Tunable Yellow-Red Photoluminescence and Persistent Afterglow in Phosphors Ca4LaO(BO3)3:Eu3+ and Ca4EuO(BO3)3

In most Eu3+ activated phosphors, only red luminescence from the D-5(0) is obtainable, and efficiency is limited by concentration quenching. Herein we report a new phosphor of Ca4LaO(BO3)(3):Eu-3 (CLBO:Eu) with advanced photoluminescence properties. The yellow luminescence emitted from the D-5(1,2) states is not thermally quenched at room temperature. The relative intensities of the yellow and red emission bands depend strongly on the Eu3+ doping concentration. More importantly, concentration quenching of Eu3+ photoluminescence is absent in this phosphor, and the stoichiometric compound of Ca4EuO(BO3)(3) emits stronger luminescence than the Eu3+ doped compounds of CLBO:Eu; it is three times stronger than that of a commercial red phosphor of Y2O3:Eu3+. Another beneficial phenomenon is that ligand-to-metal charge transfer (CT) transitions occur in the long UV region with the lowest charge transfer band (CTB) stretched down to about 3.67 eV (similar to 30 nm). The CT transitions significantly enhance Eu3+ excitation, and thus result in stronger photoluminescence and promote trapping of excitons for persistent afterglow emission. Along with structure characterization, optical spectra and luminescence dynamics measured under various conditions as a function of Eu3+ doping, temperature, and excitation wavelength are analyzed for a fundamental understanding of electronic interactions and for potential applications.