Energy transfer and relaxation phenomena in CaF2:Er3+

Abstract

A selective laser excitation technique has been used to study energy transfer between the individual ions of specific crystallographic sites in charge compensated CaF₂:Er³⁺. Unique energy transfer rates have been obtained directly from the fluorescent transients of the selectively excited sites. No energy transfer processes were observed between sites corresponding to single Er³⁺ ions. For those sites composed of Er³⁺ clusters, very efficient and complex intracluster energy transfer was observed despite large energy defects requiring phonon assistance. The ion pair relaxation processes compete efficiently with multiphonon relaxation because smaller contributions from lattice phonons are required. Analogous energy transfer interactions were found to occur between Yb³⁺ and Er³⁺ ions in mixed cluster sites in double‐doped crystals. Detailed relaxation and energy transfer mechanisms are presented. Kinetic expressions describing excited state relaxation are derived from these mechanisms and are used to provide theoretical fits to experimental fluorescence transients confirming the relaxation mechanisms proposed.