Rare earth ceramic for frequency conversion of radiation

A rare earth ceramic having a microcrystal phase buried in a glassy phase for the conversion of radiation in the near-infrared band from about 0.85 to 1.06 .mu.m into visible light, comprising a mixture of lead fluoride PbF.sub.2, ytterbium oxide Yb.sub.2 O.sub.3, at least one glass-forming oxide of an element selected from the group consisting of B.sub.2 O.sub.3, SiO.sub.2, P.sub.2 O.sub.5, GeO.sub.2, TeO.sub.2 and at least one compound of a rare earth doping element chosen as a function of the desired emission colour, selected from the group consisting of

• 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, in which the relative proportion of glass-forming oxides in the finished ceramic ranges about from 6 to 35% by weight, the relative proportion of ytterbium oxide to the glass-forming oxides and lead fluoride ranges about from 5 to 20% by weight and the proportion of rare earth doping element compound in the form of an oxide to the finished ceramic ranges from about
• 0. 01 to 5% by weight for oxide Er.sub.2 O.sub.3
• 0.003 to 0.25% by weight for oxide Tm.sub.2 O.sub.3
• 0.01 to 2% by weight for oxide Ho.sub.2 O.sub.3
• whereby the oxygen ions from the oxides are exclusively located in the glassy phase while ytterbium and the rare earth doping element are exclusively located in the microcrystal phase.

A rare earth ceramic having a microcrystal phase buried in a glassy phase for the conversion of radiation in the near-infrared band from about 0.85 to 1.06 .mu.m into visible light, comprising a mixture of lead fluoride PbF.sub.2, ytterbium oxide Yb.sub.2 O.sub.3, at least one glass-forming oxide of an element selected from the group including B.sub.2 O.sub.3, SiO.sub.2, P.sub.2 O.sub.5, GeO.sub.2, TeO.sub.2, at least one oxide of an optically neutral rare earth chosen from the group consisting of Y, La, Gd, Lu and at least one compound of a rare earth doping element chosen as a function of the desired emission colour, selected from the group consisting of

• 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 doping element are exclusively located in the microcrystal phase.