Abstract: An acid treatment, in a liquid medium, of a solid containing a halophosphate and a rare earth compound is described. Further described, is the addition of a base to the medium obtained previously and separation of a solid phase from a liquid phase; mixing and calcination of the solid obtained previously with an alkaline solid compound; redispersing the calcined product in water, separation of the solid product from the suspension obtained in the preceding step; dispersing this solid in water and acidification of the dispersion and separation of the solid from this dispersion.

Abstract: An acid treatment, in a liquid medium, of a solid containing a halophosphate and a rare earth compound is described. Further described, is the addition of a base to the medium obtained previously and separation of a solid phase from a liquid phase; mixing and calcination of the solid obtained previously with an alkaline solid compound; redispersing the calcined product in water, separation of the solid product from the suspension obtained in the preceding step; dispersing this solid in water and acidification of the dispersion and separation of the solid from this dispersion.

Abstract: A method is described for recovering rare earth elements from a solid mixture including a halophosphate and at least one compound of one or more rare earth elements. The method includes: (a) acid etching the mixture; (b) adding a base to bring the pH back up to a value of at least 1.5; (c) etching the solid from step (b) with a solution of soda or potash; (d) acid etching the solid from step (c) until a pH of less than 7 is obtained, resulting in a solid phase and a liquid phase including at least one rare earth salt, and separating the solid phase from the liquid phase.

Abstract: A method is described for recovering rare earth elements from a solid mixture including a halophosphate and at least one compound of one or more rare earth elements. The method includes: (a) acid etching the mixture; (b) adding a base to bring the pH back up to a value of at least 1.5; (c) etching the solid from step (b) with a solution of soda or potash; (d) acid etching the solid from step (c) until a pH of less than 7 is obtained, resulting in a solid phase and a liquid phase including at least one rare earth salt, and separating the solid phase from the liquid phase.

Abstract: The invention concerns a process for preparing rare earth borates, and the use of these borates in luminescence. The preparation process is characterized in that it comprises the following steps mixing boric acid and a rare earth salt; a reacting the mixture obtained with a carbonate or a bicarbonate; a calcining the precipitate obtained.

Abstract: A cerium and/or lanthanum phosphate sol includes an aqueous phase; particles of a phosphate of at least one rare earth selected from cerium and lanthanum; and an acid other than phosphoric acid, the cerium and lanthanum salts of which are soluble in water. A process for preparing this sol includes continuously introducing a first solution of salts of at least one of the rare earths into a second solution of phosphate ions with an initial pH of less than 2; controlling the pH of the precipitation medium during precipitation at a constant value of less than 2; separating the precipitate from the reaction medium and of taking up the dispersion in water then adding to the dispersion obtained at least one said rare earth salt and said acid in a quantity such that the final PO43/rare earth mole ratio in the dispersion is 1.

Abstract: The invention concerns a process for preparing rare earth borates, and the use of these borates in luminescence.

Abstract: The present invention relates to the use of a compound based on a thulium-containing lanthanum phosphate as a phosphor in a plasma or X-ray system. This phosphate may furthermore contain gadolinium. The thulium content of the compound, expressed in at % with respect to the lanthanum, is between 0.1 and 10, more particularly between 0.5 and 5. The invention also covers a lanthanum phosphate which is characterized in that it contains thulium and in that it consists of particles having a mean size of between 1 and 20 &mgr;m with a dispersion index of less than 0.6.

Abstract: Monodisperse particulates of lanthanum/cerium/terbium phosphates, the average particle size of which ranging from 1 to 15 -microns and preferably from 2 to 6 microns, and having a dispersion index of less than 0.5, preferably less than 0.4, are well suited as green luminophors displaying enhanced brilliance or precursors thereof, and are prepared via precipitation with phosphate ions at a substantially constant pH below 2, from LaCeTb solutions.

Abstract: Monodisperse particulates of a rare earth phosphate having the formula LnPO.sub.4 in which Ln is at least one rare earth, the average particle size of which ranging from 1 to 20 microns and preferably from 2 to 6 microns, and having a dispersion index of less than 0.5, preferably less than 0.4, are well suited as luminophors or precursors thereof, and are prepared via precipitation with phosphate ions at a substantially constant pH below 2, from rare earth salt solutions.