Preparation and luminescence characteristics of Eu-doped calcium chloride silicate Ca7Si2O8Cl6

Highlights: • Ca7Si2O8Cl6: Eu prepared in a reducing atmosphere contains Eu2+ and Eu3+ centers. • With increasing Eu-doping Eu2+ emission decrease and Eu3+ f–f transitions increase. • Luminescence color can be tunable Upon an excitation with near UV-light. • QE of Ca7Si2O8Cl6: 0.04Eu is 47.5% under excitation of 390 nm. -- Abstract: Eu-activated (0.1–5.0 mol%) calcium chloride silicate Ca7Si2O8Cl6 phosphors were prepared by means of ceramic method, which were characterized by X-ray powder diffraction and SEM measurements. The luminescence properties were investigated by the photoluminescence excitation and emission spectra, the luminescence decay lifetimes, the color coordinates and the internal quantum efficiency. Ca7Si2O8Cl6:Eu contains two kinds of Eu-emission centers, i.e., Eu2+ and Eu3+ ions, even it was prepared in a reducing atmosphere. Eu2+ and Eu3+ ions which present the characteristic broad band (5d → 4f) and narrow 4f → 4f luminescent features, respectively. The luminescence mechanism was discussed by analyzing the spectra, concentration-dependent emission intensity and lifetimes. With increasing Eu-doping, the energy transfer happens from Eu2+ to Eu3+ centers. Upon an excitation with near UV light, the luminescence color can be tunable from green to orange with increasing the Eu-doping because of the changes of the luminescence components from Eu3+ and Eu2+ ions in Ca7Si2O8Cl6 host. This is a potential phosphor combining both luminescence effects of Eu2+ and Eu3+ ions