Sulfur-silver-based compound, sulfur-silver-based nonlinear optical crystal and preparation method and application of sulfur-silver-based nonlinear optical crystal

Abstract

The invention discloses a sulfur-silver-based compound, a sulfur-silver-based nonlinear optical crystal and a preparation method and application of the sulfur-silver-based nonlinear optical crystal. The chemical formula of the nonlinear optical crystal is A1Ag2AsS4 or A2Ag2PS4, A1 is K or Rb, and A2 is Na, K or Rb. The nonlinear optical crystal provided by the invention has a relatively large nonlinear optical coefficient and relatively wide transmission wave band and band gap. Meanwhile, the nonlinear optical crystal has the same-component melting characteristic, is easy to grow, cut, grind, polish and preserve, is stable in air, is not easy to deliquesce, is insoluble in water, and is expected to become a new-generation novel middle-infrared band nonlinear optical material with excellent comprehensive performance.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of nonlinear optical crystals. More specifically, it relates to silver sulfide-based compounds, silver sulfide-based nonlinear optical crystals, and their preparation methods and applications. Background Art

[0002] Second-order nonlinear optical materials (NLO) have attracted great interest due to their ability to expand the frequency range of lasers and are widely used in various fields as the core components of solid-state lasers, such as optical communication, laser guidance, and instrumental spectroscopy. Currently, NLO materials in the ultraviolet, visible, and near-infrared wavelength ranges can basically meet the market demand, and a large number of NLO materials with excellent performance have been developed. However, in the mid-infrared band, there is a relative shortage of NLO materials. For example, commercially available AgGaS2 (AGS), AgGaSe2 (AGSe), and ZnGeP2 (ZGP) have large second harmonic generation (SHG) responses and suitable infrared transparent regions. Unfortunately, these crystals also have serious drawbacks. For example, AGS and AGSe have large anisotropic thermal expansion, and it is difficult to grow high-quality large-sized crystals. Coupled with low thermal conductivity, strong thermal gradients and thermal lens effects will occur during high-power pumping, resulting in an extremely low laser damage threshold and cannot be used for high-power infrared laser output. The ZGP crystal is the best material for generating 3-5μm infrared lasers at present. However, its crystal growth is extremely difficult, and there is inevitable and serious residual absorption in the near-infrared region, which makes it necessary to pump with a laser with a wavelength greater than 2μm. The above disadvantages severely limit the practical applications of the above infrared crystals. In addition, there is still a lack of nonlinear crystal materials with excellent performance in the 8-12μm infrared band. Therefore, it is particularly urgent to explore new infrared nonlinear crystals with excellent performance, which is also one of the research hotspots and difficulties in the field of nonlinear optical materials. Summary of the Invention

[0003] To solve the above problems, the first object of the present invention is to provide a silver sulfide-based compound.

[0004] The second object of the present invention is to provide a preparation method for the silver sulfide-based compound as described above.

[0005] The third object of the present invention is to provide a silver sulfide-based nonlinear optical crystal. The nonlinear optical crystal has a large nonlinear optical coefficient, a wide transmission band, and a bandgap.

[0006] The fourth object of the present invention is to provide a preparation method for the silver sulfide-based nonlinear optical crystal as described above.

[0007] The fifth object of the present invention is to provide an application of the silver sulfide-based nonlinear optical crystal as described above.

[0008] To achieve the above first object, the present invention adopts the following technical solution:

[0009] The present invention discloses a thio - silver - based compound, and the chemical formula of the thio - silver - based compound is A1Ag2AsS4 or A2Ag2PS4, where A1 = K or Rb, A2 = Na, K or Rb, specifically referring to KAg2AsS4, RbAg2AsS4, NaAg2PS4, KAg2PS4, RbAg2PS4.

[0010] To achieve the above second object, the present invention adopts the following technical solution:

[0011] The present invention discloses a preparation method of the thio - silver - based compound as described above, which is prepared by a vacuum high - temperature solid - state reaction method.

[0012] Furthermore, when preparing A1Ag2AsS4, the preparation steps are as follows:

[0013] Mix an Ag - containing compound, an As - containing compound, an S - containing compound, and an A1 - containing compound evenly according to a molar ratio of Ag:As:S:A1 of 2:1:4:1, seal them in a quartz tube, then evacuate the quartz tube to ≤10 -3 Pa and perform melting and sealing; put the sealed quartz tube into a muffle furnace, heat it at a rate of 30 - 50 °C / h to 400 - 800 °C, keep it for calcination for 10 - 72 h, and obtain polycrystalline powder of the A1Ag2AsS4 compound after cooling.

[0014] Furthermore, the Ag - containing compound is selected from at least one of Ag element, sulfides of Ag, and chlorides of Ag;

[0015] The As - containing compound is selected from at least one of As element and sulfides of As;

[0016] The A1 - containing compound is selected from at least one of K element, oxides of K, sulfides of K, carbonates of K, chlorides of K, Rb element, oxides of Rb, sulfides of Rb, carbonates of Rb, and chlorides of Rb;

[0017] The S - containing compound is selected from at least one of S element, sulfides of Ag, sulfides of As, sulfides of K, and sulfides of Rb.

[0018] In a specific embodiment, the heating rate can also be 30 - 35 °C / h, 30 - 40 °C / h, 30 - 45 °C / h, 35 - 40 °C / h, 35 - 45 °C / h, 35 - 50 °C / h, 40 - 45 °C / h, 40 - 50 °C / h, 45 - 50 °C / h, etc.

[0019] In a specific embodiment, the temperature of the heat preservation calcination can also be 400 - 500 °C, 400 - 600 °C, 400 - 700 °C, 500 - 600 °C, 500 - 700 °C, 500 - 800 °C, 600 - 700 °C, 600 - 800 °C, 700 - 800 °C, etc.

[0020] In a specific embodiment, the time of the heat preservation calcination can also be 10 - 24 h, 10 - 48 h, 24 - 48 h, 24 - 72 h, 48 - 72 h, etc.

[0021] Further, when preparing A2Ag2PS4, the preparation steps are as follows:

[0022] Mix an Ag-containing compound, a P-containing compound, an S-containing compound, and an A2-containing compound evenly according to a molar ratio of Ag:P:S:A2 of 2:1:4:1 and seal them in a quartz tube. Then, evacuate the quartz tube to ≤ 10 -3 Pa and conduct melting and sealing; place the sealed quartz tube in a muffle furnace, heat it to 400 - 800 °C at a rate of 30 - 50 °C / h, perform heat preservation calcination for 10 - 72 h, and obtain polycrystalline powder of the A2Ag2PS4 compound after cooling.

[0023] Further, the Ag-containing compound is selected from at least one of Ag elemental substance, sulfide of Ag, and chloride of Ag;

[0024] The P-containing compound is selected from at least one of P elemental substance and sulfide of P;

[0025] The A2-containing compound is selected from at least one of Na elemental substance, oxide of Na, sulfide of Na, carbonate of Na, chloride of Na, K elemental substance, oxide of K, sulfide of K, carbonate of K, chloride of K, Rb elemental substance, oxide of Rb, sulfide of Rb, carbonate of Rb, and chloride of Rb;

[0026] The S-containing compound is selected from at least one of S elemental substance, sulfide of Ag, sulfide of P, sulfide of Na, sulfide of K, and sulfide of Rb.

[0027] In a specific embodiment, the heating rate can also be 30 - 35 °C / h, 30 - 40 °C / h, 30 - 45 °C / h, 35 - 40 °C / h, 35 - 45 °C / h, 35 - 50 °C / h, 40 - 45 °C / h, 40 - 50 °C / h, 45 - 50 °C / h, etc.

[0028] In a specific embodiment, the temperature of the heat preservation and calcination can also be 400 - 500 °C, 400 - 600 °C, 400 - 700 °C, 500 - 600 °C, 500 - 700 °C, 500 - 800 °C, 600 - 700 °C, 600 - 800 °C, 700 - 800 °C, etc.

[0029] In a specific embodiment, the time of the heat preservation and calcination can also be 10 - 24 h, 10 - 48 h, 24 - 48 h, 24 - 72 h, 48 - 72 h, etc.

[0030] To achieve the above - mentioned third object, the present invention adopts the following technical solutions:

[0031] The present invention discloses a silver - sulfur - based nonlinear optical crystal, and the chemical formula of the nonlinear optical crystal is A1Ag2AsS4 or A2Ag2PS4, where A1 = K or Rb, and A2 = Na, K or Rb.

[0032] The nonlinear optical crystal provided by the present invention has relatively large nonlinear optical coefficients, a relatively wide transmission band and band gap, specifically: the powder second - harmonic generation intensities of KAg2AsS4, RbAg2AsS4, NaAg2PS4, and KAg2PS4 are 1.05×AGS, 1.28×AGS, 1.36×AGS, and 1.34×AGS respectively; the optical band gaps are 2.21 eV, 2.32 eV, 2.58 eV, and 2.67 eV respectively, and the transmission bands all cover 0.53 - 15 μm. At the same time, the nonlinear optical crystal has congruent melting characteristics, is easy to grow, cut, grind, polish and preserve, is stable in air, is not easy to deliquesce, and is insoluble in water, making it expected to become a new generation of nonlinear optical materials with excellent comprehensive performance in the mid - infrared band, and can be effectively used in tunable laser systems with a wide spectral range.

[0033] Furthermore, the chemical formula of the nonlinear optical crystal is KAg2AsS4, which is a non - centrosymmetric structure, belongs to the orthorhombic system, and the space group is The unit - cell parameters are α = β = γ = 90°, Z = 2,

[0034]

[0035] The chemical formula of the nonlinear optical crystal is RbAg2AsS4, which is a non - centrosymmetric structure, belongs to the orthorhombic system, and the space group is The unit - cell parameters are α = β = γ = 90°, Z = 2, V =

[0036]

[0037] The chemical formula of the nonlinear optical crystal is NaAg2PS4, which has a non-centrosymmetric structure, belongs to the orthorhombic crystal system, and the space group is The unit cell parameters are α = β = γ = 90°, Z = 2, V =

[0038] The chemical formula of the nonlinear optical crystal is KAg2PS4, which has a non-centrosymmetric structure, belongs to the orthorhombic crystal system, and the space group is The unit cell parameters are α = β = γ = 90°, Z = 2, V =

[0039]

[0040] The chemical formula of the nonlinear optical crystal is RbAg2PS4, which has a non-centrosymmetric structure, belongs to the orthorhombic crystal system, and the space group is The unit cell parameters are α = β = γ = 90°, Z = 2, V =

[0041]

[0042] To achieve the above fourth object, the present invention adopts the following technical solutions:

[0043] The present invention discloses a method for preparing the above-mentioned silver-sulfur-based nonlinear optical crystal, which uses the horizontal gradient condensation method or the Bridgman method to prepare the nonlinear optical crystal.

[0044] Further, when the horizontal gradient condensation method is adopted, the steps are as follows:

[0045] After encapsulating the polycrystalline powder of the A1Ag2AsS4 compound or the polycrystalline powder of the A2Ag2PS4 compound, it is placed in a crystal growth furnace with a temperature gradient of 5-10 °C / cm, heated to melt the compound and maintained for 24-72 h, and then the temperature field is moved at a speed of 5-10 mm / d. During the movement of the temperature field, the crystal is grown. After the crystal growth is completed, it is cooled to room temperature at a cooling rate of 10-30 °C / h to obtain the crystal, where the growth period of the crystal is 10-20 d.

[0046] In a specific embodiment, the temperature gradient of the crystal growth furnace can be 5 °C / cm, 6 °C / cm, 7 °C / cm, 8 °C / cm, 9 °C / cm, 10 °C / cm, etc.

[0047] In a specific embodiment, the holding time after the compound is melted can be 24 h, 36 h, 48 h, 60 h, 72 h, etc.

[0048] In a specific embodiment, the speed of the moving temperature field can be 5 mm / d, 6 mm / d, 7 mm / d, 8 mm / d, 9 mm / d, 10 mm / d, etc.

[0049] In a specific embodiment, the cooling rate can be 10 °C / h, 15 °C / h, 20 °C / h, 25 °C / h, 30 °C / h, etc.

[0050] Further, when the crucible descent method is adopted, the steps are as follows:

[0051] After encapsulating the polycrystalline powder of A1Ag2AsS4 compound or the polycrystalline powder of A2Ag2PS4 compound, it is placed in a crystal growth furnace with a temperature gradient of 5 - 10 °C / cm, heated to melt the compound. After the compound is completely melted and held for 24 - 72 h, the quartz crucible descends vertically at a speed of 0.3 - 2.0 mm / h. During the descent of the crucible, the crystal grows. After the crystal growth is completed, it is cooled to room temperature at a cooling rate of 10 - 30 °C / h, and thus obtained, where the growth period of the crystal is 10 - 30 d.

[0052] In a specific embodiment, the temperature gradient of the crystal growth furnace can be 5 °C / cm, 6 °C / cm, 7 °C / cm, 8 °C / cm, 9 °C / cm, 10 °C / cm, etc.

[0053] In a specific embodiment, the holding time after the compound is melted can be 24 h, 36 h, 48 h, 60 h, 72 h, etc.

[0054] In a specific embodiment, the vertical descent speed of the quartz crucible can be 0.3 mm / h, 0.4 mm / h, 0.5 mm / h, 0.6 mm / h, 0.7 mm / h, 0.8 mm / h, 0.9 mm / h, 1.0 mm / h, 1.1 mm / h, 1.2 mm / h, 1.3 mm / h, 1.4 mm / h, 1.5 mm / h, 1.6 mm / h, 1.7 mm / h, 1.8 mm / h, 1.9 mm / h, 2.0 mm / h, etc.

[0055] In a specific embodiment, the cooling rate can be 10 °C / h, 15 °C / h, 20 °C / h, 25 °C / h, 30 °C / h, etc.

[0056] To achieve the above fifth object, the present invention adopts the following technical solutions:

[0057] The present invention discloses a nonlinear optical device, which includes an output radiation device that generates at least one beam of output radiation with a frequency different from that of the incident electromagnetic wave after passing at least one beam of incident electromagnetic wave through at least one nonlinear optical crystal, and the nonlinear optical crystal is selected from the thio - silver - based nonlinear optical crystals as described above.

[0058] The beneficial effects of the present invention are as follows:

[0059] The infrared nonlinear optical crystals of KAg2AsS4, RbAg2AsS4, NaAg2PS4, KAg2PS4, and RbAg2PS4 provided by the present invention have a non-centrosymmetric structure, are easy to grow, transparent and free of inclusions, and have the advantages of relatively fast growth rate, low cost, and easy access to large-sized crystals; the crystals have large nonlinear optical coefficients, wide transmission bands and band gaps, and the transmission bands of the crystals all cover the wavelength range of 0.53 - 15 μm. The powder second harmonic generation intensities of KAg2AsS4, RbAg2AsS4, NaAg2PS4, and KAg2PS4 are 1.05×AGS, 1.28×AGS, 1.36×AGS, and 1.34×AGS respectively; the optical band gaps are 2.21 eV, 2.32 eV, 2.58 eV, and 2.67 eV respectively, and they also have the advantages of good mechanical properties, easy processing and preservation.

[0060] The preparation method provided by the present invention can prepare high-quality and large-sized infrared nonlinear optical crystals of KAg2AsS4, RbAg2AsS4, NaAg2PS4, KAg2PS4, and RbAg2PS4.

[0061] The infrared nonlinear optical crystals of KAg2AsS4, RbAg2AsS4, NaAg2PS4, KAg2PS4, and RbAg2PS4 provided by the present invention have good application prospects in the manufacture of infrared laser frequency conversion devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] The following further elaborates on the specific embodiments of the present invention with reference to the accompanying drawings.

[0063] Figure 1 Shows the X-ray diffraction patterns of the KAg2AsS4 compound, RbAg2AsS4 compound, NaAg2PS4 compound, KAg2PS4 compound, and RbAg2PS4 compound prepared in Examples 1 - 5 of the present invention.

[0064] Figure 2 Shows the crystal structure of KAg2AsS4 prepared in Example 1 of the present invention.

[0065] Figure 3 Shows the crystal structure of RbAg2AsS4 prepared in Example 2 of the present invention.

[0066] Figure 4 Shows the crystal structure of NaAg2PS4 prepared in Example 3 of the present invention.

[0067] Figure 5Shows the crystal structure of KAg2PS4 prepared in Example 4 of the present invention.

[0068] Figure 6 Shows the crystal structure of RbAg2PS4 prepared in Example 5 of the present invention. Detailed implementation manners

[0069] To illustrate the present invention more clearly, the present invention will be further described below in conjunction with preferred embodiments and the accompanying drawings. Similar components in the drawings are denoted by the same reference numerals. Those skilled in the art should understand that the content specifically described below is illustrative rather than restrictive, and should not be used to limit the protection scope of the present invention.

[0070] Example 1

[0071] This example provides a KAg2AsS4 compound, which is prepared by the high-temperature solid-phase reaction method. The preparation method includes the following steps:

[0072] Weigh 1.10 g of K2S, 4.96 g of Ag2S, 2.46 g of As2S3, and 0.64 g of elemental sulfur, that is, the molar ratio of K2S:Ag2S:As2S3:S is 1:2:1:2. After uniform mixing, it is loaded into a quartz tube with a diameter of Φ16 mm × 100 mm. The quartz tube is evacuated to 10 -3 Pa and then melted and sealed. It is placed in a muffle furnace and heated to 400 °C at a rate of 30 °C / h, and kept warm for 48 h. After cooling, the sample is taken out to obtain the polycrystalline powder of the KAg2AsS4 compound. The crystal structure is shown in Figure 2 .

[0073] Example 2

[0074] This example provides an RbAg2AsS4 compound, which is prepared by the high-temperature solid-phase reaction method. The preparation method includes the following steps:

[0075] Weigh 2.03 g of Rb2S, 4.96 g of Ag2S, 2.46 g of As2S3, and 0.64 g of elemental sulfur, that is, the molar ratio of Rb2S:Ag2S:As2S3:S is 1:2:1:2. After uniform mixing, it is loaded into a quartz tube with a diameter of Φ16 mm × 100 mm. The quartz tube is evacuated to 10 -3 Pa and then melted and sealed. It is placed in a muffle furnace and heated to 500 °C at a rate of 40 °C / h, and kept warm for 72 h. After cooling, the sample is taken out to obtain the polycrystalline powder of the RbAg2AsS4 compound. The crystal structure is shown in Figure 3 .

[0076] Example 3

[0077] This embodiment provides a NaAg2PS4 compound, which is prepared by a high-temperature solid-phase reaction method. The preparation method includes the following steps:

[0078] Weigh 0.78 g of Na2S, 4.96 g of Ag2S, 1.58 g of P2S3, and 0.64 g of elemental sulfur, that is, the molar ratio of Na2S:Ag2S:P2S3:S is 1:2:1:2. After uniform mixing, load it into a quartz tube with a diameter of Φ16 mm and a length of 100 mm. Vacuum the quartz tube to 10 -3 Pa and perform melting and sealing. Then place it in a muffle furnace and heat it to 500 °C at a rate of 30 °C / h, hold for 36 h. After cooling, take out the sample to obtain the polycrystalline powder of the NaAg2PS4 compound. The crystal structure is shown in Figure 4 .

[0079] Example 4

[0080] This embodiment provides a KAg2PS4 compound, which is prepared by a high-temperature solid-phase reaction method. The preparation method includes the following steps:

[0081] Weigh 1.10 g of K2S, 4.96 g of Ag2S, 1.58 g of P2S3, and 0.64 g of elemental sulfur, that is, the molar ratio of K2S:Ag2S:P2S3:S is 1:2:1:2. After uniform mixing, load it into a quartz tube with a diameter of Φ16 mm and a length of 100 mm. Vacuum the quartz tube to 10 -3 Pa and perform melting and sealing. Then place it in a muffle furnace and heat it to 500 °C at a rate of 40 °C / h, hold for 48 h. After cooling, take out the sample to obtain the polycrystalline powder of the KAg2PS4 compound. The crystal structure is shown in Figure 5 .

[0082] Example 5

[0083] This embodiment provides a RbAg2PS4 compound, which is prepared by a high-temperature solid-phase reaction method. The preparation method includes the following steps:

[0084] Weigh 2.03 g of Rb2S, 4.96 g of Ag2S, 1.58 g of P2S3, and 0.64 g of elemental sulfur, that is, the molar ratio of Rb2S:Ag2S:P2S3:S is 1:2:1:2. After uniform mixing, load it into a quartz tube with a diameter of Φ16 mm and a length of 100 mm. Vacuum the quartz tube to 10 -3 Pa and perform melting and sealing. Then place it in a muffle furnace and heat it to 600 °C at a rate of 50 °C / h, hold for 54 h. After cooling, take out the sample to obtain the polycrystalline powder of the RbAg2PS4 compound. The crystal structure is shown in Figure 6 .

[0085] Figure 1The X-ray diffraction patterns of the compounds synthesized in Examples 1 to 5 are shown, and the structural parameters of the compounds synthesized in Examples 1 to 5 are listed in Table 1.

[0086] Table 1 Structural parameters of the compounds synthesized in Examples 1 to 5

[0087]

[0088] Example 6

[0089] The KAg2AsS4 nonlinear optical crystal was prepared by the horizontal gradient condensation method, which included the following steps:

[0090] The synthesized polycrystalline powder of KAg2AsS4 compound was loaded into a Φ16mm×40mm quartz crucible. After evacuating to 10 -3 Pa, it was sealed with a hydrogen-oxygen flame and placed in a crystal growth furnace (temperature gradient of 6 °C / cm). It was slowly heated to 500 °C to completely melt the raw materials and kept for 36 h. Then, the temperature field was moved at a speed of 8 mm / d. During the movement of the temperature field, the crystal was grown. The growth period of the crystal was 12 d. After the crystal growth was completed, it was cooled to room temperature at a cooling rate of 15 °C / h to obtain a transparent KAg2AsS4 nonlinear optical crystal. The obtained crystal size was 9.6 mm×10.2 mm×18.9 mm.

[0091] Example 7

[0092] The RbAg2AsS4 nonlinear optical crystal was prepared by the horizontal gradient condensation method, which included the following steps:

[0093] The synthesized polycrystalline powder of RbAg2AsS4 compound was loaded into a Φ16mm×40mm quartz crucible. After evacuating to 10 -3 Pa, it was sealed with a hydrogen-oxygen flame and placed in a crystal growth furnace (temperature gradient of 5 °C / cm). It was slowly heated to 500 °C to completely melt the raw materials and kept for 48 h. Then, the temperature field was moved at a speed of 7 mm / d. During the movement of the temperature field, the crystal was grown. The growth period of the crystal was 15 d. After the crystal growth was completed, it was cooled to room temperature at a cooling rate of 15 °C / h to obtain a transparent RbAg2AsS4 nonlinear optical crystal. The obtained crystal size was 11.4 mm×11.2 mm×20.5 mm.

[0094] Example 8

[0095] The NaAg2PS4 nonlinear optical crystal was prepared by the horizontal gradient condensation method, which included the following steps:

[0096] The synthesized polycrystalline powder of NaAg2PS4 compound was loaded into a Φ16mm×40mm quartz crucible. After evacuating to 10 -3After 10⁻³ Pa, it is sealed with a hydrogen-oxygen flame and then placed in a crystal growth furnace (temperature gradient: 8 °C / cm). It is slowly heated to 500 °C to completely melt the raw materials and kept for 48 h. Then, the temperature field is moved at a speed of 8 mm / d, and crystal growth is carried out during the movement of the temperature field. The crystal growth period is 12 d. After the crystal growth is completed, it is cooled to room temperature at a cooling rate of 20 °C / h to obtain a transparent NaAg₂PS₄ nonlinear optical crystal. The obtained crystal size is 7.4 mm × 7.6 mm × 15.2 mm.

[0097] Example 9

[0098] The horizontal gradient freezing method is used to prepare the KAg₂PS₄ nonlinear optical crystal, which includes the following steps:

[0099] The synthesized polycrystalline powder of the KAg₂PS₄ compound is loaded into a Φ16 mm × 40 mm quartz crucible, and the vacuum is pumped to 10 - 3 Pa. After being sealed with a hydrogen-oxygen flame, it is placed in a crystal growth furnace (temperature gradient: 5 °C / cm). It is slowly heated to 500 °C to completely melt the raw materials and kept for 72 h. Then, the temperature field is moved at a speed of 5 mm / d, and crystal growth is carried out during the movement of the temperature field. The crystal growth period is 20 d. After the crystal growth is completed, it is cooled to room temperature at a cooling rate of 15 °C / h to obtain a transparent KAg₂PS₄ nonlinear optical crystal. The obtained crystal size is 8.3 mm × 8.8 mm × 25.3 mm.

[0100] Example 10

[0101] The horizontal gradient freezing method is used to prepare the RbAg₂PS₄ nonlinear optical crystal, which includes the following steps:

[0102] The synthesized polycrystalline powder of the RbAg₂PS₄ compound is loaded into a Φ16 mm × 40 mm quartz crucible, and the vacuum is pumped to 10 -3 Pa. After being sealed with a hydrogen-oxygen flame, it is placed in a crystal growth furnace (temperature gradient: 5 °C / cm). It is slowly heated to 500 °C to completely melt the raw materials and kept for 48 h. Then, the temperature field is moved at a speed of 6 mm / d, and crystal growth is carried out during the movement of the temperature field. The crystal growth period is 15 d. After the crystal growth is completed, it is cooled to room temperature at a cooling rate of 15 °C / h to obtain a transparent RbAg₂PS₄ nonlinear optical crystal. The obtained crystal size is 7.6 mm × 8.0 mm × 15.1 mm.

[0103] Example 11

[0104] The Bridgman method is used to prepare the KAg₂AsS₄ nonlinear optical crystal, which includes the following steps:

[0105] The synthesized polycrystalline powder of KAg2AsS4 compound was loaded into a quartz crucible with a size of Φ16mm×40mm. After evacuating to 10 -3 Pa, it was sealed with a hydrogen-oxygen flame and then placed in a crystal growth furnace (temperature gradient: 6℃ / cm). It was slowly heated to 500℃ to completely melt the raw materials and maintained for 36h. Then, the quartz crucible was vertically lowered at a speed of 1.0mm / h, and growth was carried out during the lowering of the crucible. The crystal growth cycle was 15d. After the crystal growth was completed, it was cooled to room temperature at a rate of 20℃ / h, and a transparent KAg2AsS4 nonlinear optical crystal was obtained. The size of the obtained crystal was 10.0mm×9.6mm×24.1mm.

[0106] Example 12

[0107] The RbAg2AsS4 nonlinear optical crystal was prepared by the Bridgman method, which included the following steps:

[0108] The synthesized polycrystalline powder of RbAg2AsS4 compound was loaded into a quartz crucible with a size of Φ16mm×40mm. After evacuating to 10 -3 Pa, it was sealed with a hydrogen-oxygen flame and then placed in a crystal growth furnace (temperature gradient: 5℃ / cm). It was slowly heated to 500℃ to completely melt the raw materials and maintained for 36h. Then, the quartz crucible was vertically lowered at a speed of 1.2mm / h, and growth was carried out during the lowering of the crucible. The crystal growth cycle was 15d. After the crystal growth was completed, it was cooled to room temperature at a rate of 25℃ / h, and a transparent RbAg2AsS4 nonlinear optical crystal was obtained. The size of the obtained crystal was 9.7mm×9.5mm×23.3mm.

[0109] Example 13

[0110] The NaAg2PS4 nonlinear optical crystal was prepared by the Bridgman method, which included the following steps:

[0111] The synthesized polycrystalline powder of NaAg2PS4 compound was loaded into a quartz crucible with a size of Φ16mm×40mm. After evacuating to 10 -3 Pa, it was sealed with a hydrogen-oxygen flame and then placed in a crystal growth furnace (temperature gradient: 5℃ / cm). It was slowly heated to 500℃ to completely melt the raw materials and maintained for 48h. Then, the quartz crucible was vertically lowered at a speed of 1.5mm / h, and growth was carried out during the lowering of the crucible. The crystal growth cycle was 12d. After the crystal growth was completed, it was cooled to room temperature at a rate of 15℃ / h, and a transparent NaAg2PS4 nonlinear optical crystal was obtained. The size of the obtained crystal was 9.2mm×9.9mm×15.2mm.

[0112] Example 14

[0113] The KAg2PS4 nonlinear optical crystal is prepared by the Bridgman method, which includes the following steps:

[0114] The synthesized polycrystalline powder of KAg2PS4 compound is loaded into a Φ16mm×40mm quartz crucible, evacuated to 10 - 3 Pa, then sealed with a hydrogen-oxygen flame and placed in a crystal growth furnace (temperature gradient: 8℃ / cm). It is slowly heated to 500℃ to completely melt the raw materials and kept for 60h. Then the quartz crucible descends vertically at a speed of 0.5mm / h, and growth occurs during the descent of the crucible. The growth period of the crystal is 18d. After the crystal growth is completed, it is cooled to room temperature at a rate of 20℃ / h to obtain a transparent KAg2PS4 nonlinear optical crystal. The size of the obtained crystal is 9.4mm×10.2mm×26.3mm.

[0115] Example 15

[0116] The RbAg2PS4 nonlinear optical crystal is prepared by the Bridgman method, which includes the following steps:

[0117] The synthesized polycrystalline powder of RbAg2PS4 compound is loaded into a Φ16mm×40mm quartz crucible, evacuated to 10 -3 Pa, then sealed with a hydrogen-oxygen flame and placed in a crystal growth furnace (temperature gradient: 8℃ / cm). It is slowly heated to 500℃ to completely melt the raw materials and kept for 72h. Then the quartz crucible descends vertically at a speed of 0.3mm / h, and growth occurs during the descent of the crucible. The growth period of the crystal is 20d. After the crystal growth is completed, it is cooled to room temperature at a rate of 30℃ / h to obtain a transparent RbAg2PS4 nonlinear optical crystal. The size of the obtained crystal is 10.2mm×10.5mm×30.8mm.

[0118] Performance test

[0119] The following diffuse reflection spectroscopy tests are carried out on KAg2AsS4 of Example 1, RbAg2AsS4 of Example 2, NaAg2PS4 of Example 3, and KAg2PS4 of Example 4:

[0120] The diffuse reflection spectra of 4 powder samples in the wavelength range of 250nm - 2500nm are measured using a Cary 7000 ultraviolet-visible-near-infrared spectrophotometer, and polytetrafluoroethylene (PTFE) is used as the 100% reflection reference standard. The obtained data are converted into absorbance through the Kubelka-Munk equation a / S = (1 - R)^2 / 2R, where R is the reflectivity, and a and S are the absorption coefficient and scattering coefficient respectively. The optical band gaps of the samples are calculated by extrapolating the fitting of the linear region, and the results are 2.21eV, 2.32eV, 2.58eV, and 2.67eV respectively.

[0121] The KAg2AsS4 of Example 6, the RbAg2AsS4 of Example 7, the NaAg2PS4 of Example 8, and the KAg2PS4 of Example 9 were subjected to the following powder second-harmonic generation (SHG) tests:

[0122] Using an improved Kurtz-Perry measurement method, a Ho:Tm:Cr:YAG Q-switched laser with a wavelength of 2100 nm (1 Hz, 50 ns) was used to perform powder SHG tests on samples ground into five different size ranges of 40 μm - 74 μm, 74 μm - 105 μm, 105 μm - 150 μm, 150 μm - 200 μm, and 200 μm - 250 μm. The average value of the five SHG data obtained was taken as the SHG intensity of the nonlinear optical crystal. The AGS crystal was selected as a reference and sieved to the same particle size range as the samples. A photomultiplier tube was used to collect the SHG signal and recorded on a digital oscilloscope. The specific SHG intensities were 1.05×AGS, 1.28×AGS, 1.36×AGS, and 1.34×AGS, respectively.

[0123] The KAg2AsS4 of Example 6, the RbAg2AsSq of Example 7, the NaAg2PS4 of Example 8, and the KAg2PS4 of Example 9 were subjected to the following transmittance spectrum tests:

[0124] The transmittance spectra of the four crystals in the 0.2 μm - 2.5 μm band at room temperature were recorded using a Perkin Elmer Lambda 900 ultraviolet-visible-near-infrared spectrophotometer; the transmittance spectra of the four crystals in the 2.5 μm - 25 μm band were measured using a Varian Excalibur 3100 Fourier transform infrared spectrometer. The light-passing surfaces of the crystals used in the tests were polished with emery and CeO2. The test results showed that the transmission bands of the four crystals all covered the wavelength range of 0.53 μm - 15 μm.

[0125] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limiting the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is impossible to enumerate all the implementation manners here. Any obvious changes or variations derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A silver sulfide-based compound, characterized in that, The chemical formula of the silver sulfide compound is A1Ag2AsS4 or A2Ag2PS4, wherein A1=K or Rb, and A2=Na, K or Rb.

2. The preparation method of the silver sulfide-based compound according to claim 1, characterized in that, It is prepared by vacuum high temperature solid phase reaction method.

3. The preparation method according to claim 2, characterized in that, When preparing AlAg2AsS4, the preparation steps are: Mix the Ag compound, As compound, S compound, and Al compound evenly according to the molar ratio of Ag:As:S:Al of 2:1:4:1, seal them in a quartz tube, and then evacuate the quartz tube to ≤10 -3 Pa and perform melting and sealing; place the sealed quartz tube in a muffle furnace, heat it at a rate of 30 - 50 °C / h to 400 - 800 °C, keep it calcined for 10 - 72 h, and obtain polycrystalline powder of the AlAg2AsS4 compound after cooling; When preparing A2Ag2PS4, the preparation steps are: Mix the Ag-containing compound, P-containing compound, S-containing compound, and A2-containing compound evenly in a molar ratio of Ag:P:S:A2 of 2:1:4:1, seal them in a quartz tube, and then evacuate the quartz tube to ≤ 10 -3 Pa and carry out melting and sealing; place the sealed quartz tube in a muffle furnace, heat it at a rate of 30 - 50 °C / h to 400 - 800 °C, keep it calcined for 10 - 72 h, and cool to obtain polycrystalline powder of A2Ag2PS4 compound.

4. The preparation method according to claim 3, characterized in that, The Ag-containing compound is selected from at least one of Ag element, Ag sulfide, and Ag chloride; The As-containing compound is selected from at least one of elemental As and As sulfides; The P-containing compound is selected from at least one of P element and P sulfide; The Al-containing compound is at least one selected from K element, K oxide, K sulfide, K carbonate, K chloride, Rb element, Rb oxide, Rb sulfide, Rb carbonate, and Rb chloride; The A2-containing compound is at least one selected from the group consisting of Na elemental substance, Na oxide, Na sulfide, Na carbonate, Na chloride, K elemental substance, K oxide, K sulfide, K carbonate, K chloride, Rb elemental substance, Rb oxide, Rb sulfide, Rb carbonate, and Rb chloride; The S-containing compound is at least one selected from the group consisting of elemental S, Ag sulfide, As sulfide, P sulfide, Na sulfide, K sulfide, and Rb sulfide.

5. Sulfur-silver-based nonlinear optical crystal, characterized in that, The chemical formula of the nonlinear optical crystal is A1Ag2AsS4 or A2Ag2PS4, wherein A1=K or Rb, and A2=Na, K or Rb.

6. The nonlinear optical crystal according to claim 5, wherein The chemical formula of the nonlinear optical crystal is KAg2AsS4, which has a non-centrosymmetric structure, belongs to the orthorhombic system, and the space group is The unit cell parameters are α = β = γ = 90°, Z = 2, The chemical formula of the nonlinear optical crystal is RbAg2AsS4, which has a non-centrosymmetric structure, belongs to the orthorhombic crystal system, and the space group is The unit cell parameters are α = β = γ = 90°, Z = 2, The chemical formula of the non-linear optical crystal is NaAg2PS4. It has a non-centrosymmetric structure, belongs to the orthorhombic crystal system, and the space group is The unit cell parameters are α = β = γ = 90°, Z = 2, The chemical formula of the nonlinear optical crystal is KAg2PS4, which has a non-centrosymmetric structure, belongs to the orthorhombic crystal system, and the space group is The unit cell parameters are α = β = γ = 90°, Z = 2, The chemical formula of the non-linear optical crystal is RbAg2PS4, which has a non-centrosymmetric structure, belongs to the orthorhombic crystal system, and the space group is The unit cell parameters are α = β = γ = 90°, Z = 2, 7. The preparation method of the silver sulfide-based nonlinear optical crystal according to claim 5 or 6, characterized in that, The nonlinear optical crystal is prepared by adopting a horizontal gradient condensation method or a crucible descent method.

8. The preparation method according to claim 7, characterized in that, When the horizontal gradient condensation method is used, the steps are: After encapsulating the polycrystalline powder of the AlAg2AsS4 compound or the polycrystalline powder of the A2Ag2PS4 compound, the powder is placed in a crystal growth furnace with a temperature gradient of 5 to 10°C / cm, heated until the compound melts and maintained for 24 to 72 hours, and then the temperature field is moved at a speed of 5 to 10 mm / d. During the movement of the temperature field, the crystal grows. After the crystal growth is completed, the temperature is lowered to room temperature at a rate of 10 to 30°C / h to obtain the result, wherein the growth period of the crystal is 10 to 20 days.

9. The preparation method according to claim 7, characterized in that, When the crucible descent method is used, the steps are: After encapsulating the polycrystalline powder of the AlAg2AsS4 compound or the polycrystalline powder of the A2Ag2PS4 compound, the powder is placed in a crystal growth furnace with a temperature gradient of 5 to 10°C / cm, and the temperature is raised until the compound melts. After the compound is completely melted and maintained for 24 to 72 hours, the quartz crucible is vertically lowered at a speed of 0.3 to 2.0 mm / h, and the crystal grows during the lowering process of the crucible. After the crystal growth is completed, the temperature is lowered to room temperature at a cooling rate of 10 to 30°C / h to obtain the result, wherein the growth period of the crystal is 10 to 30 days.

10. A nonlinear optical device, characterized in that, The invention comprises a device for generating at least one output radiation beam having a frequency different from that of the incident electromagnetic wave after passing at least one beam of incident electromagnetic wave through at least one nonlinear optical crystal, wherein the nonlinear optical crystal is selected from the silver sulfide-based nonlinear optical crystal as described in claim 5 or 6.

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