Calcium fluoride crystal doped with metal ions, preparation method of calcium fluoride crystal and application of calcium fluoride crystal in optical element

Abstract

The invention belongs to the technical field of crystals, and particularly relates to a calcium fluoride crystal doped with metal ions, a preparation method of the calcium fluoride crystal and application of the calcium fluoride crystal in optical elements. The crystal is a calcium fluoride crystal doped with magnesium ions and barium ions, and in the preparation method of the crystal, the magnesium ions and the barium ions for doping are pretreated and coated with a calcium fluoride precursor, and the calcium fluoride crystal which is uniform in doping and excellent in performance is prepared by combining a traditional Bridgman-Stockbarger method with a gradient doping process. The crystal is applied to an excimer laser lighting system, and after an optical element manufactured by the crystal is exposed to gamma radiation larger than 2.8 Mrads, the 515 / 380 nm transmittance loss ratio of the optical element is lower than 0.4.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of crystals, in particular to a metal ion doped calcium fluoride crystal, a preparation method thereof and application thereof in optical elements. BACKGROUND

[0002] Calcium fluoride crystal (CaF2) is an ionic crystal with excellent optical and physical properties, which has a typical fluorite-type cubic structure, Ca 2+ is located inside the face-centered cubic lattice, and F - is located at the lattice points of the face-centered cubic lattice. Ca 2+ is combined with eight F - ions around it to form an eight-coordination, and F - is combined with four Ca 2+ ions around it to form a four-coordination. At the same time, it is also a typical brittle material, with a high thermal expansion coefficient, a low thermal conductivity, a very low fracture toughness, and optical properties such as a wide transmission wavelength range, a low dispersion effect, and strong anti-laser damage capability. It is widely used in the fields of semiconductor manufacturing, optical window manufacturing, medical imaging device component manufacturing, etc.

[0003] Metal ion doping is one of the common technical means to improve and optimize the optical properties, mechanical properties and lattice defects of calcium fluoride crystals. For example, the doping of magnesium ions, barium ions, strontium ions and rare earth metal ions, etc. Calcium fluoride has a cubic fluorite structure, Ca 2+ occupies the nodes of the face-centered cubic lattice, and F - fills the tetrahedral interstitial sites. When other metal ions are introduced, the other metal ions act as dopant ions by replacing Ca 2+ lattice sites to achieve doping.

[0004] Chinese patent application CN 116377580 A discloses a method for reducing the cleavage characteristics of calcium fluoride crystals by doping rare earth ions. By doping Y 3+ or trivalent lanthanide element ions La 3+ ~ Lu 3+ , the cleavage effect of calcium fluoride crystals is reduced, thereby improving the laser damage threshold of the crystals. Chinese patent application CN

[0005] 118422312A discloses a method for improving the visible band radiation damage resistance performance of calcium fluoride crystals by doping trace elements. By introducing trace amounts of variable valence ions Yb 3+ , when the crystal receives high-energy radiation, Yb 3+ preferentially captures electrons, thereby inhibiting the formation of F vacancies, and ultimately improving the performance of the crystal in the visible light band in terms of radiation damage resistance. Therefore, metal ion doped calcium fluoride crystals have become the research focus for developing optical materials with superior performance.

[0006] Most of the preparation methods of calcium fluoride crystals adopt the techniques such as the crucible lowering method and the pulling method, the crucible lowering method is the most commonly used technical means, the process is simple, easy to operate, and is suitable for the growth of large-size and complex-shaped crystals, but when the metal-doped calcium fluoride crystals are prepared by the method, the segregation of the doped metal in the solid-liquid two phases will cause the composition gradient along the growth direction, especially for the high-concentration doped or multi-doped system, local segregation may occur, affecting the uniformity of the performance. Therefore, the raw material pretreatment or gradient doping design is needed to alleviate. SUMMARY

[0007] The present application aims to provide a metal ion-doped calcium fluoride crystal and a preparation method and application in optical elements thereof, which can be used in 193nm excimer laser illumination system. Fluoride magnesium and barium coated with calcium fluoride precursor are adopted to avoid the formation of negative ion vacancies or intermetallic gap defects; gradient doping combined with the crucible lowering method is adopted to dope the surface modified magnesium ions and barium ions in high-purity calcium fluoride crystals, so that the optical performance of the crystal blank is improved, especially the laser damage resistance is improved, and the typical service life is prolonged. After the crystal and the optical element manufactured therefrom are exposed to gamma radiation greater than 2.8Mrads, the transmittance loss ratio of 515 / 380nm is less than 0.4.

[0008] To achieve the above-mentioned purpose, the present application provides a preparation method of a metal ion-doped calcium fluoride crystal, comprising:

[0009] Step S1, dissolving a calcium salt in anhydrous ethanol, adding ammonium fluoride, adjusting the pH value to 3-5, and stirring to obtain a calcium fluoride precursor solution;

[0010] Step S2, dispersing fluoride magnesium in the precursor solution, adding a catalyst, and stirring to promote gelation, to obtain a crude product of calcium fluoride precursor coated fluoride magnesium, and after centrifugation, washing, drying and sintering, surface modified fluoride magnesium is obtained, and surface modified fluoride barium is prepared under the same conditions;

[0011] Step S3, placing calcium fluoride raw material in a crucible, sealing, maintaining vacuum state, and heating to a preset temperature to ensure that the calcium fluoride crystal is melted;

[0012] Step S4, using a feeding device, gradient doping surface modified fluoride barium and surface modified fluoride magnesium in the crystal growth process according to the set program combined with the crucible lowering method, to prepare a metal ion-doped calcium fluoride crystal.

[0013] Preferably, in the step S1, the calcium salt is any one or more of calcium nitrate and calcium acetate.

[0014] Preferably, in the step S1, the mass ratio of the ethanol, calcium salt and ammonium fluoride ethanol solution is 1:(0.025-0.05):(0.012-0.025).

[0015] Preferably, in the step S2, the catalyst is any one or more of hydrochloric acid, acetic acid.

[0016] Preferably, in the step S2, the mass ratio of the precursor solution, magnesium fluoride and catalyst is 1:(0.2-0.5):(0.01-0.05).

[0017] In the step S2, the stirring time is 2-4h.

[0018] Preferably, in the step S2, the solvent for washing is anhydrous ethanol.

[0019] Preferably, in the step S2, the drying temperature is 40-60℃, and the drying time is 8-12h.

[0020] Preferably, in the step S2, the sintering temperature is 300-500℃, and the sintering time is 1-3h.

[0021] Preferably, in the step S3, both the outer crucible and the inner crucible are graphite crucibles. The graphite crucible is a high-purity graphite crucible, which needs to be treated by high-temperature graphitization to avoid impurity pollution, and the inner wall of the crucible is polished to reduce the probability of defects generated during crystal growth.

[0022] Preferably, in the step S3, the vacuum degree of the vacuum state is 10 -3 Pa. Fluoride ion volatilization is inhibited, and raw material oxidation is prevented.

[0023] Preferably, in the step S3, the temperature rising rate is 50℃ / h.

[0024] Preferably, in the step S3, the preset temperature is 1410-1460℃. The temperature needs to be higher than the melting point of calcium fluoride by 50-100℃ to ensure complete melting of the raw material, and the temperature needs to be controlled to prevent dopant loss.

[0025] Preferably, in the step S3, the stirring time is 3-4h.

[0026] Preferably, in the step S4, the preparation process of the gradient doping combined with the crucible lowering method is as follows:

[0027] The initial stage is 0-10h, the surface modified magnesium fluoride feed amount is set to 1.6-12.8mg / h, the surface modified barium fluoride feed amount is set to 0.04-0.1mg / h, and the crucible descending speed is 0.5-1mm / h. The solid-liquid interface is ensured to be stable nucleation, and the polycrystal growth is avoided.

[0028] The stable stage is 10-90h, the surface modified magnesium fluoride feed amount is set to 1.6-12.8mg / h, the surface modified barium fluoride feed amount is set to 0.04-0.1mg / h, the calcium fluoride is supplemented at 6-6.5g per hour, and the crucible descending speed is 1-3mm / h.

[0029] The end stage is 90-100h, the surface modified magnesium fluoride feed amount is gradually reduced from 1.6-12.8mg / h to 0, the surface modified barium fluoride feed amount is gradually reduced from 0.04-0.1mg / h to 0, and the crucible descending speed is 0.5mm / h. The dopant concentration is gradually reduced, and the end enrichment is avoided.

[0030] The cooling stage is cooled at a speed of 10-15℃ / h. Slow cooling reduces the stress concentration at the end of the crystal, avoids the cracking caused by excessive internal stress of the crystal, and the cooling time can be extended to 72-96h for large-size crystals.

[0031] The annealing stage is under vacuum, the temperature is increased to 800-1000℃ at a speed of 20-50℃ / h, the temperature is kept for 24-48h, the temperature is decreased to room temperature at a speed of 10-20℃ / h, and the metal ion doped calcium fluoride crystal is obtained. The annealing treatment can reduce or eliminate the lattice defects and internal stress, and improve the optical uniformity of the crystal.

[0032] The application provides a metal ion doped calcium fluoride crystal, which is prepared by the above method.

[0033] The application also provides an application of the metal ion doped calcium fluoride crystal in an optical element.

[0034] Compared with the prior art, the application has the beneficial effects of:

[0035] (1) The present application dopes magnesium ions and barium ions in high-purity calcium fluoride crystals to improve the performance of calcium fluoride crystals. In terms of optical performance, magnesium ion doping can inhibit lattice defects, reduce ultraviolet absorption centers, widen the deep ultraviolet transmission range, enhance lattice stability, reduce thermal defects, and improve laser damage resistance; barium ion doping can reduce lattice vibration absorption in the infrared band, improve mid-infrared transmittance, and relieve lattice thermal stress under laser irradiation, making the crystal more suitable for high-power laser systems in cooperation with magnesium ions. In terms of mechanical properties and thermal stability, pure calcium fluoride crystals have high brittleness and low fracture toughness, magnesium ion doping improves hardness and wear resistance through lattice strengthening effect; barium ions improve the thermal expansion matching of the crystal, reduce cracking caused by temperature changes, and are particularly suitable for extreme environment applications. In addition, single doping of magnesium ions can cause vacancy aggregation due to lattice contraction, while the lattice expansion of barium ions offsets part of the stress, reduces dislocation density and impurity segregation, and improves the optical uniformity of the crystal.

[0036] (2) In the present application, the magnesium ions and barium ions to be doped are coated with calcium fluoride precursors, and are prepared by traditional crucible lowering method combined with gradient doping. The calcium fluoride precursor has high lattice matching degree with the main body calcium fluoride, can be used as a transition layer to guide the uniform diffusion of the dopant, and can reduce interfacial segregation. At the same time, the coating layer can prevent the direct reaction of magnesium fluoride or barium fluoride with the calcium fluoride melt at high temperature, which can avoid the formation of negative ion vacancies or intermetallic gap defects. Based on the traditional crucible lowering method, combined with gradient doping, by dynamically adjusting the supply amount of the dopant, gradient doping with different concentrations at different parts of the crystal is realized, which is beneficial to alleviate the problem of stress concentration in the crystal. In traditional uniform doping, high concentration doping can easily lead to excessive lattice mismatch, resulting in defects such as dislocations and cracks, while gradient doping gradually transitions the lattice distortion through gradual change of concentration. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 A physical picture of calcium fluoride crystal doped with metal ions.

[0038] Figure 2 XRD diffraction pattern of calcium fluoride crystal prepared in Example 1.

[0039] Figure 3 XRD diffraction pattern of calcium fluoride crystal prepared in Example 2.

[0040] Figure 4 XRD diffraction pattern of calcium fluoride crystal prepared in Example 3. DETAILED DESCRIPTION

[0041] The following examples are only used to more clearly illustrate the technical solutions of the present application, and cannot be used to limit the protection scope of the present application.

[0042] The compounds used in the examples and comparative examples are all commercially available and are not subjected to any further purification.

[0043] Example 1

[0044] A metal ion doped calcium fluoride crystal, the preparation method comprising:

[0045] Step S1, 2.5 g of calcium nitrate is dissolved in 100 g of anhydrous ethanol, 1.2 g of ammonium fluoride is added, the pH value is adjusted to 3-5, and stirring is performed at 25℃ to obtain a calcium fluoride precursor solution.

[0046] Step S2, 20 g of magnesium fluoride is dispersed in 100 g of the calcium fluoride precursor solution, 1 g of hydrochloric acid is added, stirring is performed for 2 h to promote gelation, a crude product of magnesium fluoride coated with the calcium fluoride precursor is obtained, centrifugation is performed, washing is performed with anhydrous ethanol, drying is performed at 40℃ for 12 h, sintering is performed at 300℃ for 3 h, and surface modified magnesium fluoride is obtained.

[0047] Step S3, 20 g of barium fluoride is dispersed in 100 g of the calcium fluoride precursor solution, 1 g of hydrochloric acid is added, stirring is performed for 2 h to promote gelation, a crude product of barium fluoride coated with the calcium fluoride precursor is obtained, centrifugation is performed, washing is performed with anhydrous ethanol, drying is performed at 40℃ for 12 h, sintering is performed at 300℃ for 3 h, and surface modified barium fluoride is obtained.

[0048] Step S4, 10 kg of calcium fluoride powder with a purity of 99% is placed in a graphite crucible, the crucible is sealed, a vacuum state is maintained, and the temperature is maintained at 10 -3 Pa, the temperature is raised to 1410℃ at a rate of 50℃ / h, and the temperature is kept constant for 4 h to ensure that the calcium fluoride powder is melted.

[0049] Step S5, from 0 h to 10 h, the feeding amount of the surface modified magnesium fluoride is set to 1.6 mg / h, the feeding amount of the surface modified barium fluoride is set to 0.04 mg / h, and the descending speed of the crucible is adjusted to 0.5 mm / h. From 10 h to 90 h, the feeding amount of the surface modified magnesium fluoride is set to 1.6 mg / h, the feeding amount of the surface modified barium fluoride is set to 0.04 mg / h, 6 g of calcium fluoride is supplemented every hour, and the descending speed of the crucible is adjusted to 1 mm / h. From 90 h to 100 h, the feeding amount of the surface modified magnesium fluoride is gradually reduced from 1.6 mg / h to 0, the feeding amount of the surface modified barium fluoride is gradually reduced from 0.04 mg / h to 0, and the descending speed of the crucible is adjusted to 0.5 mm / h. The temperature is lowered to room temperature at a rate of 10℃ / h, finally, the temperature is raised to 800℃ at a rate of 20℃ / h under a vacuum state, the temperature is kept constant for 48 h, the temperature is lowered to room temperature at a rate of 10℃ / h, and a metal ion doped calcium fluoride crystal is obtained, as shown in FIG. 1. Figure 1 .

[0050] Example 2

[0051] A metal ion doped calcium fluoride crystal, a preparation method thereof comprises the following steps:

[0052] Step S1, 4g of calcium acetate is dissolved in 100g of anhydrous ethanol, 2g of ammonium fluoride is added, the pH value is adjusted to 3-5, and stirring is performed at 30℃ to obtain a calcium fluoride precursor solution.

[0053] Step S2, 30g of magnesium fluoride is dispersed in 100g of the calcium fluoride precursor solution, 3g of acetic acid is added, stirring is performed for 3h to promote gelation, a crude product of the calcium fluoride precursor coated magnesium fluoride is obtained, centrifugation is performed, washing is performed with anhydrous ethanol, drying is performed at 50℃ for 10h, sintering is performed at 400℃ for 2h, and a surface modified magnesium fluoride is obtained.

[0054] Step S3, 30g of barium fluoride is dispersed in 100g of the calcium fluoride precursor solution, 3g of acetic acid is added, stirring is performed for 3h to promote gelation, a crude product of the calcium fluoride precursor coated barium fluoride is obtained, centrifugation is performed, washing is performed with anhydrous ethanol, drying is performed at 50℃ for 10h, sintering is performed at 400℃ for 2h, and a surface modified barium fluoride is obtained.

[0055] Step S4, 10kg of calcium fluoride powder with a purity of 99% is placed in a graphite crucible, sealing is performed, a vacuum state is maintained, and the temperature is maintained at 10 -3 Pa, the temperature is increased to 1430℃ at a speed of 50℃ / h, stirring is performed for 3h to ensure that the calcium fluoride powder is melted.

[0056] Step S5, from 0h to 10h, the feeding amount of the surface modified magnesium fluoride is set to 7.8mg / h, the feeding amount of the surface modified barium fluoride is set to 0.08mg / h, and the speed of the crucible descending is adjusted to 0.75mm / h. From 10h to 90h, the feeding amount of the surface modified magnesium fluoride is set to 7.8mg / h, the feeding amount of the surface modified barium fluoride is set to 0.08mg / h, 6.25g of calcium fluoride is supplemented every hour, and the speed of the crucible descending is adjusted to 2mm / h. From 90h to 100h, the feeding amount of the surface modified magnesium fluoride is gradually reduced from 7.8mg / h to 0, the feeding amount of the surface modified barium fluoride is gradually reduced from 0.08mg / h to 0, and the speed of the crucible descending is adjusted to 0.5mm / h. The temperature is decreased to room temperature at a speed of 15℃ / h, finally, the temperature is increased to 900℃ at a speed of 35℃ / h under a vacuum state, and the temperature is maintained for 36h, and then the temperature is decreased to room temperature at a speed of 15℃ / h to obtain a metal ion doped calcium fluoride crystal, as shown in FIG. 1. Figure 1 .

[0057] Example 3

[0058] A metal ion doped calcium fluoride crystal, a preparation method thereof comprises the following steps:

[0059] Step S1, 5g of calcium nitrate is dissolved in 100g of anhydrous ethanol, 2.5g of ammonium fluoride is added, the pH value is adjusted to 3-5, and stirring is performed at 40℃ to obtain a calcium fluoride precursor solution.

[0060] Step S2, 50g of magnesium fluoride was dispersed in 100g of calcium fluoride precursor solution, 5g of hydrochloric acid was added, stirred for 4h to promote gelation, to obtain a crude product of calcium fluoride precursor coated magnesium fluoride, centrifuged, washed with anhydrous ethanol, dried at 60℃ for 8h, sintered at 500℃ for 1h to obtain surface modified magnesium fluoride.

[0061] Step S3, 50g of barium fluoride was dispersed in 100g of calcium fluoride precursor solution, 5g of hydrochloric acid was added, stirred for 4h to promote gelation, to obtain a crude product of calcium fluoride precursor coated barium fluoride, centrifuged, washed with anhydrous ethanol, dried at 60℃ for 8h, sintered at 500℃ for 1h to obtain surface modified barium fluoride.

[0062] Step S4, 10kg of calcium fluoride powder with a purity of 99% was placed in a graphite crucible, sealed, kept in a vacuum state, maintained at 10 -3 Pa, heated to 1460℃ at a rate of 50℃ / h, stirred for 3h to ensure the calcium fluoride powder was melted.

[0063] Step S5, from 0h to 10h, the feeding amount of surface modified magnesium fluoride was set to 12.8mg / h, the feeding amount of surface modified barium fluoride was set to 0.1mg / h, and the speed of the crucible descending was adjusted to 1mm / h. From 10h to 90h, the feeding amount of surface modified magnesium fluoride was set to 12.8mg / h, the feeding amount of surface modified barium fluoride was set to 0.1mg / h, 6.5g of calcium fluoride was supplemented every hour, and the speed of the crucible descending was adjusted to 3mm / h. From 90h to 100h, the feeding amount of surface modified magnesium fluoride was gradually reduced from 12.8mg / h to 0, the feeding amount of surface modified barium fluoride was gradually reduced from 0.1mg / h to 0, and the speed of the crucible descending was adjusted to 0.5mm / h. Then, it was cooled to room temperature at a rate of 15℃ / h, and finally, it was heated to 1000℃ at a rate of 50℃ / h, kept for 24h in a vacuum state, and then cooled to room temperature at a rate of 20℃ / h to obtain a calcium fluoride crystal doped with metal ions, as shown in FIG. 1. Figure 1

[0064] Comparative Example 1

[0065] A calcium fluoride crystal doped with metal ions, the difference between the preparation method and Example 1 is that in Step S2, the magnesium fluoride is not coated and modified by calcium fluoride precursor.

[0066] Comparative Example 2

[0067] A calcium fluoride crystal doped with metal ions, the difference between the preparation method and Example 1 is that in Step S3, the barium fluoride is not coated and modified by calcium fluoride precursor.

[0068] Comparative Example 3

[0069] ​A metal ion doped calcium fluoride crystal, the difference between the preparation method and embodiment 1 is that in step S2, the magnesium fluoride is not coated and modified by calcium fluoride precursor, and in step S3, the barium fluoride is not coated and modified by calcium fluoride precursor.

[0070] Comparative example 4

[0071] A metal ion doped calcium fluoride crystal, the difference between the preparation method and embodiment 1 is that in step S5, the traditional uniform doping crucible lowering method is used.

[0072] XRD diffraction data of metal ion doped calcium fluoride crystal:

[0073] Table 1 Crystal XRD diffraction peak table

[0074]

[0075] According to Figures 2-4 The data in Table 1 can be obtained, according to the data, the diffraction peak positions of the calcium fluoride crystals prepared in embodiments 1-3 all appear at 28.140°, it is known that the crystal face diffraction peak of pure calcium fluoride crystal is about 28.3°, the radius of magnesium ion is smaller than that of calcium ion, and the doping of magnesium ion will make the diffraction peak crystal face spacing decrease, and the diffraction peak shift to high angle direction, while the radius of barium ion is larger than that of calcium ion, and the doping of barium ion will make the diffraction peak crystal face spacing increase, and the diffraction peak shift to low angle direction; due to the fact that the doping concentration of magnesium ion is significantly higher than that of barium ion, and the 4-coordination characteristics of magnesium ion, the local lattice distortion of calcium fluoride crystal is caused, which further affects the fine structure of the diffraction peak, mainly affecting the right shift of the peak position caused by lattice shrinkage, so the diffraction peak shifts to 28.140°.

[0076] The half-width is contributed by grain refinement and lattice strain, which can be calculated by the Scherrer formula, the half-width of pure calcium fluoride crystal is usually between 0.05-0.1°, doping can inhibit or promote the growth of grains, doping of magnesium ion and barium ion hinders the growth of calcium fluoride grains, the grain size decreases, and the peak width increases, so the half-width of the crystals prepared in embodiments 1-3 is 0.1-0.3°.

[0077] Performance test:

[0078] (1) Density: the size of the calcium fluoride crystals prepared in embodiments 1-3 and comparative examples 1-4 is φ50x100mm (volume is 196.25cm 3 ), the weight of the calcium fluoride crystal is weighed, and the density of the calcium fluoride crystal is calculated.

[0079] (2) Bubbles: The crystal was processed into a sample of φ20x20mm, the number of bubbles (size about greater than 0.1mm) in the calcium fluoride crystal blank was detected under 40nW laser, and then the number of bubbles (size about greater than 0.01mm) in the calcium fluoride crystal was observed by microscope.

[0080] (3) Stress birefringence: The crystal sample was processed into a sample of φ20x20mm, and the stress birefringence of the crystal was measured by a polarizing stress instrument (Hinds 150AT, USA).

[0081] (4) Optical uniformity: The crystal sample was processed into a sample of φ20x20mm, and the optical uniformity was measured by a Fizeau interferometer (zygo MST, USA).

[0082] (5) Transmittance: The crystal was processed into a sample of φ20x20mm, and the transmittance of the crystal at 248nm was tested by a full-energy spectrophotometer (Agilent Cary 7000).

[0083] Table 2 Crystal physical properties and appearance quality

[0084]

[0085] According to Table 2, the densities of the calcium fluoride crystal blanks prepared in Examples 1-3 and Comparative Examples 1-4 were all between 3.16-3.18g / cm3. The crystal blanks prepared in Examples 1-3 had no bubbles under 40nW laser by microscope detection; the crystal blanks prepared in Comparative Examples 1-3 had a small amount of bubbles.

[0086] Table 3 Crystal optical properties

[0087]

[0088]

[0089] According to Table 3, the stress birefringence of the calcium fluoride crystal blanks prepared in Examples 1-3 were all below 2.0nm / cm, which was significantly lower than that of Comparative Examples 1-4; the optical uniformity of the calcium fluoride crystal blanks prepared in Examples 1-3 was significantly higher than that of Comparative Examples 1-4; the transmittance of the calcium fluoride crystal blanks prepared in Examples 1-3 was all above 93%, and the transmittance of the calcium fluoride crystal blanks prepared in Comparative Examples 1-4 was slightly lower than that of Examples 1-3.

[0090] The above only describes the preferred embodiments of the present application, and it should be noted that those skilled in the art can make several improvements and modifications without departing from the technical principles of the present application, and these improvements and modifications should also be considered as the protection scope of the present application.

Claims

1. A method for producing a metal ion-doped calcium fluoride crystal, characterized by, The application relates to a method for preparing a calcium fluoride crystal doped with metal ions. The method comprises the following steps: S1, dissolving a calcium salt in anhydrous ethanol, adding ammonium fluoride, adjusting the pH value to 3-5, and stirring to obtain a calcium fluoride precursor solution; S2, dispersing magnesium fluoride in the calcium fluoride precursor solution, adding a catalyst, stirring to promote gelation, obtaining a magnesium fluoride product coated with the calcium fluoride precursor, and obtaining surface-modified magnesium fluoride after centrifugation, washing, drying and sintering; surface-modified barium fluoride is prepared under the same conditions; S3, placing calcium fluoride raw material in a crucible, sealing, keeping a vacuum state, and heating to a preset temperature to ensure that the calcium fluoride raw material is molten; 2. The method of claim 1, wherein the metal ion-doped calcium fluoride crystal is prepared by the steps of: (a) preparing a solution of calcium fluoride and a metal salt; (b) precipitating the metal ion-doped calcium fluoride crystal from the solution; and (c) washing and drying the metal ion-doped calcium fluoride crystal. S4, using a feeding device, gradient doping of the surface-modified barium fluoride and the surface-modified magnesium fluoride in the process of crystal growth according to a set program combined with a crucible lowering method, and preparing the calcium fluoride crystal doped with metal ions.

3. The method of claim 1, wherein the metal ion-doped calcium fluoride crystal is prepared by the steps of: (a) preparing a solution of calcium fluoride and a metal salt; (b) precipitating the metal ion-doped calcium fluoride crystal from the solution; and (c) washing and drying the metal ion-doped calcium fluoride crystal. In the step S1, the calcium salt is any one or more of calcium nitrate and calcium acetate.

4. The method of claim 1, wherein the metal ion-doped calcium fluoride crystal is prepared by the steps of: (a) preparing a solution of calcium fluoride and a metal salt; (b) precipitating the metal ion-doped calcium fluoride crystal from the solution; and (c) washing and drying the metal ion-doped calcium fluoride crystal. In the step S1, the mass ratio of the ethanol, the calcium salt and the ammonium fluoride ethanol solution is 1:(0.025-0.05):(0.012-0.025); and the stirring temperature is 25-40 DEG C.

5. The method of claim 1, wherein the metal ion-doped calcium fluoride crystal is prepared by the steps of: (a) preparing a solution of calcium fluoride and a metal salt; (b) precipitating the metal ion-doped calcium fluoride crystal from the solution; and (c) washing and drying the metal ion-doped calcium fluoride crystal. In the step S2, the catalyst is any one or more of hydrochloric acid and acetic acid; and the mass ratio of the calcium fluoride precursor solution, the magnesium fluoride and the catalyst is 1:(0.2-0.5):(0.01-0.05).

6. The method of claim 1, wherein the metal ion-doped calcium fluoride crystal is prepared by the steps of: (a) preparing a solution of calcium fluoride and a metal salt; (b) precipitating the metal ion-doped calcium fluoride crystal from the solution; and (c) washing and drying the metal ion-doped calcium fluoride crystal. The step S3, the crucible is graphite crucible; the vacuum degree of the vacuum state is 10 -3 Pa.

7. The method of claim 1, wherein the metal ion-doped calcium fluoride crystal is prepared by the steps of: (a) preparing a solution of calcium fluoride and a metal salt; (b) precipitating the metal ion-doped calcium fluoride crystal from the solution; and (c) washing and drying the metal ion-doped calcium fluoride crystal. In the step S2, the stirring time is 2-4 h; the washing solvent is anhydrous ethanol; the drying temperature is 40-60 DEG C, and the drying time is 8-12 h; and the sintering temperature is 300-500 DEG C, and the sintering time is 1-3 h.

8. The method of claim 1, wherein the metal ion-doped calcium fluoride crystal is prepared by the steps of: (a) preparing a solution of calcium fluoride and a metal salt; (b) precipitating the metal ion-doped calcium fluoride crystal from the solution; and (c) washing and drying the metal ion-doped calcium fluoride crystal. In the step S3, the heating rate is 50 DEG C / h, and the preset temperature is 1410-1460 DEG C. In the step S4, the preparation process is as follows: in the initial stage of 0-10 h, the feeding amount of the surface-modified magnesium fluoride is set to be 1.6-12.8 mg / h, the feeding amount of the surface-modified barium fluoride is set to be 0.04-0.1 mg / h, and the crucible lowering speed is 0.5-1 mm / h; in the stable stage of 10-90 h, the feeding amount of the surface-modified magnesium fluoride is set to be 1.6-12.8 mg / h, the feeding amount of the surface-modified barium fluoride is set to be 0.04-0.1 mg / h, 6-6.5 g of calcium fluoride is supplemented every hour, and the crucible lowering speed is 1-3 mm / h; in the finishing stage of 90-100 h, the feeding amount of the surface-modified magnesium fluoride is gradually reduced from 1.6-12.8 mg / h to 0, the feeding amount of the surface-modified barium fluoride is gradually reduced from 0.04-0.1 mg / h to 0, and the crucible lowering speed is 0.5 mm / h; in the cooling stage, the temperature is reduced at a speed of 10-15 DEG C / h; and in the annealing stage, the temperature is raised to 800-1000 DEG C at a speed of 20-50 DEG C / h under a vacuum state, the temperature is reduced to room temperature at a speed of 10-20 DEG C / h, and the calcium fluoride crystal doped with metal ions is obtained.

9. A calcium fluoride crystal doped with metal ions, characterized in that, The metal ion doped calcium fluoride crystal prepared by the preparation method according to any one of claims 1-8 has a magnesium ion doping concentration of 100-300 ppm, a magnesium ion content in the crystal of 10-80 ppm, a barium ion doping concentration of 5-50 ppm, and a barium ion content in the crystal of 4-10 ppm.

10. Use of the metal ion doped calcium fluoride crystal according to claim 9 in an optical element.

Images