Abstract: A rare earth ceramic having a microcrystal phase buried in a glassy phase for the coversion of radiation in the near-infrared band from about 0.85 to 1.06 um into visible light. It comprises a mixture of lead fluoride PbF.sub.2, ytterbium oxide Yb.sub.2 O.sub.3, at least one glass-forming oxide selected from the oxides of B, Si, P, Ge, Te, and at least one compound of a rare earth doping element chosen as a function of the desired emission color, i.e.A compound containing thulium ions Tm.sup.3.sup.+ for a blue emission mixture;A compound containing erbium ions Er.sup.3.sup.+ for a green emission mixture;A compound containing holmium ions Ho.sup.3.sup.+ for a green emission mixture;A compound containing erbium ions Er.sup.3.sup.+ for a red emission mixture, whereby the oxygen ions from the oxides are exclusively located in the glassy phase while ytterbium and the rare earth are exclusively located in the microcrystal phase.