VISIBLE EMISSION FROM RARE-EARTH IONS IN NANOCRYSTAL-CONTAINING GLASSES

Rare earth-doped glasses are of great interest for their optical and f luorescence properties. However, phonon-mediated non-radiative transit ions are a major obstacle to their use and the quantum efficiencies ar e sensitive to the environment of the rare earth ion. Recently, comple x glasses containing fluorides have been developed in which fluoride c rystallites can be made to form with a high solubility for rare earth ions. We have performed a study of the visible emission of Pr3+ in the se glasses and have identified three groups of fluorescence lines comi ng from transitions between the P and the H levels. The phonons play a n important role, both in up-conversion as well as in non-radiative de cay between levels in these two sets. This effect is illustrated by th e temperature dependence of the fluorescence spectra measured from 295 K to 4 K and for three different wavelengths, 514 nm, 488 nm and 476 nm in the quenched glasses and in the heat-treated or crystallite-cont aining glasses. Comparison of fluorescence spectra from glasses contai ning either Pr3+/Y3+ Or Pr3+/Gd3+ also reveal an energy transfer betwe en praseodymium that is increased by the presence of yttrium. (C) 1997 Elsevier Science B.V.