Electron trapping by self-trapped hole pairs and small rare-earth clusters in Sm-doped CaF2

In this paper we investigate the mechanisms for electron trapping, following photoionization of Sm2+ in gamma- and non-gamma-irradiated samples of Sm-doped CaF2. Using linear absorption, fluorescence and site-selective coherent anti-Stokes Raman excitation spectroscopy, we show that the electron traps in non-gamma-irradiated CaF2:Sm are small clusters of trivalent Sm ions. In the gamma-irradiated samples, we observe the formation of self-trapped holes after photoionization, which provides us with additional evidence for the existence of self-trapped hole pairs in gamma-irradiated rare-earth-doped CaF2. (C) 1998 Elsevier Science B.V. All rights reserved.