Observation of cluster formation of rare earth ions in wide band gap fluorine dielectric crystals using transmission electron microscopy

Transmission electron microscopy was used to investigate the cluster formation of trivalent rare earth (RE) ions in wide band gap dielectric crystal hosts with atomic resolution. Various defects and areas with variation in chemical composition with dimensions of 5 nmwere observed. This finding sets the limit in the value of the refractive index, and thus in the optical quality of these crystals. # 2003 Elsevier B.V. All rights reserved