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

Abstract

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 Ca₆BaP₄O₁₇:0.02Eu²⁺,0.015Ho³⁺ 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 Ca₆BaP₄O₁₇:0.02Eu²⁺,0.015Ho³⁺ 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.