CERIUM AND/OR TERBIUM PHOSPHATE, OPTIONALLY WITH LANTHANUM, PHOSPHOR RESULTING FROM SAID PHOSPHATE

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The invention relates to a rare earth element phosphate (Ln), where Ln is either at least one rare earth element selected from cerium and terbium, or lanthanum in combination with at least one of the above two rare earth elements, having a crystalline structure either of the rhabdophane type with a sodium content of 6000 ppm at most, or of the monazite type with a sodium content of 4000 ppm at most. The phosphate is obtained by the precipitation of a rare earth element chloride at a constant pH lower than 2, and then calcining and redispersing the same in hot water. The invention also relates to a phosphor obtained by calcining the phosphate at at least 1000°C.