Temperature-dependent luminescence and energy transfer in europium and rare earth codoped nanostructured xerogel and sol-gel silica glasses

Luminescence and decay times of Eu3+ ions codoped with other rare-earth ions (Nd3+, Sm3+, Dy3+, Er3+ and Yb3+) were measured at temperatures between 10 and 300 K in order to investigate the excitation energy transfer processes in the nanostructured xerogel and annealed sol-gel silica glasses. Decay-time profiles were analyzed as the sum of two exponents by applying two models for the electric dipole-dipole type of resonant energy transfer. The critical distances (R-o) of energy transfer in Dexter model are confined to be in the range of 0.88 +/- 0.07 nm (at 300 K), 0.92 +/- 0.08 nm (at 10 K) for annealed glasses and 0.93 +/- 0.11 nm at 300 K for xerogels. The energy transfer processes are considered to reflect optical properties of confined nanostructured networks in the sol-gel SiO2 glasses. (C) 1999 Elsevier Science B.V. All rights reserved.