Color-control of long-lasting phosphorescence (LLP) through rare earth ion-doped cadmium metasilicate phosphors

We report on a novel luminescent phenomenon in one-component cadmium metasilicate phosphors doped with various rare earth ions. After irradiation by a 254 nm ultraviolet lamp, these phosphors emit bright long-lasting phosphorescence (LLP), and their phosphorescence can be seen with the naked eye (0.32 x 10(-3) cd m(-2)) in the darkroom clearly for 2-5 hours even after the irradiation light sources have been removed. Furthermore, color-control of the LLP is also available in these cadmium metasilicate luminescent materials. By selecting appropriate rare earth ions single or double doped into cadmium metasilicate, optional three-dimensional image patterns emitting LLP in various colors, covering most of the visible light region from short wavelength indigo blue to long wavelength deep red, can be formed under the same wavelength ultraviolet light excitation. X-Ray diffraction (XRD), photo luminescence (PL), long-lasting phosphorescence (LLP), and thermo stimulated luminescence (TSL) spectra are used to characterize the synthesized phosphors. PL and LLP spectra reveal that there are two different kinds of LLP emissions in RE3+-doped CdSiO3 (the similar to 420 nm self-trapped excitation (STE) emission and the characteristic rare earth ions emissions). It is found that these two kinds of emissions are the origin of the multi-colored LLP phenomenon in these phosphors. The finding has enlarged the family of long-lasting phosphors available, and offers a promising approach for controlling the LLP color of other materials.