Cooperative processes in KYb(WO4)(2) crystal doped with Eu3(+.)and Tb3+ ions

The cooperative processes occurring between EU3+ (Tb3+) and Yb3+ ions in th e KYb(WO4)(2) crystal are reported. In this crystal the excited state of Yb 3+. (F-2(5/2)) is far Of resonance with EU3+ and Tb3+ ions. In particular, the emission processes following the Stokes excitation and the anti-Stokes excitation, e.g. down-conversion and up-conversion, respectively, were inve stigated. It was found that the Yb3+ emission was fairly intense in spite o f the fact that the cross-relaxation is of the non-resonant type. The up-co nversion emission of EU3+ (red) and Tb3+ (green) ions following a direct ex citation of Yb3+ ions was observed at room temperature. The dependence of e mission intensity on incident laser power was measured. It was found that t he efficiency of Stokes emissions is described by the slope of allometric c urve less than 1 whereas for the anti-Stokes emission (up-conversion) the s lope was around 2. The mechanisms of down-and up-conversion processes are b riefly discussed. (C) 2000 Elsevier Science B.V. All rights reserved.