Spectra and energy levels of Yb3+ ions in CaF2 transparent ceramics
Abstract Fluoride CaF 2 :Yb 3+ transparent ceramics for high power lasers are obtained by vacuum sintering and hot pressing of nanoparticles synthesized through a soft chemistry route. Comparative investigation of the luminescent properties of CaF 2 :Yb 3+ ceramics with the properties of single crystals counterpart is performed. A detailed spectroscopic analysis of the crystal-field splitting of the energy levels of Yb 3+ in CaF 2 ceramics is reported based on assignments made to the absorption and selective emission spectra observed between 905 nm and 1100 nm obtained at 20 K. The experimental Stark energy levels of the two Yb 3+ manifolds are established for all the present site symmetries in the CaF 2 ceramics host. Furthermore, a crystal field investigation of Yb 3+ doped CaF 2 transparent ceramics is presented. Very satisfactory agreement was obtained between calculated and experimental Stark energy levels of Yb 3+ ion corresponding to isolated and complex sites. Using the calculated Stark energy levels, the majority of the emission lines is attributed to the cubic ( O h ), tetragonal ( C 4v ) and trigonal ( C 3v ) site symmetries of Yb 3+ in CaF 2 ceramics, which are the dominant luminescent centers at low ytterbium concentrations (0.5 at%). For higher dopant concentrations, above the 2.5 at%, these emission lines are related only for one dominant class of Yb 3+ centers which corresponds to some hexameric clusters (Yb 6 F 36 and Yb 6 F 37 ).