Search

Investigation of optical properties of Ce 3+ -activated phosphors is not only of practical importance for various applications but also of fundamental importance for providing a basis to understand relevant properties of other lanthanide ions in the same host. We report herein a combined experimental and theoretical study of optical properties of Ce 3+ in Li 4 SrCa(SiO 4 ) 2 . Photoluminescence properties of the material prepared by a solid-state reaction method are investigated with excitation energies in the vacuum-ultraviolet (VUV) to ultraviolet (UV) range at low temperatures. The band maxima in the excitation spectra are assigned with respect to 4f → 5d transitions of Ce 3+ at the Sr and Ca sites, from comparison between experimental and ab initio predicted transition energies. As a result of the two-site occupation, the material displays luminescence at 300-500 nm with a high thermal quenching temperature (>500 K), consistent with the calculated large gaps (∼1.40 eV) between the emitting 5d levels and the bottom of the host conduction band. On the basis of experimental and calculated results for Ce 3+ in Li 4 SrCa(SiO 4 ) 2 , the energy-level diagram for the 4f ground states and the lowest 5d states of all trivalent and divalent lanthanide ions at the Sr and Ca sites of the same host is constructed and discussed in association with experimental findings.

A series of Ce 3+ -doped (Ca,Sr) 2 Al 2 SiO 7 phosphors with different Ce 3+ and Ca 2+ /Sr 2+ concentrations were prepared by a high temperature solid-state reaction technique. To get insight into the structure-luminescence relationship, the impact of incorporation of Sr 2+ on structure of (Ca,Sr) 2 Al 2 SiO 7 was first investigated via Rietveld refinement of high quality X-ray diffraction (XRD) data, and then the VUV-UV excitation and UV-vis emission spectra of (Ca,Sr) 2 Al 2 SiO 7 :Ce 3+ were collected at low temperature. The results reveal that the crystal structure evolution of (Ca,Sr) 2 Al 2 SiO 7 :Ce 3+ has influences on band gaps and Ce 3+ luminescence properties including 4f-5d i (i = 1-5) transition energies, radiative lifetime, emission intensity, quantum efficiency, and thermal stability. Moreover, the influence of Sr 2+ content on the energy of Eu 3+ -O 2- charge-transfer states (CTS) in (Ca,Sr) 2 Al 2 SiO 7 :Eu 3+ was studied in order to construct vacuum referred binding energy (VRBE) schemes with the aim to further understand the luminescence properties of (Ca,Sr) 2 Al 2 SiO 7 :Ce 3+ . Finally, X-ray excited luminescence (XEL) spectra were measured to evaluate the possibility of (Ca,Sr) 2 Al 2 SiO 7 :Ce 3+ as a scintillation material.