Abstract: A rare earth (Ln) phosphate is described, wherein Ln is either: (1) at least one rare earth selected from cerium and terbium, or (2) lanthanum in combination with at least one of the two above-mentioned rare earths and wherein the phosphate has a crystalline structure of the rhabdophane type or of the mixed rhabdophane/monazite type with a potassium content of 7000 ppm at most. The phosphate can be obtained by the precipitation of a rare earth chloride at a constant pH lower than 2, by calcination at a temperature lower than 500° C. and by redispersion in hot water. A phosphor obtained by the calcination of the phosphate at at least 1000° C. is also described.