Photoconductivity and delocalization in rare earth activated insulators

We show that by comparing the optical spectra of these materials with complementary measurements such as photoconductivity (PC), the absolute energy level structure of the ions with respect to the intrinsic bands of the host can be determined. This positioning is crucial to the luminescence efficiency of RE-activated solids; the quenching of luminescence can arise from the conversion of energy into mobile charges. We believe that this process provides us with a sensitive way to probe the delocalization of optical energy in activated solids and gives additional insights on the nature of the high lying excitations in these materials. (C) 1999 Elsevier Science B.V. All rights reserved.