UPCONVERSION IN ER-3+-DOPED FLUORITE-TYPE CRYSTALS PUMPED BY 1.5 MU-M TUNABLE DIODE-LASER

The upconversion properties of Er3+ (4 mol%) in SrF2, SrxCd1-xF2 and CdF2 crystals are studied, following 4I 13 2 excitation with a tunable InGaAsP diode laser. The anti-Stokes fluorescence of Er3+ at 300 K is predominantly green in SrF2 and Srx Cd1-xF2, predominantly red in CdF2. The emission colour depends on the spatial distribution of Er3+ ions within the crystal: green, when the ions are randomly distributed; red, when they are preferentially paired. We conclude that the tendency to form pairs of neighbouring Er3+ ions decreases from CdF2 to SrF2. In SrxCd1-xF2, small amounts of Tm 3+ increase the red-to-green intensity ratio, so that the Er3+ emission becomes predominantly red. © 1990.