Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
  • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
  • C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
  • C09K11/7766—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing two or more rare earth metals
  • C09K11/7777—Phosphates
  • C09K11/7778—Phosphates with alkaline earth metals
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B25/00—Phosphorus; Compounds thereof
  • C01B25/16—Oxyacids of phosphorus; Salts thereof
  • C01B25/26—Phosphates
  • C01B25/45—Phosphates containing plural metal, or metal and ammonium
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
  • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
  • C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
  • Y10T428/2982—Particulate matter [e.g., sphere, flake, etc.]

Definitions

• the present invention relates to a cerium and / or terbium phosphate, optionally with lanthanum, a phosphor derived from this phosphate and processes for their preparation.
• LAP Mixed phosphates of lanthanum, terbium and cerium and mixed phosphates of lanthanum and terbium, hereinafter generally referred to as LAP, are well known for their luminescence properties. For example, when they contain cerium and terbium, they emit a bright green light when they are irradiated by certain energetic radiations of wavelengths lower than those of the visible range (UV or VUV radiation for lighting systems or visualization). Phosphors exploiting this property are commonly used on an industrial scale, for example in fluorescent tri-chromium lamps, in backlight systems for liquid crystal displays or in plasma systems.
• An object of the invention is the development of a process for preparing LAP without rejecting nitrogen products.
• Another object of the invention is to provide phosphors which nevertheless have the same properties as those of currently known phosphors, or even superior properties.
• the invention provides a rare earth phosphate (Ln) Ln representing either at least one rare earth chosen from cerium and terbium, or lanthanum in combination with at least one of the two said rare earths and which is characterized in that it has a crystalline structure of rhabdophane or mixed rhabdophane / monazite type and in that it contains potassium, the potassium content being at most 7000 ppm.
• Ln rare earth phosphate
• the invention relates to a phosphor based on a rare earth phosphate (Ln), Ln having the same meaning as above, and which is characterized in that it has a crystalline structure of the monazite type and in it contains potassium, the potassium content being at most 350 ppm.
• Ln rare earth phosphate
• the phosphors of the invention despite the presence of an alkali, potassium, have good luminescence properties and good durability. They can even perform better than known products.
• the phosphates of the invention which are thus the precursors of the phosphors, also have interesting properties because they lead, under identical calcination conditions, to phosphors with improved properties compared to the phosphors obtained by the precursors of the prior art. .
• Other features, details and advantages of the invention will appear even more fully on reading the description which follows, as well as various concrete but non-limiting examples intended to illustrate it.
• rare earth for rare earth is meant for the remainder of the description the elements of the group consisting of yttrium and the elements of the periodic classification of atomic number inclusive between 57 and 71.
• the measurement of the potassium content is made according to two techniques.
• the first is the X-ray fluorescence technique and it measures potassium levels that are at least about 100 ppm. This technique will be used more particularly for phosphates or precursors or phosphors for which the potassium contents are the highest.
• the second technique is Inductively Coupled Plasma (ICP) - Atomic Emission Spectroscopy) or ICP - OES (Optical Emission Spectroscopy). This technique will be used more particularly here for precursors or phosphors for which the potassium contents are the lowest, especially for contents of less than about 100 ppm.
• ICP Inductively Coupled Plasma
• ICP - OES Optical Emission Spectroscopy
• the invention relates to two types of products: phosphates, also called precursors, and phosphors obtained from these precursors.
• phosphates also called precursors
• phosphors obtained from these precursors.
• the luminophores themselves have sufficient luminescence properties to make them directly usable in the desired applications.
• the precursors have no luminescence properties or possibly luminescence properties that are too low for use in these same applications.
• Phosphates or precursors are essentially, the presence of other phosphate-like species being indeed possible, and preferably completely of the orthophosphate type of formula LnPO 4 , Ln being as defined above.
• the phosphates of the invention are lanthanum phosphates in combination with at least one of these two rare earths, and it can also be very particularly lanthanum, cerium and terbium phosphates.
• the phosphates of the invention essentially comprise a product which can satisfy the following general formula (1):
• x may be more particularly between 0.2 and 0.98 and even more particularly between 0.4 and 0.95.
• the presence of the other phosphate species mentioned above may result in the molar ratio Ln (all the rare earths) / PO 4 being less than 1 for all the phosphate.
• z is at most 0.5, and z may be between 0.05 and 0.2 and more preferably between 0. , 1 and 0.2. If y and z are both different from 0, x may range from 0.2 to 0.7 and more particularly from 0.3 to 0.6.
• y may be more particularly between 0.02 and 0.5 and even more particularly between 0.05 and 0.25. If y is 0, z can be more particularly between 0.05 and
• z may be more particularly between 0.1 and 0.4.
• the phosphate of the invention may comprise other elements that typically play a role, in particular a promoter of the luminescence properties or of stabilizing the oxidation levels of the cerium and terbium elements.
• a promoter of the luminescence properties or of stabilizing the oxidation levels of the cerium and terbium elements By way of example of these elements, mention may be made more particularly of boron and other rare earths such as scandium, yttrium, lutetium and gadolinium. When lanthanum is present, the aforementioned rare earths may be more particularly present in substitution for this element.
• These promoter or stabilizer elements are present in an amount generally of at most 1% by weight of element relative to the total weight of the phosphate of the invention in the case of boron and generally at most 30% for the others. elements mentioned above.
• the phosphates of the invention are also characterized by their granulometry.
• They consist in fact of particles generally having an average size of between 1 and 15 ⁇ m, more particularly between 2 ⁇ m and 6 ⁇ m.
• the average diameter referred to is the volume average of the diameters of a particle population.
• the granulometry values given here and for the rest of the description are measured by means of a Malvern laser particle size analyzer on a sample of particles dispersed in ultrasonic water (130 W) for 1 minute 30 seconds.
• the particles preferably have a low dispersion index, typically at most 0.5 and preferably at most 0.4.
• dispersion index of a population of particles is meant, for the purposes of this description, the ratio I as defined below: where: 0s 4 is the particle diameter for which 84% of the particles have a diameter less than 0s 4 ;
• 016 is the particle diameter for which 16% of the particles have a diameter less than 0- ⁇ 6 ;
• 050 is the average particle diameter, diameter for which 50% of particles have a diameter less than 0 5 o This definition of the dispersion index given here to the precursor particles also applies to the rest of the description to phosphors.
• phosphates of the invention An important characteristic of the phosphates of the invention is the presence of potassium. It may be thought that potassium is not present in phosphate simply as a mixture with the other constituents of it but is chemically bound with one or more constituent chemical elements of the phosphate. The chemical character of this bond can be demonstrated by the fact that a simple washing, with pure water and under atmospheric pressure, does not make it possible to eliminate the potassium present in the phosphate.
• the potassium content of the phosphate according to the invention is at most 7000 ppm, more particularly at most 6000 ppm and even more particularly at most 5000 ppm. This content is expressed, here and for the entire description, as a mass of potassium element relative to the total weight of the phosphate.
• the minimum potassium content is not critical. It may correspond to the minimum value detectable by the analytical technique used to measure the potassium content. However, generally this minimum content is at least 300 ppm, more particularly at least 1200 ppm.
• the phosphate contains, as alkaline element, only potassium.
• the phosphates of the invention may have two types of crystalline structure. These crystalline structures can be demonstrated by the X-ray diffraction technique (XRD).
• the phosphates can thus have a rhabdophane type structure and they can be in this case phasically pure, that is to say that the XRD diagrams show only one and only phase rhabdophane. Nevertheless, the phosphates of the invention may also not be phasically pure and in this case, the X-ray product diagrams show the presence of very minor residual phases.
• Phosphates may also have a mixed-type rhabdophane / monazite structure.
• the rhabdophane structure corresponds to phosphates that have not undergone heat treatment at the end of their preparation or have undergone a heat treatment at a temperature generally not exceeding 500 ° C., in particular ranging between 400 ° C. and 500 ° C. .
• the mixed-type rhabdophane / monazite structure corresponds to phosphates having undergone heat treatment at a temperature above 500 ° C. and up to a temperature of less than about 650 ° C.
• the phosphate consists of particles themselves consisting of an aggregation of crystallites whose size, measured in the (012) plane, is at least 25 nm, more particularly at least 30 nm. This size may vary depending on the temperature of the heat treatment or the calcination suffered by the precursor during its preparation.
• the value measured in XRD corresponds to the size of the coherent domain calculated from the width of the main diffraction line corresponding to the crystallographic plane (012).
• the Scherrer model is used for this measurement, as described in the book "Theory and technique of radioallstallography", A. Guinier, Dunod, Paris, 1956.
• Phosphates that have not undergone heat treatment are usually hydrated; however, simple drying operations, for example between 60 and 100 ° C, are sufficient to remove most of this residual water and lead to substantially anhydrous rare earth phosphates, the minor amounts of remaining water being removed by calcinations conducted at higher temperatures and above about 400 ° C.
• the phosphors of the invention have characteristics in common with the phosphates or precursors which have just been described.
• the phosphors have a crystalline structure of the monazite type. This crystalline structure can also be demonstrated by the X-ray diffraction technique (XRD). According to a preferred embodiment, the phosphors of the invention are phasically pure, that is to say that the XRD diagrams show only the single monazite phase. Nevertheless, the phosphors of the invention may also not be phasically pure and in this case, the X-ray product diagrams show the presence of very minor residual phases.
• XRD X-ray diffraction technique
• the phosphors of the invention contain potassium in a content of at most 350 ppm. This content is also expressed in mass of potassium element relative to the total mass of the phosphor.
• the minimum potassium content is not critical. Here again, as for phosphates, it can correspond to the minimum value detectable by the analysis technique used to measure the potassium content. However, generally this minimum content is at least 10 ppm, more particularly at least 50 ppm. This potassium content may be more particularly between a value equal to or greater than 100 ppm and at most 350 ppm or between a value greater than 200 ppm and 350 ppm.
• the phosphors of the invention consist of particles whose coherence length, measured in the (012) plane, is at least 250 nm.
• This length which is measured by the same technique as for the precursors, may vary depending on the temperature of the heat treatment or calcination undergone by the phosphor during its preparation.
• This coherence length may be at least 280 nm, more particularly at least 330 nm, and it may in particular be between 280 nm and 300 nm.
• this length of coherence is greater than those of the phosphors of the prior art obtained after heat treatment at the same temperature and may also have the same particle size. This again reflects a better crystallization of the products which is beneficial for their luminescence property, especially for the luminescence yield.
• the particles constituting the phosphors of the invention may have a substantially spherical shape. These particles are dense.
• a first solution containing rare earth chlorides (Ln) is continuously introduced into a second solution containing phosphate ions and having an initial pH of less than 2; during the introduction of the first solution in the second, the pH of the medium thus obtained is controlled at a constant value and less than 2, whereby a precipitate is obtained, the setting at a pH below 2 of the second solution for the first step or the pH control for the second step or both being carried out at least partly with potash; the precipitate thus obtained is recovered and, if appropriate, calcined at a temperature below 650 ° C .;
• the product obtained is redispersed in hot water and then separated from the liquid medium.
• a direct precipitation is carried out at controlled pH of a rare earth phosphate (Ln), and this by reacting a first solution containing chlorides of one or more rare earths (Ln), these elements being then present in the proportions required to obtain the product of desired composition, with a second solution containing phosphate ions.
• Ln rare earth phosphate
• a certain order of introduction of the reagents must be respected, and more precisely still, the chlorides solution of the rare earth element (s) must be introduced, progressively and continuously, into the solution containing the phosphate ions.
• the initial pH of the solution containing the phosphate ions must be less than 2, and preferably between 1 and 2.
• the pH of the precipitation medium must then be controlled at a pH value of less than 2, and preferably of between 1 and 2.
• controlled pH is meant a maintenance of the pH of the precipitation medium to a certain value, constant or substantially constant, by addition of a basic compound in the solution containing the phosphate ions, and this simultaneously with the introduction into this last of the solution containing the rare earth chlorides.
• the pH of the medium will thus vary by at most 0.5 pH units around the fixed setpoint, and more preferably by at most 0.1 pH units around this value.
• the fixed set value will advantageously correspond to the initial pH (less than 2) of the solution containing the phosphate ions.
• Precipitation is preferably carried out in an aqueous medium at a temperature which is not critical and which is advantageously between room temperature (15 ° C - 25 ° C) and 100 ° C. This precipitation takes place with stirring. reaction medium.
• the concentrations of rare earth chlorides in the first solution can vary within wide limits.
• the total concentration of rare earths can be between 0.01 mol / liter and 3 mol / liter.
• the solution of rare earth chlorides may further comprise other metal salts, including chlorides, such as salts of the promoter or stabilizer elements described above, that is to say boron and other rare earths.
• Phosphate ions intended to react with the solution of the rare earth chlorides can be provided by pure or in solution compounds, for example phosphoric acid, alkali phosphates or other metallic elements giving with the anions associated with the rare earths a soluble compound.
• the phosphate ions are present in such a quantity that there is, between the two solutions, a molar ratio PO 4 / Ln greater than 1, and advantageously between 1, 1 and 3.
• the solution containing the phosphate ions must initially have (ie before the beginning of the introduction of the solution of rare earth chlorides) a pH of less than 2, and preferably included between 1 and 2. Also, if the solution used does not naturally have such a pH, it is brought to the desired suitable value either by adding a basic compound or by adding an acid (for example, hydrochloric acid, in the case of an initial solution with too high pH).
• the pH of the precipitation medium gradually decreases; also, according to one of the essential features of the process according to the invention, for the purpose of maintaining the pH of the precipitation medium at the desired constant working value, which must be less than 2 and preferably between 1 and 2, a basic compound is introduced simultaneously into this medium.
• the basic compound which is used either to bring the initial pH of the second solution containing the phosphate ions to a value of less than 2 or to control the pH during the precipitation is, at less in part, potash.
• potash By “at least in part” is meant that it is possible to use a mixture of basic compounds of which at least one is potash.
• the other basic compound may be, for example, ammonia.
• a basic compound which is only potash is used and according to another even more preferred embodiment potash alone is used and for the two aforementioned operations, that is both to bring the pH of the second solution at the appropriate value and for the control of the precipitation pH.
• the rejection of nitrogen products which may be provided by a basic compound such as ammonia is reduced or eliminated.
• a phosphate of rare earth (Ln) is obtained directly, possibly additive by other elements.
• the overall concentration of rare earths in the final precipitation medium is then advantageously greater than 0.25 mol / liter.
• the phosphate precipitate can be recovered by any means known per se, in particular by simple filtration. Indeed, under the conditions of the process according to the invention, a non-gelatinous rare earth phosphate is precipitated and easily filtered.
• the recovered product is then washed, for example with water, and then dried.
• the product can then be subjected to heat treatment or calcination.
• the temperature and duration of this calcination are a function of the desired crystalline structure for the phosphate that will be derived therefrom.
• the calcination temperature is at least about 400 ° C. and is usually at most about 500 ° C. in the case of a product with a rhabdophane structure, a structure which is also that presented by the non-calcined product derived from precipitation.
• the calcination temperature is generally greater than 500 ° C. and can be up to a temperature of less than 650 ° C.
• the duration of calcination is generally lower as the temperature is high. By way of example only, this duration can be between 1 and 3 hours.
• Heat treatment is usually done under air.
• the crystallite size of the phosphate will be greater the higher the calcination temperature.
• the product resulting from the calcination or from the precipitation in the absence of heat treatment is then redispersed in hot water.
• This redispersion is done by introducing the solid product into the water and stirring.
• the suspension thus obtained is kept stirring for a period which may be between 1 and 6 hours, more particularly between 1 and 3 hours.
• the temperature of the water may be at least 30 ° C, more preferably at least 60 ° C and may be between about 30 ° C and 90 ° C, preferably between 60 ° C and 90 ° C at atmospheric pressure. It is possible to carry out this operation under pressure, for example in an autoclave, at a temperature which can then be between 100 ° C. and 200 ° C., more particularly between 100 ° C. and 150 ° C. In a final step is separated by any known means, for example by simple filtration of the solid liquid medium. It is possible to repeat, one or more times, the redispersion step under the conditions described above, possibly at a temperature different from that at which the first redispersion was conducted.
• the separated product can be washed, especially with water, and can be dried.
• the rare earth phosphate (Ln) of the invention is thus obtained, having the required potassium contents.
• the phosphor preparation process The luminophores of the invention are obtained by calcination at a temperature of at least 1000 ° C. of a phosphate or precursor as described above or of a phosphate or precursor obtained by the process which has also been described previously. This temperature can be between 1000 0 C and 1300 ° C. By this treatment, the phosphates or precursors are converted into effective phosphors.
• the calcination can be carried out under air, under an inert gas but also and preferably under a reducing atmosphere (H 2 , N 2 / H 2 or Ar / H 2 for example), in the latter case, to convert all the species This and Tb at their oxidation state (+ III).
• a reducing atmosphere H 2 , N 2 / H 2 or Ar / H 2 for example
• the calcination can be carried out in the presence of a flux or fluxing agent such as, for example, lithium fluoride, lithium tetraborate, lithium chloride, lithium carbonate, lithium phosphate, chloride ammonium, boric oxide and boric acid and ammonium phosphates, and mixtures thereof.
• a flux or fluxing agent such as, for example, lithium fluoride, lithium tetraborate, lithium chloride, lithium carbonate, lithium phosphate, chloride ammonium, boric oxide and boric acid and ammonium phosphates, and mixtures thereof.
• a luminophore which exhibits luminescence properties which, generally, are at least equivalent to those of known phosphors.
• the advantage of the most important invention here is that the phosphors come from precursors which are themselves derived from a process that rejects less nitrogen products than known methods or not at all.
• the precursors of the invention make it possible to obtain phosphors with the same luminescence properties more rapidly, that is to say at lower temperatures, than phosphors originating from the precursors of the invention. prior art.
• the particles are advantageously washed, so as to obtain the purest phosphor possible and in a deagglomerated or weakly agglomerated state. In the latter case, it is possible to deagglomerate the phosphor by subjecting it to deagglomeration treatment under mild conditions.
• the phosphors of the invention resulting from a fluxless calcination have, compared to phosphors of the prior art obtained under the same calcination conditions, an improved luminescence efficiency. Without wishing to be bound by theory, it may be thought that this better yield is the consequence of a better crystallization of the phosphors of the invention, this better crystallization being also the consequence of a better crystallization of the precursor phosphates.
• the luminophores of the invention exhibit intense luminescence properties for electromagnetic excitations corresponding to the various absorption domains of the product.
• the cerium and terbium phosphors of the invention can be used in lighting or visualization systems having an excitation source in the UV range (200-280 nm), for example around 254 nm .
• an excitation source in the UV range (200-280 nm), for example around 254 nm .
• mercury vapor trichromatic lamps, backlighting lamps for liquid crystal systems, in tubular or planar form LCD Back Lighting
• They exhibit a high gloss under UV excitation, and a lack of luminescence loss as a result of thermal post-treatment. Their luminescence is particularly stable under UV at relatively high temperatures (100 - 300 0 C).
• the phosphors based on terbium and lanthanum or lanthanum, cerium and terbium of the invention are also good candidates as green phosphors for VUV (or "plasma") excitation systems, such as for example plasma screens. and the trichromatic lamps without mercury, especially Xenon excitation lamps (tubular or planar).
• the luminophores of the invention have a high green emission under VUV excitation (for example, around 147 nm and 172 nm).
• the phosphors are stable under VUV excitation.
• the phosphors of the invention can also be used as green phosphors in LED devices. They can be used especially in systems excitable in the near UV.
• UV excitation labeling systems They can also be used in UV excitation labeling systems.
• the luminophores of the invention can be implemented in lamp and screen systems by well known techniques, for example by screen printing, sputtering, electrophoresis or sedimentation. They can also be dispersed in organic matrices (for example, plastic matrices or transparent polymers under UV ...), mineral (for example, silica) or organo-mineral hybrids.
• the invention also relates to luminescent devices of the above-mentioned type, comprising, as a source of green luminescence, the phosphors as described above or the phosphors obtained from the process also described above.
• the potassium content is determined, as indicated above, by two measurement techniques.
• the X-ray fluorescence technique it is a semi-quantitative analysis performed on the powder of the product as such.
• the apparatus used is a spectrometer of
• the luminescence yield is measured on the products in powder form by comparing the areas under the emission spectrum curve between 380 nm and 750 nm recorded with a spectrofluorometer under excitation.
• This example relates to the preparation of a lanthanum phosphate, cerium and terbium according to the prior art.
• composition precursor (La 0 , 44 Ce 0 , 4 3Tb 0 , 13) PO 4 is obtained.
• This example relates to the preparation of a lanthanum phosphate, cerium and terbium according to the invention.
• 1 L of a solution of 1.5 mol / L of phosphoric acid H 3 PO 4 analytical grade previously brought to pH 1, 6 by adding potassium hydroxide and heated to 60 ° C are added in one hour 1 L of a solution of 4N purity rare earth chlorides with an overall concentration of 1.3 mol / L and decomposing as follows: 0.57 mol / L of lanthanum chloride, 0.56 mol / L of cerium chloride and 0.17 mol / L of terbium chloride.
• the pH during the precipitation is regulated to 1, 6 by adding potassium hydroxide.
• the mixture is further maintained for 15 minutes at 60 ° C.
• the resulting precipitate is then recovered by filtration, washed with water and then dried at 60 ° C. in air and then subjected to a heat treatment for 2 h at 500 ° C. in air.
• the product obtained is redispersed in water at 80 ° C for 3h, then washed and filtered, and finally dried.
• a precursor composition (Lao, 44 Ceo, 4 3 ⁇ rbo, i3) PO 4.
• Table 1 The characteristics of the products of Examples 1 and 2 are presented in Table 1 below.
• the precursor phosphate 2 of the invention is better crystallized than that of the prior art 1 while maintaining similar particle size characteristics.
• COMPARATIVE EXAMPLE 3 This example relates to the preparation of a luminophore according to the prior art obtained from the phosphate of Example 1.
• Example 1 The precursor phosphate obtained in Example 1 is reprocessed under a reducing atmosphere (Ar / H 2) for 2 h at 1000 ° C. The calcination product obtained is then washed in hot water at 80 ° C. for 3 h, then filtered and dried. .
• a reducing atmosphere Ar / H 2
• This example relates to the preparation of a luminophore according to the invention obtained from the phosphate of Example 2.
• Example 2 The precursor phosphate obtained in Example 2 is reprocessed under the same conditions as those of Example 3.
• the characteristics of the products of Examples 3 and 4 are presented in Table 2 below.
• the luminescence yield of the product of the invention is calculated relative to the comparison phosphor 3.
• the luminophore of the invention therefore has a significantly improved crystallinity and luminescence yield compared to the phosphor obtained in the comparative example, while retaining the same quality of particle size.

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