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
  • C01B25/37—Phosphates of heavy 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

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. Several processes for the preparation of LAPs are known. These methods are of two types.
• dry processes in which a mixture of oxides or a mixed oxide is phosphated in the presence of diammonium phosphate. These processes, which may be relatively long and complicated, pose a particular problem for the control of the size and chemical homogeneity of the products obtained.
• An object of the invention is the development of a process for the preparation of LAP limiting the rejection of nitrogen products, or even without rejecting these 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 rare earths mentioned above, characterized in that it has a crystalline structure of either rhabdophane or mixed rhabdophane / monazite type and in that it contains sodium, the sodium content being at most 6000 ppm.
• the invention also relates to a rare earth phosphate (Ln), Ln having the same meaning as above, and which is characterized in that it has a crystalline structure of monazite type and in that it contains sodium, the content with sodium being at most 4000 ppm.
• the invention also 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 monazite type and in that it contains sodium, the sodium content being at most 350 ppm.
• Ln rare earth phosphate
• the phosphors of the invention despite the presence of an alkali, sodium, have good luminescence properties and good durability. They may even have a better luminescence yield than the known products.
• 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 sodium content is made according to two techniques.
• the first is the X-ray fluorescence technique and it measures sodium levels that are at least about 100 ppm. This technique will be used more particularly for phosphates or precursors or phosphors for which the sodium contents are the highest.
• the second technique is the Inductively Coupled Plasma (ICP) technique - AES (Atomic Emission Spectroscopy) or ICP - OES (Optical Emission Spectroscopy). This technique will be used more particularly here for the precursors or phosphors for which the sodium contents are the lowest, especially for contents less than about 100 ppm.
• ICP Inductively Coupled Plasma
• 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.
• the phosphates of the invention are in two embodiments which differ from each other in the crystallographic structure of the products. The characteristics common to these two embodiments will be described first.
• the phosphates of the invention are essentially, the presence of other residual phosphates 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 cerium or terbium phosphates or a combination of these two rare earths. It can also be lanthanum phosphates in combination with at least one of these two rare earths mentioned above and it can also be very particularly lanthanum, cerium and terbium phosphates.
• the phosphates of the invention essentially comprise a product that can respond to the general formula (1): La x Ce y Tb z PO 4 (1) wherein the sum x + y + z is equal to 1 and at least one of y and z is different from 0.
• 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.
• 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.
• z may be more particularly between 0.05 and 0.6 and even more particularly between 0.08 and 0.3.
• z may be more particularly between 0.1 and 0.4.
• compositions may be mentioned:
• 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 particle size values given here and for the remainder 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
• phosphates of the invention An important characteristic of the phosphates of the invention and common to both embodiments is the presence of sodium.
• the amount of sodium depends on the embodiment. It may be thought that sodium 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. According to a particular embodiment, the phosphates contain only sodium as alkaline.
• the two embodiments of the phosphates of the invention also have more specific characteristics which will be described below.
• the phosphate has a crystalline structure of rhabdophane type or mixed type rhabdophane / monazite.
• the crystalline structures referred to herein and in the remainder of the description can be demonstrated by the X-ray diffraction technique (XRD).
• XRD X-ray diffraction technique
• 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 a single phase rhabdophane. Nevertheless, the phosphates of the invention may also not to be phasically pure and in this case, the DRX diagrams of the products show the presence of very minor residual phases.
• Phosphates may also have a mixed-type rhabdophane / monazite structure.
• the rhabdophane or mixed rhabdophane / monazite structure corresponds to phosphates that have not undergone a heat treatment at the end of their preparation or have undergone heat treatment at a temperature generally not exceeding 600 ° C., in particular between 400 ° C. 0 C and 500 ° C.
• the sodium content of the phosphate according to this first embodiment is at most 6000 ppm, more particularly at most 5000 ppm. This content is expressed, here and for the entire description, as a mass of sodium element relative to the total weight of the phosphate.
• the minimum sodium content is not critical. It may correspond to the minimum value detectable by the analytical technique used to measure the sodium content. However, generally this minimum sodium content is generally at least 300 ppm, more preferably at least 1200 ppm.
• the phosphate of crystalline structure of rhabdophane type consists of particles themselves consisting of an aggregation of crystallites whose size, measured in the (012) plane, is at least 35 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 as described in the book Theory and Technique of Radiocrystallography, A.Guinier, Dunod, Paris, 1956, is used for this measurement. It should be noted that the description that has just been given of the size of crystallites applies mainly to the case of phosphates of rhabdophane structure because the determination of this size by the DRX technique becomes much more difficult in the case of a mixed type structure rhabdophane / monazite.
• This size of crystallite which is greater than that of phosphates of the prior art obtained after a heat treatment at the same temperature and which may also have the same particle size, results in a better crystallization of the products.
• the phosphates of the first embodiment which have not undergone heat treatment are generally hydrated; however, simple drying, operated for example between 60 and 100 0 C, 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 phosphates have a monazite-type crystalline structure which corresponds to products which are obtained after a higher heat treatment than in the case of the phosphates of the first mode and operated at a temperature of at least 600 ° C. C, advantageously between 700 and 1000 ° C.
• the phosphates can in this case be phasically pure, that is to say that the XRD diagrams show only one single monazite phase. 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.
• the sodium content of the phosphate according to this second embodiment is at most 4000 ppm, more particularly at most 3000 ppm.
• the minimum sodium content is not critical and may correspond to the minimum value detectable by the analytical technique used to measure the sodium content.
• this minimum sodium content is generally at least 300 ppm, more preferably at least 1200 ppm.
• Phosphates of monazite crystalline structure consist of particles themselves consisting of an aggregation of crystallites whose size, measured in the (012) plane, is at least 40 nm, more particularly at least 80 nm and more more particularly at least 100 nm, this size also varies according to the calcination temperature experienced by the precursor during its preparation.
• the same remark can be made here as before concerning the best crystallization of the phosphates of the invention compared with phosphates of the same structure of the prior art.
• the phosphates or precursors according to the invention have, for those having undergone calcination or heat treatment at a temperature generally greater than 600 ° C, and advantageously included between 800 and 900 ° C., luminescence properties at wavelengths that vary according to the composition of the product and after exposure to a given wavelength ray (for example emission at a wavelength of about 550 nm , ie in green after exposure to a wavelength radius of 254 nm for lanthanum phosphate, cerium and terbium), it is possible and even necessary to further improve these properties. luminescence by proceeding with the products to post-treatments, and this in order to obtain a real luminophore directly usable as such in the desired application. It is understood that the boundary between a single rare earth phosphate and a real phosphor remains arbitrary, and depends on the only luminescence threshold from which it is considered that a product can be directly implemented in a manner acceptable to a user.
• rare earth phosphates according to the invention which have not been subjected to heat treatments greater than about 900 ° C., since such The products generally have luminescence properties which can be judged as not satisfying the minimum brightness criterion of commercial phosphors which can be used directly and as such without any subsequent processing.
• rare earth phosphates which, possibly after being subjected to appropriate treatments, develop suitable glosses which are sufficient to be used directly by an applicator, for example in lamps or lamps, can be qualified as phosphors. television screens.
• 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.
• 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.
• the luminophores of the invention contain sodium in a content of at most 350 ppm, more particularly at most 250 ppm and even more particularly at most 100 ppm. This content is also expressed in the mass of sodium element relative to the total mass of the phosphor.
• the minimum sodium content is not critical.
• phosphates it may correspond to the minimum value detectable by the analytical technique used to measure the sodium content.
• this content is at least 10 ppm and more particularly at least 50 ppm.
• the phosphors contain no element other than sodium as an alkaline element.
• 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 290 nm. As for the precursors, it is also observed here that 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.
• the processes for preparing precursors and phosphors of the invention will now be described.
• the processes for preparing the phosphates or precursors The first method which will be described concerns the preparation of the precursors according to the first embodiment, that is to say those with a crystalline structure, either of the rhabdophane type or of the mixed rhabdophane / monazite type.
• This method is characterized in that it comprises the following steps:
• 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;
• 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 pH control for the second step or both being made at least partly with sodium hydroxide;
• the precipitate thus obtained is recovered and, if appropriate, calcined at a temperature of less than 600 ° 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 desired composition product, with a second solution containing phosphate ions.
• 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 the latter 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.
• 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, in order to maintain the pH of the precipitation medium at the desired constant work value, which must be less than 2 and preferably between 1 and 2, is introduced simultaneously into this medium a basic compound.
• 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, soda.
• at least in part is meant that it is possible to use a mixture of basic compounds of which at least one is sodium hydroxide.
• the other basic compound may be, for example, ammonia.
• a basic compound which is solely sodium hydroxide is used and according to another even more preferential embodiment, soda alone is used and for the two abovementioned 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.
• a calcination temperature up to about 400 0 C provides a product rhabdophane structure, which is also that presented by the non-calcined product from precipitation.
• the calcination temperature is generally at least about 400 ° C. and it can go up to a temperature below 600 0 C; it can thus be between 400 ° C. and 500 ° 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 under 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.
• 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 process for the preparation of rare earth phosphates (Ln) according to the second embodiment of the invention is very similar to that which has just been described. It differs only in that the product resulting from the precipitation is calcined at a temperature of at least 600 ° C. What has been described above for the preceding steps in the process for the preparation of the phosphates of the first mode is therefore likewise applicable here for the process for the preparation of phosphates of the second mode.
• the heat treatment or calcination can be carried out more particularly at a temperature of between 800 and 900 ° C.
• the crystallite size of the phosphate will be greater the higher the calcination temperature.
• the rest of the process and in particular the redispersion step in water is identical to that described above for the phosphates according to the first embodiment.
• the luminophores of the invention are obtained by calcination at a temperature of at least 1000 ° C. of a phosphate or precursor according to the two embodiments as described above or of a phosphate or precursor obtained by the processes which have also been described previously.
• This temperature can be between 1000 ° C and 1300 0 C.
• 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 flux or fluxing agent such as, for example, lithium fluoride, lithium tetraborate, lithium chloride, lithium carbonate, lithium phosphate, chloride of potassium, ammonium chloride, 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 particles are advantageously washed, so as to obtain the purest phosphor possible and in a deagglomerated or weakly agglomerated state.
• 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 mercury-free trichromatic lamps, 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 luminophores 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.
• 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 processes described above.
• the sodium 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.
• COMPARATIVE EXAMPLE 1 This example relates to the preparation of a lanthanum phosphate, cerium and terbium according to the prior art.
• 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 addition of sodium hydroxide and brought to 60 0 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 sodium 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 hours at 840 ° C. in air.
• the product obtained is redispersed in hot 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.
• the precursor phosphate of the invention is better crystallized than that of the prior art while maintaining similar granulometric characteristics.
• This example relates to the preparation of a phosphor 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 luminescence efficiency of the phosphor of the invention is given with respect to the comparative phosphor 3.
• the phosphor of the invention thus has an improved crystallinity and a luminescence efficiency equivalent to the phosphor obtained in the comparative example, while maintaining the same quality of particle size.

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