Structure and luminescence properties of a novel yellow super long-lasting phosphate phosphor Ca6BaP4O17:Eu2+,Ho3+

A novel yellow-emitting long-lasting phosphate phosphor Ca6BaP4O17:Eu2+,Ho3+ is developed. The incorporation of Ho3+ ions, which act as trap centers, largely extends the thermoluminescence characteristics and evidently enhances the persistent luminescence behavior of the phosphor. Both the fluorescence and phosphorescence spectra of Ca6BaP4O17:0.02Eu(2+),0.015Ho(3+) reveal only one asymmetric broad emission band located at 553 nm, ascribed to the 5d-4f transitions of Eu2+ ions in two different Ca2+ sites. After 15 min of excitation, the initial long-lasting phosphorescence (LLP) intensity of Ca6BaP4O17:0.02Eu(2+),0.015Ho(3+) can reach about 0.13 cd m(-2) and its LLP can last more than 47 h above the recognizable intensity level (0.32 mcd m(-2)), a phenomenon that is infrequent and excellent. Furthermore, the direct bandgap of about 4.081 eV for Ca6BaP4O17 provides a suitable bandgap for Eu2+ and Ho3+ ions. The results indicate that the phosphor has the potential to become a novel commercial LLP phosphor used in the field of emergency lighting and display. Detailed processes and a possible mechanism are studied and discussed.