Series of alkali metal composite cadmium molybdate halides, alkali metal composite cadmium molybdate halide nonlinear optical crystal, and preparation method and application of series of alkali metal composite cadmium molybdate halide nonlinear optical crystal

Abstract

The invention relates to a series of alkali metal composite cadmium molybdate halides and alkali metal composite cadmium molybdate halide nonlinear optical crystals as well as a preparation method and application of the alkali metal composite cadmium molybdate halide nonlinear optical crystals, the chemical general formula of the series of compounds and the crystals thereof is A2Cd2NaX3 (MoO4) 2, A is Rb and Cs, and X is Cl and Br and is Rb2Cd2NaCl3 (MoO4) 2, Cs2Cd2NaCl3 (MoO4) 2, Rb2Cd2NaBr3 (MoO4) 2 or Cs2Cd2NaBr3 (MoO4) 2. The series of crystals belong to an orthorhombic crystal system, the space group is Pba2, the cell parameter is # imgabs0 # # imgabs1 #, the series of alkali metal composite cadmium molybdate halides are synthesized by adopting a solid-phase reaction method or a hydrothermal method, and the series of nonlinear optical crystals grow by adopting a high-temperature melt method, a hydrothermal method or an aqueous solution method. The material can be used for manufacturing second harmonic generators, upper and lower frequency converters, optical parametric oscillators and the like.

Description

Technical Field

[0001] The present invention relates to a series of alkali metal composite cadmium molybdate halides and alkali metal composite cadmium molybdate halide nonlinear optical crystals and a preparation method and application thereof, and in particular to the application of nonlinear optical crystals in nonlinear optical devices, belonging to the field of nonlinear optical crystals in visible and infrared bands. Technical Background

[0002] Mid- and far-infrared coherent light with wavelengths between 3 and 14 μm is becoming increasingly important due to its potential applications in semiconductor lithography, laser micromachining, and modern scientific instruments. For solid-state lasers, obtaining mid- and far-infrared coherent light is achieved through cascade frequency conversion technology of nonlinear optical crystals. However, for applicable mid- and far-infrared nonlinear optical crystals, they must meet the following stringent structural and performance requirements, including i) non-centrosymmetric structure; ii) large second-order nonlinear optical coefficient (d ij ), at least with KDP's d 36 The following are some of the key properties of wide-bandgap materials: 1) high transparency in the mid- and far-infrared region; 2) moderate birefringence (Δn = 0.03-0.1), which satisfies the phase-matching conditions for mid- and far-infrared second harmonic generation; and 3) ease of preparation, non-toxicity, chemical stability, and good mechanical properties. However, paradoxically, wide-bandgap materials often exhibit small SHG response and birefringence, making the design and synthesis of mid- and far-infrared nonlinear optical crystals a significant challenge. Summary of the Invention

[0003] In order to solve the above technical problems, the present invention proposes a series of alkali metal composite cadmium molybdate halides and a series of alkali metal composite cadmium molybdate halide nonlinear optical crystals and their preparation methods and uses.

[0004] To achieve the above objectives, the present invention provides the following technical solutions:

[0005] One of the purposes of the present invention is to provide a preparation method of a series of alkali metal composite cadmium molybdate halides.

[0006] The second object of the present invention is to provide a method for preparing a series of alkali metal composite cadmium molybdate halide nonlinear optical crystals.

[0007] The third object of the present invention is to provide applications of a series of alkali metal composite cadmium molybdate halide nonlinear optical crystals.

[0008] One of the purposes of the present invention is achieved in that:

[0009] The present invention aims to provide a series of alkali metal composite cadmium molybdate halides, characterized in that the chemical formula of the series of alkali metal composite cadmium molybdate halides is A2Cd2NaX3(MoO4)2(A=Rb, Cs, X=Cl, Br), the molecular formula is Rb2Cd2NaCl3(MoO4)2, Cs2Cd2NaCl3(MoO4)2, Rb2Cd2NaBr3(MoO4)2 or Cs2Cd2NaBr3(MoO4)2, and the molecular weights are 844.98, 939.89, 978.33 and 1073.21 respectively. The series of alkali metal composite cadmium molybdate halide compounds are prepared by a solid phase reaction method, a hydrothermal method or an aqueous solution method according to the following chemical reaction formula:

[0010] 1)A2O(A=Rb,Cs)+2CdO+NaX(X=Cl,Br)+2HX(X=Cl,Br)+2MoO3→A2Cd2NaX3(MoO

[0011] 4)2(A=Rb, Cs, X=Cl, Br)+H2O↑

[0012] 2)A2CO3(A=Rb,Cs)+2CdX2(X=Cl,Br)+NaF+2H2MoO4→A2Cd2NaX3(MoO4)2(A=Rb,

[0013] Cs, X=Cl, Br)+CO2↑+HX↑(X=Cl, Br)+HF↑+H2O↑

[0014] 3)2AX(A=Rb,Cs,X=Cl,Br)+2CdCO3+NaOH+HX(X=Cl,Br)+(NH4)2Mo2O7→A2Cd2

[0015] NaX3(MoO4)2(A=Rb, Cs, X=Cl, Br)+2H2O↑+2CO2↑+2NH3↑

[0016] 4) 2AF(A=Rb, Cs)+2CdO+NaX(X=Cl, Br)+2HX(X=Cl, Br)+2MoO3→A2Cd2NaX3(MoO

[0017] 4)2(A=Rb, Cs, X=Cl, Br)+2HF↑

[0018] 5)A2CO3(A=Rb,Cs)+2CdCO3+NaOH+3HX(X=Cl,Br)+2MoO3→A2Cd2NaX3(MoO4)2(A

[0019] =Rb, Cs, X=Cl, Br)+2H2O↑+3CO2↑

[0020] 6)2AX(A=Rb,Cs,X=Cl,Br)+2Cd(HCO3)2+NaX(X=Cl,Br)+2(NH4)2MoO4→A2Cd2Na

[0021] X3(MoO4)2(A=Rb,Cs,X=Cl,Br)+4H2O↑+4CO2↑+4NH3↑

[0022] 7)2AOH(A=Rb,Cs)+Cd(HCO3)2+CdX2(X=Cl,Br)+NaX(X=Cl,Br)+2MoO3→A2Cd2Na

[0023] X3(MoO4)2(A=Rb,Cs,X=Cl,Br)+2H2O↑+2CO2↑

[0024] 8)AOH(A=Rb,Cs)+AF(A=Rb,Cs)+Cd(OH)2+CdX2(X=Cl,Br)+NaX(X=Cl,Br)+2H2

[0025] MoO4→A2Cd2NaX3(MoO4)2(A=Rb,Cs,X=Cl,Br)+3H2O↑+HF↑

[0026] 9)2AX(A=Rb,Cs,X=Cl,Br)+2CdF2+NaX(X=Cl,Br)+2(NH4)2MoO4→A2Cd2NaX3(Mo

[0027] O4)2(A=Rb,Cs,X=Cl,Br)+4HF↑+4NH3↑

[0028] 10)2AOH(A=Rb,Cs)+2Cd(OH)2+NaOH+3HX(X=Cl,Br)+2H2MoO4→A2Cd2NaX3(MoO4)

[0029] 2(A=Rb,Cs,X=Cl,Br)+7H2O↑

[0030] 11)A2SO3(A=Rb,Cs)+2CdSO3+NaOH+3HX(X=Cl,Br)+2(NH4)2MoO4→A2Cd2NaX3(Mo

[0031] O4)2(A=Rb,Cs,X=Cl,Br)+4H2O↑+3SO2↑+4NH3↑

[0032] 12)2AHCO3(A=Rb,Cs)+2Cd(HCO3)2+NaHCO3+3HX(X=Cl,Br)+2(NH4)2MoO4→A2Cd2

[0033] NaX3(MoO4)2(A=Rb, Cs, X=Cl, Br)+7H2O↑+7CO2↑+4NH3↑

[0034] The second object of the present invention is achieved in this way:

[0035] The present invention aims to provide a series of alkali metal composite cadmium molybdate halide nonlinear optical crystals, characterized in that the chemical formula of the series of alkali metal composite cadmium molybdate halide nonlinear optical crystals is A2Cd2NaX3(MoO4)2, wherein A=Rb, Cs, X=Cl, Br, has no symmetry center, belongs to the orthorhombic crystal system, has a space group Pba2, and has a unit cell parameter of Z = 2. A series of alkali metal composite cadmium molybdate halide nonlinear optical crystals are grown by a high temperature melt method, a hydrothermal method or an aqueous solution method.

[0036] The high-temperature melt method is used to grow A2Cd2NaX3(MoO4)2, wherein A=Rb, Cs, X=Cl, Br nonlinear optical crystals, and the molecular formulas are Rb2Cd2NaCl3(MoO4)2, Cs2Cd2NaCl3(MoO4)2, Rb2Cd2NaBr3(MoO4)2 or Cs2Cd2NaBr3(MoO4)2, respectively. The specific operation is carried out according to the following steps:

[0037] a. uniformly mixing a series of alkali metal composite cadmium molybdate halide single-phase polycrystalline powders with a flux, heating the mixture to a temperature of 350-700° C., maintaining the temperature for a period of time to obtain a mixed melt, and then cooling the mixture to a temperature of 300-650° C., wherein the molar ratio of the series of alkali metal composite cadmium molybdate halide single-phase polycrystalline powders to the flux is 1:0-20;

[0038] Alternatively, a mixture of a compound containing A=Rb, Cs, a compound containing cadmium, a compound containing sodium, a compound containing X=Cl, Br, and a molybdenum compound, or a mixture of a compound containing A=Rb, Cs, a compound containing cadmium, a compound containing sodium, a compound containing X=Cl, Br, a molybdenum compound and a flux is directly heated to a temperature of 350-700° C., kept constant for a period of time to obtain a mixed melt, and then cooled to a temperature of 300-650° C., wherein the molar ratio of the compound containing A=Rb, Cs, the compound containing cadmium, the compound containing sodium, the compound containing X=Cl, Br, the molybdenum compound and the flux is 1.5-2.5:1.5-2.5:0.5-1.5:2.5-3.5:1.5-2.5:0-20;

[0039] The flux mainly includes alkali metal salts, namely alkali metal carbonates, alkali metal nitrates, alkali metal sulfates, alkali metal phosphates, alkali metal halides, alkali metal oxides, alkali metal hydroxides, and at least one or more of cadmium carbonate, cadmium fluoride, cadmium oxide, hydrochloric acid, ammonium chloride, ammonium bromide, lead chloride, lead bromide, and molybdenum oxide.

[0040] The series of alkali metal composite cadmium molybdate halide single-phase polycrystalline powders are prepared by a solid-phase synthesis method, comprising the following steps: mixing a compound containing A=Rb, Cs, a cadmium-containing compound, a sodium-containing compound, a compound containing X=Cl, Br, and a molybdenum-containing compound, and adopting a solid-phase reaction method to prepare the series of compound alkali metal composite cadmium molybdate halide, wherein the molar ratio of the elements A=Rb, Cs in the compound containing A=Rb, Cs, the element cadmium in the cadmium-containing compound, the element sodium in the sodium-containing compound, the element X=Cl, Br in the compound containing X=Cl, Br, and the element molybdenum in the molybdenum-containing compound is 0.01%. The ratio is 1.5-2.5:1.5-2.5:0.5-1.5:2.5-3.5:1.5-2.5. Raw materials containing A=Rb, Cs compound, cadmium compound, sodium compound, X=Cl, Br compound and molybdenum compound are uniformly mixed, ground and placed in a muffle furnace, pre-burned to remove moisture and gas in the raw materials, cooled to room temperature, taken out and ground, placed in a muffle furnace for calcination, heated to 350-700°C, kept constant temperature for a period of time, cooled to room temperature, taken out and ground to obtain a series of alkali metal composite cadmium molybdate halide single-phase polycrystalline powders.

[0041] b. Preparing a series of alkali metal composite cadmium molybdate halide seed crystals: slowly cooling the mixed melt obtained in step a to room temperature, and spontaneously crystallizing to obtain a series of alkali metal composite cadmium molybdate halide seed crystals;

[0042] c. Place the crucible containing the mixed melt obtained in step a into a crystal growth furnace, fix the seed crystal obtained in step b on the seed crystal rod, lower the seed crystal from the top of the crystal growth furnace, preheat the seed crystal rod, lower the seed crystal until it contacts the surface of the mixed melt or melts back in the mixed melt, maintain the temperature for a period of time, and then slowly reduce the temperature to the saturation temperature;

[0043] d. Continue to slowly cool down and rotate the seed crystal rod to grow the crystal. After the single crystal grows to the required size, lift the crystal from the surface of the mixed melt and slowly cool it to room temperature. Then take the crystal out of the furnace to obtain a series of alkali metal composite cadmium molybdate halide nonlinear optical crystals.

[0044] The aqueous solution method for growing A2Cd2NaX3(MoO4)2, wherein A=Rb, Cs, X=Cl, Br nonlinear optical crystals, is specifically performed in the following steps:

[0045] A compound containing A=Rb, Cs, a cadmium compound, a sodium compound, a compound containing X=Cl, Br, and a molybdenum compound are added to a beaker, followed by 0.1-400 mL of deionized water. The solution is stirred until clear. The beaker is then placed on a heating table and heated to 25-400°C. After a period of time, a series of alkali metal complex cadmium molybdate halide nonlinear optical crystals are obtained. To further grow the crystals, seed crystals of the series are suspended in the solution using a fine platinum wire. To reduce water evaporation, the beaker is covered with a polyethylene sheet pierced with several dozen millimeter-sized holes. After a period of time, a centimeter-sized alkali metal complex cadmium molybdate halide nonlinear optical crystal is removed from the solution.

[0046] The hydrothermal method for growing A2Cd2NaX3(MoO4)2, wherein A=Rb, Cs, X=Cl, Br nonlinear optical crystals, is specifically performed in the following steps:

[0047] a. Adding an A=Rb, Cs compound, a cadmium-containing compound, a sodium-containing compound, an X=Cl, Br compound and a molybdenum-containing compound to a polytetrafluoroethylene liner of an autoclave, and then adding 0.1-50 mL of deionized water and 0.1-50 g of a mineralizer, and mixing them thoroughly to obtain a mixed solution, wherein the molar ratio of the A=Rb, Cs compound, the cadmium-containing compound, the sodium-containing compound, the X=Cl, Br compound and the molybdenum-containing compound is 1-3:1-3:0-2:2-4:1-3;

[0048] b. Tighten the polytetrafluoroethylene-lined lid of the mixed solution in step a, then place it into the corresponding high-pressure reactor, and tighten the reactor piston;

[0049] c. Place the autoclave in step b in a thermostat, heat it to 160-250°C at a heating rate of 10°C / h, keep the temperature constant for a period of time, and then cool it to room temperature;

[0050] d. Open the high-pressure reactor and filter the solution containing the crystals to obtain a series of transparent alkali metal composite cadmium molybdate halide nonlinear optical crystals.

[0051] The third object of the present invention is achieved in this way:

[0052] The aforementioned series of alkali metal composite cadmium molybdate halide nonlinear optical crystals are suitable for use in mid- and far-infrared laser frequency conversion devices, infrared communication devices, infrared laser guidance devices, and in the preparation of nonlinear optical devices such as second harmonic generators, up- or down-frequency converters, or optical parametric oscillators. The series of alkali metal composite cadmium molybdate halide nonlinear optical crystals obtained using the method of the present invention can be used as a nonlinear optical device, depending on the device application requirements. The device comprises a device that generates at least one output beam of radiation having a frequency different from the incident electromagnetic radiation after passing at least one nonlinear optical device through at least one incident electromagnetic radiation. The nonlinear optical crystal is an A2Cd2NaX3(MoO4)2 (A=Rb, Cs, X=Cl, Br) crystal, with the molecular formulas being Rb2Cd2NaCl3(MoO4)2, Cs2Cd2NaCl3(MoO4)2, Rb2Cd2NaBr3(MoO4)2, or Cs2Cd2NaBr3(MoO4)2, respectively.

[0053] Compared with the existing technology, the present invention has the following advantages and technical effects: the series of alkali metal composite cadmium molybdate halide nonlinear optical crystal products are high in purity, the crystals are easy to grow and are transparent and without wrapping, and have the advantages of fast growth rate, low cost, and easy acquisition of larger-sized crystals; the obtained crystals have a relatively wide light transmission band, high hardness, good mechanical properties, are not easy to break and deliquesce, and are easy to process and preserve. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The accompanying drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0055] Figure 1 The XRD spectrum of the compound Cs2Cd2NaCl3(MoO4)2 powder prepared in Example 1 of the present invention;

[0056] Figure 2 The crystal structure diagram of the series of alkali metal composite cadmium molybdate halides A2Cd2NaX3(MoO4)2, A=Rb, Cs, X=Cl, Br prepared in Example 1 of the present invention;

[0057] Figure 3 This is a working principle diagram of the nonlinear optical device made in the present invention, where 1 is the laser, 2 is the emitted light beam, 3 is a series of nonlinear optical crystals of alkali metal composite cadmium molybdate halides, 4 is the output light beam, and 5 is the filter. DETAILED DESCRIPTION

[0058] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0059] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0060] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0061] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0062] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0063] The technical solution of the present invention is further illustrated by the following examples.

[0064] Example 1

[0065] According to the reaction formula: A2O(A=Rb, Cs)+2CdO+NaX+2HX(X=Cl, Br)+2MoO3→A2Cd2NaX3(MoO4)2(A=Rb, Cs, X=Cl, Br)+H2O↑, the compound A2Cd2NaX3(MoO4)2(A=Rb, Cs, X=Cl, Br) is synthesized:

[0066] a. Weigh A2O (A = Rb, Cs), CdO, NaX (X = Cl, Br), HX (X = Cl, Br), and MoO3 in a molar ratio of 1:2:1:2:2, add them to a polytetrafluoroethylene liner of a 23 mL autoclave, and then add 1 mL of deionized water and mix thoroughly to obtain a mixed solution;

[0067] b. Tighten the polytetrafluoroethylene-lined lid of the mixed solution in step a, then place it into a clean and pollution-free high-pressure reactor, and tighten the reactor piston;

[0068] c. Place the autoclave in step b in a thermostat, raise the temperature to 220°C at a heating rate of 10°C / h, maintain the temperature for 10 days, and then cool to room temperature at a cooling rate of 3°C / h;

[0069] d. Open the high-pressure reactor and filter the solution containing the crystals to obtain a series of alkali metal complex cadmium molybdate halides, and the obtained products are transparent crystals.

[0070] Example 2

[0071] According to the reaction formula: A2CO3(A=Rb,Cs)+2CdX2(X=Cl,Br)+NaF+2H2MoO4→A2Cd2NaX3(MoO4)2(A=Rb,Cs,X=Cl,Br)+CO2↑+HX↑(X=Cl,Br)+HF↑+H2O↑, the compound A2Cd2NaX3(MoO4)2(A=Rb,Cs,X=Cl,Br) is synthesized:

[0072] A2CO3 (A=Rb, Cs), CdX2 (X=Cl, Br), NaF, and H2MoO4 are weighed in a molar ratio of 1:2:1:2 and placed in a mortar, mixed and carefully ground, then loaded into an open corundum crucible of Φ100mm×100mm, placed in a muffle furnace, slowly heated to 350°C, maintained at this temperature for 24 hours, cooled to room temperature, taken out and placed in a muffle furnace after grinding for the second time, then heated to 550°C, maintained at this temperature for 24 hours, cooled to room temperature, taken out and placed in a muffle furnace after grinding for the third time, then maintained at this temperature at 550°C for 48 hours, taken out and ground to obtain a series of alkali metal composite cadmium molybdate halide single-phase polycrystalline powders, and the product is subjected to X-ray analysis, and the obtained X-ray spectrum is consistent with the X-ray spectrum obtained from the single crystal structure of the series of alkali metal composite cadmium molybdate halide A2Cd2NaX3(MoO4)2(A=Rb, Cs, X=Cl, Br);

[0073] The obtained series of alkali metal composite cadmium molybdate halide A2Cd2NaX3(MoO4)2 (A=Rb, Cs, X=Cl, Br) single-phase polycrystalline powders were placed in a Φ100mm×100mm open platinum crucible, heated to 650°C at a heating rate of 30°C / h, kept at this temperature for 3 hours to obtain a mixed melt, and then cooled to 610°C;

[0074] The temperature was slowly lowered to room temperature at a rate of 0.5°C / h, and a series of alkali metal complex cadmium molybdate halide seed crystals were obtained by spontaneous crystallization;

[0075] Growing crystals in compound melts: Fix the obtained A2Cd2NaX3(MoO4)2 (A=Rb, Cs, X=Cl, Br) seed crystals on a seed crystal rod and remove them from the top of the crystal growth furnace. Preheat the seed crystals on the surface of the mixed melt for 10 minutes, immerse them in the liquid surface, and allow them to melt back in the mixed melt. Keep the temperature constant for 30 minutes and then quickly cool them to the saturation temperature of 600℃.

[0076] Then cool down at a rate of 0.1℃ / day, rotate the seed crystal rod at a speed of 10rpm, and after the crystal growth is completed, separate the crystal from the liquid surface and cool the temperature to room temperature at a rate of 10℃ / h to obtain A2Cd2NaX3(MoO4)2(A=Rb, Cs, X=Cl, Br) crystals with a size of 18mm×11mm×5mm.

[0077] Example 3

[0078] According to the reaction formula: 2ACl(A=Rb,Cs)+2CdCO3+NaOH+HX(X=Cl,Br)+(NH4)2Mo2O7→A2Cd2NaX3(MoO4)2(A=Rb,Cs,X=Cl,Br)+2H2O↑+2CO2↑+2NH3↑, the compound A2Cd2NaX3(MoO4)2(A=Rb,Cs,X=Cl,Br) is synthesized:

[0079] A solution of ACl (A = Rb, Cs), CdCO₃, NaOH, HX (X = Cl, Br), and (NH₄)₂Mo₂Oₐ (in a molar ratio of 2:2:1:1:1) was weighed directly into a 1000mL beaker. 400mL of deionized water was then added and stirred until the solution became clear. The beaker was then placed on a heating plate and heated to 400°C. After seven days, the resulting series of alkali metal complex cadmium molybdate halide nonlinear optical crystals were obtained. To further grow the crystals, seed crystals of the series were suspended in the solution using a fine platinum wire. To minimize water evaporation, the beaker was covered with a polyethylene sheet punctured with several dozen millimeter-sized holes. After five weeks, a centimeter-sized alkali metal complex cadmium molybdate halide nonlinear optical crystal was removed from the solution.

[0080] Example 4

[0081] According to the reaction formula: 2AF (A = Rb, Cs) + 2CdO + NaX (X = Cl, Br) + 2HX (X = Cl, Br) + 2MoO3 → A2Cd2NaX3 (MoO4)2 (A = Rb, Cs, X = Cl, Br) + 2HF↑, the compound A2Cd2NaX3 (MoO4)2 (A = Rb, Cs, X = Cl, Br) is synthesized:

[0082] a. Weigh AF (A = Rb, Cs), CdO, NaX (X = Cl, Br), HX (X = Cl, Br), and MoO3 in a molar ratio of 2:2:1:2:2, add them to the polytetrafluoroethylene liner of a 150 mL autoclave, and then add 30 mL of deionized water, mix them thoroughly, and obtain a mixed solution;

[0083] b. Tighten the polytetrafluoroethylene-lined lid of the mixed solution in step a, then place it into a clean and pollution-free high-pressure reactor, and tighten the reactor piston;

[0084] c. Place the autoclave in step b in a thermostat, raise the temperature to 160°C at a heating rate of 10°C / h, maintain the temperature for 10 days, and then cool to room temperature at a cooling rate of 3°C / h;

[0085] d. Open the high-pressure reactor and filter the solution containing the crystals to obtain a series of alkali metal complex cadmium molybdate halides, and the obtained products are transparent crystals.

[0086] Example 5

[0087] According to the reaction formula: A2CO3(A=Rb, Cs)+2CdCO3+NaOH+3HX(X=Cl, Br)+2MoO3→A2Cd2NaX3(MoO4)2(A=Rb, Cs, X=Cl, Br)+2H2O↑+3CO2↑, the compound A2Cd2NaX3(MoO4)2(A=Rb, Cs, X=Cl, Br) is synthesized:

[0088] a. Weigh A2CO3 (A = Rb, Cs), CdCO3, NaOH, HX (X = Cl, Br), and MoO3 in a molar ratio of 1:2:1:3:2, add them to a polytetrafluoroethylene liner of a 100 mL autoclave, and then add 25 mL of deionized water, mix them thoroughly, and obtain a mixed solution;

[0089] b. Tighten the polytetrafluoroethylene-lined lid of the mixed solution in step a, then place it into a clean and pollution-free high-pressure reactor, and tighten the reactor piston;

[0090] c. Place the autoclave in step b in a thermostat, raise the temperature to 250°C at a heating rate of 10°C / h, maintain the temperature for 10 days, and then cool to room temperature at a cooling rate of 3°C / h;

[0091] d. Open the high-pressure reactor and filter the solution containing the crystals to obtain a series of alkali metal complex cadmium molybdate halides, and the obtained products are transparent crystals.

[0092] Example 6

[0093] According to the reaction formula: 2AX(A=Rb,Cs)+2Cd(HCO3)2+NaX(X=Cl,Br)+2(NH4)2MoO4→A2Cd2NaX3(MoO4)2(A=Rb,Cs,X=Cl,Br)+4H2O↑+4CO2↑+4NH3↑, the compound A2Cd2NaX3(MoO4)2(A=Rb,Cs,X=Cl,Br) is synthesized:

[0094] AX (A = Rb, Cs), Cd (HCO3) 2, NaX (X = Cl, Br), (NH4) 2MoO4 are directly weighed in a molar ratio of 2:2:1:2, and the weighed raw materials are mixed with a flux Cd (HCO3) 2-MoO3 in a molar ratio of 7:3, wherein the molar ratio of Cd (HCO3) 2 to MoO3 is 2:1, and the mixture is placed in a Φ100 mm × 100 mm open platinum crucible, heated to 550 ° C, kept at this temperature for 30 hours to obtain a mixed melt, and then cooled to 530 ° C;

[0095] The temperature was slowly lowered to room temperature at a rate of 3.5°C / h, and a series of alkali metal complex cadmium molybdate halide seed crystals were obtained by spontaneous crystallization;

[0096] The obtained A2Cd2NaX3(MoO4)2 (A=Rb, Cs, X=Cl, Br) seed crystals were fixed on a seed crystal rod and unloaded from the top of the crystal growth furnace. The seed crystals were preheated on the surface of the mixed melt for 10 minutes, immersed in the liquid surface, and melted back in the mixed melt. The temperature was kept constant for 30 minutes and then rapidly cooled to the saturation temperature of 515℃.

[0097] Then slowly cool down the temperature at a rate of 3°C / day without rotating the seed crystal rod. After the crystal growth is completed, separate the crystal from the liquid surface and cool the temperature to room temperature at a rate of 20°C / h. Then take the crystal out of the furnace to obtain A2Cd2NaX3(MoO4)2 (A=Rb, Cs, X=Cl, Br) crystals with a size of 18mm×11mm×5mm.

[0098] Example 7

[0099] According to the reaction formula: 2AOH(A=Rb,Cs)+Cd(HCO3)2+CdX2(X=Cl,Br)+NaX(X=Cl,Br)+2MoO3→A2Cd2NaX3(MoO4)2(A=Rb,Cs,X=Cl,Br)+2H2O↑+2CO2↑, the compound A2Cd2NaX3(MoO4)2(A=Rb,Cs,X=Cl,Br) is synthesized:

[0100] AOH (A = Rb, Cs), Cd (HCO3)2, CdX2 (X = Cl, Br), NaX (X = Cl, Br), and MoO3 are directly weighed in a molar ratio of 2:1:1:1:2, and the weighed raw materials are mixed with flux AOH (A = Rb, Cs)-MoO3 in a molar ratio of 7:4, wherein the molar ratio of AOH (A = Rb, Cs) to MoO3 is 3:5, and the mixture is placed in an open platinum crucible of Φ100mm×100mm, heated to 700°C, kept at this temperature for 30 hours to obtain a mixed melt, and then cooled to 650°C;

[0101] The temperature was slowly lowered to room temperature at a rate of 1.5°C / h, and a series of alkali metal complex cadmium molybdate halide seed crystals were obtained by spontaneous crystallization;

[0102] The obtained A2Cd2NaX3(MoO4)2 (A=Rb, Cs, X=Cl, Br) seed crystals were fixed on a seed crystal rod and unloaded from the top of the crystal growth furnace. The seed crystals were preheated on the surface of the mixed melt for 10 minutes, immersed in the liquid surface, and melted back in the mixed melt. The temperature was kept constant for 30 minutes and then rapidly cooled to the saturation temperature of 600℃.

[0103] The temperature is then lowered at a rate of 1°C / day without rotating the seed crystal rod. After the crystal growth is complete, the crystal is separated from the liquid surface and the temperature is lowered to room temperature at a rate of 20°C / h. The crystal is then removed from the furnace to obtain an A2Cd2NaX3(MoO4)2 (A=Rb, Cs, X=Cl, Br) crystal with a size of 15mm×10mm×4mm. Example 8

[0104] According to the reaction formula: AOH (A = Rb, Cs) + AF (A = Rb, Cs) + Cd (OH) 2 + CdX 2 (X = Cl, Br) + NaX (A = Rb, Cs) + 2H 2 MoO 4 → A 2 Cd 2 NaX 3 (MoO 4) 2 (A = Rb, Cs, X = Cl, Br) + 3H 2 O ↑ + HF ↑, the compound A 2 Cd 2 NaX 3 (MoO 4) 2 (A = Rb, Cs, X = Cl, Br) is synthesized:

[0105] AOH (A = Rb, Cs), AF (A = Rb, Cs), Cd (OH) 2, CdX 2 (X = Cl, Br), NaX (X = Cl, Br), and H 2 MoO 4 are directly weighed in a molar ratio of 1:1:1:1:1:2, and the weighed raw materials are mixed with a flux NaOH-H 2 MoO 4 in a molar ratio of 7:3, wherein the molar ratio of NaOH to H 2 MoO 4 is 2:5, and the mixture is placed in an open platinum crucible of Φ100 mm × 100 mm, and the temperature is raised to 350° C. and kept constant for 60 hours to obtain a mixed melt, which is then cooled to 330° C.;

[0106] The temperature was slowly lowered to room temperature at a rate of 3.5°C / h, and a series of alkali metal complex cadmium molybdate halide seed crystals were obtained by spontaneous crystallization;

[0107] The obtained A2Cd2NaX3(MoO4)2 (A=Rb, Cs, X=Cl, Br) seed crystals were fixed on a seed crystal rod and unloaded from the top of the crystal growth furnace. The seed crystals were preheated on the surface of the mixed melt for 15 minutes, immersed in the liquid surface, and melted back in the mixed melt. The temperature was kept constant for 30 minutes and then rapidly cooled to the saturation temperature of 315°C.

[0108] Then cool down at a rate of 3°C / day, rotate the seed crystal crucible at a speed of 5 rpm, and after the crystal growth is completed, separate the crystal from the liquid surface and cool the temperature to room temperature at a rate of 1°C / h. Then take the crystal out of the furnace to obtain A2Cd2NaX3(MoO4)2 (A=Rb, Cs, X=Cl, Br) crystals with a size of 18mm×11mm×5mm.

[0109] Example 9

[0110] According to the reaction formula: 2AX(A=Rb,Cs)+2CdF2+NaA(A=Rb,Cs)+2(NH4)2MoO4→A2Cd2NaX3(MoO4)2(A=Rb,Cs,X=Cl,Br)+4HF↑+4NH3↑, the compound A2Cd2NaX3(MoO4)2(A=Rb,Cs,X=Cl,Br) is synthesized:

[0111] AX (A = Rb, Cs), CdF2, NaX (X = Cl, Br), (NH4)2MoO4 are directly weighed in a molar ratio of 2:2:1:2, and the weighed raw materials are mixed with flux AOH (A = Rb, Cs)-NaOH-H2MoO4 in a molar ratio of 1:5, wherein the molar ratio of NaOH, AOH (A = Rb, Cs) and H2MoO4 is 3:3:5, and the mixture is placed in a Φ100mm×100mm open platinum crucible, heated to 450°C, kept at this temperature for 60 hours to obtain a mixed melt, and then cooled to 400°C;

[0112] The temperature was slowly lowered to room temperature at a rate of 3.5°C / h, and a series of alkali metal complex cadmium molybdate halide seed crystals were obtained by spontaneous crystallization;

[0113] The obtained A2Cd2NaX3(MoO4)2 (A=Rb, Cs, X=Cl, Br) seed crystals were fixed on a seed crystal rod and unloaded from the top of the crystal growth furnace. The seed crystals were preheated on the surface of the mixed melt for 15 minutes, immersed in the liquid surface, and melted back in the mixed melt. The temperature was kept constant for 30 minutes and then rapidly cooled to the saturation temperature of 405℃.

[0114] Then cool down at a rate of 3°C / day without rotating the seed crystal rod. After the crystal growth is completed, separate the crystal from the liquid surface and cool the temperature to room temperature at a rate of 1°C / h. Then take the crystal out of the furnace to obtain A2Cd2NaX3(MoO4)2 (A=Rb, Cs, X=Cl, Br) crystals with a size of 18mm×11mm×5mm.

[0115] Example 10

[0116] According to the reaction formula: 2AOH (A = Rb, Cs) + 2Cd (OH) 2 + NaOH + 3HX (X = Cl, Br) + 2H2MoO4 → A2Cd2Na X3 (MoO4) 2 (A = Rb, Cs, X = Cl, Br) + 7H2O↑, the compound A2Cd2NaX3 (MoO4) 2 (A = Rb, Cs, X = Cl, Br) is synthesized:

[0117] AOH (A = Rb, Cs), Cd(OH)2, NaOH, HX (X = Cl, Br), and H2MoO4 were weighed directly into a 100mL beaker in a molar ratio of 2:2:1:3:2. 20mL of deionized water was then added and stirred until the solution was clear. The beaker was then placed on a heating plate and heated to 300°C. After seven days, the resulting series of alkali metal complex cadmium molybdate halide nonlinear optical crystals were obtained. To further grow the crystals, seed crystals of the series were suspended in the solution using a fine platinum wire. To minimize water evaporation, the beaker was covered with a polyethylene sheet punctured with several dozen millimeter-sized holes. After three weeks, a centimeter-sized alkali metal complex cadmium molybdate halide nonlinear optical crystal was removed from the solution.

[0118] Example 11

[0119] According to the reaction formula: A2SO3(A=Rb,Cs)+2CdSO3+NaOH+3HX(X=Cl,Br)+2(NH4)2MoO4→A2Cd2NaX3(MoO4)2(A=Rb,Cs,X=Cl,Br)+4H2O↑+3SO2↑+4NH3↑, the compound A2Cd2NaX3(MoO4)2(A=Rb,Cs,X=Cl,Br) is synthesized:

[0120] A2SO3 (A = Rb, Cs), CdSO3, NaOH, HX (X = Cl, Br), and (NH4)2MoO4 were weighed directly into a 50mL beaker in a molar ratio of 1:2:1:3:2. 10mL of deionized water was then added and stirred until the solution was clear. The beaker was then placed on a heating plate and heated to 150°C. After 9 days, the resulting series of alkali metal complex cadmium molybdate halide nonlinear optical crystals were obtained. To further grow the crystals, seed crystals of the series were suspended in the solution using a fine platinum wire. To minimize water evaporation, the beaker was covered with a polyethylene sheet punctured with several dozen millimeter-sized holes. After 5 weeks, a centimeter-sized series of alkali metal complex cadmium molybdate halide nonlinear optical crystals were removed from the solution.

[0121] Example 12

[0122] According to the reaction formula: 2AHCO3(A=Rb,Cs)+2Cd(HCO3)2+NaHCO3+3HX(X=Cl,Br)+2(NH4)2MoO4→A2Cd2NaX3(MoO4)2(A=Rb,Cs,X=Cl,Br)+7H2O↑+7CO2↑+4NH3↑, the compound A2Cd2NaX3(Mo O4)2(A=Rb,Cs,X=Cl,Br) is synthesized:

[0123] AHCO₃ (A = Rb, Cs), Cd(HCO₃)₂, NaHCO₃, HX (X = Cl, Br), and (NH₄)₂MoO₄ were weighed directly into a 10mL beaker in a molar ratio of 2:2:1:3:2. 2mL of deionized water was then added and stirred until the solution became clear. The beaker was then placed on a heating plate and heated to 25°C. After seven days, the resulting series of alkali metal complex cadmium molybdate halide nonlinear optical crystals were obtained. To further grow the crystals, seed crystals of the series were suspended in the solution using a fine platinum wire. To minimize water evaporation, the beaker was covered with a polyethylene sheet punctured with several dozen millimeter-sized holes. After four weeks, a centimeter-sized alkali metal complex cadmium molybdate halide nonlinear optical crystal was removed from the solution.

[0124] Example 13

[0125] Process any Rb2Cd2NaCl3(MoO4)2, Cs2Cd2NaCl3(MoO4)2, Rb2Cd2NaBr3(MoO4)2 or Cs2Cd2NaBr3(MoO4)2 crystal obtained in Examples 1-12 into a single crystal device in a matching direction. Figure 3 As shown in the position 3, at room temperature, a Nd:YAG Q-switched laser light source with a wavelength of 1064nm is used as a pump source to inject Rb2Cd2NaCl3(MoO4)2, Cs2Cd2NaCl3(MoO4)2, Rb2Cd2NaBr3(MoO4)2 or Cs2Cd2NaBr3(MoO4)2 nonlinear optical crystal 3 to generate frequency-doubled light with a wavelength of 532nm. The output light beam 4 contains infrared light with a wavelength of 1064nm and frequency-doubled light of 532nm, which is filtered out by the filter 5 to obtain a laser with a wavelength of 532nm.

[0126] Example 14

[0127] Any Rb2Cd2NaCl3(MoO4)2, Cs2Cd2NaCl3(MoO4)2, Rb2Cd2NaBr3(MoO4)2 or Cs2Cd2NaBr3(MoO4)2 crystals obtained in Examples 1-12 are processed into single crystal devices after directional cutting and polishing. A 1064nm Nd:YAG Q-switched laser light source is used as a pump source to generate a laser output with a wavelength shorter than 532nm.

[0128] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A series of alkali metal composite cadmium molybdate halides, characterized in that: The general molecular formula of this series of alkali metal complex cadmium molybdate halides is A2Cd2NaX3(MoO4)2, wherein A=Rb, Cs, X=Cl, Br, and the molecular formulas are Rb2Cd2NaCl3(MoO4)2, Cs2Cd2NaCl3(MoO4)2, Rb2Cd2NaBr3(MoO4)2 or Cs2Cd2NaBr3(MoO4)2, and the molecular weights are 844.98, 939.89, 978.33, and 1073.21, respectively.

2. A method for preparing a series of alkali metal composite cadmium molybdate halides, characterized in that: Prepared by solid phase reaction method or hydrothermal method.

3. The method for preparing a series of alkali metal composite cadmium molybdate halide compounds according to claim 2, wherein: The specific operation of preparing A2Cd2NaX3(MoO4)2, wherein A=Rb, Cs, X=Cl, Br compound, by the solid phase reaction method is as follows: uniformly mixing a compound containing A=Rb, Cs, a cadmium-containing compound, a sodium-containing compound, a compound containing X=Cl, Br, and a molybdenum-containing compound, grinding the mixture, calcining and grinding the mixture in a muffle furnace, and obtaining a series of alkali metal composite cadmium molybdate halide single-phase polycrystalline powders, wherein the molar ratio of the element A in the compound containing A=Rb, Cs, the element cadmium in the cadmium-containing compound, the element sodium in the sodium-containing compound, the element X in the compound containing X=Cl, Br, and the element molybdenum in the molybdenum-containing compound is 1.5-2.5:1.5-2.5:0.5-1.5:2.5-3.5:1.5-2.5; The specific operation of preparing A2Cd2NaX3(MoO4)2, wherein A=Rb, Cs, X=Cl, Br, by the hydrothermal method is as follows: adding a compound containing A=Rb, Cs, a cadmium-containing compound, a sodium-containing compound, a compound containing X=Cl, Br, and a molybdenum-containing compound to a polytetrafluoroethylene liner of an autoclave, then adding 0.1-50 mL of deionized water and 0.1-50 g of a mineralizer, and mixing them thoroughly to obtain a mixed solution, wherein the molar ratio of the compound containing A=Rb, Cs, the cadmium-containing compound, the sodium-containing compound, the compound containing X=Cl, Br, and the molybdenum-containing compound is 1-3:1-3:1-2:1-4:1-3, placing the polytetrafluoroethylene liner into the autoclave, and placing the autoclave in a constant temperature. The method comprises heating the mixture in an incubator at a heating rate of 10° C. / h to 160-250° C., maintaining the temperature for 10 days, cooling the mixture to room temperature, and filtering the solution containing the powder to obtain a series of alkali metal complex cadmium molybdate halides; the mineralizer comprises at least one or more of AOH, A2O, A2CO3, AF, ACl, ABr, CdO, Cd(OH)2, Cd(NO3)2, CdCO3, CdCl2, NaOH, Na2O, NaH2PO4, Na2SO4, Na2SiO3, NH4X, KX, CaX2, MoO3, H2MoO4, (NH4)2Mo2O7, and (NH4)2MoO4, wherein A=Rb, Cs, and X=Cl, or Br; The compound containing A=Rb, Cs includes at least one of AOH, A2O and an alkali metal salt, and the alkali metal salt includes at least one of A2CO3, AF, ACl, ABr, AI, ANO3, A2SO4, A2SO3, and AHCO3, wherein A=Rb, Cs; The cadmium-containing compound includes at least one of CdO, Cd(OH)2, Cd(NO3)2, CdCO3, CdCl2, CdF2, CdBr2, CdI2, CdSO4, CdSO3, and Cd(HCO3)2; The sodium-containing compound includes at least one of NaOH, Na2O and alkali metal salts; the alkali metal salt includes at least one of NaH2PO4, Na2SO4, Na2SiO3, Na2CO3, NaHCO3, NaCl, Na2B4O7, NaBO2, NaBF4, NaF, NaBr, and CH3COONa; The X=Cl, Br compound includes at least one of PbX2, Ca(XO)2, LiX, SrX2, NH4X, KX, CaX2, MgX2, NaX, AlX3, SnX2, CdX2, SbX3, BaX2, BiX3, ZnX2, SrX2, CsX, RbX, MnX2, CuX, LaX3, GaX3, SmX3, YX3, and AgX, wherein X=Cl, Br; The molybdenum-containing compound includes at least one of MoO3, H2MoO4 and molybdate; the molybdate includes (NH4)6Mo7O 24 , MoCl6, MoF6, (NH4)2Mo2O7, (NH4)2MoO4, at least one of.

4. Series of alkali metal composite cadmium molybdate halide nonlinear optical crystals, characterized by The chemical formula of this series of crystals is A2Cd2NaX3(MoO4)2(A=Rb, Cs, X=Cl, Br), and the molecular formulas are Rb2Cd2NaCl3(MoO4)2, Cs2Cd2Na Cl3(MoO4)2, Rb2Cd2NaBr3(MoO4)2 or Cs2Cd2NaBr3(MoO4)2, all of which crystallize in the orthorhombic system, space group Pba2, unit cell parameters Z=2.

5. The method for preparing a series of alkali metal composite cadmium molybdate halide nonlinear optical crystals according to claim 4, characterized in that: A series of alkali metal composite cadmium molybdate halide nonlinear optical crystals were grown using high-temperature melt method, hydrothermal method and aqueous solution method.

6. The method for preparing the series of alkali metal composite cadmium molybdate halide nonlinear optical crystals according to claim 5, characterized in that: The specific operation of growing A2Cd2NaX3(MoO4)2, wherein A=Rb, Cs, X=Cl, Br nonlinear optical crystals, by the high-temperature melt method is as follows: heating a series of alkali metal composite cadmium molybdate halide single-phase polycrystalline powders or a mixture of a series of alkali metal composite cadmium molybdate halide single-phase polycrystalline powders and a flux, or directly heating a mixture of a compound containing A=Rb, Cs, a cadmium-containing compound, a sodium-containing compound, a compound containing X=Cl, Br, a molybdenum compound, or a mixture of a compound containing A=Rb, Cs, a cadmium-containing compound, a sodium-containing compound, a compound containing X=Cl, Br, a molybdenum compound and a flux until it melts to obtain a mixed melt; then placing a crucible containing the mixed melt in a crystal growth furnace for heating, cooling it to a saturation temperature point, at which time extending a seed crystal rod below the liquid surface, and then lifting the seed crystal rod out of the liquid surface before the melt solidifies, to prepare a series of alkali metal composite cadmium molybdate halide nonlinear optical crystals; The hydrothermal method for growing A2Cd2NaX3(MoO4)2, wherein A=Rb, Cs, X=Cl, Br, nonlinear optical crystals, is specifically performed as follows: adding a series of alkali metal composite cadmium molybdate halide single-phase polycrystalline powders or a mixture of a series of alkali metal composite cadmium molybdate halide single-phase polycrystalline powders and a mineralizer, or directly adding a mixture of a compound containing A=Rb, Cs, a cadmium-containing compound, a sodium-containing compound, a compound containing X=Cl, Br, a molybdenum-containing compound, or a mixture of a compound containing A=Rb, Cs, a cadmium-containing compound, a sodium-containing compound, a compound containing X=Cl, Br, a molybdenum-containing compound and a mineralizer to a polytetrafluoroethylene liner of an autoclave, then adding deionized water and thoroughly mixing the mixture to obtain a mixed solution, placing the polytetrafluoroethylene liner into the autoclave, and placing the autoclave in a constant temperature box for heating. After maintaining the temperature for a period of time, the autoclave is cooled to room temperature, and the solution containing the crystals is filtered to obtain a transparent series of alkali metal composite cadmium molybdate halide nonlinear optical crystals; The specific operation of growing A2Cd2NaX3(MoO4)2, wherein A=Rb, Cs, X=Cl, Br nonlinear optical crystals, by the aqueous solution method is as follows: adding a series of alkali metal composite cadmium molybdate halide single-phase polycrystalline powders or a mixture of the series of alkali metal composite cadmium molybdate halide single-phase polycrystalline powders obtained according to claim 3 and a solvent, or directly adding a mixture of a compound containing A=Rb, Cs, a cadmium-containing compound, a sodium-containing compound, a compound containing X=Cl, Br, a molybdenum-containing compound, or a mixture of a compound containing A=Rb, Cs, a cadmium-containing compound, a sodium-containing compound, a compound containing X=Cl, Br, a molybdenum-containing compound and a solvent into a beaker; then adding deionized water to dissolve, stirring the solution until it is clear, and then placing the beaker in air to evaporate the solution to grow a series of alkali metal composite cadmium molybdate halide nonlinear optical crystals.

7. The method for preparing the series of alkali metal composite cadmium molybdate halide nonlinear optical crystals according to claim 6, characterized in that: The high-temperature melt method grows A2Cd2NaX3(MoO4)2, wherein A=Rb, Cs, X=Cl, Br nonlinear optical crystals, and the molar ratio of the series of alkali metal composite cadmium molybdate halide single-phase polycrystalline powder to the flux is 1:0-20; or the molar ratio of the compound containing A=Rb, Cs, the cadmium-containing compound, the sodium-containing compound, the X=Cl, Br compound, the molybdenum-containing compound to the flux is 1.5-2.5:1.5-2.5:0.5-1.5:2.5-3.5:1.5-2.5:0-20; wherein the flux includes alkali metal salts, namely alkali metal carbonates, alkali metal nitrates, alkali metal sulfates, alkali metal phosphates, alkali metal halides, alkali metal oxides, alkali metal hydroxides, and at least one or more of cadmium carbonate, cadmium fluoride, cadmium oxide, hydrochloric acid, ammonium chloride, ammonium bromide, lead chloride, lead bromide, and molybdenum oxide; The hydrothermal method grows A2Cd2NaX3(MoO4)2, wherein A=Rb, Cs, X=Cl, Br nonlinear optical crystals, and the molar ratio of the series of alkali metal composite cadmium molybdate halide single-phase polycrystalline powder to the mineralizer is 1:0-10; or the molar ratio of the compound containing A=Rb, Cs, the cadmium-containing compound, the sodium-containing compound, the X=Cl, Br compound, the molybdenum-containing compound to the mineralizer is 1-3:1-3:0-2:2-4:1-3:0-10; the mineralizer Including at least one or more of AOH, A2O, A2CO3, AF, ACl, ABr, CdO, Cd(OH)2, Cd(NO3)2, CdCO3, CdCl2, NaOH, Na2O, NaH2PO4, Na2SO4, Na2SiO3, NH4X, KX, CaX2, MoO3, H2MoO4, (NH4)2Mo2O7, (NH4)2MoO4, wherein A=Rb, Cs, X=Cl, Br; The molar ratio of the series of alkali metal composite cadmium molybdate halide single-phase polycrystalline powder to the solvent is 1:0-30; or the molar ratio of the compound containing A=Rb, Cs, the cadmium-containing compound, the sodium-containing compound, the X=Cl, Br compound, and the molybdenum-containing compound to the solvent is 1.5-2.5:1.5-2.5:0.5-1.5:2.5-3.5:1.5-2.5:0-30, and the flux includes alkali metal salts, namely alkali metal carbonates, alkali metal nitrates, alkali metal sulfates, alkali metal phosphates, alkali metal halides, alkali metal oxides, alkali metal hydroxides, and at least one or more of cadmium carbonate, cadmium fluoride, cadmium oxide, hydrochloric acid, ammonium chloride, ammonium bromide, lead chloride, lead bromide, and molybdenum oxide.

8. A nonlinear optical device comprising means for passing at least one incident electromagnetic radiation through at least one nonlinear optical crystal to generate at least one output radiation having a frequency different from that of the incident electromagnetic radiation, wherein: The nonlinear optical crystal is the series of alkali metal composite cadmium molybdate halide nonlinear optical crystal A2Cd2NaX3(MoO4)2, wherein A=Rb, Cs, X=Cl, Br.

9. Use of the series of alkali metal composite cadmium molybdate halide nonlinear optical crystals according to claim 4, characterized in that: Used to prepare multi-band frequency doubling devices or optical elements.

10. The use of the series of alkali metal composite cadmium molybdate halide nonlinear optical crystals according to claim 9, characterized in that: This series of alkali metal composite cadmium molybdate halide nonlinear optical crystals are used in nonlinear optical devices such as second harmonic generators, up and down frequency converters, optical parametric oscillators, laser frequency conversion devices, and laser communications.

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