinc-based metal complex ultraviolet nonlinear optical crystal materials ( Figure 4 c).

[0110] like Figure 11 As shown in a, Zn(C5H4NO)2 exhibits excellent thermal stability and does not decompose significantly below 300°C. Figure 11 b and Figure 12 It was shown that the structural integrity of Zn(C5H4NO)2 remained unchanged after exposure to ambient air and humidity for up to 6 months, with no obvious degradation or deliquescence. The present inventors further experimentally studied the water resistance of Zn(C5H4NO)2 and Zn(C5H5NO)2Cl2 and found that Zn(C5H5NO)2Cl2 dissolved rapidly in water and completely dissolved in about 10 minutes, while Zn(C5H4NO)2 remained insoluble after being immersed in water for 10 days. The inventors analyzed that Zn(C5H4NO)2 is insoluble in water because it has a polar structure. In addition, it is worth noting that, Figure 13 As shown in the figure, the SHG intensity of Zn(C5H4NO)2 did not change after being immersed in 1064nm laser irradiation for 10 days, indicating that it has stable performance in extreme environments and high potential application value.

[0111] like Figure 17 As shown in e, Zn(C5H4NO)2 shows photoluminescence properties, emitting blue light for 5s after being excited by 365nm ultraviolet light. It has emission peaks at 440nm and 420nm ( Figure 14 , Figure 15 , Figure 17 b). TRPL shows that the lifetime of Zn(C5H4NO)2 is 588ms and that of Zn(C5H5NO)2Cl2 is 183ms ( Figure 16 , Figure 17 c), which is the longest among zinc-based semi-organic crystals (Table 5). In addition, based on the normalized profile ( Figure 16 ) and temperature-dependent photoluminescence (PL) studies ( Figure 17 d), delayed fluorescence (DF) may exist in Zn(C5H4NO)2.

[0112] First-principles calculations using CASTEP in Materials Studio show that Zn(C5H4NO)2 has significant π-π stacking between its organic rings A and B, with a distance of The HOMO is mainly from the (C5H4NO)-π orbital, while the LUMO is from the π* orbital. This interaction enhances the spin-orbital coupling, improving the light-emitting efficiency of the compound.

[0113] Theoretical calculations show that Zn(C5H4NO)2 has a direct band gap of 4.38 eV, which is very consistent with the experimental result of 4.40 eV. DOS and PDOS analysis reveals that the conduction band is mainly composed of C-2p, N-2p and O-2p states, the valence band is mainly composed of N-2p, O-2p and C-2p orbitals, and the participation of Zn-3d is minimal. The band gap is mainly affected by the interaction of the C-O bond in the ring with the C-C and C-N bonds and the interaction of the ring with Zn - . 2+

[0114] The second-order nonlinear optical coefficient (d ij ) of Zn(C5H4NO)2 is calculated to be d 31 = 9.71, d 32 = 21.7, and d 33 = 16.52 × 10 -9 pm / V at 1064 nm (1.165 eV). The d 36 value of KDP is 0.39 pm / V Figure 4 b), and the calculated d 32 is 21.7 times that of KDP.

[0115] The above description is only a specific embodiment of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features applied herein.​

Claims

1. An ultraviolet nonlinear optical crystal material, characterized in that: The crystal chemical formula is Zn(C5H4NO)2, C5H4NO represents 4-hydroxypyridine, 4-hydroxypyridine and Zn 2+ [ZnN2O2] tetrahedron is formed by coordination bonds; the crystal belongs to the orthorhombic crystal system and the space group is Fdd2.

2. The ultraviolet nonlinear optical crystal material according to claim 1, characterized in that: The ultraviolet nonlinear optical crystal material has a regular lattice-shaped two-dimensional layer structure, and the atomic arrangement of the [ZnN2O2] tetrahedron is consistent on the same two-dimensional layer and on different two-dimensional layers.

3. The ultraviolet nonlinear optical crystal material according to claim 1, characterized in that: The unit cell parameters of the crystal are: α=90°, β=90°, γ=90°, Z=8.

4. The ultraviolet nonlinear optical crystal material according to claim 1, characterized in that: The band gap of Zn(C5H4NO)2 is 4.40eV.

5. The ultraviolet nonlinear optical crystal material according to claim 1, characterized in that: The birefringence of Zn(C5H4NO)2 at a wavelength of 532 nm is Δn=0.073, and the birefringence at a wavelength of 1064 nm is Δn=0.

074.

6. The ultraviolet nonlinear optical crystal material according to claim 1, characterized in that: The ultraviolet nonlinear optical crystal material has phosphorescence and blue afterglow under the excitation light with a wavelength of 330-420nm.

7. A method for preparing an ultraviolet nonlinear optical crystal material, characterized in that: The process comprises the following steps: 2+ The 4-hydroxypyridine and the zinc source are mixed uniformly at a molar ratio greater than 2, kept at 155-200° C. for at least 72 hours, cooled, and unreacted products are washed away to obtain an ultraviolet nonlinear optical crystal material.

8. The method for preparing the ultraviolet nonlinear optical crystal material according to claim 7, wherein: 4-Hydroxypyridine and Zn 2+ The molar ratio is 5:1 to 2; and / or, The zinc source is ZnF2; and / or, The holding temperature is 180℃±10℃; and / or, The unreacted products are washed away with alcohol and / or water.

9. Use of the ultraviolet nonlinear optical crystal material according to any one of claims 1 to 6 in the field of nonlinear optics.

10. The use according to claim 9, characterized in that: The applications include deep ultraviolet laser lithography, semiconductor chip defect detection, shortwave communications, high-density storage, biological tissue imaging, laser micromachining, military confrontation, and environmental monitoring.

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