Near ultraviolet excitable cyan-green phosphors of Ba6La2Al3ScO15:Ce3+ and Ba6La2Al3ScO15:Ce3+,Tb3+: investigations on the crystal structure, site assignment of Ce3+ and Tb3+ ions, and an energy transfer process from Ce3+ to Tb3.

Abstract

An energy transfer from Ce3+ to Tb3+ is feasible in energy transition processes for the development of optical devices, especially phosphor-converted white LEDs (pc-wLEDs). Most of the energy transfer phosphors co-doped with Ce3+ and Tb3+, unfortunately, have weak absorption under a near-ultraviolet light of around 405 nm and blue light excitation, making them incapable for use as near ultraviolet or blue LEDs. In this study, novel energy transfer luminescent materials, Ba6La2Al3ScO15:Ce3+,Tb3+, isostructural with existing Ba6La2(Al,Fe)4O15, were successfully synthesized through a conventional solid-state reaction as a single phase. The phosphors showed a broad cyan emission of Ce3+ and narrow green emissions of Tb3+ under a near-ultraviolet light of 405 nm, which was nearly located at an emission wavelength of near-ultraviolet LEDs. The occurrence of energy transfer from Ce3+ to Tb3+ was evidenced by emission lifetime measurements. The lifetime analysis based on formulated energy transfer models, such as Inokuti-Hirayama, Yokota-Tanimota and Martin models, revealed that an energy transfer process from Ce3+ to Tb3+ took place dominantly by a dipole-dipole interaction with low migration among the donors of Ce3+.