A study on the tunable emission induced by energy transfer in rare-earth-free calcite- and vaterite-type CaCO3 co-doped with Sn2+ and Mn2+ phosphors

Abstract

Development of rare-earth-free phosphors is quite significant. It is well known that luminescence of Sn2+ depends strongly on the structure of the host crystal. The emission of Mn2+ is often very weak due to forbidden 4T1 → 6A1 transition. However, it can be enhanced by means of energy transfer. This work deals with the photoluminescence of calcite- and vaterite-type CaCO3 doped with Sn2+, Mn2+ phosphors. The phosphor particles were prepared via a simple co-precipitation method. The phase purity of the synthesized particles was determined by X-ray powder diffraction. Scanning electron microscopy images were obtained to study the particle morphology. Photoluminescence properties were determined by recording the emission spectra and excitation spectra. Furthermore, the fluorescence lifetimes were recorded to investigate decay and energy transfer behavior of the samples. The emission colors of calcite-CaCO3:Sn2+ and vaterite-CaCO3:Sn2+ are different under 254 nm UV excitation, which is explained by the different coordination environment of Ca2+. For the Sn2+-Mn2+ co-doped samples, the emission intensity of Mn2+ becomes stronger than that of Mn2+ singly doped sample, which is attributed to Sn2+ → Mn2+ energy transfer. Inokuti-Hirayama model is used to analysis of the involved energy transfer mechanism. The color tone of the samples can be tuned in the visible spectral region through adjusting the Mn2+ doping concentration. Near cold white-light emission can also be achieved in a single host co-doped with Sn2+ and Mn2+.