F−-Eu3+ charge transfer energy and local crystal environment in Eu3+ doped calcium fluoride

A series of CaF2:xEu3+ (x = 0.01-0.05) phosphors were synthesized by coprecipitation and high temperature solid-state method. Three different F--Eu3+ charge transfer (CT) bands in CaF2:xEu3+ (x = 0.01-0.05) were detected through the PL spectra. Three local crystal environments (deformed Oh octahedron, C3V, C4V) were proposed in Eu3+ doped CaF2. The broad peak at 277 nm is F- → Eu3+ CT peak, in which Eu3+ ions located deformed Oh octahedron sites, the broad peak at 312 nm is due to Eu3+ ions situating at C4v sites, also, Eu3+ ions with C3v sites can make the F- → Eu3+ CT produce a 38-nm redshift to 315 nm. Density functional theory (DFT) was performed to calculate the energy band gap(Eg) according to the three models. The calculation results consist with the experiment. The excitation peaks can be tuned in the same host through changing the local structure of Eu3+.