Suppression of Eu2+ luminescence and enhancement of Eu3+ emission in Eu: CaF2 single crystal via Gd3+ co-doping

Abstract Eu-doped calcium fluoride (CaF2) single crystals co-doped with various concentrations of Gd3+ were synthesized by the Bridgman-Stockbarge method. A broad excitation band in the ultraviolet (UV) region were observed in the crystal, which is attributed to the existence of Eu2+ ions with the help of XPS measurements. The concentrations of Gd3+ were found to have significantly influence on the luminescence properties of the Eu: CaF2, resulting in a suppression of Eu2+ luminescence and enhancement of Eu3+ emission with higher Gd3+ co-doping level. The photoluminescence excitation and emission spectra of Eu2+ and Eu3+ ions were measured using luminescence spectrometer. Local site symmetry of crystals were investigated to explain the influence of Gd3+ on suppression of Eu2+ luminescence and emission of 5D3→7FJ (J=1, 2, 3) in Eu3+ transition. The fluorescence emissions of the 3at.%Eu6at.%Eu: CaF2 and 3at.%Eu12at.%Gd: CaF2 crystals excited at 398 nm present the CIE color coordinates of (0.6012, 0.3870) and (0.5930, 0.3953), respectively. A highest quantum yield of 40.53 % and 5D0→7F1 transition decay time of 9.54 ms were obtained on the 3at.%Eu6at.%Gd: CaF2 crystal. This investigation suggests that Eu,Gd: CaF2 has great potentials for optimizing solid state UV-visible converter performances through appropriate concentration tuning of dopants.