Fluorinated rare earth particles as well as preparation method and application thereof

Abstract

The invention relates to fluorinated rare earth particles as well as a preparation method and application thereof. The particle size of the rare earth fluoride particles is 1-10 mm, and the purity is larger than or equal to 99.99%. The preparation method of the rare earth fluoride particles comprises the following steps: S1, heating a rare earth fluoride raw material to be molten in a protective atmosphere with air partial pressure not greater than 10 Pa; the heating temperature t1 and the melting point t0 of the rare earth fluoride meet the following relation: t1-t0 is greater than or equal to 100-200 DEG C; s2, molten rare earth fluoride is transferred into the multiple pits and cooled; and the diameter of the concave pit is 1 to 10 mm. The rare earth fluoride particles can be applied to the infrared antireflection film, and the transmittance, the laser damage threshold value and other properties of the film layer are better.

Description

Technical Field

[0001] The invention relates to rare earth fluoride particles and a preparation method and application thereof. Background Art

[0002] With the development of infrared detection, infrared imaging and other fields, especially the field of high-energy laser systems, optical devices or films are required to have characteristics such as high laser damage threshold, high transmittance, and low infrared absorption rate, so as to meet the requirements of low power, high signal-to-noise ratio and high stability of optical systems.

[0003] Rare earth fluorides are widely used in infrared anti-reflection coatings due to their excellent infrared transmittance and low infrared absorption, such as the use of ytterbium fluoride in infrared guidance systems and wide-spectrum filtering systems for all-day detectors.

[0004] However, currently rare earth fluoride is prepared into film by evaporation in the form of micron-sized powder evaporation materials. Micron-sized powder is very easy to be lifted up during the evaporation process, thereby contaminating the plated parts and the furnace chamber, or being sucked away in large quantities when the coating is vacuumed, affecting the coating quality and efficiency.

[0005] However, when preparing rare earth fluoride particles with larger particle sizes, their morphology, crystal form and purity are difficult to control, and there is currently little research in this area. Summary of the invention

[0006] The present invention provides a rare earth fluoride particle and a preparation method and application thereof to solve the problems that the morphology, crystal form and purity of rare earth fluoride particles in the prior art are difficult to grasp. The present invention can obtain rare earth fluoride particles with a particle size of 1-10 mm and a purity of ≥99.99%.

[0007] In a first aspect, the present invention provides a rare earth fluoride particle having a particle size of 1-10 mm and a purity of ≥99.99%;

[0008] When the rare earth fluoride of the rare earth fluoride particles is lanthanum fluoride, in the rare earth fluoride particles, the content of lanthanum fluoride crystals in the lanthanum fluoride accounts for more than 98%; the lanthanum fluoride crystals have diffraction peaks at 28.1°±0.2°, 31.8°±0.2°, 40.7°±0.2°, 50.5°±0.2° and 57.1°‌±0.2° in an X-ray powder diffraction pattern expressed in 2θ angles using Cu-Kα radiation;

[0009] When the rare earth fluoride of the rare earth fluoride particles is gadolinium fluoride, in the rare earth fluoride particles, the content of gadolinium fluoride crystals accounts for more than 98% of the gadolinium fluoride; the gadolinium fluoride crystals have diffraction peaks at 29.8°±0.2°, 32.0°±0.2°, 35.1°±0.2°, 54.5°±0.2° and 57.1°‌±0.2° in an X-ray powder diffraction pattern using Cu-Kα radiation and expressed in 2θ angles;

[0010] When the rare earth fluoride of the rare earth fluoride particles is ytterbium fluoride, the stoichiometric ratio of F to Yb in the rare earth fluoride particles is (2.9-3): 1.

[0011] In the present invention, the purity of the rare earth fluoride particles is the mass ratio of the main component elements of the rare earth fluoride particles minus the impurity elements, that is, the relative purity. For example, the purity of ytterbium fluoride particles is equal to the mass ratio of the remaining elements of the rare earth fluoride particles minus the impurity elements other than fluorine and ytterbium, which is the ytterbium fluoride purity.

[0012] In the present invention, preferably, the content of the lanthanum fluoride crystal form in the lanthanum fluoride accounts for 100%.

[0013] In the present invention, preferably, the X-ray powder diffraction pattern of the lanthanum fluoride crystal form is as follows Figure 5 shown.

[0014] In the present invention, preferably, the content of the gadolinium fluoride crystal form in the gadolinium fluoride accounts for 100%.

[0015] In the present invention, preferably, the X-ray powder diffraction pattern of the gadolinium fluoride crystal is as follows Figure 6 shown.

[0016] In the present invention, preferably, in the rare earth fluoride particles, the stoichiometric ratio of F to Yb is 3:1.

[0017] In the present invention, the rare earth fluoride of the rare earth fluoride particles may be lanthanum fluoride, yttrium fluoride, gadolinium fluoride or ytterbium fluoride (YbF3).

[0018] In the present invention, the particle size of the rare earth fluoride particles may be 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm or 10 mm.

[0019] In certain specific embodiments of the present invention, the particle size of the rare earth fluoride particles may be 1-3 mm, 3-6 mm, 6-8 mm or 8-10 mm.

[0020] In a second aspect, the present invention provides a method for preparing rare earth fluoride particles, comprising the following steps:

[0021] S1. In a protective atmosphere with an air partial pressure of no more than 10 Pa, heating a rare earth fluoride raw material until it is melted; the heating temperature t1 and the melting point t0 of the rare earth fluoride satisfy the following relationship: t1-t0≥100~200°C;

[0022] S2. Transferring the molten rare earth fluoride to a plurality of pits and cooling them; the diameter of the pits is 1-10 mm.

[0023] In the present invention, in step S1, the air partial pressure of the protective atmosphere may be 2 Pa.

[0024] In the present invention, in step S1, the protective atmosphere conventionally further comprises a protective gas, wherein the protective gas is a gas that does not participate in the reaction, preferably an inert gas, such as argon.

[0025] In the present invention, in step S1, the total pressure of the protective atmosphere may be no greater than 0.05 MPa, for example, 0.03 MPa.

[0026] In the present invention, in step S1, the rare earth fluoride raw material may be lanthanum fluoride, yttrium fluoride, gadolinium fluoride or ytterbium fluoride (YbF3).

[0027] In the present invention, in step S1, the heating rate of the heating may be 30-60°C / min, for example, 50°C / min.

[0028] In the present invention, in step S1, when the temperature reaches t1, the temperature can be kept warm for 1-2 hours.

[0029] In the present invention, in step S1, t1-t0 may be 125-130°C.

[0030] In the present invention, in step S2, the pits may be pre-sprayed with a boron nitride coating.

[0031] In the present invention, in step S2, the pit may be a hemispherical structure.

[0032] In the present invention, in step S2, the diameter of the pit may be 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm or 10 mm.

[0033] In the present invention, in step S2, guide grooves may be provided between each of the pits.

[0034] In the present invention, in step S2, the pit may be provided on a mold.

[0035] In the present invention, in step S2, after cooling, the cooled material can be crushed and screened. During the screening, the diameter of the screen used is 1-10 mm, for example, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm or 10 mm. In step S1, the rare earth fluoride raw material can be rare earth fluoride that does not meet the particle size requirements after the screening, for example, particles with a particle size greater than 10 mm or less than 1 mm.

[0036] In a specific embodiment of the present invention, the air partial pressure of the protective atmosphere is 2 Pa. The protective atmosphere also includes a protective gas, which is argon. The total pressure of the protective atmosphere is 0.03 MPa. The rare earth fluoride raw material is lanthanum fluoride. The heating rate is 50°C / min. When the heating reaches the temperature t1, the temperature is kept warm for 1 h, and t1-t0=125°C.

[0037] In a specific embodiment of the present invention, the air partial pressure of the protective atmosphere is 2 Pa, the protective atmosphere also includes a protective gas, the protective gas is argon, the total pressure of the protective atmosphere is 0.03 MPa, the rare earth fluoride raw material is gadolinium fluoride, the heating rate is 50°C / min, and when the heating reaches the temperature t1, the temperature is kept warm for 1 h, and t1-t0=130°C.

[0038] In a specific embodiment of the present invention, the air partial pressure of the protective atmosphere is 2 Pa. The protective atmosphere also includes a protective gas, which is argon. The total pressure of the protective atmosphere is 0.03 MPa. The fluorinated rare earth raw material is ytterbium fluoride (YbF3). The heating rate is 50°C / min. When the temperature reaches t1, the temperature is kept warm for 1 h, and t1-t0=130°C.

[0039] In a third aspect, the present invention provides rare earth fluoride particles prepared by the method for preparing rare earth fluoride particles as described above.

[0040] In a fourth aspect, the present invention provides a use of the above-mentioned rare earth fluoride particles in an infrared anti-reflection film.

[0041] Without violating the common sense in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0042] The reagents and raw materials used in the present invention are commercially available.

[0043] The positive and progressive effects of the present invention are:

[0044] (1) In the present invention, when preparing rare earth fluoride particles, the particles are kept warm at a temperature much higher than the melting point of the rare earth fluoride. The particles obtained have a certain gloss on the surface, a large grain size and a certain degree of transparency, and the particles are not easy to fall off the surface;

[0045] (2) In the present invention, when preparing rare earth fluoride particles, a sufficiently high vacuum degree can remove the impurity gas in the furnace to prevent the impurity gas from reacting with the rare earth fluoride during the smelting process, thereby obtaining white particles with good crystallization and no tendency to fall off;

[0046] (3) In the present invention, the large-particle rare earth fluoride particles prepared are used in infrared anti-reflection films, and the transmittance, laser damage threshold and other properties of the film layer are better. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 is the appearance morphology of the gadolinium fluoride particles in Example 2;

[0048] Figure 2 This is the appearance morphology of the gadolinium fluoride particles in Comparative Example 1;

[0049] Figure 3 is the appearance morphology of the ytterbium fluoride particles in Example 3;

[0050] Figure 4 This is the appearance morphology of the ytterbium fluoride particles in Comparative Example 2 (when not broken);

[0051] Figure 5 is the XRD pattern of the lanthanum fluoride particles in Example 1;

[0052] Figure 6 is the XRD pattern of the gadolinium fluoride particles in Example 2;

[0053] Figure 7 is the energy spectrum of the ytterbium fluoride particles in Example 3;

[0054] Figure 8 This is the energy spectrum of the ytterbium fluoride particles in Comparative Example 2. DETAILED DESCRIPTION

[0055] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0056] Example 1: Lanthanum fluoride particles and preparation method thereof

[0057] This embodiment includes the following steps:

[0058] S1,

[0059] Add 2 kg of lanthanum fluoride (melting point 1493°C) into a crucible in a vacuum melting furnace;

[0060] Evacuate the vacuum melting furnace to 2 Pa (absolute pressure), then introduce argon gas into the furnace until the vacuum gauge reads -0.07 MPa;

[0061] Heat the vacuum melting furnace at a heating rate of 50°C / min until the temperature exceeds the melting point of lanthanum fluoride, 125°C, and then run the heat preservation program for 1 hour until the lanthanum fluoride in the crucible is completely melted. During this period, the changes in the material in the crucible can be observed through the observation mirror;

[0062] S2,

[0063] The molten lanthanum fluoride is cast from the crucible into each honeycomb mold. The honeycomb mold is pre-sprayed with a boron nitride coating. After cooling to room temperature, the material is taken out and crushed. The pits in each honeycomb mold are hemispherical structures with diameters of 3 mm, 6 mm, and 10 mm, respectively. Small guide grooves are provided between the pits. Since rare earth fluoride will remain in the guide grooves, the particles between the pits will adhere together through the remaining materials in the guide grooves after cooling, and need to be separated by crushing and screening;

[0064] The above-mentioned crushed materials are sieved using sieves with mesh diameters of 1 mm, 3 mm, 6 mm, 8 mm, and 10 mm, respectively. The sieves of corresponding sizes are stacked together in order from large to small according to the mesh size, and placed on a vibrating screening machine. Then, the material to be screened is poured into the top sieve, and the vibrating screening is started after the protective cover is closed to obtain lanthanum fluoride particles with particle sizes of 1-3 mm, 3-6 mm, 6-8 mm, and 8-10 mm, respectively, with a purity of ≥99.99%.

[0065] Example 2: Gadolinium fluoride particles and preparation method thereof

[0066] This embodiment includes the following steps:

[0067] S1,

[0068] Add 2 kg of gadolinium fluoride (melting point 1231°C) into a crucible in a vacuum melting furnace;

[0069] Evacuate the vacuum melting furnace to 2 Pa (absolute pressure), then introduce argon gas into the furnace until the vacuum gauge reads -0.07 MPa;

[0070] Heat the vacuum melting furnace at a heating rate of 50°C / min until the temperature exceeds the melting point of gadolinium fluoride, 130°C, and then run the heat preservation program for 1 hour until the gadolinium fluoride in the crucible is completely melted. During this period, the changes in the material in the crucible can be observed through the observation mirror;

[0071] S2,

[0072] The molten gadolinium fluoride is cast from the crucible into each honeycomb mold. The honeycomb mold is pre-sprayed with a boron nitride coating. After cooling to room temperature, the material is taken out and crushed. The pits in each honeycomb mold are hemispherical structures with diameters of 3 mm, 6 mm, and 10 mm, respectively. Small guide grooves are provided between the pits. Since rare earth fluoride will remain in the guide grooves, the particles between the pits will adhere together through the remaining materials in the guide grooves after cooling, and need to be separated by crushing and screening;

[0073] The above-mentioned crushed materials are sieved using sieves with mesh diameters of 1 mm, 3 mm, 6 mm, 8 mm, and 10 mm, respectively. The sieves of corresponding sizes are stacked together in order from large to small according to the mesh size, and placed on a vibrating screening machine. Then the material to be screened is poured into the top sieve, and the vibrating screening is started after the protective cover is closed to obtain yttrium fluoride particles with particle sizes of 1-3 mm, 3-6 mm, 6-8 mm, and 8-10 mm, respectively, with a purity of ≥99.99%.

[0074] Example 3: Ytterbium fluoride (YbF3) particles and preparation method thereof

[0075] This embodiment includes the following steps:

[0076] S1,

[0077] Add 2 kg of ytterbium fluoride (melting point 1161.85°C) into the crucible in the vacuum melting furnace;

[0078] Evacuate the vacuum melting furnace to 2 Pa (absolute pressure), then introduce argon gas into the furnace until the vacuum gauge reads -0.07 MPa;

[0079] Heat the vacuum melting furnace at a heating rate of 50°C / min until the temperature exceeds the melting point of ytterbium fluoride, 130°C, and then run the heat preservation program for 1 hour until the ytterbium fluoride in the crucible is completely melted. During this period, the changes in the material in the crucible can be observed through the observation mirror;

[0080] S2,

[0081] The molten ytterbium fluoride is cast from the crucible into each honeycomb mold. The honeycomb mold is pre-sprayed with a boron nitride coating. After cooling to room temperature, the material is taken out and crushed. The pits in each honeycomb mold are hemispherical structures with diameters of 3 mm, 6 mm, and 10 mm, respectively. Small guide grooves are provided between the pits. Since rare earth fluoride will remain in the guide grooves, the particles between the pits will adhere together through the remaining materials in the guide grooves after cooling, and need to be separated by crushing and screening;

[0082] The above-mentioned crushed materials are sieved using sieves with mesh diameters of 1 mm, 3 mm, 6 mm, 8 mm and 10 mm respectively. The sieves of corresponding sizes are stacked together in descending order according to the mesh size and placed on a vibrating screening machine. Then the material to be screened is poured into the top sieve, and the vibrating screening is started after the protective cover is closed to obtain ytterbium fluoride particles with particle sizes of 1-3 mm, 3-6 mm, 6-8 mm and 8-10 mm, respectively, with a purity of ≥99.99%.

[0083] Comparative Example 1: Gadolinium fluoride particles and preparation method thereof

[0084] Compared with Example 2, the only difference is that in step S1, the heating end point temperature is only 30° C. higher than the melting point of gadolinium fluoride.

[0085] Comparative Example 2: Ytterbium fluoride particles and preparation method thereof

[0086] Compared with Example 3, the only difference is that in step S1, the vacuum melting furnace is evacuated to 15 Pa (absolute pressure).

[0087] Effect Example 1: Macroscopic Morphology of Rare Earth Fluoride Particles

[0088] 1. Test objects: the rare earth fluoride particles in Example 2, Example 3, Comparative Example 1 and Comparative Example 2.

[0089] 2. Test method: Use a camera to photograph the appearance of rare earth fluoride particles.

[0090] 3. Test results:

[0091] like Figure 1 In Example 2, the holding temperature is 130°C above the melting point of gadolinium fluoride. After holding for 1 hour, the particles obtained are white in appearance and have a certain gloss on the surface, indicating that the sample has a large grain size and a certain degree of transparency, and the particle surface is not easy to fall off. Figure 2 In comparative example 1, the holding temperature was only 30°C above the melting point of gadolinium fluoride for 1 hour. The prepared particles were gray in appearance and easily fell into debris. They fell into powder during the coating process, forming particles with a particle size of less than 1 mm, which affected the film performance and quality.

[0092] like Figure 3 In Example 3, the vacuum degree is reduced to 2 Pa when smelting the ytterbium fluoride particle product. A sufficiently high vacuum degree can remove the impurity gas in the furnace to prevent it from reacting with the ytterbium fluoride during the smelting process. Thus, white particles with good crystallization and low powder loss are obtained. Figure 4 In comparative example 2, the vacuum degree during smelting is insufficient, and the color of the product after smelting will appear light yellow, affecting the quality.

[0093] Effect Example 2: Purity of rare earth fluoride particles

[0094] 1. Test object: the rare earth fluoride particles in all the above embodiments and comparative examples.

[0095] 2. Test method: The GD-MS analysis method commonly used in this field is used. Purity refers to the physical distribution and mutual proportion of the components in a substance. In the present invention, purity is the mass proportion of the main component elements in the fluoride rare earth product minus the impurity elements, that is, the relative purity. For example, in the GDMS report of ytterbium fluoride, the purity is equal to the remaining part after deducting the percentage of the tested impurity elements, which is the purity of ytterbium fluoride. For example, if the total content of the impurity atoms tested is less than 100 ppm, the relative purity of ytterbium fluoride is greater than 99.99%.

[0096] 3. Test results: The purity of the rare earth fluoride particles in Example 1, Example 2 and Example 3 is ≥99.99%. The purity of Comparative Example 1 and Comparative Example 2 is ≥99.99%. Among them, the GD-MS analysis of the rare earth fluoride particles in Example 1 and Example 3 is as shown in Table 1-Table 2:

[0097] Table 1 Example 1 Lanthanum fluoride GDMS

[0098]

[0099] Table 2 Example 3 Ytterbium fluoride GDMS

[0100]

[0101] It should be noted that GD-MS is used to analyze the content of trace elements. After testing, the purity of the main components Yb and F is ≥99.99%. GD-MS cannot distinguish between YbF2 and YbF3.

[0102] Effect Example 3: XRD spectrum of fluorinated rare earth particles

[0103] 1. Test object: the rare earth fluoride particles in Example 1 and Example 2.

[0104] 2. Test method: Use the common test method in this field.

[0105] 3. Test results: Figure 5 As shown, the XRD spectrum of the lanthanum fluoride particles prepared in Example 1 almost completely matches its standard spectrum, that is, the content of lanthanum fluoride crystals in lanthanum fluoride accounts for almost 100%; Figure 6 As shown, the XRD spectrum of the gadolinium fluoride particles prepared in Example 2 is almost completely matched with its standard spectrum, and the content of gadolinium fluoride crystals in gadolinium fluoride accounts for almost 100%.

[0106] Effect Example 4: Chemical Ratio of Rare Earth Fluoride Particles

[0107] 1. Test object: ytterbium fluoride particles in Example 3 and Comparative Example 2.

[0108] 2. Test method: The field emission electron microscope energy spectrum analysis method commonly used in this field is adopted.

[0109] 3. Test results: Figure 7 , the ytterbium fluoride particles in Example 3 are YbF3, that is, the stoichiometric ratio of F to Yb in the ytterbium fluoride particles is 3:1. Figure 8 The chemical ratio of the particles in Comparative Example 2 has changed, and most of them have been converted into YbF2, that is, the chemical ratio of F to Yb in the ytterbium fluoride particles is much less than 2.9:1.

Claims

1. A rare earth fluoride particle, characterized in that: Its particle size is 1-10 mm and purity is ≥99.99%; When the rare earth fluoride of the rare earth fluoride particles is lanthanum fluoride, in the rare earth fluoride particles, the content of lanthanum fluoride crystals in the lanthanum fluoride accounts for more than 98%; the lanthanum fluoride crystals have diffraction peaks at 28.1°±0.2°, 31.8°±0.2°, 40.7°±0.2°, 50.5°±0.2° and 57.1°‌±0.2° in an X-ray powder diffraction pattern expressed in 2θ angles using Cu-Kα radiation; When the rare earth fluoride of the rare earth fluoride particles is gadolinium fluoride, in the rare earth fluoride particles, the content of gadolinium fluoride crystals accounts for more than 98% of the gadolinium fluoride; the gadolinium fluoride crystals have diffraction peaks at 29.8°±0.2°, 32.0°±0.2°, 35.1°±0.2°, 54.5°±0.2° and 57.1°‌±0.2° in an X-ray powder diffraction pattern using Cu-Kα radiation and expressed in 2θ angles; When the rare earth fluoride of the rare earth fluoride particles is ytterbium fluoride, the stoichiometric ratio of F to Yb in the rare earth fluoride particles is (2.9-3):

1.

2. The rare earth fluoride particles according to claim 1, characterized in that: It satisfies at least one of the following conditions: (1) The rare earth fluoride of the rare earth fluoride particles is lanthanum fluoride, yttrium fluoride, gadolinium fluoride or ytterbium fluoride; (2) The particle size of the rare earth fluoride particles is 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm or 10 mm; (3) The content of the lanthanum fluoride crystal form in the lanthanum fluoride is 100%; (4) the content of the gadolinium fluoride crystal form in the gadolinium fluoride is 100%; (5) In the rare earth fluoride particles, the stoichiometric ratio of F to Yb is 3:

1.

3. The rare earth fluoride particles according to claim 1, characterized in that: It satisfies at least one of the following conditions: ① The X-ray powder diffraction pattern of the crystalline form of lanthanum fluoride is shown in FIG5 ; ② The X-ray powder diffraction pattern of the crystalline form of gadolinium fluoride is shown in FIG6 ; ③ The particle size of the rare earth fluoride particles is 1-3 mm, 3-6 mm, 6-8 mm or 8-10 mm.

4. A method for preparing rare earth fluoride particles, characterized in that: It includes the following steps: S1. In a protective atmosphere with an air partial pressure of no more than 10 Pa, heating a rare earth fluoride raw material until it is melted; the heating temperature t1 and the melting point t0 of the rare earth fluoride satisfy the following relationship: t1-t0≥100~200°C; S2. Transferring the molten rare earth fluoride to a plurality of pits and cooling them; the diameter of the pits is 1-10 mm.

5. The method for preparing rare earth fluoride particles according to claim 4, characterized in that: It satisfies at least one of the following conditions: (1) In step S1, the air partial pressure of the protective atmosphere is 2 Pa; (2) In step S1, the protective atmosphere further includes an inert gas; (3) In step S1, the total pressure of the protective atmosphere is no more than 0.05 MPa; (4) In step S1, the rare earth fluoride raw material is lanthanum fluoride, yttrium fluoride, gadolinium fluoride or ytterbium fluoride YbF3; (5) In step S1, the heating rate is 30-60°C / min; (6) In step S1, when the heating reaches the temperature t1, the temperature is kept constant; (7) In step S1, t1-t0=125~130℃; (8) In step S2, the pit is pre-sprayed with a boron nitride coating; (9) In step S2, the pit is a hemispherical structure; (10) In step S2, the diameter of the pit is 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm or 10 mm; (11) In step S2, a guide groove is provided between each pit; (12) In step S2, the recess is provided on a mold; (13) In step S2, after cooling, the cooled material is crushed and screened.

6. The method for preparing rare earth fluoride particles according to claim 5, characterized in that: It satisfies at least one of the following conditions: ① In step S1, the inert gas is argon; ② In step S1, the total pressure of the protective atmosphere is 0.03 MPa; ③ In step S1, the heating rate is 50°C / min; ④ In step S1, the insulation time is 1-2 h; ⑤ In step S2, during the screening, the diameter of the sieve used is 1-10 mm.

7. The method for preparing rare earth fluoride particles according to claim 6, characterized in that: It satisfies one of the following conditions: Condition 1: in step S1, the rare earth fluoride raw material is particles having a particle size greater than 10 mm or less than 1 mm after screening; Condition two: in step S2, during the screening, the diameter of the sieve used is 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm or 10 mm.

8. The method for preparing rare earth fluoride particles according to claim 4, characterized in that: It satisfies one of the following combinations of conditions: Condition combination 1, the air partial pressure of the protective atmosphere is 2 Pa, the protective atmosphere further includes a protective gas, the protective gas is argon, the total pressure of the protective atmosphere is 0.03 MPa, the rare earth fluoride raw material is lanthanum fluoride, the heating rate is 50°C / min, when the heating reaches the temperature t1, the temperature is kept warm, the holding time is 1h, t1-t0=125°C; Condition combination 2: the air partial pressure of the protective atmosphere is 2 Pa, the protective atmosphere further includes a protective gas, the protective gas is argon, the total pressure of the protective atmosphere is 0.03 MPa, the rare earth fluoride raw material is gadolinium fluoride, the heating rate is 50°C / min, and when the heating reaches the temperature t1, the temperature is kept warm for 1h, and t1-t0=130°C; Condition combination three, the air partial pressure of the protective atmosphere is 2 Pa, the protective atmosphere also includes a protective gas, the protective gas is argon, the total pressure of the protective atmosphere is 0.03 MPa, the rare earth fluoride raw material is ytterbium fluoride YbF3, the heating rate is 50°C / min, and when the heating reaches the temperature t1, the insulation is carried out, and the insulation time is 1 h, t1-t0=130°C.

9. A rare earth fluoride particle obtained by the method for preparing rare earth fluoride particles according to any one of claims 4 to 8.

10. Use of the fluorinated rare earth particles according to any one of claims 1 to 3 and 9 in an infrared anti-reflection film.

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