EP3374466A1

EP3374466A1 - Sol-gel process for synthesising a luminescent material with general formulation: axbyfz:mn

Info

Publication number: EP3374466A1
Application number: EP16809984.4A
Authority: EP
Inventors: Anthony BARROS; Rodolphe Deloncle; Jérôme Deschamps; Geneviève CHADEYRON; Damien Boyer; Philippe BOUTINAUD
Original assignee: Centre National de la Recherche Scientifique CNRS; Linxens Holding SAS; Universite Blaise Pascal Clermont Ferrand II; Sigma Clermont
Current assignee: Centre National de la Recherche Scientifique CNRS; Linxens Holding SAS; Universite Clermont Auvergne; Sigma Clermont
Priority date: 2015-11-13
Filing date: 2016-11-10
Publication date: 2018-09-19
Also published as: CA3004389A1; FR3043687A1; KR20180100112A; CN108699439B; US20190071601A1; CA3004389C; JP2019500312A; FR3043687B1; WO2017081428A1; KR102132757B1; US11505741B2; CN108699439A

Abstract

The invention relates to a sol-gel process for synthesising a luminescent material with general formulation: AxByFz:Mn, wherein A is an element of group 1, 2, 4, NR₄ or a combination of elements belonging to said groups, with R=H or an alkyl chain or a combination of chains, B being an element of group 5, 6, 13, 14 and 0<x≤5, 0<y≤2, 5≤z≤7, characterised in that it includes at least the following steps: a) producing a liquid precursor (2, 3) in an alcohol solution by mixing metal reagents (1), selected among metal salts such as halogenides, nitrates, hydrides, amidides, acetates, carbonates or alkoxides, with manganese, the mixture being made at pH < 8; b) obtaining a solid precursor (5, 6) from the liquid precursor (2, 3) obtained in step a), by eliminating (4) the solvent; c) crystallising (7, 70) the solid precursor (5, 6) obtained in step b), by thermal treatment in fluorinated atmosphere; and d) retrieving the fluorescent crystalline powder (8) obtained at the end of step c).

Description

SOL-GEL PROCESS FOR THE SYNTHESIS OF A LUMINESCENT MATERIAL

GENERAL FORMULATION: AxByFz: Mn

The present invention relates to a sol-gel method for synthesizing a luminescent material of general formula: AxByFz: Mn.

Here, A represents an element belonging to one of the following groups of the Periodic Table of Elements also known as the Mendeleyev Table: Groups 1, 2, 4, NR ₄ or a combination of elements, with the proviso that R is hydrogen or an alkyl chain, alone or in combination. B represents an element belonging to one of the groups 5, 6, 13, 14, x is a value greater than zero and less than or equal to five, y is a value greater than zero and less than or equal to two and z is greater than or equal to at five and less than or equal to seven.

Luminescent materials, that is to say materials that under the action of an excitation emit light, are used in the field of lighting, lasers, medical imaging among others. In particular luminescent materials are used in the production of Electro-Luminescent Diodes or LEDs according to the acronym generally used. For environmental reasons, cost, durability, consumption and ease of use, LEDs are increasingly present for so-called traditional lighting, replacing, for example, halogen or incandescent lamps. In particular, the white LEDs provide lighting similar to natural light.

Most white LEDs are manufactured by combining a semiconductor emitting between 400 nm and 500 nm with a yellow / green phosphor emitting between 480 nm and 650 nm. The manufacture of white LEDs with high color rendering index, or CRI, requires the addition of a red component enhancing the emission between 600 nm and 700 nm. Currently, for this red component, the compounds of the family of nitrides doped with europium are a solution of choice. They characterized by intense red emission and thermal stability. However, these compounds remain expensive and difficult to produce. Also an emerging solution is the use of complex fluorinated compounds of the general formula AxByFz: Mn ⁴⁺ . These materials have a narrow emission range favorable to obtaining a high CRI and are less expensive because of the absence of rare earths in their composition.

It is known from US-A-0166 887 a process for the preparation of a luminescent material by co-precipitation reactions involving fluorinated precursors dissolved in hydrofluoric acid. This acid is considered extremely corrosive and toxic, which implies significant safety constraints during its storage and implementation.

As a result, other modes of production have been explored. Among these, the sol-gel type processes allow the production of low temperature luminescent materials, namely a temperature lower than that of conventional ceramization pathways. For example, in the case of silica, ceramization can be obtained at temperatures below 100 ° C. This type of process is based on an inorganic polymerization, starting from precursors in solution, which gives rise to an organometallic network precursor of the final solid. In the process, colloids are formed as well as polymeric gels. After drying and sintering, it is possible to obtain fibers, monoliths or powders.

In the case of the manufacture of non-fluorinated luminescent materials, we know Audrey Caumond-Potdevin's thesis ("sol-gel synthesis and characterization of nanostructured luminescent materials applicable in a new generation of clean lamps" of June 2007) a process in which metal alkoxides in solution in an organic solvent are used as the precursor. In general, the process comprises reactions of the hydrolysis type and then of the condensation type. These combined reactions lead to the development of molecules having a three-dimensional structure.

The thesis of Jessica Labeguerie-Egea, ("soft-chemistry syntheses of rare earth-doped fluorides for optical applications" of 2007) also describes a sol-gel process using isopropanol as solvent and trifluoroacetic acid as fluorinating agent for obtaining simple fluorinated derivatives of CaF ₂ type doped with europium. It is also known from Damien Boyer and Al, optical materials 28, 2006, 53-57, to produce a fluorescent powder, in this case a europium-doped lithium and yttrium fluoride, from a solution heterometallic alkoxide. Here, the fluorine source is trifluoroacetic acid introduced at the beginning of the process, the latter taking place in a basic medium. This powder finds its application in, among others, the field of lasers.

The matrix structure of these various processes is characterized by crystallographic sites easily incorporating rare earths. These sites are unsuitable for the reception of transition ions of electronic configuration d ³ , such as Cr ³⁺ or Mn ⁴⁺ . In order to obtain the performance levels necessary for an application on LEDs, it is necessary to obtain more fluorinated structures, namely containing more than four fluorine atoms, whose crystalline field makes it possible to obtain an optimized luminescence of the manganese. In addition, the use of rare earths is disadvantageous in terms of costs.

In other words, it is interesting to produce a rare earth-free fluoride, having at least five fluorine atoms in the matrix structure, easy to produce and store.

The invention aims more particularly at providing a sol-gel synthesis process, easy to implement, without organic source of fluorine, without hydrofluoric acid and without rare earths.

To this end, the subject of the invention is a sol-gel method for synthesizing a luminescent material of general formula: AxByFz: Mn, with A being a Group 1, 2, 4, NR ₄ element or a combination of elements belonging to these groups, with R = H or an alkyl chain or a combination of chains, B being an element of group 5, 6, 13, 14, and 0 <x <5, 0 <y <2, 5 <z <7, characterized in that it comprises at least the following steps:

a) producing a liquid precursor, in alcoholic solution, by mixing metal reagents, chosen from metal salts such as halides, nitrates, hydrides, amides, acetates, carbonates or alkoxides, with manganese, the mixture being carried out at pH <8,

b) obtaining a solid precursor from the liquid precursor obtained in step a), by removing the solvent,

c) of crystallization of the solid precursor obtained in step b), by thermal treatment in a fluorinated atmosphere,

d) recovering the fluorescent crystalline powder obtained at the end of step c).

With such a method, no source of fluorine in solution or rare earth is used. Here, the source of fluorine is provided only at the penultimate step, so just before the recovery of the final product, during the heat treatment. In other words, the process proceeds in the absence of fluorine in solution. Security is improved and storage and handling are also facilitated.

According to advantageous but non-mandatory aspects of the invention, such a method may comprise one or more of the following features:

- In step a), the pH is maintained below 8 by the addition of an acid, chosen, without limitation, from carboxylic acids such as formic acid, acetic acid, propanoic acid, citric acid, tartaric acid, oxalic acid, among sulfonic acids such as benzene sulphonic acid, paratoluene sulphonic acid, among anhydrous acids, hydrochloric acid in solution in diethyl ether, in dioxane or in gaseous form.

- In step a), the pH is maintained below 8 by adding a carboxylic acid: acetic acid.

step a) is carried out at a temperature of between 15 ° C. and the boiling point of the solvent used.

The liquid precursor obtained in step a) is, if necessary, stored for a subsequent implementation of step b).

- The solid precursor obtained in step b) is, if necessary, stored for a subsequent implementation of step c). The metal reagents used in step a) are all chosen from alkoxides.

The metal reagents used in step a) are mixtures of metal salts.

Step c) is carried out at a temperature of between 100 ° C. and 1000 ° C. for at least 30 minutes.

The fluorinated agent used in step c) to generate a fluorinated atmosphere is chosen from: F ₂ , HF, BrF ₃ , TbF ₄ , XeF ₂ , XeF 4 and XeF ₆ , NH ₄ F, NH ₄ HF ₂ , CoF ₃ , SbF ₃ , SbF ₅ , ArF ₃ , KrF, BrF ₅ , CIF, CIF ₃ and CIF ₅ , HF0 ₃ S, AuF ₃ , IF ₅ , MnF ₃ and MnF ₄ , NOF and N0 ₂ F NF ₃ , ClO ₃ F, PtF ₆ , SeF, SiF, AgF ₂ , SF, SF ₆ , KF, PbF ₂ , ZnF ₂ , SnF ₂ , CdF ₂ alone or in combination.

- In step c), the atmosphere contains at least 1% of fluorinated agent.

In step c), the fluorinated atmosphere is static or dynamic.

- At the end of step d), the particles obtained are reintroduced into a liquid precursor, in step a).

In this new step a), the liquid precursor is chosen to ensure double luminescence, for magnetic properties or for other characteristics.

The invention will be better understood and other advantages thereof will appear more clearly on reading the description of several embodiments of the invention, given by way of non-limiting example and with reference to the following drawing in which:

FIG. 1 is a simplified diagram illustrating the different steps of the method according to one embodiment of the invention.

With reference to FIG. 1, there will be described the production of a compound from transition metals in general and, more particularly, according to an advantageous embodiment of the invention, with, inter alia, manganese, it being understood that the invention is also applicable with, for example, chromium, iron or any other transition element of groups 3 to 12 of the periodic table of elements. It is conceivable that the use of this or that transition metal makes it possible to obtain luminescence in different spectral domains, therefore in different colors. In in all cases, luminescence is obtained by excitation of the transition element in a range from ultraviolet to infrared, followed by radiative deexcitation.

By way of a preferred example, the use of manganese as one of the metal reagents makes it possible to obtain a luminescence in the red, ie between 600 nm and 700 nm.

It should be borne in mind that the final fluorinated material, thus the resulting luminescent crystalline powder, is a compound of formulation: AxByFz: C ^{m +}

In general, the families of matrices making it possible to obtain a luminescent material are those with:

A = element of group 1, 2, 4, NR ₄ or a combination of elements belonging to these groups being understood that R = H or a small alkyl chain or a combination of chains. Here, the term "small size" refers to an alkyl chain having 1 to 4 carbon atoms.

B = element of group 5, 6, 13, 14.

C ^{m +} = 3d transition metal ⁿ (with n = [1; 10]) at a degree of oxidation m, by transition metals, are designated elements of atomic number between 21 and 30.

0 <x <5, 0 <y <2

5 <z <7.

In the invention, A, B, C are also simple or complex metal reagents. By this term, there are as many metals as for example Manganese, Chromium, Iron or any other transition element as salts of these metals or a mixture of these metals. By way of nonlimiting examples, mention may be made of halides, nitrates, hydrides, amides, acetates, carbonates or, preferably in one embodiment of the invention, alkoxides.

These metal reagents are known per se and are either produced in situ prior to the implementation of the process or are of commercial origin. In other words, the user gets them upstream from a supplier.

The use, preferably, of metal alkoxides as metallic reagents makes it possible to produce a heteroatomic polymeric network in solution, when of step a), which subsequently promotes the formation of the desired final matrix. However, it is possible to use other metal reagents than metal alkoxides, as mentioned above.

Here, it will be described the method object of the invention by the implementation of metal alkoxides.

In a first step, represented under the reference 1, the metal sources A, B and manganese are reacted together with alcohol. The alcohol or mixture of alcohols is chosen according to the metal reagents, in order to ensure optimal solubilization.

The reaction is carried out, under a neutral atmosphere, in a stirred reactor and at a temperature between 15 ° C and the boiling point of the solvent and for a reaction time of between a few minutes and several hours. Preferably, the optimal reaction time is close to 4h. Manganese, unlike Rare Earths, is sensitive to pH. In basic medium, manganese can be oxidized by dissolved oxygen and form Mn0 ₂ . Such a property is known, it is also used in a method, called Winckler, dissolved oxygen assay. In other words, the reaction, during step a), must be carried out in a non-basic medium, namely in this case at a pH of less than 8. Advantageously, the pH is between 1 and 7, preferably close to 5. In addition, the reaction must take place in an anhydrous medium. As a result, the pH is regulated by the addition of an anhydrous acid, advantageously chosen, in a nonlimiting manner, from carboxylic acids such as formic acid, acetic acid, propanoic acid, and the acid. citric acid, tartaric acid, oxalic acid, among sulfonic acids such as benzene sulfonic acid, paratoluene sulphonic acid, among anhydrous acids, hydrochloric acid in solution in ethyl ether , in dioxane or in gaseous form.

Preferably, acetic acid is used.

When the reaction is complete, a liquid precursor 2 is obtained at the conditions of normal temperature and pressure. We understand that step 1 can be performed at any time and / or place in relation to the rest of the process. Thus, the liquid precursor 2 can easily be stored, as illustrated by reference 3. It is thus possible to relocate the production of the liquid precursor 2. In this case, it should be that the conditions of storage and / or transport do not alter not the liquid precursor and the continuation of the process. In particular, it should be borne in mind that the liquid precursor is a flammable product that must be stored away from light.

Alternatively, the liquid precursor 2 is used from its production, either continuously or discontinuously.

The second step of the process, illustrated by the arrows 4, is then implemented, either from the liquid precursor 2 produced or from the stored liquid precursor 3.

Subsequently, the liquid precursor will be referenced 2 if it is used directly and referenced 3 if it is a previously stored liquid precursor.

This step 4 makes it possible to obtain a solid precursor 5. For this, the alcoholic solvent is eliminated. Advantageously but not exclusively, the alcohol is evaporated by heating at a temperature corresponding to the boiling temperature of the alcoholic solvent, this temperature having no effect on the other constituents of the liquid precursor. Alternatively, the solvent is removed by evaporation under reduced pressure, by dring spray, freeze drying or any other technique known per se.

The object of this step 4 is to initiate and solidify a reaction intermediate containing the elements A, B and C. For this, the parameters of step 4 are variable and depend on the solvent used and the removal method chosen. .

Once the solid precursor 5 has been obtained, and similarly to the liquid precursor 2, it is possible to store the solid precursor for further use and / or at another location, as is apparent from FIG.

It should be noted that, until now, the process has not used fluorinated agent in solution. In other words, the fluorine source is not yet present in the process, which makes it possible to safely handle, transport and store the various precursors, while managing the moment of incorporation of the fluorine source. The next step, illustrated by the arrows 7 or 70 depending on whether the solid precursor 5 is used immediately or whether it is a stored solid precursor 6, consists of a heat treatment which makes it possible to supply the fluorine in the form of atomic and / or molecular, to the solid precursor from its production, according to reference 5, or to the solid precursor stored, according to reference 6. It should be noted that the fluorine intake is carried out only in step 7, 70 and not before.

In other words, step 7, 70 is carried out under a fluorinated atmosphere. By way of non-limiting examples, mention may be made, as fluorinating agent, of: F ₂ , HF, BrF ₃ , TbF ₄ , XeF ₂ , XeF ₆ , NH ₄ F, CoF ₃ , SbF ₃ , ArF ₃ , BrF ₅ , CIF , CIF ₃ , CIF ₅ , HFO ₃ S, AuF ₃ , IF ₅ , MnF ₃ , MnF ₄ , NOF, NO ₂ F, Cl ₃ F, PtF ₆ , SeF ₄ , AgF ₂ , SF ₄ .

The heat treatment carried out during this step 7, 70 is carried out between 100 ° C. and 1000 ° C. for a duration of at least 30 minutes under a fluorinated atmosphere containing at least 1% of fluorine. Indeed, it is not necessary that the atmosphere is saturated with fluorine, the rest of the atmosphere may be a neutral gas such as nitrogen.

The following synthetic examples illustrate the implementation of the method which is the subject of the invention.

Example 1

K ₂ SiF ₆ : Mn (IV) is synthesized from MnCl ₂ , K metal and tetraethyl orthosilicate (TEOS). The solvent used is anhydrous ethanol. To a solution of MnCl ₂ (0.1713 g) is added a solution of K (3.6432 g). After stirring for 1 hour at reflux, TEOS (9.3272 g) is added to the previous solution. After stirring for 30 minutes at reflux, acetic acid (1.18 ml) is added in order to adjust the pH to 5. After refluxing for 4 hours, the salts are removed from the solution and the solution is evaporated. dried up. The precursor thus obtained is heat-treated at 500 ° C. under a flow of F ₂ for 15 hours.

Example 2

Na ₂ TiF ₆ : Mn (IV) is synthesized from MnCl ₂ , Na metal and tetraethyl orthotitanate (TEOT). The solvent used is anhydrous isopropanol. To a solution of MnCl ₂ (0.1817 g) is added a solution of Na (0.7268 g). After 1 hour of agitation at reflux, the TEOT (3.6801 g) is added to the previous solution. After stirring for 30 minutes at reflux, acetic acid (3.79 ml) is added in order to adjust the pH to 5. After refluxing for 3 hours, the salts are removed from the solution and the solution is evaporated at room temperature. dry. The precursor thus obtained is heat-treated at 500 ° C. under a flow of F ₂ for 15 hours.

Example 3

Na ₃ AIF ₆ was synthesized from Na metal and aluminum isopropoxide. The solvent used is anhydrous methanol. To a solution of Na (1.6675 g) is added aluminum isopropoxide (4.9135 g). After stirring for 30 minutes at reflux, acetic acid (8.71 ml) was added to adjust the pH to 5. After 2 hours of reflux, the solution was cooled to 25 ° C. In the latter, the Na ₂ TiF ₆ : Mn (IV) powder obtained in Example 2 is dispersed in a molar ratio of 3: 1 to Na ₂ TiF ₆ : Mn (IV). The dispersion thus obtained is evaporated and then heat treated at 650 ° C. under a flow of F ₂ for 3 hours.

Example 4

LiSrAIFe: Cr (III) is synthesized from lithium ethoxide, strontium isopropoxide, chromium acetylacetonate and aluminum isopropoxide. The solvent used is anhydrous isopropanol. To a solution of lithium ethoxide (0.7171 g), strontium isopropoxide (2.6132 g) and chromium acetylacetonate (0.1336 g) is added aluminum isopropoxide (2.5408 g). After stirring for 30 minutes at reflux, acetic acid (3.18 ml) was added in order to adjust the pH to 5. After 6 hours of reflux, the solution was cooled to 25 ° C. In the latter, is dispersed the K ₂ SiF ₆ : Mn (IV) powder obtained in Example 1, in a molar ratio of 9 to 1 in K ₂ SiF ₆ : Mn (IV). The dispersion thus obtained is evaporated and then heat-treated at 600 ° C. under a flow of F ₂ for 10 hours.

The fact that the percentage of gaseous fluorine remains low contributes to improving safety. Moreover, the heat treatment is preferably carried out dynamically, that is to say under a stream of fluorinated gas. Alternatively, it is performed in a static manner: step 7, 70 then taking place in a closed volume, in a fluorinated atmosphere. At the end of step 7 or 70, depending on the origin of the solid precursor, 5 or 6, a crystalline powder 8 is obtained. The size of the particles obtained is a function of the nature of the solid precursor and the conditions of the treatment. 7. Generally, the size of the particles is close to 200 nm. The particles may be in the form of aggregates whose size is of the order of one micron. Such a particle size is particularly suitable for allowing the phosphor to be shaped and deposited, for example on an LED 9.

If necessary, it is possible to increase the particle size by depositing one or more additional layers. For this, it is sufficient to bring the solid particles 8 into contact with the liquid precursor 2 or 3 by dispersing them in the latter, and to carry out at least one other solvent removal step 4 followed by a step 7, 70 heat treatment. In this case, this additional cycle is performed on a mixture of liquid precursor 2 or 3 and 8 particles, so under conditions that are not necessarily the same as those of the initial step 7, 70. It is conceivable that the repetition of the cycle is carried out several times as much as necessary.

The addition of at least one additional cycle, or even more, makes it possible, by modifying the nature of the liquid precursor 2 or 3, to introduce other characteristics to the powder 8. Thus, it is possible to introduce other functional properties to the powder 8, for example a second luminescence in a spectral range different from that, initial, of the powder 8. Thus, one can achieve a double luminescence, that is to say in another range of color than red, for example yellow, by introducing a liquid precursor that does not contain manganese. By way of example, mention may be made of a mixture of fluorinated chromium and fluorinated manganese.

The method also makes it possible to protect the powder from the aggressions of its immediate environment by depositing a passivation layer during this or these additional cycle (s). For example, by reintroducing the powder 8 in a liquid precursor 2 or 3 Na ₃ AIF _6, also known as the synthetic cryolite, the particles are coated with a protective layer. It is also possible to deposit one or more layers on the particles conferring on the latter other characteristics, such as, without limitation, magnetic properties or a characteristic ensuring the identification and traceability of the final product.

It is also possible to coat other particles, which may or may not be luminescent, and to impregnate objects of the ceramic preform type by dispersing them in the liquid precursor 2 or 3 and carrying out at least one evaporation and treatment cycle 4. 7. As a non-limiting example, mention may be made of Al ₂ O ₃ particles coated with K ₂ SiF ₆ : Mn. In other words, fluorescence characteristics are given to alumina particles.

Such a method is therefore of flexible and easy use, which allows, safely, to produce different luminescent products.

Such a method makes it possible, for the various steps of production of a solid precursor (step b) and of crystallization (step c), to use, respectively, liquid and solid precursors originating either directly from the preceding step or from a storage, 3 or 6, a mixture, in variable proportion, of precursors derived partly from storage and partly from the previous step. It is thus possible to regulate the production, in each of steps b) and c), adjusting if necessary the amount of precursors used from the precursors 3 or 6 stored.

Claims

1 .- Sol-gel method for synthesizing a luminescent material of general formula: AxByFz: Mn, with A being an element of group 1, 2, 4, NFU or a combination of elements belonging to these groups, with R = H or an alkyl chain or a

combination of chains, B being an element of group 5, 6, 13, 14 and 0 <x <5, 0 <y <2, 5 <z <7, characterized in that it comprises at least the following steps: a) producing a liquid precursor (2, 3), in alcoholic solution, by mixing metal reagents (1), chosen from metal salts such as halides, nitrates, hydrides, amides, acetates, carbonates or alkoxides, with manganese, the mixture being carried out at pH <8,

b) obtaining a solid precursor (5, 6) from the liquid precursor (2, 3) obtained in step a), by elimination (4) of the solvent,

c) of crystallization (7, 70) of the solid precursor (5, 6) obtained in step b), by thermal treatment in a fluorinated atmosphere,

d) recovering the fluorescent crystalline powder (8) obtained at the end of step c).

2. A process according to claim 1, characterized in that during step a), the pH is maintained below 8 by the addition of an acid, selected from carboxylic acids such as formic acid acetic acid, propanoic acid, citric acid, tartaric acid, oxalic acid, among sulfonic acids such as benzene sulfonic acid, paratoluene sulphonic acid, among anhydrous acids, hydrochloric acid in solution in ethyl ether, in dioxane or in gaseous form.

3. A process according to claim 2, characterized in that during step a), the pH is maintained below 8 by the addition of a carboxylic acid: acetic acid.

4. - Process according to claim 1, characterized in that step a) is carried out at a temperature between 15 ° C and the boiling temperature of the solvent used.

5. - Method according to one of the preceding claims, characterized in that the liquid precursor, obtained in step a), is, if necessary, stored (3) for a subsequent implementation of step b).

6. - Method according to one of the preceding claims, characterized in that the solid precursor obtained in step b) is, if necessary, stored (6) for a subsequent implementation of step c).

7. - Process according to claim 1, characterized in that the metal reactants used in step a) are all chosen from alkoxides.

8. - Process according to claim 1, characterized in that the metal reactants used in step a) are mixtures of metal salts.

9. - Method according to one of the preceding claims, characterized in that step c) is carried out at a temperature between 100 ° C and 1000 ° C for at least 30 minutes.

10. - Method according to one of the preceding claims, characterized in that the fluorinated agent used in step c) to generate a fluorinated atmosphere is selected from: F ₂ , HF, BrF ₃ , TbF ₄ , XeF ₂ , XeF4 and XeF _6, NH ₄ F, NH ₄ HF _2, CoF _3, SbF _3, SbF _5, ArF _3, KrF, BrF _5, CIF, CIF ₃ and CIF _5, HF0 ₃ S, AuF _3, IF _5, MnF ₃ and MnF ₄ , NOF and N0 ₂ F NF ₃ , ClO ₃ F, PtF ₆ , SeF ₄ , SiF ₄ , AgF ₂ , SF, SF ₆ , KF, PbF ₂ , ZnF ₂ , SnF ₂ , CdF ₂ alone or in combination.

11. - Process according to claim 8, characterized in that during step c), the atmosphere contains at least 1% of fluorinated agent.

12. - Method according to one of claims 8 to 10, characterized in that during step c), the fluorinated atmosphere is static or dynamic.

13.- Method according to one of the preceding claims, characterized in that at the end of step d), the particles obtained (8) are reintroduced into a liquid precursor, in step a).

14.- Method according to claim 13, characterized in that during this new step a), the liquid precursor is chosen to ensure double luminescence, for magnetic properties or for other characteristics.