Preparation method and application of sodium 5-hydroxypyridine-2-carboxylate monohydrate nonlinear optical crystal

Abstract

The invention discloses a preparation method and application of a sodium 5-hydroxypyridine-2-carboxylate monohydrate nonlinear optical crystal, and relates to the technical field of crystal preparation. According to the invention, 5-hydroxypyridine-2-formic acid and sodium hydroxide are used as raw materials, a crystal is grown through an aqueous solution volatilization method, the monohydrate 5-hydroxypyridine-2-sodium carboxylate nonlinear optical crystal is obtained, the space group of the crystal is Ia, the cell parameters are # imgabs0 # imgabs1 #, alpha = gamma = 90 degrees, beta = 95.89 degrees, and the crystal has the characteristics that: the crystal has a linear structure; the monohydrate 5-hydroxypyridine-2-sodium carboxylate nonlinear optical crystal provided by the invention has excellent physical and chemical performance stability and excellent nonlinear optical effect, can be used for preparing nonlinear optical devices, and has application potential in harsh scenes such as industrial laser processing and medical equipment.

Description

Technical Field

[0001] The present invention relates to the technical field of crystal preparation, in particular to a preparation method and application of a 5-hydroxypyridine-2-carboxylate sodium monohydrate nonlinear optical crystal. Background Art

[0002] Lasers, with their high brightness, excellent directionality, exceptional monochromaticity, and strong coherence, have found widespread application in laser communications, medical cosmetology, scientific research, information storage and processing, and materials processing. However, due to limitations in materials and technology, the wavelengths directly output by existing lasers are relatively limited, with significant gaps remaining between the deep ultraviolet and far infrared bands.

[0003] To overcome this limitation, frequency conversion using nonlinear optical materials has become an effective method. Through this technology, tunable laser output can be achieved, greatly expanding the output wavelength range of solid-state lasers and enabling their application in a wider range of fields.

[0004] In recent years, nonlinear optical crystals have played an important role in laser frequency conversion, electro-optical modulation, and photorefractive crystal memory and storage. Among them, KDP (KH2PO4), BBO (β-BaB2O4), and LBO (LiB3O5) are the most commonly used nonlinear optical crystal materials. While the preparation processes for these materials are relatively mature, some challenges remain. For example, some crystal materials (such as KDP) are sensitive to ambient humidity and easily deliquesce, affecting their long-term stability; the crystal growth process is time-consuming, making it difficult to meet the demands of large-scale production; and some raw materials are toxic, potentially posing a threat to the environment and human health.

[0005] Therefore, the development of new nonlinear optical crystal materials that are easy to grow and have excellent comprehensive properties is of great significance. The research and development of such materials not only fills the gaps in the current laser wavelength range but also further promotes the development of laser technology and expands its applications in cutting-edge fields such as precision manufacturing, biomedical imaging, and space communications, demonstrating significant scientific value and broad application prospects. Summary of the Invention

[0006] The purpose of the present invention is to provide a preparation method and use of a monohydrated 5-hydroxypyridine-2-carboxylate sodium nonlinear optical crystal to solve the problems existing in the above-mentioned prior art.

[0007] To achieve the above object, the present invention provides the following solutions:

[0008] One of the objectives of the present invention is to provide a nonlinear optical crystal of sodium 5-hydroxy-2-pyridinecarboxylate monohydrate, with the chemical formula Na2(C6H4NO3)2·H2O, a molecular weight of 340.2, a space group of Ia, and unit cell parameters as α = γ = 90°, β = 95.89°, and the unit cell volume is

[0009] The nonlinear optical effect of the nonlinear optical crystal of sodium 5-hydroxy-2-pyridinecarboxylate monohydrate of the present invention is about 6.2 times that of KH2PO4 (KDP), the ultraviolet absorption edge is located at 282 nm, and the optical band gap is about 3.6 eV.

[0010] Another objective of the present invention is to provide a preparation method for the above-mentioned nonlinear optical crystal of sodium 5-hydroxy-2-pyridinecarboxylate monohydrate. Using 5-hydroxy-2-pyridinecarboxylic acid and sodium hydroxide as raw materials, crystals are grown by the aqueous solution evaporation method to obtain the nonlinear optical crystal of sodium 5-hydroxy-2-pyridinecarboxylate monohydrate.

[0011] Furthermore, the preparation method includes the following steps:

[0012] Prepare a saturated solution of 5-hydroxy-2-pyridinecarboxylic acid and sodium hydroxide in deionized water, and grow crystals at 25 - 50 °C to obtain the nonlinear optical crystal of sodium 5-hydroxy-2-pyridinecarboxylate monohydrate.

[0013] Furthermore, the molar ratio of 5-hydroxy-2-pyridinecarboxylic acid to sodium hydroxide is 1:1.

[0014] Furthermore, the crystal growth time is 5 - 90 days.

[0015] Furthermore, during the preparation of the saturated solution, ultrasonic treatment can be combined, and the preferred ultrasonic time is 10 - 30 min.

[0016] Even further, during the crystal preparation process, a seed crystal can also be suspended in the saturated solution and then crystal growth is carried out.

[0017] Even further, the preparation process also includes impurity removal treatment of the saturated solution to ensure that there is only one nucleation center, and then crystal growth is carried out in a static environment without shaking, pollution, and air convection. In the specific implementation process, the container can be sealed with plastic wrap, and small holes can be pricked on the plastic wrap to control the evaporation rate of water.

[0018] The present invention grows large-sized crystals by the aqueous solution evaporation method, which has the characteristics of simple operation, low cost, less pollution, low toxicity of the raw materials used, and short growth cycle. The grown nonlinear optical crystal of sodium 5-hydroxy-2-pyridinecarboxylate monohydrate has good quality, large size, and regular morphology.

[0019] The third object of the present invention is to provide the application of the above-mentioned nonlinear optical crystal of sodium 5-hydroxy-2-pyridinecarboxylate monohydrate as an optical device; especially its application in the preparation of frequency doubling generators, up-frequency converters, down-frequency converters or optical parametric oscillators.

[0020] The nonlinear optical crystal of sodium 5-hydroxy-2-pyridinecarboxylate monohydrate prepared by the present invention can be used as a crystal material for preparing nonlinear optical devices, including the preparation of frequency doubling generators, up or down frequency converters, and optical parametric oscillators. The nonlinear optical device made of the nonlinear optical crystal of sodium 5-hydroxy-2-pyridinecarboxylate monohydrate of the present invention can convert at least one incident fundamental frequency light into at least one coherent light output with a frequency different from that of the incident light.

[0021] By regulating the crystallization temperature and time, the present invention can prepare nonlinear optical crystals of sodium 5-hydroxy-2-pyridinecarboxylate monohydrate with different sizes. The reagents and raw materials used have low toxicity to the human body, short growth cycle, and are easy to obtain high-quality and large-sized crystals, etc., and have no special requirements for processing accuracy.

[0022] The present invention discloses the following technical effects:

[0023] The nonlinear optical crystal of sodium 5-hydroxy-2-pyridinecarboxylate monohydrate provided by the present invention has excellent physical and chemical property stability and excellent nonlinear optical effect, can be used for preparing nonlinear optical devices, and has application potential in harsh scenarios such as industrial laser processing and medical equipment. Description of the Drawings

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0025] Figure 1 It is the theoretical powder X-ray diffraction (XRD) pattern of the Na2(C6H4NO3)2·H2O optical crystal of the present invention;

[0026] Figure 2It is a comparison chart between the theoretical powder X-ray diffraction pattern of the Na2(C6H4NO3)2·H2O optical crystal of the present invention and the powder X-ray diffraction pattern obtained from the experimental test of the Na2(C6H4NO3)2·H2O crystal prepared in Example 1;

[0027] Figure 3 It is a schematic structural diagram of the Na2(C6H4NO3)2·H2O crystal of the present invention;

[0028] Figure 4 It is a crystal photograph of the Na2(C6H4NO3)2·H2O crystal of the present invention;

[0029] Figure 5 It is a working principle diagram of the non-linear optical device fabricated by the present invention; wherein, 1 - laser, 2 - converging lens, 3 - non-linear optical crystal (sodium 5-hydroxy-pyridine-2-carboxylate monohydrate crystal), 4 - beam splitter prism, 5 - filter;

[0030] Figure 6 It is a comparison chart of the powder frequency doubling effect between the Na2(C6H4NO3)2·H2O crystal of the present invention and the commercial KDP crystal at different particle sizes;

[0031] Figure 7 It is a comparison chart of the powder frequency doubling effect between the Na2(C6H4NO3)2·H2O crystal of the present invention and the commercial KDP crystal at the same particle size. Detailed Description of the Invention

[0032] Now, various exemplary embodiments of the present invention will be described in detail. This detailed description should not be construed as a limitation on the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0033] It should be understood that the terms used in the present invention are only for describing specific embodiments and are not intended to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0034] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although this invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of this invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the said documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0035] Without departing from the scope or spirit of this invention, various modifications and variations can be made to the specific embodiments of the description of this invention, which are obvious to those skilled in the art. Other embodiments obtained from the description of this invention are obvious to those skilled in the art. The description and examples of this invention are merely exemplary.

[0036] Regarding the use of "comprising", "including", "having", "containing", etc. herein, they are all open-ended terms, meaning including but not limited to.

[0037] The following describes this invention in detail with reference to the examples. It should be noted that the operations not detailed in this invention are all conventional operation means in the art and are not the focus of this invention.

[0038] In this invention, room temperature refers to 25 °C.

[0039] The chemical reaction formula for preparing sodium 5-hydroxypyridine-2-carboxylate monohydrate in this invention is:

[0040] 2C6H5NO3 + 2NaOH + H2O → Na2(C6H4NO3)2·H2O.

[0041] Example 1

[0042] Preparation of sodium 5-hydroxypyridine-2-carboxylate monohydrate:

[0043] a. Weigh sodium hydroxide and 5-hydroxypyridine-2-carboxylic acid in a molar ratio of 1:1 (0.4800 g: 1.6700 g) and put them into a clean small beaker. Add 10 mL of deionized water to prepare a saturated aqueous solution, and perform ultrasonic treatment for 20 minutes to fully mix and dissolve them;

[0044] b. Filter the solution obtained in step a using qualitative filter paper to remove possible impurities. The purpose of this operation is to ensure that there is only one nucleation center in the solution, thereby improving the quality and purity of crystal growth;

[0045] c. Transfer the solution filtered in step b to a clean beaker and seal it with plastic wrap. To ensure gas exchange, pierce several small holes in the plastic wrap with a needle. Subsequently, place the beaker in a water bath at 40 °C and let it stand for 5 days to obtain colorless and transparent micron-sized Na2(C6H4NO3)2·H2O crystals.

[0046] Example 2

[0047] Preparation of sodium 5-hydroxypyridine-2-carboxylate monohydrate:

[0048] a. Weigh sodium hydroxide and 5-hydroxypyridine-2-carboxylic acid in a molar ratio of 1:1 (0.3200 g: 1.1120 g) and place them in a clean crystallizing dish. Add 10 mL of deionized water to prepare a saturated aqueous solution, and ultrasonically treat it for 15 minutes to fully mix and dissolve them;

[0049] b. Filter the solution obtained in step a using qualitative filter paper to remove possible impurities. The purpose of this operation is to ensure that there is only one nucleation center in the solution, thereby improving the quality and purity of crystal growth;

[0050] c. Place the solution filtered in step b in a beaker, seal it with plastic wrap, and pierce several small holes in the plastic wrap with a needle. Let it stand in a water bath at 50 °C for 7 days to obtain colorless and transparent micron-sized Na2(C6H4NO3)2·H2O crystals.

[0051] Example 3

[0052] Preparation of sodium 5-hydroxypyridine-2-carboxylate monohydrate:

[0053] a. Weigh sodium hydroxide and 5-hydroxypyridine-2-carboxylic acid in a molar ratio of 1:1 (0.3600 g: 1.2520 g) and place them in a clean beaker. Add 15 mL of deionized water to prepare a saturated aqueous solution, and ultrasonically treat it for 15 minutes to fully mix and dissolve them;

[0054] b. Filter the solution obtained in step a using qualitative filter paper to remove possible impurities. The purpose of this operation is to ensure that there is only one nucleation center in the solution, thereby improving the quality and purity of crystal growth;

[0055] c. Place the solution filtered in step b in a beaker, seal it with plastic wrap, and pierce several small holes in the plastic wrap with a needle. Let it stand in a water bath at 40 °C for  14 days to obtain colorless and transparent sub-millimeter-sized Na2(C6H4NO3)2·H2O crystals.

[0056] Example 4

[0057] Preparation of sodium 5-hydroxypyridine-2-carboxylate monohydrate:

[0058] a. Weigh sodium hydroxide and 5 - hydroxypyridine - 2 - carboxylic acid in a molar ratio of 1:1 (0.6000 g:2.0866 g) and put them into a clean beaker. Add 20 mL of deionized water to prepare a saturated aqueous solution, and ultrasonically treat it for 20 minutes to fully mix and dissolve them.

[0059] b. Filter the solution obtained in step a using qualitative filter paper to remove any possible impurities. The purpose of this operation is to ensure that there is only one nucleation center in the solution, thereby improving the quality and purity of crystal growth.

[0060] c. Place the solution filtered in step b in a beaker, seal it with plastic wrap, and prick several small holes in the plastic wrap with a needle. Let it stand in a water bath at 30 °C for 20 days to obtain colorless and transparent millimeter - sized Na2(C6H4NO3)2·H2O crystals.

[0061] Example 5

[0062] Preparation of sodium 5 - hydroxypyridine - 2 - carboxylate monohydrate:

[0063] a. Weigh sodium hydroxide and 5 - hydroxypyridine - 2 - carboxylic acid in a molar ratio of 1:1 (0.2400 g:0.8350 g) and put them into a clean beaker. Add 5 mL of deionized water to prepare a saturated aqueous solution, and ultrasonically treat it for 30 minutes to fully mix and dissolve them.

[0064] b. Filter the solution obtained in step a using qualitative filter paper to remove any possible impurities. The purpose of this operation is to ensure that there is only one nucleation center in the solution, thereby improving the quality and purity of crystal growth.

[0065] c. Place the solution filtered in step b in a beaker, seal it with plastic wrap, and prick several small holes in the plastic wrap with a needle. Let it stand at room temperature for 20 days to obtain colorless and transparent millimeter - sized Na2(C6H4NO3)2·H2O crystals.

[0066] Example 6

[0067] Preparation of sodium 5 - hydroxypyridine - 2 - carboxylate monohydrate:

[0068] a. Weigh sodium hydroxide and 5 - hydroxypyridine - 2 - carboxylic acid in a molar ratio of 1:1 (0.4000 g:1.3911 g) and put them into a clean crystallizing dish. Add 30 mL of deionized water to prepare a saturated aqueous solution, and ultrasonically treat it for 30 minutes to fully mix and dissolve them.

[0069] b. Filter the solution obtained in step a using qualitative filter paper to remove any possible impurities. The purpose of this operation is to ensure that there is only one nucleation center in the solution, thereby improving the quality and purity of crystal growth;

[0070] c. Place the solution filtered in step b in a beaker, seal it with plastic wrap, and pierce several small holes in the plastic wrap with a needle. Leave it to stand at room temperature for 60 days to obtain colorless and transparent centimeter-sized Na2(C6H4NO3)2·H2O crystals.

[0071] Example 7

[0072] Preparation of sodium 5-hydroxypyridine-2-carboxylate monohydrate:

[0073] a. Weigh sodium hydroxide and 5-hydroxypyridine-2-carboxylic acid in a molar ratio of 1:1 (0.4457 g: 1.550 g) and place them in a clean crystallization dish. Add 50 mL of deionized water to make a saturated aqueous solution, and ultrasonically treat it for 30 minutes to fully mix and dissolve them;

[0074] b. Filter the solution obtained in step a using qualitative filter paper to remove any possible impurities. The purpose of this operation is to ensure that there is only one nucleation center in the solution, thereby improving the quality and purity of crystal growth;

[0075] c. Place the solution filtered in step b in a beaker, seal it with plastic wrap, and pierce several small holes in the plastic wrap with a needle. Leave it to stand at room temperature for 90 days to obtain colorless and transparent centimeter-sized Na2(C6H4NO3)2·H2O crystals.

[0076] Example 8

[0077] Preparation of sodium 5-hydroxypyridine-2-carboxylate monohydrate:

[0078] a. Weigh sodium hydroxide and 5-hydroxypyridine-2-carboxylic acid in a molar ratio of 1:1 (0.3000 g: 1.0433 g) and place them in a clean beaker. Add 10 mL of deionized water to make a saturated aqueous solution, and ultrasonically treat it for 20 minutes to fully mix and dissolve them;

[0079] b. Seal the beaker in step a with plastic wrap and pierce several small holes with a needle. Leave it to stand in a 40 °C water bath for 15 days;

[0080] c. Wait until crystal grains grow at the bottom of the solution in step b until the size of the crystal grains no longer changes significantly, indicating the end of growth, to obtain millimeter-sized seed crystals;

[0081] d. Reconfigure the solution: Weigh sodium hydroxide and 5-hydroxypyridine-2-carboxylic acid in a molar ratio of 1:1 (0.3400 g: 1.1824 g) and put them into a clean beaker. Add 40 mL of deionized water to prepare a saturated aqueous solution, and perform ultrasonic treatment for 30 minutes to fully mix and dissolve them. Then filter the system using qualitative filter paper to ensure that there is only one nucleation center in the solution;

[0082] e. Select the millimeter-sized seed crystal with better quality in step c, suspend the seed crystal in the solution prepared in step d, and grow it at room temperature for 30 days to obtain colorless and transparent centimeter-sized Na2(C6H4NO3)2·H2O crystals.

[0083] Perform single-crystal X-ray diffraction test on the nonlinear optical crystal sodium 5-hydroxypyridine-2-carboxylate monohydrate prepared in Example 1. Obtain its crystal structure parameters by analyzing the diffraction data and resolving the structure: the space group is Ia, and the unit cell parameters are α = γ = 90°, β = 95.89°, and the unit cell volume is The theoretical powder X-ray diffraction pattern can be derived from the single-crystal structure, as shown in Figure 1 Shown. Then put the nonlinear optical crystal sodium 5-hydroxypyridine-2-carboxylate monohydrate prepared in Example 1 into a mortar for grinding, and perform powder X-ray diffraction analysis on it. The obtained powder X-ray diffraction spectrum is consistent with the theoretical spectrum, as shown in Figure 2 Shown.

[0084] Effect verification example

[0085] Figure 5 This is the working principle diagram of the nonlinear optical device made by the present invention; among them, 1 - laser, 2 - converging lens, 3 - nonlinear optical crystal (sodium 5-hydroxypyridine-2-carboxylate monohydrate), 4 - beam splitter prism, 5 - filter.

[0086] The refractive light frequency of the prepared nonlinear optical device is equal to the incident light frequency or twice the incident light frequency.

[0087] Figure 5 Shows the working principle of the nonlinear optical effect: The Q-switched Nd:YAG laser 1 emits infrared fundamental light with a wavelength of 1064 nm, which is focused by the converging lens 2 and then incident on the nonlinear optical crystal 3 (sodium 5-hydroxypyridine-2-carboxylate monohydrate prepared in Example 3). Based on the second harmonic generation effect of the crystal, the incident fundamental light is excited to generate green second harmonic light with a wavelength of 532 nm. After passing through the beam splitter prism 4, the outgoing light beam contains the un-converted 1064 nm infrared light and the newly generated 532 nm green light. After selectively filtering out the infrared component by the filter 5, a single-wavelength 532 nm second harmonic green light output is finally obtained.

[0088] Figure 6 This is a comparison chart of the powder second harmonic generation effects of the Na2(C6H4NO3)2·H2O crystal of the present invention and a commercial KDP crystal at different particle sizes. Figure 7 This is a comparison chart of the powder second harmonic generation effects of the Na2(C6H4NO3)2·H2O crystal of the present invention and a commercial KDP crystal at the same particle size. The output intensity of the crystal material of the present invention is about 6.2 times that of KDP under the same conditions, and it is suitable for high-power laser devices. The specific implementation process is as follows:

[0089] Take the sample in Example 3 and a commercial KDP crystal for grinding and sieving to obtain powder samples and standard samples with different particle sizes (<45μm, 45 - 62μm, 62 - 75μm, 75 - 109μm, 109 - 150μm, and 150 - 212μm) respectively, and then load them into sample cells. Select the incident light source as the fundamental frequency light with a wavelength of 1064nm generated by a Nd:YVO4 Q-switched laser. After the laser passes through the powder sample, filter out the fundamental frequency light and only let the second harmonic light (532nm) pass through, and collect the second harmonic signal intensity with a PMT photomultiplier tube. The results are recorded in a Tektronix 4000 500-MHz oscilloscope for data analysis. After recording different intensities, the maximum particle size can be obtained by using origin Figure 6 。 Figure 7 This is a comparison chart of the second harmonic signals obtained at the maximum particle size derived.

[0090] The sodium 5-hydroxy-2-carboxypyridine monohydrate crystal prepared by the present invention is significantly superior to the traditional KDP crystal in terms of frequency conversion performance. Its efficient conversion of the 1064nm fundamental frequency light to the 532nm second harmonic light directly reflects the excellent phase matching ability and second harmonic generation (SHG) performance of the crystal, which are the core technical indicators for a nonlinear optical crystal to achieve frequency conversion. Experimental data show that the output intensity of the second harmonic light of this crystal reaches 6.2 times that of the KDP crystal under the same conditions, demonstrating excellent nonlinear optical effects.

[0091] In terms of optical properties, the ultraviolet absorption edge of this crystal is located at 282nm, and the optical band gap is about 3.6eV. It has good light transmittance in the ultraviolet-visible band (from 282nm to the visible light range), providing an ideal material basis for laser frequency conversion in this band. The nonlinear optical crystal of the present invention is not prone to deliquescence after long-term placement and has good stability.

[0092] In practical applications, the crystal can be directly integrated with optical components such as a plano-convex lens and a filter in a laser system, and there are no special requirements for the machining accuracy. It has good machining adaptability and is suitable for large-scale preparation of nonlinear optical devices. When high-power pulsed light output by a Q-switched Nd:YAG laser is incident, the crystal can stably generate second-harmonic light, which benefits from the dual advantages of its low nonlinear optical effect threshold and high laser damage threshold, enabling it to work stably in a high-power density environment and further expanding its application potential in harsh scenarios such as industrial laser processing and medical equipment.

[0093] The embodiments described above are only for describing the preferred mode of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A nonlinear optical crystal of sodium 5-hydroxy-2-pyridinecarboxylate monohydrate, characterized in that, The space group is Ia, and the unit cell parameters are α = γ = 90°, β = 95.89°, and the unit cell volume is 2. The preparation method of the 5-hydroxy-pyridine-2-carboxylic acid sodium monohydrate nonlinear optical crystal according to claim 1, characterized in that, Using 5-hydroxypyridine-2-carboxylic acid and sodium hydroxide as raw materials, the nonlinear optical crystal of sodium 5-hydroxypyridine-2-carboxylate monohydrate is obtained by growing crystals through the aqueous solution evaporation method.

3. The preparation method according to claim 2, characterized in that, It includes the following steps: Prepare a saturated solution of 5-hydroxypyridine-2-carboxylic acid and sodium hydroxide in deionized water, and grow crystals at 25 - 50 °C to obtain the nonlinear optical crystal of sodium 5-hydroxypyridine-2-carboxylate monohydrate.

4. The preparation method according to claim 2, characterized in that, The molar ratio of the 5-hydroxypyridine-2-carboxylic acid to sodium hydroxide is 1:

1.

5. The preparation method according to claim 3, characterized in that, The time for growing crystals is 5 - 90 days.

6. Application of the nonlinear optical crystal of sodium 5-hydroxypyridine-2-carboxylate monohydrate as claimed in claim 1 in optical devices.

7. Application of the nonlinear optical crystal of sodium 5-hydroxypyridine-2-carboxylate monohydrate as claimed in claim 1 in the preparation of frequency doubling generators, up frequency converters, down frequency converters or optical parametric oscillators.

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