Abstract
•CaF2:Yb3+ transparent ceramics are synthesized by vacuum sintering.•A great similarity with the single fluoride crystal can be deduced.•Emission and absorption spectra show the presence of several luminescent centers.•The hexameric clusters dominate over all the isolated centers for high concentrations.•The Crystal field calculation for the isolated centers of CaF2:Yb3+ was established.
Fluoride CaF2:Yb3+ 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 CaF2:Yb3+ ceramics with the properties of single crystals counterpart is performed. A detailed spectroscopic analysis of the crystal-field splitting of the energy levels of Yb3+ in CaF2 ceramics is reported based on assignments made to the absorption and selective emission spectra observed between 905nm and 1100nm obtained at 20K. The experimental Stark energy levels of the two Yb3+ manifolds are established for all the present site symmetries in the CaF2 ceramics host. Furthermore, a crystal field investigation of Yb3+ doped CaF2 transparent ceramics is presented. Very satisfactory agreement was obtained between calculated and experimental Stark energy levels of Yb3+ ion corresponding to isolated and complex sites.
Using the calculated Stark energy levels, the majority of the emission lines is attributed to the cubic (Oh), tetragonal (C4v) and trigonal (C3v) site symmetries of Yb3+ in CaF2 ceramics, which are the dominant luminescent centers at low ytterbium concentrations (0.5at%). For higher dopant concentrations, above the 2.5at%, these emission lines are related only for one dominant class of Yb3+ centers which corresponds to some hexameric clusters (Yb6F36 and Yb6F37).