Powerful visible (530-770 nm) luminescence in Yb,Ho:GGG with IR diode pumping

Powerful visible luminescence in a Gadolinium Gallium Garnet (GGG) crystal, co-activated with Yb3+ (similar to15 at.%) and Ho3+ (similar to0.1 at.%) ions, is investigated under CW laser diode pumping (lambda = 938 and 976 nm). The main visible emission band is observed in the green with its peak at (lambda similar to540 nm) and measured to be about 10% with respect to Yb3+ IR luminescence (lambda similar to1000 nm). Red (lambda similar to650 nm) and near-IR (lambda similar to755 nm) emission bands are also observed but are weaker (about 3-5%). Analysis of the crystal absorption and luminescence spectra allows one to conclude that Yb3+ Ho3+ stepwise up-conversion is the mechanism explaining the phenomenon. Ho3+ ions embedded in the crystal in small concentration are shown to form an effective reservoir for energy transferred from the excited Yb3+ subsystem and to be an efficient source of the visible emission. (C) 2002 Optical Society of America.