A yttrium lithium fluoride composite crystal and its preparation method

Abstract

The present invention relates to the technical field of yttrium lithium fluoride crystal bonding, and specifically relates to a yttrium lithium fluoride composite crystal and a preparation method thereof. The preparation method includes the following steps: S1, polishing the bonding surfaces of a yttrium lithium fluoride crystal with a c-axis crystal orientation and a doped yttrium lithium fluoride crystal with an a-axis crystal orientation; S2, performing immersion treatment with different organic solutions after polishing; S3, obtaining a first intermediate product through a direct bonding technique; S4, subjecting the first intermediate product to a pressure treatment to obtain a second intermediate product; S5, subjecting the second intermediate product to hot isostatic pressing and annealing treatments to obtain a yttrium lithium fluoride composite crystal. The yttrium lithium fluoride composite crystal prepared by the present invention is polished with different polishing liquids and subjected to immersion treatment, which improves the van der Waals force between the two laser crystals, strengthens the strength of the bonding surface of the bonded crystals, and improves the yield rate.

Description

Technical Field

[0001] The present invention relates to the technical field of yttrium lithium fluoride crystal bonding, and specifically to a yttrium lithium fluoride composite crystal and a preparation method thereof. Background Art

[0002] Yttrium lithium fluoride is an excellent laser matrix crystal material with good spectral and laser properties, capable of achieving laser output at multiple wavelengths from mid-infrared to visible light and ultraviolet light at room temperature. More particularly, yttrium lithium fluoride has anti-ultraviolet radiation and is suitable for multi-doping characteristics. Doped yttrium lithium fluoride prepared by doping different activator ions can emit lasers of different wavelengths at room temperature. Due to its small non-linear refractive index, it can be used as the working substance of the oscillator and pre-amplifier of a high-power and high-energy laser device.

[0003] In order to change the properties of yttrium lithium fluoride crystals, sometimes it is necessary to bond two crystals to form a yttrium lithium fluoride composite crystal. The published document CN104099665B discloses a yttrium lithium fluoride composite crystal and a preparation method thereof. By bonding a doped yttrium lithium fluoride crystal with the a-axis crystal orientation to a yttrium lithium fluoride crystal with the c-axis crystal orientation, a yttrium lithium fluoride composite crystal is prepared, which improves the output efficiency of the laser. The inventor found that when using the above preparation method to prepare the yttrium lithium fluoride composite crystal, the interfacial strength per unit area (kg / cm 2 ) and the interfacial damage threshold (J / cm 2 ) of the yttrium lithium fluoride composite crystal prepared by this method are both relatively low. In addition, the preparation of the yttrium lithium fluoride composite crystal by the above method has relatively high requirements for temperature, pressure and treatment time during the hot isostatic pressing process.

[0004] Therefore, in view of the problems raised in the above background art, the present invention provides a method for bonding laser crystals, which effectively improves the interfacial strength per unit area and the interfacial damage threshold between two bonded crystals, improves the bonding surface strength, and at the same time, the treatment pressure, temperature and time of hot isostatic pressing are relatively low. Summary of the Invention

[0005] The purpose of the present invention is to provide a yttrium lithium fluoride composite crystal and a preparation method thereof to solve the problems raised in the above background art.

[0006] To achieve the above purpose, the present invention provides the following technical solutions:

[0007] A preparation method of a yttrium lithium fluoride composite crystal includes the following steps:

[0008] S1. Polish the bonding surface of the yttrium lithium fluoride crystal with the c-axis crystal orientation using polishing liquid A, and polish the bonding surface of the doped yttrium lithium fluoride crystal with the a-axis crystal orientation using polishing liquid B;

[0009] S2. Place the bonding surface of the yttrium lithium fluoride crystal with the c-axis crystal orientation after polishing in step S1 into a mixed solution of 3-hydroxypropyltriethoxysilane and ethanol for 1 - 3 h. Then, repeatedly wash it with an excessive amount of organic solvent and naturally dry it to obtain a pre-treated yttrium lithium fluoride crystal with the c-axis crystal orientation. Place the bonding surface of the doped yttrium lithium fluoride crystal with the a-axis crystal orientation in step S1 into a mixed solution of 11-carboxyundecyltriethoxysilane and ethanol for 2 - 5 h. Then, repeatedly wash it with an excessive amount of organic solvent and naturally dry it to obtain a pre-treated doped yttrium lithium fluoride crystal with the a-axis crystal orientation.

[0010] S3. Through the direct bonding technique, pre-bond the pre-treated yttrium lithium fluoride crystal with the c-axis crystal orientation obtained in step S2 to the end of the pre-treated doped yttrium lithium fluoride crystal with the a-axis crystal orientation to obtain a first intermediate product.

[0011] S4. Apply a pressure of 1 - 5 MPa in the direction perpendicular to the bonding surface of the first intermediate product obtained in step S3 for 2 - 10 h to obtain a second intermediate product.

[0012] S5. Perform hot isostatic pressing on the second intermediate product obtained in step S4. The pressure of the hot isostatic pressing is 2 - 60 MPa, the temperature is 250 - 450 °C, and the time is 2 - 10 h. After the hot isostatic pressing, perform vacuum annealing. The pressure of the vacuum annealing is 0.001 - 10 Pa, the time is 2 - 32 h, and the temperature is 300 - 500 °C to obtain a yttrium lithium fluoride composite crystal.

[0013] Further, the doped yttrium lithium fluoride crystal with the a-axis crystal orientation is doped with a rare earth element, and the rare earth element is selected from at least one of thulium, holmium, erbium, and praseodymium.

[0014] Further, the components of the A polishing liquid in step S1 include cetyltrimethylammonium bromide, ammonium fluoride, nano-silica, and deionized water. The mass ratio between cetyltrimethylammonium bromide, ammonium fluoride, nano-silica, and deionized water is 1:(2 - 3):(4 - 10):(40 - 80).

[0015] Further, the components of the B polishing liquid in step S1 include sodium dodecyl sulfate, 68 wt% nitric acid, 98 wt% sulfuric acid, deionized water, and nano-vermiculite. The mass ratio between sodium dodecyl sulfate, 68 wt% nitric acid, 98 wt% sulfuric acid, nano-vermiculite, and deionized water is 1:(3 - 6):(2 - 5):(7 - 12):(80 - 110).

[0016] Further, the surface finish of both the yttrium lithium fluoride crystal with the c-axis crystal orientation and the doped yttrium lithium fluoride crystal with the a-axis crystal orientation after polishing in step S1 reaches 10 / 5, and the roughness of the polished yttrium lithium fluoride crystal and doped yttrium lithium fluoride crystal is not greater than 0.8 nm.

[0017] Further, the organic solvent in step S2 is a mixture of ethanol and acetone, and the mass ratio between acetone and ethanol is 1:(2 - 5).

[0018] Further, the mass ratio between 3 - hydroxypropyltriethoxysilane and ethanol in step S2 is 1:(20 - 45).

[0019] Further, the mass ratio between 11 - carboxyundecyltriethoxysilane and ethanol in step S2 is 1:(25 - 40).

[0020] A lithium yttrium fluoride crystal is prepared by the above - mentioned preparation method of the lithium yttrium fluoride composite crystal.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] In the present invention, compared with the prior art where the bonding surfaces of two crystals are polished with two different polishing fluids respectively, and the bonding surfaces of the two polished crystals are treated with different organic solutions, the van der Waals force between the two lithium yttrium fluorides is increased, the strength of the bonding surface of the bonded crystals is enhanced, the interfacial strength per unit area and the interfacial damage threshold are both improved. At the same time, the temperature and pressure required for treating the bonded crystals in the present invention are relatively low. Brief Description of the Drawings

[0023] Figure 1 It is a process flow chart for preparing the lithium yttrium fluoride composite crystal of the present invention;

[0024] Figure 2 It is a bonding schematic diagram of the lithium yttrium fluoride crystal and the doped lithium yttrium fluoride crystal in the present invention.

[0025] In the figure: 1. Lithium yttrium fluoride crystal with c - axis crystal orientation; 2. Doped lithium yttrium fluoride crystal with a - axis crystal orientation. Detailed Embodiments

[0026] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0027] Please refer to Figure 1-2 , the present invention provides a technical solution:

[0028] Embodiment 1

[0029] A preparation method of a lithium yttrium fluoride composite crystal, comprising the following steps:

[0030] S1. Polish the bonding surface of a yttrium lithium fluoride crystal with a c-axis crystal orientation using polishing solution A. The components of polishing solution A include cetyltrimethylammonium bromide, ammonium fluoride, nano-silica, and deionized water. The mass ratio of cetyltrimethylammonium bromide, ammonium fluoride, nano-silica, and deionized water is 1:2.5:8:60;

[0031] Polish the bonding surface of a doped yttrium lithium fluoride crystal with an a-axis crystal orientation using polishing solution B. The doped yttrium lithium fluoride crystal with an a-axis crystal orientation is doped with 3 at% thulium. The components of polishing solution B include sodium dodecyl sulfate, 68 wt% nitric acid, 98 wt% sulfuric acid, deionized water, and nano-vermiculite. The mass ratio of sodium dodecyl sulfate, 68 wt% nitric acid, 98 wt% sulfuric acid, nano-vermiculite, and deionized water is 1:4:4:11:95;

[0032] The surface finish of both the yttrium lithium fluoride crystal with a c-axis crystal orientation and the doped yttrium lithium fluoride crystal with an a-axis crystal orientation after polishing reaches 10 / 5, and the roughness of the polished yttrium lithium fluoride crystal and doped yttrium lithium fluoride crystal is 0.6 nm;

[0033] S2. Immerse the bonding surface of the polished yttrium lithium fluoride crystal with a c-axis crystal orientation obtained in step S1 into a mixed solution of 3-hydroxypropyltriethoxysilane and ethanol for 2 h. The mass ratio of 3-hydroxypropyltriethoxysilane and ethanol is 1:35. Then, repeatedly wash it with an excessive mixed solution of acetone and ethanol, where the mass ratio of acetone and ethanol is 1:3, and naturally dry it to obtain a pre-treated yttrium lithium fluoride crystal with a c-axis crystal orientation;

[0034] Immerse the bonding surface of the doped yttrium lithium fluoride crystal with an a-axis crystal orientation obtained in step S1 into a mixed solution of 11-carboxyundecyltriethoxysilane and ethanol for 4 h. The mass ratio of 11-carboxyundecyltriethoxysilane and ethanol is 1:30. Then, repeatedly wash it with an excessive mixed solution of acetone and ethanol, where the mass ratio of acetone and ethanol is 1:3, and naturally dry it to obtain a pre-treated doped yttrium lithium fluoride crystal with an a-axis crystal orientation;

[0035] S3. Through the direct bonding technique, pre-bond the pre-treated yttrium lithium fluoride crystal with a c-axis crystal orientation obtained in step S2 to the end of the pre-treated doped yttrium lithium fluoride crystal with an a-axis crystal orientation to obtain a first intermediate product;

[0036] S4. Apply a pressure of 4 MPa in the direction perpendicular to the bonding surface of the first intermediate product obtained in step S3 for 3 hours to obtain a second intermediate product;

[0037] S5. Perform hot isostatic pressing on the second intermediate product obtained in step S4. The pressure of the hot isostatic pressing is 30 MPa, the temperature is 300 °C, and the time is 6 hours. After the hot isostatic pressing, perform vacuum annealing. The pressure of the vacuum annealing is 4 Pa, the time is 18 hours, and the temperature is 400 °C to obtain a yttrium lithium fluoride composite crystal.

[0038] Example 2

[0039] A method for preparing a yttrium lithium fluoride composite crystal, comprising the following steps:

[0040] S1. Polish the bonding surface of the yttrium lithium fluoride crystal with a c-axis crystal orientation using polishing liquid A. The components of polishing liquid A include cetylammonium bromide, ammonium fluoride, nano-silica, and deionized water. The mass ratio of cetylammonium bromide, ammonium fluoride, nano-silica, and deionized water is 1:2.5:8:60;

[0041] Polish the bonding surface of the doped yttrium lithium fluoride crystal with an a-axis crystal orientation using polishing liquid B. The doped yttrium lithium fluoride crystal with an a-axis crystal orientation is doped with 2 at% thulium. The components of polishing liquid B include sodium dodecyl sulfate, 68 wt% nitric acid, 98 wt% sulfuric acid, deionized water, and nano-vermiculite. The mass ratio of sodium dodecyl sulfate, 68 wt% nitric acid, 98 wt% sulfuric acid, nano-vermiculite, and deionized water is 1:3:2:7:80;

[0042] The surface finish of both the yttrium lithium fluoride crystal with a c-axis crystal orientation and the doped yttrium lithium fluoride crystal with an a-axis crystal orientation after polishing reaches 10 / 5, and the surface roughness of the yttrium lithium fluoride crystal and the doped yttrium lithium fluoride crystal after polishing is 0.6 nm;

[0043] S2. Immerse the bonding surface of the yttrium lithium fluoride crystal with a c-axis crystal orientation polished in step S1 into a mixed solution of 3-hydroxypropyltriethoxysilane and ethanol for 1 h. The mass ratio of 3-hydroxypropyltriethoxysilane and ethanol is 1:20. Then, repeatedly wash with an excessive mixed solution of acetone and ethanol. The mass ratio of acetone and ethanol is 1:2, and naturally dry to obtain a pre-treated yttrium lithium fluoride crystal with a c-axis crystal orientation;

[0044] Immerse the bonding surface of the doped yttrium lithium fluoride crystal with an a-axis crystal orientation polished in step S1 into a mixed solution of 11-carboxyundecyltriethoxysilane and ethanol for 2 h. The mass ratio of 11-carboxyundecyltriethoxysilane and ethanol is 1:25. Then, repeatedly wash with an excessive mixed solution of acetone and ethanol. The mass ratio of acetone and ethanol is 1:2, and naturally dry to obtain a pre-treated doped yttrium lithium fluoride crystal with an a-axis crystal orientation;

[0045] S3. By means of direct bonding technology, pre-bond the pre-treated lithium yttrium fluoride crystal with a c-axis crystal orientation obtained in step S2 to the end of the doped lithium yttrium fluoride crystal with a pre-treated a-axis crystal orientation to obtain a first intermediate product;

[0046] S4. Apply a pressure of 1 MPa in the direction perpendicular to the bonding surface of the first intermediate product obtained in step S3 for 2 hours to obtain a second intermediate product;

[0047] S5. Perform hot isostatic pressing on the second intermediate product obtained in step S4. The pressure of the hot isostatic pressing is 2 MPa, the temperature is 250 °C, and the time is 2 hours. After the hot isostatic pressing, perform vacuum annealing. The pressure of the vacuum annealing is 0.001 Pa, the time is 2 hours, and the temperature is 300 °C to obtain a lithium yttrium fluoride composite crystal.

[0048] Example 3

[0049] A preparation method of a lithium yttrium fluoride composite crystal, comprising the following steps:

[0050] S1. Polish the bonding surface of the lithium yttrium fluoride crystal with a c-axis crystal orientation with polishing liquid A. The components of polishing liquid A include cetyltrimethylammonium bromide, ammonium fluoride, nano-silica, and deionized water. The mass ratio between cetyltrimethylammonium bromide, ammonium fluoride, nano-silica, and deionized water is 1:3:10:80;

[0051] Polish the bonding surface of the doped lithium yttrium fluoride crystal with an a-axis crystal orientation with polishing liquid B. The doped lithium yttrium fluoride crystal with an a-axis crystal orientation is doped with 3 at% thulium. The components of polishing liquid B include sodium dodecyl sulfate, 68 wt% nitric acid, 98 wt% sulfuric acid, deionized water, and nano-vermiculite. The mass ratio between sodium dodecyl sulfate, 68 wt% nitric acid, 98 wt% sulfuric acid, nano-vermiculite, and deionized water is 1:6:5:12:110;

[0052] The surface finish of both the lithium yttrium fluoride crystal with a c-axis crystal orientation and the doped lithium yttrium fluoride crystal with an a-axis crystal orientation after polishing reaches 10 / 5, and the roughness of the lithium yttrium fluoride crystal and the doped lithium yttrium fluoride crystal after polishing is 0.8 nm;

[0053] S2. Immerse the bonding surface of the pre-polished lithium yttrium fluoride crystal with a c-axis crystal orientation obtained in step S1 into a mixed solution of 3-hydroxypropyltriethoxysilane and ethanol for 3 h. The mass ratio between 3-hydroxypropyltriethoxysilane and ethanol is 1:45. Then, repeatedly wash with a mixed solution of excessive acetone and ethanol. The mass ratio between acetone and ethanol is 1:5, and air-dry naturally to obtain a pre-treated lithium yttrium fluoride crystal with a c-axis crystal orientation;

[0054] Put the bonding surface of the yttrium lithium fluoride crystal doped with the a-axis crystal orientation in step S1 into a mixed solution of 11-carboxyundecyltriethoxysilane and ethanol for 2 h. The mass ratio between 11-carboxyundecyltriethoxysilane and ethanol is 1:40. Then, wash it repeatedly with a mixed solution of excessive acetone and ethanol, and the mass ratio between acetone and ethanol is 1:5. Dry it naturally to obtain the pre-treated yttrium lithium fluoride crystal doped with the a-axis crystal orientation;

[0055] S3. Through the direct bonding technique, pre-bond the pre-treated yttrium lithium fluoride crystal with the c-axis crystal orientation obtained in step S2 to the end of the pre-treated yttrium lithium fluoride crystal doped with the a-axis crystal orientation to obtain a first intermediate product;

[0056] S4. Apply a pressure of 5 MPa to the first intermediate product obtained in step S3 in the direction perpendicular to the bonding surface for 10 hours to obtain a second intermediate product;

[0057] S5. Perform hot isostatic pressing on the second intermediate product obtained in step S4. The pressure of the hot isostatic pressing is 60 MPa, the temperature is 450 °C, and the time is 10 hours. After the hot isostatic pressing, perform vacuum annealing. The pressure of the vacuum annealing is 10 Pa, the time is 32 hours, and the temperature is 500 °C to obtain the yttrium lithium fluoride composite crystal.

[0058] Example 4

[0059] A preparation method of a yttrium lithium fluoride composite crystal includes the following steps:

[0060] S1. Polish the bonding surface of the yttrium lithium fluoride crystal with the c-axis crystal orientation through polishing solution A. The components of polishing solution A include cetyltrimethylammonium bromide, ammonium fluoride, nano-silica, and deionized water. The mass ratio between cetyltrimethylammonium bromide, ammonium fluoride, nano-silica, and deionized water is 1:3:6:50;

[0061] Polish the bonding surface of the yttrium lithium fluoride crystal doped with the a-axis crystal orientation through polishing solution B. The yttrium lithium fluoride crystal doped with the a-axis crystal orientation is doped with 1 at% of holmium and 2 at% of erbium. The components of polishing solution B include sodium dodecyl sulfate, 68 wt% nitric acid, 98 wt% sulfuric acid, deionized water, and nano-vermiculite. The mass ratio between sodium dodecyl sulfate, 68 wt% nitric acid, 98 wt% sulfuric acid, nano-vermiculite, and deionized water is 1:4:3:10:90;

[0062] The surface finish of both the yttrium lithium fluoride crystal with the c-axis crystal orientation and the yttrium lithium fluoride crystal doped with the a-axis crystal orientation after polishing reaches 10 / 5, and the roughness of the yttrium lithium fluoride crystal and the doped yttrium lithium fluoride crystal after polishing is 0.7 nm;

[0063] S2. Place the bonding surface of the polished yttrium lithium fluoride crystal with the c-axis crystal orientation in step S1 into a mixed solution of 3-hydroxypropyltriethoxysilane and ethanol for 2 h. The mass ratio between 3-hydroxypropyltriethoxysilane and ethanol is 1:30. Then, repeatedly wash it with an excessive mixed solution of acetone and ethanol, where the mass ratio between acetone and ethanol is 1:4, and naturally dry it to obtain a pre-treated yttrium lithium fluoride crystal with the c-axis crystal orientation;

[0064] Place the bonding surface of the doped yttrium lithium fluoride crystal with the a-axis crystal orientation in step S1 into a mixed solution of 11-carboxyundecyltriethoxysilane and ethanol for 3 h. The mass ratio between 11-carboxyundecyltriethoxysilane and ethanol is 1:35. Then, repeatedly wash it with an excessive mixed solution of acetone and ethanol, where the mass ratio between acetone and ethanol is 1:4, and naturally dry it to obtain a pre-treated doped yttrium lithium fluoride crystal with the a-axis crystal orientation;

[0065] S3. Through the direct bonding technique, pre-bond the pre-treated yttrium lithium fluoride crystal with the c-axis crystal orientation obtained in step S2 to the end of the pre-treated doped yttrium lithium fluoride crystal with the a-axis crystal orientation to obtain a first intermediate product;

[0066] S4. Apply a pressure of 3 MPa in the direction perpendicular to the bonding surface of the first intermediate product obtained in step S3 for 5 h to obtain a second intermediate product;

[0067] S5. Perform hot isostatic pressing on the second intermediate product obtained in step S4. The pressure of the hot isostatic pressing is 10 MPa, the temperature is 300 °C, and the time is 3 h. After the hot isostatic pressing, perform vacuum annealing. The pressure of the vacuum annealing is 0.1 Pa, the time is 8 h, and the temperature is 350 °C to obtain a yttrium lithium fluoride composite crystal.

[0068] Example 5

[0069] A method for preparing a yttrium lithium fluoride composite crystal, comprising the following steps:

[0070] S1. Polish the bonding surface of the yttrium lithium fluoride crystal with the c-axis crystal orientation by using A polishing solution. The components of the A polishing solution include cetyltrimethylammonium bromide, ammonium fluoride, nano-silica, and deionized water. The mass ratio between cetyltrimethylammonium bromide, ammonium fluoride, nano-silica, and deionized water is 1:3:6:50;

[0071] The bonding surface of the doped yttrium lithium fluoride crystal with the a-axis crystal orientation is polished with B polishing solution. The doped yttrium lithium fluoride crystal with the a-axis crystal orientation is doped with 1 at% thulium, 1 at% holmium, 1 at% erbium, and 1 at% praseodymium. The composition of the B polishing solution includes sodium dodecyl sulfate, 68 wt% nitric acid, 98 wt% sulfuric acid, deionized water, and nano-vermiculite. The mass ratio between sodium dodecyl sulfate, 68 wt% nitric acid, 98 wt% sulfuric acid, nano-vermiculite, and deionized water is 1:3:5:12:100;

[0072] The surface finish of both the c-axis oriented yttrium lithium fluoride crystal and the doped yttrium lithium fluoride crystal with the a-axis crystal orientation after polishing reaches 10 / 5, and the roughness of the polished yttrium lithium fluoride crystal and doped yttrium lithium fluoride crystal is 0.6 nm;

[0073] S2. Immerse the bonding surface of the polished c-axis oriented yttrium lithium fluoride crystal in step S1 into a mixed solution of 3-hydroxypropyltriethoxysilane and ethanol for 3 h. The mass ratio between 3-hydroxypropyltriethoxysilane and ethanol is 1:35. Then, repeatedly wash it with an excessive mixed solution of acetone and ethanol. The mass ratio between acetone and ethanol is 1:4, and naturally dry it to obtain the pretreated c-axis oriented yttrium lithium fluoride crystal;

[0074] Immerse the bonding surface of the doped yttrium lithium fluoride crystal with the a-axis crystal orientation in step S1 into a mixed solution of 11-carboxyundecyltriethoxysilane and ethanol for 3 h. The mass ratio between 11-carboxyundecyltriethoxysilane and ethanol is 1:35. Then, repeatedly wash it with an excessive mixed solution of acetone and ethanol. The mass ratio between acetone and ethanol is 1:4, and naturally dry it to obtain the pretreated doped yttrium lithium fluoride crystal with the a-axis crystal orientation;

[0075] S3. Through the direct bonding technique, pre-bond the pretreated c-axis oriented yttrium lithium fluoride crystal obtained in step S2 to the end of the pretreated doped yttrium lithium fluoride crystal with the a-axis crystal orientation to obtain the first intermediate product;

[0076] S4. Apply a pressure of 2 MPa to the first intermediate product obtained in step S3 in the direction perpendicular to the bonding surface for 7 hours to obtain the second intermediate product;

[0077] S5. Perform hot isostatic pressing on the second intermediate product obtained in step S4. The pressure of the hot isostatic pressing is 30 MPa, the temperature is 350 °C, and the time is 6 hours. After the hot isostatic pressing, perform vacuum annealing. The pressure of the vacuum annealing is 5 Pa, the time is 10 hours, and the temperature is 300 °C to obtain the yttrium lithium fluoride composite crystal.

[0078] Comparative Example 1

[0079] The difference between Comparative Example 1 and Example 1 is that in step S1, a common non-abrasive polishing liquid is used for both yttrium lithium fluoride crystals and doped yttrium lithium fluoride crystals. The main components of the common non-abrasive polishing liquid are deionized water and ethanol, and the remaining steps are exactly the same as those in Example 1.

[0080] Comparative Example 2

[0081] The difference between Comparative Example 2 and Example 1 is that in step S1, a common abrasive polishing liquid is used for both yttrium lithium fluoride crystals and doped yttrium lithium fluoride crystals. The common abrasive polishing liquid is composed of additives such as silicon dioxide, sodium phosphate, and aluminum nitrate and deionized water, and the remaining steps are exactly the same as those in Example 1.

[0082] Comparative Example 3

[0083] The difference between Comparative Example 3 and Example 1 is that step S2 is omitted. After the polishing of yttrium lithium fluoride crystals and doped yttrium lithium fluoride crystals is completed in step S1 respectively, they are directly cleaned and dried, and the remaining steps are exactly the same as those in Example 1.

[0084] Comparative Example 4

[0085] The difference between Comparative Example 4 and Comparative Example 3 is not only that step S2 is omitted, but also that in step S1, a common abrasive polishing liquid is used for polishing both yttrium lithium fluoride crystals and doped yttrium lithium fluoride crystals, and the remaining steps are exactly the same as those in Example 1.

[0086] Comparative Example 5

[0087] Comparative Example 5 is a yttrium lithium fluoride composite crystal prepared by the preparation method in Example 1 of Publication No. CN104099665B.

[0088] Through Examples 1-5 and Comparative Examples 1-5 above, 10 groups of yttrium lithium fluoride composite crystals are prepared respectively. The interfacial strength per unit area (kg / cm 2 ) and interfacial damage threshold (J / cm 2 ) of these 10 groups of yttrium lithium fluoride composite crystals are tested, and the test results are shown in Table 1 below:

[0089] Table 1: Test table of interfacial strength per unit area and interfacial damage threshold of yttrium lithium fluoride composite crystals prepared in Examples 1-5 and Comparative Examples 1-5

[0090] <![CDATA[Interface strength per unit area (kg / cm 2 )]]> <![CDATA[Interface damage threshold (J / cm 2 )]]> Example 1 45 32 Example 2 36 27 Example 3 44 32 Example 4 48 35 Example 5 45 33 Comparative Example 1 40 25 Comparative Example 2 36 28 Comparative Example 3 32 23 Comparative Example 4 29 18 Comparative Example 5 36 22

[0091] From the data of Example 1 and Comparative Examples 1-4 in Table 1 above, it can be seen that when the composition of the polishing liquid was changed in the present invention or the process of crystal soaking was cancelled in step S2, the interfacial strength per unit area and the interfacial damage threshold of the yttrium lithium fluoride composite crystal were both reduced, which proves that the bonding interfacial strength of the yttrium lithium fluoride composite crystal prepared by the present application can be effectively improved. At the same time, the interfacial strength per unit area and the interfacial damage threshold of the yttrium lithium fluoride composite crystals prepared in Examples 1-5 of the present invention are also effectively improved compared with those of the yttrium lithium fluoride composite crystal prepared in Example 1 of CN104099665B.

[0092] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a yttrium lithium fluoride composite crystal, characterized in that, It includes the following steps: S1. Polish the bonding surface of the yttrium lithium fluoride crystal with the c-axis crystal orientation using polishing solution A, and polish the bonding surface of the doped yttrium lithium fluoride crystal with the a-axis crystal orientation using polishing solution B; S2. Immerse the bonding surface of the polished yttrium lithium fluoride crystal with the c-axis crystal orientation obtained in step S1 into a mixed solution of 3-hydroxypropyltriethoxysilane and ethanol for 1 - 3 h, then repeatedly wash it with an excessive amount of organic solvent and naturally dry it to obtain a pre-treated yttrium lithium fluoride crystal with the c-axis crystal orientation; Immerse the bonding surface of the doped yttrium lithium fluoride crystal with the a-axis crystal orientation obtained in step S1 into a mixed solution of 11-carboxyundecyltriethoxysilane and ethanol for 2 - 5 h, then repeatedly wash it with an excessive amount of organic solvent and naturally dry it to obtain a pre-treated doped yttrium lithium fluoride crystal with the a-axis crystal orientation; S3. Through the direct bonding technique, pre-bond the pre-treated yttrium lithium fluoride crystal with the c-axis crystal orientation obtained in step S2 to the end of the pre-treated doped yttrium lithium fluoride crystal with the a-axis crystal orientation to obtain a first intermediate product; S4. Apply a pressure of 1 - 5 MPa in the direction perpendicular to the bonding surface of the first intermediate product obtained in step S3 for 2 - 10 hours to obtain a second intermediate product; S5. Perform hot isostatic pressing on the second intermediate product obtained in step S4. The pressure of the hot isostatic pressing is 2 - 60 MPa, the temperature is 250 - 450 °C, and the time is 2 - 10 hours. After the hot isostatic pressing, perform vacuum annealing. The pressure of the vacuum annealing is 0.001 - 10 Pa, the time is 2 - 32 hours, and the temperature is 300 - 500 °C to obtain a yttrium lithium fluoride composite crystal; The components of polishing solution A in step S1 include cetylammonium bromide, ammonium fluoride, nano-silica, and deionized water. The mass ratio between cetylammonium bromide, ammonium fluoride, nano-silica, and deionized water is 1:(2 - 3):(4 - 10):(40 - 80); The components of polishing solution B in step S1 include sodium dodecyl sulfate, 68 wt% nitric acid, 98 wt% sulfuric acid, deionized water, and nano-vermiculite. The mass ratio between sodium dodecyl sulfate, 68 wt% nitric acid, 98 wt% sulfuric acid, nano-vermiculite, and deionized water is 1:(3 - 6):(2 - 5):(7 - 12):(80 - 110); The organic solvent in step S2 is a mixture of ethanol and acetone. The mass ratio between acetone and ethanol is 1:(2 - 5); The mass ratio between 3-hydroxypropyltriethoxysilane and ethanol in step S2 is 1:(20 - 45); The mass ratio between 11-carboxyundecyltriethoxysilane and ethanol in step S2 is 1:(25 - 40).

2. The preparation method of the yttrium lithium fluoride composite crystal according to claim 1, characterized in that, The doped yttrium lithium fluoride crystal with the a-axis crystal orientation is doped with rare earth elements, and the rare earth elements are selected from at least one of thulium, holmium, erbium, and praseodymium.

3. The preparation method of the yttrium lithium fluoride composite crystal according to claim 1, characterized in that, The surface finish of the polished yttrium lithium fluoride crystal with the c-axis crystal orientation and the polished doped yttrium lithium fluoride crystal with the a-axis crystal orientation in step S1 both reach 10 / 5, and the roughness of the polished yttrium lithium fluoride crystal and the polished doped yttrium lithium fluoride crystal is not greater than 0.8 nm.

4. A yttrium lithium fluoride composite crystal, characterized in that, Prepared by the preparation method of the yttrium lithium fluoride composite crystal according to any one of claims 1-3.

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