Zeolite-like structure nitrogen oxide silicate nonlinear optical crystal as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of nonlinear optical crystals, and particularly relates to a zeolite-like structure nitrogen oxide silicate nonlinear optical crystal and a preparation method and application thereof, the chemical general formula of the crystal is Ba3Si3N5OCl, the crystal belongs to a hexagonal system, the cell parameters of the crystal are as follows: a is 9.5147 (6), c is 5.5002 (4), V is 431.22 (6) 3, Z is 2, the space group is P-62c, and the crystal has a non-centrosymmetric structure. The Ba3Si3N5OCl crystal provided by the invention is used as a novel zeolite-like structure nitrogen oxide silicate, successfully integrates nonlinear optical activity and phase matching capability, can generate frequency doubling response which is about 0.2 times of KDP (potassium dihydrogen phosphate) under 1064 nm laser pumping, and can realize phase matching, so that the Ba3Si3N5OCl crystal becomes a nonlinear optical material with practical device application potential.

Description

Technical Field

[0001] This invention relates to a zeolite-like structure oxynitride silicate nonlinear optical crystal, its preparation method and application, belonging to the field of nonlinear optical crystal technology. Background Technology

[0002] Zeolites are a class of three-dimensional network aluminosilicate crystal materials with a regular porous structure, formed by [TO4] tetrahedra (T is usually Si, Al, etc.) connected by shared vertices. Due to their unique porous structure and high specific surface area, zeolites have wide applications in industrial processes such as catalysis, ion exchange, adsorption, and separation.

[0003] In recent years, with the development of synthetic techniques, a series of oxynitride silicate materials have been developed by introducing nitrogen atoms to partially replace oxygen atoms in the framework of oxynitride silicates. Due to the differences between nitrogen and oxygen in electronegativity, coordination mode, and charge distribution, the introduction of nitrogen significantly enriches the framework structure and chemical diversity of these materials, expanding the research scope of traditional zeolite chemistry. For example, the research team of Schnick et al. has successively reported a variety of oxynitride silicates and oxynitride phosphates with AB2-type tetrahedral network structures. These materials exhibit diverse structural features and physicochemical properties. For instance, the compound P4N4(NH)4(NH3) with a PN(NH)-type cage structure shows potential in ammonia adsorption and storage, and Ba3P5N with a JOZ-type structure... 10 X:Eu 2+ / Ce 3+ Phosphors can be used in light-emitting devices excited by blue light chips.

[0004] In the field of nonlinear optical materials, nitrides (oxides) also show promising application prospects. For example, the M2Si5N8 (M=Ca,Sr,Ba) material system has a high refractive index and excellent effective optical quality factor (Merit Meff value), and its nonlinear optical performance is comparable to that of the benchmark material LiIO3. Second-order nonlinear optical crystals are core components in technologies such as laser frequency conversion, optical communication, and holographic storage, and their performance directly determines the efficiency of related devices. However, the overall performance of existing nonlinear optical materials is still insufficient to fully meet the ever-increasing technological demands. Therefore, developing novel and efficient nonlinear optical crystal materials has significant scientific research value and practical application value. Summary of the Invention

[0005] To address the aforementioned technical problems in the prior art, this invention provides a zeolite-like structure oxynitride silicate nonlinear optical crystal, its preparation method, and its applications.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: One objective of this invention is to provide a zeolite-like structure oxynitride silicate nonlinear optical crystal with the general chemical formula Ba3Si3N5OCl, belonging to the hexagonal crystal system, and with cell parameters a=9.5147(6)Å, c=5.5002(4)Å, and V=431.22(6)Å. 3 Z=2, space group is P-62c, and it has a non-centrosymmetric structure.

[0007] The structure of the zeolite-like oxynitride silicate nonlinear optical crystal of the present invention is as follows: [SiN4] tetrahedrons are used as the basic structural units. These tetrahedrons are connected by shared vertices to form structural units containing three-membered and six-membered rings, and further constructed into a highly condensed three-dimensional quadruple network framework; Ba 2+ The ions are distributed in six independent crystallographic sites within the voids of this three-dimensional framework.

[0008] Based on the above technical solution, the present invention can also be improved as follows: Furthermore, the crystal generates second harmonics under 1064nm laser light, with a frequency doubling efficiency ≥0.1 times KDP (potassium dihydrogen phosphate), and can achieve phase matching.

[0009] Furthermore, the average particle size of the crystal is ≥200μm.

[0010] Furthermore, the signal strength generated by the second harmonic of the crystal is responsive to changes in external pressure; when the external pressure exceeds 3.7 GPa, the signal strength of its second harmonic weakens.

[0011] The zeolite-like structure oxynitride silicate nonlinear optical crystal of the present invention has the following beneficial effects: I. The Ba3Si3N5OCl crystal provided by this invention is a novel zeolite-like structure oxynitride silicate that successfully combines nonlinear optical activity and phase matching capability. Under 1064 nm laser pumping, it can generate a frequency doubling response of about 0.2 times KDP and achieve phase matching, making it a nonlinear optical material with potential for practical device applications.

[0012] Second, the Ba3Si3N5OCl crystal provided by this invention exhibits unique pressure response characteristics. Its second harmonic signal will be significantly weakened or even turned off under external pressure exceeding 3.7 GPa. This characteristic makes it go beyond the scope of traditional nonlinear optical crystals that are only used for frequency conversion, and provides a unique material basis for the development of new pressure optical sensors or pressure-controllable optical switches.

[0013] Third, the crystal size of the present invention is considerable, with an average particle size of up to 500 micrometers and a maximum size of up to 1 mm, which is significantly better than similar oxynitride silicate crystals in the prior art, which are usually micrometer-sized (50 μm). This greatly facilitates the actual processing and performance testing of optical devices.

[0014] Fourth, the crystal material has the characteristic of melting with the same composition, indicating the feasibility of growing larger single crystals through the flux method, laying a solid foundation for its future industrial application.

[0015] The second objective of this invention is to provide a method for preparing the zeolite-like structure oxynitride silicate nonlinear optical crystal as described above, comprising the following steps: using a compound containing Ba and a compound containing Si as raw materials, adding a flux, and performing a high-temperature sintering reaction under a protective atmosphere or a reducing atmosphere to generate the crystal; wherein the flux is metallic Mg powder.

[0016] Furthermore, the Ba-containing compounds include BaCl2 and Ba3N2; the Si-containing compounds are amorphous Si3N4.

[0017] Furthermore, the molar ratio of BaCl2:Ba3N2:Si3N4:Mg is 0.3-0.5:1:0.9-1.2:1.5-2.0, and preferably, the molar ratio of BaCl2:Ba3N2:Si3N4:Mg is 0.4:1:1.14:1.7.

[0018] Furthermore, the protective atmosphere or reducing atmosphere is a mixture of N2 and H2, wherein the volume ratio of N2 to H2 is 8-10:1.

[0019] Furthermore, the sintering temperature of the high-temperature sintering reaction is 1350℃-1450℃, preferably 1400℃, and the sintering time is 5 hours-12 hours, preferably 8 hours.

[0020] The beneficial effects of the preparation method provided by this invention are as follows: Through ingenious process design, this invention successfully achieves the efficient and stable synthesis of large-size, high-quality nitride single crystals. This invention innovatively uses metallic Mg powder as a flux, significantly reducing the synthesis temperature to 1350℃-1450℃. Compared to the synthesis temperature of similar materials in the background technology (generally 1550℃-1600℃), the sintering temperature of this invention is reduced by approximately 200℃. This not only significantly reduces energy consumption and the stringent requirements for the high-temperature resistance of equipment, but also effectively reduces the volatilization and loss of raw materials at high temperatures, improving the economy and repeatability of the process. Simultaneously, this invention preferentially uses amorphous Si3N4 with higher reactivity as the silicon source, replacing the commonly used crystalline α-Si3N4, promoting mass transfer and diffusion of the raw materials during sintering, which is more conducive to crystal nucleation and growth, directly leading to the formation of large single crystals with an average size of 500 micrometers. The entire process is carried out in a N2-H2 reducing atmosphere. The operation steps are simple and clear, and the parameters are highly controllable, providing a reliable and easy-to-promote solution for the controllable preparation of this new type of functional material.

[0021] The third objective of this invention is to provide applications for the nonlinear optical crystals described above, primarily for the fabrication of nonlinear optical devices, pressure optical sensors, or pressure-controlled optical switches.

[0022] Furthermore, the nonlinear optical device is used for laser frequency conversion, photoelectric modulation, or optical signal processing.

[0023] The beneficial effects of the above-mentioned applications of this invention are as follows: This invention fully explores and utilizes the unique properties of Ba3Si3N5OCl crystal, opening up diversified application prospects in the field of optoelectronic technology. In the traditional field of nonlinear optics, this crystal can be used to manufacture nonlinear optical devices such as laser frequency converters, optoelectronic modulators, or holographic storage devices. Its value lies in providing a new and reliable nitride material option for related devices by utilizing its stable frequency doubling performance and phase matching capability. A more innovative application lies in putting its unique pressure response characteristics into practical use. This crystal can be used as a core sensing material to prepare pressure optical sensors or pressure-controllable optical switches. Its effect is that it can directly convert invisible mechanical pressure changes into precisely measurable optical signal (second harmonic intensity) changes, thereby realizing a highly sensitive and electromagnetic interference-resistant optical pressure sensing and switching mechanism. This shows irreplaceable application potential in fields such as high-pressure physics research, precision sensing, or advanced optical control systems. Attached Figure Description

[0024] Figure 1 The X-ray diffraction pattern of the Ba3Si3N5OCl crystal sample of Example 1 of this invention; Figure 2This is a schematic diagram of the Ba3Si3N5OCl crystal along the

[001] direction in Embodiment 1 of the present invention; Figure 3 This is a single-particle scanning electron microscope image of the Ba3Si3N5OCl crystal from Example 1 of the present invention; Figure 4 This is a comparison diagram of the frequency doubling effect between the Ba3Si3N5OCl crystal and KDP in Example 1 of the present invention; Figure 5 The polarization dependence of the second harmonic generation (SHG) signal of Ba3Si3N5OCl crystal under high voltage in Embodiment 1 of the present invention; Figure 6 The evolution of the maximum and minimum second harmonic signals of the Ba3Si3N5OCl crystal under different pressures in Embodiment 1 of the present invention; Figure 7 X-ray diffraction patterns of Ba3Si3N5OCl crystals synthesized with different amounts of flux Mg powder; Figure 8 X-ray diffraction patterns of Ba3Si3N5OCl crystals synthesized at different sintering temperatures; Figure 9 The image shows a scanning electron microscope (SEM) image of a crystal synthesized using α-Si3N4 as the raw material. Figure 10 This is a scanning electron microscope image of a crystal synthesized using α-Si3N4 as the raw material and Mg powder as a flux. Figure 11 The image shows a scanning electron microscope (SEM) image of the Ba3Si3N5OCl crystal from Example 1. Detailed Implementation

[0025] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0026] Example 1 Synthesis of Ba3Si3N5OCl, a zeolite-like structured oxynitride silicate nonlinear optical crystal material: In an argon-filled glove box (O2 < 1 ppm, H2O < 0.1 ppm), BaCl2, Ba3N2, and amorphous Si3N4 with an average particle size of 0.5 μm were weighed, along with Mg powder. The molar ratio was 0.4:1:1.14:1.7. After grinding for 40 minutes using an agate mortar, the resulting mixture was placed in a tungsten crucible. The tungsten crucible containing the mixed raw material powder was then placed in a high-temperature tube furnace (containing a large amount of Li and Mg). The calcination operation is as follows: First, use a vacuum pump to create a negative pressure inside the tube containing the sample, then introduce a nitrogen-hydrogen mixture with a volume ratio of 9:1 to restore the pressure inside the tube to normal. Repeat this operation (7-9 times) to remove as much air as possible from the tube, making the calcination atmosphere a nitrogen-hydrogen reducing atmosphere. First, heat the tube from room temperature to 200℃ at a heating rate of 5℃ / min, then heat it to 1000℃ at a heating rate of 10℃ / min, then heat it to 1400℃ at a heating rate of 5℃ / min, and hold it at 1400℃ for 8 hours.

[0027] After the reaction was complete and the temperature cooled to room temperature, the sample was removed from the crucible. Crystals were selected under an optical microscope and single-crystal tests were performed using a Rigaku single-crystal analyzer. The obtained single-crystal data were analyzed, and the sample was found to belong to the hexagonal crystal system, space group P-62c (No. 190), with cell parameters a = 9.5147(6) Å, c = 5.5002(4) Å, and V = 431.22(6) Å. 3 Z=2.

[0028] The Ba3Si3N5OCl crystal prepared in Example 1 exhibits a structure based on [SiN4] tetrahedra as the basic structural unit. These tetrahedra are connected by shared vertices to form structural units containing ternary and hexa-membered rings, constructing a highly condensed three-dimensional four-linked network framework. The results are shown in […]. Figure 2 At the same time, Ba 2+ The ions are distributed in six independent crystallographic sites within the voids of this three-dimensional framework.

[0029] The X-ray diffraction pattern of Ba3Si3N5OCl crystal is shown below. Figure 1 The morphology of the sample was characterized using scanning electron microscopy. The compound had a grain size of approximately 500 μm and exhibited good crystal structure. The results are shown in the figure. Figure 3 .

[0030] The obtained Ba3Si3N5OCl crystal was subjected to ten energy dispersive X-ray spectroscopy tests using a scanning electron microscope with an attached X-ray energy dispersive X-ray spectrometer. The average value was taken, and the types of elements and the average atomic ratio were found to be Ba:Si:N:O:Cl≈23.60:22.43:38.85:7.80:7.32, which is basically consistent with the atomic ratio of the chemical formula of Ba3Si3N5OCl crystal.

[0031] Table 1. Tenth-order energy dispersive spectroscopy values ​​of Ba3Si3N5OCl crystal in Example 1

[0032] The frequency doubling test of the Ba3Si3N5OCl crystal is as follows: A 1064nm wavelength laser was used as the fundamental frequency light to illuminate the crystal under test. The generated second harmonic was detected using a photomultiplier tube, and the harmonic intensity was displayed on an oscilloscope. Under the same test conditions, the second harmonic intensities generated by the Ba3Si3N5OCl crystal sample and potassium dihydrogen phosphate (KDP) were compared to obtain the relative intensity of the frequency doubling effect. The test results are as follows: Figure 4 As shown, from Figure 4 The results show that the zeolite-like structure oxynitride silicate Ba3Si3N5OCl crystal of the present invention has a good frequency doubling effect. Under high current 1064nm laser pumping, its second harmonic intensity is about 0.2 times that of potassium dihydrogen phosphate (KDP), and phase matching can be achieved.

[0033] The specific measurements of the second harmonic signal intensity of Ba3Si3N5OCl crystal under different pressures are as follows: The second harmonic signal variation of Ba3Si3N5OCl crystal was detected using the HP SHG experiment (high-voltage second harmonic effect experiment). The Ba3Si3N5OCl crystal underwent a one-step switching of its second harmonic properties, which can be divided into two states: "SHG-high" (strong second harmonic signal) and "SHG-off" (no second harmonic signal). The Ba3Si3N5OCl crystal maintained the "SHG-high" state under low pressure. Above 3.7 GPa, the SHG intensity dropped sharply, entering the "SHG-off" state, and above 15 GPa, the SHG intensity dropped to zero. Figure 5 This describes the polarization dependence of the second harmonic signal intensity of the Ba3Si3N5OCl crystal under compression. Above 3.7 GPa, the original polarization curve changes significantly, and the second harmonic signal intensity of the Ba3Si3N5OCl crystal begins to decrease until it becomes undetectable.

[0034] Figure 6 Detailed information on the polarized SHG curves (intensity) is provided. The evolution of the maximum and minimum SHG signals under different pressures is consistent with the polarization dependence trend of the SHG signal intensity under compression.

[0035] The change in the polar properties of Ba3Si3N5OCl crystals proves its feasibility as a one-step SHG pressure-controlled switching material.

[0036] Comparative Examples 1-3 Comparative Examples 1-3 investigated the effect of different amounts of Mg powder added as flux on crystallinity. The procedures of Example 1 were followed, except for the amount of Mg powder added; the amounts of other substances remained the same as in Example 1, so that the molar ratios of Ba and Mg were as shown in Table 2. The crystal properties of the products are characterized in Table 2 below.

[0037] Table 2. Effect of the amount of flux Mg powder added on crystal properties characterization

[0038] The results showed that the amount of flux magnesium powder added had a significant impact on the phase purity of the product. For example... Figure 7 As shown, the X-ray diffraction patterns of samples with different amounts of magnesium powder indicate that the highest phase purity of the obtained Ba3Si3N5OCl crystal is obtained when the molar ratio of barium to magnesium is 1:0.5. The mechanism is that an appropriate amount of magnesium powder at high temperatures may promote atomic diffusion and lattice rearrangement of the reactants by forming low-melting-point liquid phases such as Mg-Si-O (e.g., Mg2SiO4), thus facilitating crystal purification and growth. However, when the molar ratio reaches 1:1, impurity peaks appear in the diffraction pattern, and the product yield decreases. This may be due to excessive magnesium powder addition, which triggers unnecessary side reactions, leading to the formation of intermediate byproducts such as magnesium silicate. After the reaction, the remaining intermediate byproducts become impurities, thus affecting the purity of the target product.

[0039] Comparative Example 4-5 The effect of improper sintering temperature on crystal quality was investigated. Comparative Examples 4-5 were performed following the steps of Example 1, except that the sintering temperature was changed to 1300℃ and 1500℃, respectively. The crystal properties of the products are characterized in Table 3 below.

[0040] Table 3 Sintering temperature and its effect on crystal property characterization

[0041] From the data in Table 3 and Figure 8 The spectral results show that 1400℃, used in Example 1 of this invention, is the optimal sintering temperature. At this temperature, crystal growth is complete and the risk of thermal decomposition is lowest. High temperatures may cause the Ba3Si3N5OCl crystal to partially decompose into BaCl2 and Si3N4.

[0042] Note, Figures 7-8 In this context, PDF-Ba3Si3N5OCl refers to the diffraction pattern of the Ba3Si3N5OCl material in the standard XRD data card of the PDF card in the crystallography database, with the number ICSD-418216.

[0043] Comparative Examples 6-7 The effect of silicon source material type on crystal morphology and size was investigated. Comparative Examples 6-7 were performed following the steps of Example 1, except that amorphous α-Si3N4 was replaced with an equimolar amount of crystalline α-Si3N4. Specifically, Mg powder was added without and with Mg powder as a flux, respectively. The scanning electron microscopy results of the crystal samples are shown in the figures below. Figure 9 , Figure 10 As shown in the figure. The crystal properties of the product are characterized in Table 4 below.

[0044] Table 4. Types of silicon source materials and their influence on crystal performance characterization

[0045] See Figure 9 Scanning electron microscopy revealed that the synthesized sample using α-Si3N4 as the raw material, without the addition of Mg powder, exhibited irregular morphology, uneven particle size, and generally small size (<50 μm), along with severe agglomeration. See also... Figure 10 The figure shows a sample synthesized using α-Si3N4 as raw material and with the addition of Mg powder as flux. As can be seen from the figure, even with the addition of Mg powder as flux, although some rod-shaped crystals can be observed, the agglomeration problem is still significant.

[0046] Therefore, Example 1, using highly reactive amorphous Si3N4 as the silicon source and combined with an optimized flux, effectively promoted uniform nucleation and crystal growth, successfully preparing large-sized single crystals with an average size of 500 μm and good dispersion, which is significantly better than the effect of using traditional α-Si3N4 raw materials (see...). Figure 11 ).

[0047] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A zeolite-like structure oxynitride silicate nonlinear optical crystal, characterized in that, Its general chemical formula is Ba3Si3N5OCl, it belongs to the hexagonal crystal system, space group P-62c, and has a non-centrosymmetric structure.

2. The zeolite-like structure oxynitride silicate nonlinear optical crystal according to claim 1, characterized in that, It generates second harmonics under 1064nm laser light, with a frequency doubling efficiency ≥0.1 times KDP (potassium dihydrogen phosphate), and can achieve phase matching.

3. The zeolite-like structure oxynitride silicate nonlinear optical crystal according to claim 1 or 2, characterized in that, Its average particle size is ≥200μm.

4. The zeolite-like structure oxynitride silicate nonlinear optical crystal according to claim 1 or 2, characterized in that, The intensity of its second harmonic signal is responsive to changes in external pressure; when the external pressure exceeds 3.7 GPa, the intensity of its second harmonic signal weakens.

5. A method for preparing a zeolite-like structure oxynitride silicate nonlinear optical crystal as described in any one of claims 1-4, characterized in that, Includes the following steps: The crystal is generated by using compounds containing Ba and compounds containing Si as raw materials and adding flux, and then carrying out a high-temperature sintering reaction under a protective atmosphere or a reducing atmosphere; wherein the flux is metallic Mg powder.

6. The method for preparing a zeolite-like structure oxynitride silicate nonlinear optical crystal according to claim 5, characterized in that, The compounds containing Ba include BaCl2 and Ba3N2; the compounds containing Si are amorphous Si3N4.

7. The method for preparing the zeolite-like structure oxynitride silicate nonlinear optical crystal according to claim 6, characterized in that, The molar ratio of BaCl2:Ba3N2:Si3N4:Mg is 0.3-0.5:1:0.9-1.2:1.5-2.

0.

8. The method for preparing a zeolite-like structure oxynitride silicate nonlinear optical crystal according to claim 5, characterized in that, The protective atmosphere or reducing atmosphere is a mixture of N2 and H2, wherein the volume ratio of N2 to H2 is 8-10:

1.

9. The method for preparing a zeolite-like structure oxynitride silicate nonlinear optical crystal according to claim 4, characterized in that, The sintering temperature of the high-temperature sintering reaction is 1350℃-1450℃, and the sintering time is 5-12 hours.

10. The application of the nonlinear optical crystal as described in any one of claims 1-4, characterized in that, Used to fabricate nonlinear optical devices, pressure optical sensors, or pressure-controlled optical switches.

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