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A rare earth element phosphate (Ln) is described, wherein Ln is either : (1) at least one rare earth element selected from cerium and terbium, or (2) lanthanum in combination with at least one of the above two rare earth elements, and wherein the phosphate has a crystalline structure of the rhabdophane type or of the monazite type with a lithium content of at most 300 ppm. 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. A phosphor obtained by calcining the phosphate at at least 1000° C. is also described.