Optical material prepared based on plasma-assisted PVD evaporation and preparation method thereof

Abstract

The invention discloses an optical material prepared based on plasma assisted PVD evaporation and a preparation method of the optical material, and belongs to the technical field of glass surface treatment. According to the method, the surface treatment is performed on the fused quartz by adopting a plasma-assisted PVD evaporation process, so that the optical material capable of being used for deep ultraviolet optics is obtained. A modified plating material with a calcium fluoride and aluminum fluoride core-shell structure is successfully prepared through a sol-gel method and a solid-phase fluorination conversion process, two fluorides are integrated into a single plating material, in-situ fluorine supplementation is achieved by means of nitrogen trifluoride plasma during evaporation, and the situation that fluorine in the fluorides is lost at the high temperature, and then the optical performance of the material is affected is avoided. Through the design of the core-shell structure, the fractionation effect during multi-component evaporation is relieved, and the uniform coating is deposited on the surface of the fused quartz in combination with auxiliary deposition of the ion beam led out by the plasma and can be used as a deep ultraviolet optical material.

Description

Technical Field

[0001] This invention relates to the field of glass surface treatment technology, specifically to an optical material prepared by plasma-assisted PVD evaporation and its preparation method. Background Technology

[0002] Fused silica, with its unique and superior combination of optical properties, has become the material of choice for many high-end and critical optical applications. Fused silica can transmit deep ultraviolet light and possesses extremely high optical homogeneity and extremely low birefringence, making it one of the preferred substrate materials in the field of deep ultraviolet optics.

[0003] Plasma-assisted PVD evaporation is a surface treatment process that has become one of the mainstream technologies for preparing high-performance optical coatings due to its advantages such as high coating density, strong compositional controllability, and excellent adhesion to the substrate. In the preparation of deep ultraviolet optical coatings, fluoride materials (such as calcium fluoride and aluminum fluoride) are widely used as core materials for coatings because of their high transmittance and tunable refractive index in the deep ultraviolet band. Chinese patent application CN114276025A discloses a method for producing glass products with a PVD conductive layer by applying a protective film. By reasonably setting the protective film, the cost of laser engraving equipment is saved, and problems such as damage to the stress layer and reduced transmittance of the glass surface are avoided, resulting in glass products with a PVD conductive layer. However, it does not mention any modification treatment of the coating material. Chinese patent application CN120398423A discloses an unequal-thickness ultrathin glass and its preparation method. The method involves attaching a mask to the surface of UTG glass, laser drilling, and then using fluoride as a coating material to form a gradient thickness coating in the bending area via PVD evaporation. An arc-shaped thinning surface is then prepared by acid etching, ultimately significantly improving the glass's flexibility and bending performance. However, the fluoride coating is only used as an intermediate etching medium to improve the glass's mechanical properties and does not involve optimizing the glass's optical properties.

[0004] Therefore, it is very important to develop a multilayer coating material with good coating uniformity and a simple vapor deposition process. Summary of the Invention

[0005] The purpose of this invention is to provide an optical material and its preparation method based on plasma-assisted PVD evaporation. The substrate of this optical material is fused silica, and an optical thin film is formed on its surface through plasma-assisted PVD evaporation, enabling its application in the deep ultraviolet field. Since aluminum fluoride is easily decomposed by heat, fluorine-containing plasma can be used to replenish fluorine during the evaporation process, avoiding performance loss in the coating. The plasma also makes the coating more uniform. Through rational design of the coating structure, a calcium fluoride@aluminum fluoride core-shell structure is constructed. Due to the different evaporation temperatures of calcium fluoride and aluminum fluoride, a gradient composite thin film can be formed on the substrate surface during evaporation, eliminating the need for frequent switching of the evaporation source.

[0006] To achieve the above objectives, in a first aspect, the present invention provides an optical material prepared by plasma-assisted PVD evaporation, the optical material comprising a substrate and a coating, wherein the substrate is fused silica and the coating is calcium fluoride@aluminum fluoride core-shell structure powder; the calcium fluoride@aluminum fluoride core-shell structure powder is deposited on the substrate by plasma-assisted PVD evaporation.

[0007] Secondly, the present invention provides a method for preparing optical materials based on plasma-assisted PVD evaporation, comprising the following steps:

[0008] Step S1: After cleaning the substrate, fix it on the substrate holder in the vacuum chamber, fill the evaporation boat with calcium fluoride@aluminum fluoride core-shell structure powder, evacuate the chamber, heat and keep it warm;

[0009] Step S2: Introduce argon and oxygen into the vacuum chamber, turn on the ion source, bombard the substrate with an ion beam, and heat the substrate;

[0010] Step S3: Remove oxygen, retain argon, heat, then introduce nitrogen trifluoride, turn on the ion source, assist in the deposition of the coating, and obtain the optical material.

[0011] Furthermore, in step S1, the heating temperature is 200-250℃, the heating rate is 3-5℃ / min, and the holding time is 30-60min.

[0012] Further, in step S2, the pressure ratio of argon to oxygen is (95-97):(3-5); the energy of the ion beam extracted after the ion source is turned on is 100-200 eV, and the density of the ion beam is 50-100 µA / cm². 2 The bombardment time is 10-20 min; the heating temperature is 220-280℃, and the heating rate is 5-10℃ / min.

[0013] Further, in step S3, the heating temperature is 1400-1450℃, and the heating rate is 2-5℃ / min; the pressure ratio of nitrogen trifluoride to argon is (0.5-1.5):(98.5-99.5); the energy of the ion beam extracted after the ion source is turned on is 150-250 eV, and the ion beam density is 120-200 µA / cm². 2 .

[0014] Further, in step S1, the preparation method of the calcium fluoride@aluminum fluoride core-shell structure powder includes:

[0015] Step A1: Add calcium fluoride to nitric acid for treatment, centrifuge and wash until the pH of the supernatant is 5.5-6.5, disperse the precipitate in deionized water, add polyethylene glycol, and sonicate to obtain a calcium fluoride suspension;

[0016] Step A2: Add aluminum nitrate solution to calcium fluoride suspension, stir to obtain mixed solution, add sodium acetate buffer, sonicate to obtain pre-prepared solution;

[0017] Step A3: Heat the pre-prepared solution, add ammonia to adjust the pH to 6.5-7.5, keep warm, age, centrifuge, collect the precipitate, wash with anhydrous ethanol, and vacuum dry to obtain calcium fluoride@aluminum hydroxide core-shell powder;

[0018] Step A4: Heat calcium fluoride@aluminum hydroxide core-shell powder and ammonium fluoride powder together in a reaction vessel, keep warm, cool down, wash the solid product with anhydrous ethanol, and vacuum dry to obtain calcium fluoride@aluminum fluoride core-shell structure powder.

[0019] Further, in step A1, the concentration of the nitric acid is 2-4 wt.%, the treatment time is 15-20 min; the mass ratio of polyethylene glycol to calcium fluoride is (0.5-1.5):100; the ultrasonication time is 20-40 min; and the concentration of the calcium fluoride suspension is 0.08-0.12 mol / L.

[0020] Further, in step A2, the volume ratio of the calcium fluoride suspension to the aluminum nitrate solution is 1:(1-1.5); the concentration of the aluminum nitrate solution is 0.1-0.2 mol / L; the stirring time is 5-10 min; the volume ratio of the mixed solution to the sodium acetate buffer is 100:(5-7); the concentration of the sodium acetate buffer is 0.08-0.12 mol / L, and the pH of the sodium acetate buffer is 4.5-5.0; the sonication time is 15-30 min.

[0021] Further, in step A3, the heating temperature is 65-85℃; the concentration of the ammonia water is 2-4mol / L, and the rate of adding the ammonia water is 1-3mL / min; the holding time is 20-40min; the aging time is 1.5-2.5h; the vacuum drying temperature is 100-120℃, and the drying time is 60-90min.

[0022] Further, in step A4, the mass ratio of ammonium fluoride to calcium fluoride@aluminum hydroxide core-shell powder is (2-3):1; the heating temperature is 280-320℃, and the heating rate is 2-5℃ / min; the holding time is 4-6h; the vacuum drying temperature is 45-55℃, and the drying time is 8-12h.

[0023] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0024] This invention utilizes plasma-assisted PVD evaporation technology to deposit an antireflective film with UV-enhancing effects on the surface of fused silica. A calcium fluoride@aluminum hydroxide core-shell structure is constructed using a sol-gel method, and ammonium fluoride is used to convert the aluminum hydroxide in the shell layer into aluminum fluoride, forming a calcium fluoride@aluminum fluoride core-shell structure, which is then used as a modified coating material for the surface treatment of fused silica. By constructing the core-shell structure, the two components are integrated into a single modified coating material, optimizing the plasma-assisted PVD evaporation process and alleviating the inefficiency and film interface problems caused by the frequent switching of evaporation sources due to different coating materials. During heating, heat is first transferred between the shells of the modified coating material, causing the aluminum fluoride shell in the modified coating material on the surface of the evaporation boat to evaporate and deposit an aluminum-rich layer on the substrate surface. At the same time, nitrogen trifluoride plasma is used to replenish fluorine to prevent fluorine loss caused by the pyrolysis of aluminum fluoride. After further heating, the calcium fluoride on the surface of the evaporation boat, which has lost its shell, is heated and evaporates together with the aluminum fluoride shell in the middle part to form a calcium fluoride / aluminum fluoride doped layer. Finally, the calcium fluoride core at the bottom of the evaporation boat evaporates to form a calcium-rich layer, resulting in fused silica with the final surface treatment, which can be used as an optical material in the deep ultraviolet field. Attached Figure Description

[0025] Figure 1 A process flow diagram for preparing calcium fluoride@aluminum fluoride core-shell structured powder provided by the present invention;

[0026] Figure 2 Transmittance curves of uncoated fused silica and optical materials prepared by plasma-assisted PVD evaporation in Examples 4-6 and Comparative Examples 1-4. Detailed Implementation

[0027] The technical solution of the present invention will be described in detail below through specific embodiments. It should be understood that the embodiments of the present invention and the specific features in the embodiments are detailed descriptions of the technical solution of the present invention, rather than limitations on the technical solution of the present invention. In the absence of conflict, the embodiments of the present invention and the technical features in the embodiments can be combined with each other.

[0028] The term "and / or" simply describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. Additionally, the character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0029] Example 1

[0030] like Figure 1 As shown, a method for preparing calcium fluoride@aluminum fluoride core-shell structured powder includes the following steps:

[0031] Step A1: Add calcium fluoride to 3 wt.% nitric acid and treat for 17 min. Centrifuge and wash until the pH of the supernatant is 6.0. Disperse the precipitate in deionized water and add polyethylene glycol. The mass ratio of polyethylene glycol to calcium fluoride is 1:100. Then sonicate for 30 min to obtain a calcium fluoride suspension with a concentration of 0.1 mol / L.

[0032] Step A2: Add 0.15 mol / L aluminum nitrate solution to the calcium fluoride suspension, with a volume ratio of 1:1.2; stir for 7 min to obtain a mixed solution, add 0.1 mol / L sodium acetate buffer solution with pH=4.7, with a volume ratio of 100:6 between the mixed solution and the sodium acetate buffer solution, and sonicate for 20 min to obtain the pre-prepared solution;

[0033] Step A3: Heat the pre-prepared solution to 75°C, add 3 mol / L ammonia water dropwise to the pre-prepared solution at a rate of 1.5 mL / min until pH=7.0, keep warm for 30 min, let stand and age for 2 h, then centrifuge, wash the precipitate with anhydrous ethanol, and vacuum dry at 110°C for 75 min to obtain calcium fluoride@aluminum hydroxide core-shell powder.

[0034] Step A4: Calcium fluoride@aluminum hydroxide core-shell powder and ammonium fluoride powder are respectively placed in two Teflon-lined crucibles, and the two crucibles are placed in a Teflon-lined reactor. The crucible containing ammonium fluoride powder is placed below the crucible containing calcium fluoride@aluminum hydroxide core-shell powder. The mass ratio of ammonium fluoride to calcium fluoride@aluminum hydroxide core-shell powder is 2.5:1. The reactor is heated to 300℃ at a rate of 3℃ / min and held at that temperature for 5 hours. After cooling to room temperature with the furnace, the precipitate is washed with anhydrous ethanol and then vacuum dried at 50℃ for 10 hours to obtain calcium fluoride@aluminum fluoride core-shell structure powder.

[0035] Example 2

[0036] like Figure 1 As shown, a method for preparing calcium fluoride@aluminum fluoride core-shell structured powder includes the following steps:

[0037] Step A1: Add calcium fluoride to 2 wt.% nitric acid and treat for 20 min. Centrifuge and wash until the pH of the supernatant is 6.5. Disperse the precipitate in deionized water and add polyethylene glycol. The mass ratio of polyethylene glycol to calcium fluoride is 0.5:100. Then sonicate for 40 min to obtain a calcium fluoride suspension with a concentration of 0.08 mol / L.

[0038] Step A2: Add 0.1 mol / L aluminum nitrate solution to the calcium fluoride suspension, with a volume ratio of 1:1.5; stir for 5 min to obtain a mixed solution, add 0.12 mol / L sodium acetate buffer solution with pH=4.5, with a volume ratio of 100:5 between the mixed solution and the sodium acetate buffer solution, and sonicate for 15 min to obtain the pre-prepared solution;

[0039] Step A3: Heat the pre-prepared solution to 65°C, add 2 mol / L ammonia water dropwise to the pre-prepared solution at a rate of 2 mL / min until pH=6.5, keep warm for 20 min, let stand and age for 1.5 h, then centrifuge, wash the precipitate with anhydrous ethanol, and vacuum dry at 100°C for 90 min to obtain calcium fluoride@aluminum hydroxide core-shell powder.

[0040] Step A4: Place the calcium fluoride@aluminum hydroxide core-shell powder and ammonium fluoride powder separately into two Teflon-lined crucibles, and place the two crucibles in a Teflon-lined reactor. The crucible containing ammonium fluoride powder is placed below the crucible containing calcium fluoride@aluminum hydroxide core-shell powder. The mass ratio of ammonium fluoride to calcium fluoride@aluminum hydroxide core-shell powder is 2:1. Heat the reactor to 280°C at a rate of 2°C / min and hold for 6 hours. After cooling to room temperature with the furnace, wash the precipitate with anhydrous ethanol, and then vacuum dry at 45°C for 12 hours to obtain calcium fluoride@aluminum fluoride core-shell structure powder.

[0041] Example 3

[0042] like Figure 1 As shown, a method for preparing calcium fluoride@aluminum fluoride core-shell structured powder includes the following steps:

[0043] Step A1: Add calcium fluoride to 4 wt.% nitric acid and treat for 15 min. Centrifuge and wash until the pH of the supernatant is 5.5. Disperse the precipitate in deionized water and add polyethylene glycol. The mass ratio of polyethylene glycol to calcium fluoride is 1.5:100. Then sonicate for 20 min to obtain a calcium fluoride suspension with a concentration of 0.12 mol / L.

[0044] Step A2: Add 0.2 mol / L aluminum nitrate solution to the calcium fluoride suspension, with a volume ratio of 1:1 between the calcium fluoride suspension and the aluminum nitrate solution; stir for 10 min to obtain a mixed solution; add 0.08 mol / L sodium acetate buffer solution with pH=5.0, with a volume ratio of 100:7 between the mixed solution and the sodium acetate buffer solution; sonicate for 30 min to obtain the pre-prepared solution.

[0045] Step A3: Heat the pre-prepared solution to 85°C, add 4 mol / L ammonia water dropwise to the pre-prepared solution at a rate of 1 mL / min until pH=7.5, keep warm for 40 min, let stand and age for 2.5 h, then centrifuge, wash the precipitate with anhydrous ethanol, and vacuum dry at 120°C for 60 min to obtain calcium fluoride@aluminum hydroxide core-shell powder.

[0046] Step A4: Calcium fluoride@aluminum hydroxide core-shell powder and ammonium fluoride powder are respectively placed in two Teflon-lined crucibles, and the two crucibles are placed in a Teflon-lined reactor. The crucible containing ammonium fluoride powder is placed below the crucible containing calcium fluoride@aluminum hydroxide core-shell powder. The mass ratio of ammonium fluoride to calcium fluoride@aluminum hydroxide core-shell powder is 3:1. The reactor is heated to 320°C at a rate of 5°C / min and held at that temperature for 4 hours. After cooling to room temperature with the furnace, the precipitate is washed with anhydrous ethanol and then vacuum dried at 55°C for 8 hours to obtain calcium fluoride@aluminum fluoride core-shell structure powder.

[0047] Example 4

[0048] An optical material prepared by plasma-assisted PVD evaporation, the preparation method of which includes:

[0049] Step S1: After cleaning the substrate, fix it on the substrate holder in the vacuum chamber, fill the calcium fluoride@aluminum fluoride core-shell structure powder prepared in Example 1 into the evaporation boat, evacuate the chamber, heat the evaporation boat to 220°C at a rate of 4°C / min, and then keep it at that temperature for 45min.

[0050] Step S2: Introduce argon and oxygen into the vacuum chamber, with a pressure ratio of argon to oxygen of 96:4; turn on the ion source, extracting energy of 150 eV and density of 75 µA / cm³. 2 The substrate was bombarded with an ion beam for 15 minutes, and then heated to 250°C at a rate of 7°C / min.

[0051] Step S3: Remove oxygen, retain argon, heat the evaporation boat to 1425°C at a rate of 3°C / min, and introduce nitrogen trifluoride to make the pressure ratio of nitrogen trifluoride to argon 1:99; turn on the ion source, extracting energy of 200 eV and density of 150 µA / cm³. 2 An ion beam is used to assist in the deposition of coatings, resulting in optical materials prepared based on plasma-assisted PVD evaporation.

[0052] Example 5

[0053] An optical material prepared by plasma-assisted PVD evaporation, the preparation method of which includes:

[0054] Step S1: After cleaning the substrate, fix it on the substrate holder in the vacuum chamber, fill the evaporation boat with the calcium fluoride@aluminum fluoride core-shell structure powder prepared in Example 2, close the chamber door, evacuate the chamber, heat the evaporation boat to 200°C at a rate of 3°C / min, and then keep it at that temperature for 60min.

[0055] Step S2: Introduce argon and oxygen into the vacuum chamber, with a pressure ratio of 97:3; turn on the ion source, extracting an energy of 100 eV and a density of 50 µA / cm³. 2 The substrate was bombarded with an ion beam for 20 minutes, and then heated to 220°C at a rate of 5°C / min.

[0056] Step S3: Remove the oxygen, leaving argon, and heat the evaporation boat to 1400°C at a rate of 2°C / min. Introduce nitrogen trifluoride to maintain a pressure ratio of 0.5:99.5 between nitrogen trifluoride and argon. Turn on the ion source with an extraction energy of 150 eV and a density of 120 µA / cm³. 2 An ion beam is used to assist in the deposition of coatings, resulting in optical materials prepared based on plasma-assisted PVD evaporation.

[0057] Example 6

[0058] An optical material prepared by plasma-assisted PVD evaporation, the preparation method of which includes:

[0059] Step S1: After cleaning the substrate, fix it on the substrate holder in the vacuum chamber, fill the evaporation boat with the calcium fluoride@aluminum fluoride core-shell structure powder prepared in Example 3, close the chamber door, evacuate the chamber, heat the evaporation boat to 250°C at a rate of 5°C / min, and then keep it at that temperature for 30min.

[0060] Step S2: Introduce argon and oxygen into the vacuum chamber, with a pressure ratio of argon to oxygen of 95:5; turn on the ion source, with an extraction energy of 200 eV and a density of 100 µA / cm³. 2 The substrate was bombarded with an ion beam for 10 min, and then heated to 280°C at a rate of 10°C / min.

[0061] Step S3: Remove oxygen, retain argon, heat the evaporation boat to 1450°C at a rate of 5°C / min, and introduce nitrogen trifluoride to make the pressure ratio of nitrogen trifluoride to argon 1.5:98.5; turn on the ion source with an extraction energy of 250 eV and a density of 200 µA / cm³. 2 An ion beam is used to assist in the deposition of coatings, resulting in optical materials prepared based on plasma-assisted PVD evaporation.

[0062] Comparative Example 1

[0063] An optical material prepared by plasma-assisted PVD evaporation is described. The preparation method differs from that of Example 4 in that the coating material used is a mixture of calcium fluoride and aluminum fluoride in a mass ratio of 1:1. Other operation steps and process parameters are exactly the same as those in Example 4.

[0064] Comparative Example 2

[0065] An optical material prepared by plasma-assisted PVD evaporation is prepared in a manner that differs from that of Example 4 in that the heating process in step S1 is omitted, and the evaporation boat is directly evaporated from room temperature to 1425°C. Other operating steps and process parameters are exactly the same as those in Example 4.

[0066] Comparative Example 3

[0067] An optical material prepared by plasma-assisted PVD evaporation is described. The preparation method of this material differs from that of Example 4 in that nitrogen trifluoride is not introduced in step S3, and argon is used in the vacuum chamber. Other operating steps and process parameters are exactly the same as those in Example 4.

[0068] Comparative Example 4

[0069] An optical material prepared by plasma-assisted PVD evaporation is different from that in Example 4 in that the ion source is not turned on in step S3, and the evaporation process lacks ion beam-assisted deposition. Other operation steps and process parameters are exactly the same as in Example 4.

[0070] Performance testing:

[0071] Deep ultraviolet transmittance testing: The transmittance of the optical materials prepared by plasma-assisted PVD evaporation in Examples 4-6 and Comparative Examples 1-4 in the 200-460 nm range was measured using a Platinum Elmer Spectrum 3 infrared spectrometer. Uncoated fused silica was used as a blank control group.

[0072] Table 1. Transmittance at 200 nm of optical materials prepared by plasma-assisted PVD evaporation in Examples 4-6 and Comparative Examples 1-4.

[0073] Transmittance (%) Blank control group 90.76 Example 4 93.55 Example 5 92.55 Example 6 92.32 Comparative Example 1 87.84 Comparative Example 2 85.28 Comparative Example 3 67.54 Comparative Example 4 90.08

[0074] From Table 1 and Figure 2 The data shows that the optical materials prepared by plasma-assisted PVD evaporation in Examples 4-6 all have a transmittance of over 92% at 200nm, which is an improvement compared to uncoated fused silica. This means that the optical materials prepared according to Examples 4-6 of the present invention have good light transmittance at 200nm, and the coating deposited on the fused silica can be used as a deep ultraviolet antireflective coating.

[0075] Comparative Example 1 used a simple mixture of two components as the coating material, without integrating them into a single coating material through a core-shell structure. The evaporation rates of calcium fluoride and aluminum fluoride differed significantly, resulting in independent evaporation. Fractionation and phase separation caused disordered refractive index of the coating, leading to a decrease in its anti-reflection function. Its transmittance at 200 nm was significantly lower than in Examples 4-6, but still higher than the other comparative examples. Comparative Example 2 lacked the first-stage heating process, and the water adsorbed on the surface of the modified coating material in the evaporation boat was not removed. During evaporation, the water reacted with the evaporated aluminum fluoride to form aluminum oxide. The Al-O bond has strong absorption at 200 nm, causing a decrease in the material's transmittance. Furthermore, moisture accelerated fluorine loss during the evaporation process. Although the ion beam containing nitrogen trifluoride could replenish fluorine, a small number of fluorine vacancies were still formed, further reducing the transmittance. Comparative Example 3 lacked nitrogen trifluoride supplementation during the evaporation process, leading to fluorine loss during aluminum fluoride evaporation. This resulted in a large number of fluorine vacancies in the aluminum-rich layer, causing enhanced light absorption at 200 nm and a decrease in light transmittance. Furthermore, the fluorine vacancies formed in the aluminum-rich layer absorbed residual oxygen in the vacuum chamber, forming aluminum oxide within the aluminum-rich layer, further enhancing light absorption at 200 nm, resulting in the lowest light transmittance for Comparative Example 3. Comparative Example 4 lacked ion beam assistance during evaporation, but nitrogen trifluoride gas was still introduced into its vacuum chamber. At the high temperature of evaporation, the nitrogen trifluoride gas decomposed thermally, partially filling the fluorine vacancies formed by the high-temperature decomposition of aluminum fluoride. However, the lack of ion beam bombardment during evaporation resulted in insufficient atomic diffusion in the film layer, leading to an unevenly deposited film layer with a small number of pores, increasing light scattering loss, and causing a decrease in transmittance for Comparative Example 4.

[0076] In summary, this invention uses an ion beam extracted from plasma as an auxiliary means in the PVD evaporation process. Before the coating material evaporates, the ion beam can clean the substrate, preventing residual impurities on the substrate surface from affecting the adhesion of the coating and the optical properties of subsequent materials. During the evaporation of the coating material, the ion beam can make the coating deposition more uniform. To avoid vapor phase fractionation caused by the difference in vapor pressure and evaporation rate between calcium fluoride and aluminum fluoride, the calcium fluoride and aluminum fluoride are integrated into a single coating material through a core-shell structure through a rational design of the coating material structure. During heated evaporation, the heat transfer rate between the shell layers is greater than the heat transfer rate from the shell layer to the core. Therefore, the aluminum fluoride shell layer on the surface of the evaporation boat is evaporated first and deposited on the substrate to form an aluminum-rich layer. Subsequently, the calcium fluoride that has lost its aluminum fluoride shell layer and the middle part of the aluminum fluoride shell layer evaporate together, depositing a calcium fluoride / aluminum fluoride composite layer on the aluminum fluoride layer. Finally, the calcium fluoride that has lost its shell layer at the bottom of the evaporation boat is evaporated, depositing a calcium-rich layer on the calcium fluoride / aluminum fluoride composite layer to form the final optical material.

[0077] The embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. An optical material prepared by plasma-assisted PVD evaporation, characterized in that, The optical material consists of a substrate and a coating. The substrate is fused silica, and the coating is calcium fluoride@aluminum fluoride core-shell structure powder. The calcium fluoride@aluminum fluoride core-shell structure powder is deposited on the substrate after plasma-assisted PVD evaporation.

2. The method for preparing optical materials based on plasma-assisted PVD evaporation according to claim 1, characterized in that, The preparation method includes the following steps: Step S1: After cleaning the substrate, fix it on the substrate holder in the vacuum chamber, fill the evaporation boat with calcium fluoride@aluminum fluoride core-shell structure powder, evacuate the chamber, heat and keep it warm; Step S2: Introduce argon and oxygen into the vacuum chamber, turn on the ion source, bombard the substrate with an ion beam, and heat the substrate; Step S3: Remove oxygen, retain argon, heat, then introduce nitrogen trifluoride, turn on the ion source, assist in the deposition of the coating, and obtain the optical material.

3. The method for preparing optical materials based on plasma-assisted PVD evaporation according to claim 2, characterized in that, In step S1, the heating temperature is 200-250℃, the heating rate is 3-5℃ / min, and the holding time is 30-60min.

4. The method for preparing optical materials based on plasma-assisted PVD evaporation according to claim 2, characterized in that, In step S2, the pressure ratio of argon to oxygen is (95-97):(3-5); the energy of the ion beam extracted after the ion source is turned on is 100-200 eV, and the density of the ion beam is 50-100 µA / cm³. 2 The bombardment time is 10-20 min; the heating temperature is 220-280℃, and the heating rate is 5-10℃ / min.

5. The method for preparing optical materials based on plasma-assisted PVD evaporation according to claim 2, characterized in that, In step S3, the heating temperature is 1400-1450℃, and the heating rate is 2-5℃ / min; the pressure ratio of nitrogen trifluoride to argon is (0.5-1.5):(98.5-99.5); the energy of the ion beam extracted after the ion source is turned on is 150-250 eV, and the ion beam density is 120-200 µA / cm³. 2 .

6. The method for preparing optical materials based on plasma-assisted PVD evaporation according to claim 2, characterized in that, In step S1, the preparation method of the calcium fluoride@aluminum fluoride core-shell structure powder includes: Step A1: Add calcium fluoride to nitric acid for treatment, centrifuge and wash until the pH of the supernatant is 5.5-6.5, disperse the precipitate in deionized water, add polyethylene glycol, and sonicate to obtain a calcium fluoride suspension; Step A2: Add aluminum nitrate solution to calcium fluoride suspension, stir to obtain mixed solution, add sodium acetate buffer, sonicate to obtain pre-prepared solution; Step A3: Heat the pre-prepared solution, add ammonia to adjust the pH to 6.5-7.5, keep warm, age, centrifuge, collect the precipitate, wash with anhydrous ethanol, and vacuum dry to obtain calcium fluoride@aluminum hydroxide core-shell powder; Step A4: Heat calcium fluoride@aluminum hydroxide core-shell powder and ammonium fluoride powder together in a reaction vessel, keep warm, cool down, wash the solid product with anhydrous ethanol, and vacuum dry to obtain calcium fluoride@aluminum fluoride core-shell structure powder.

7. The method for preparing optical materials based on plasma-assisted PVD evaporation according to claim 6, characterized in that, In step A1, the concentration of nitric acid is 2-4 wt.%, and the treatment time is 15-20 min; the mass ratio of polyethylene glycol to calcium fluoride is (0.5-1.5):100; the ultrasonic treatment time is 20-40 min; and the concentration of the calcium fluoride suspension is 0.08-0.12 mol / L.

8. The method for preparing optical materials based on plasma-assisted PVD evaporation according to claim 6, characterized in that, In step A2, the volume ratio of the calcium fluoride suspension to the aluminum nitrate solution is 1:(1-1.5); the concentration of the aluminum nitrate solution is 0.1-0.2 mol / L; the stirring time is 5-10 min; the volume ratio of the mixed solution to the sodium acetate buffer is 100:(5-7); the concentration of the sodium acetate buffer is 0.08-0.12 mol / L, and the pH of the sodium acetate buffer is 4.5-5.0; the sonication time is 15-30 min.

9. The method for preparing optical materials based on plasma-assisted PVD evaporation according to claim 6, characterized in that, In step A3, the heating temperature is 65-85℃; the concentration of ammonia water is 2-4 mol / L, and the rate of ammonia water addition is 1-3 mL / min; the holding time is 20-40 min; the aging time is 1.5-2.5 h; the vacuum drying temperature is 100-120℃, and the drying time is 60-90 min.

10. The method for preparing optical materials based on plasma-assisted PVD evaporation according to claim 6, characterized in that, In step A4, the mass ratio of ammonium fluoride to calcium fluoride@aluminum hydroxide core-shell powder is (2-3):1; the heating temperature is 280-320℃, and the heating rate is 2-5℃ / min; the holding time is 4-6h; and the vacuum drying temperature is 45-55℃, and the drying time is 8-12h.

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