N I,1,11 1I Visible emission from rare earth ions in nanocrystal-containing glasses

Rare earth-doped glasses are of great interest for their optical and fluorescence properties. However, phononmediated non-radiative transitions are a major obstacle to their use and the quantum efficiencies are sensitive to the environment of the rare earth ion. Recently, complex glasses containing fluorides have been developed in which fluoride crystallites can be made to form with a high solubility for rare earth ions. We have performed a study of the visible emission of Pr 3÷ in these glasses and have identified three groups of fluorescence lines coming from transitions between the P and the H levels. The phonons play an important role, both in up-conversion as well as in non-radiative decay between levels in these two sets. This effect is illustrated by the 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-containing glasses. Comparison of fluorescence spectra from glasses containing either p r3+ /Y 3+ or p r 3 + / G d 3+ also reveal an energy transfer between praseodymium that is increased by the presence of yttrium. © 1997 Elsevier Science B.V.