Ca6BaP4O17:Eu2+,Gd3+: a yellow emitting long-lasting phosphor with high brightness and long afterglow duration

Abstract

A yellow emitting long-lasting phosphor based on a Ca₆BaP₄O₁₇ matrix was successfully synthesized by means of solid state method in a reducing atmosphere. The persistent phosphor was characterized in detail by X-ray powder diffraction (XRD), photoluminescence (PL), persistent luminescence and decay curves as well as thermoluminescence (TL) spectra. When irradiated by ultraviolet light in advance, Ca₆BaP₄O₁₇:0.02Eu²⁺,0.015Gd³⁺ phosphor shows a yellow persistent luminescence dominating at ∼553 nm at room temperature due to the 5d–4f transitions of Eu²⁺ ions and the chromaticity coordinate was calculated to be (0.431, 0.545), which is in the yellow region. Moreover, investigation of TL curves reveals that the incorporation of Gd³⁺ ion creates more appropriate energy traps and increases the density of intrinsic traps leading to the enhancement of afterglow. Consequently, the initial long lasting phosphorescence (LLP) intensity of Ca₆BaP₄O₁₇:0.02Eu²⁺,0.015Gd³⁺ (0.21 cd m⁻²) is significantly enhanced by a factor of 2 compared with Ca₆BaP₄O₁₇:0.02Eu²⁺,0.015Ho³⁺ and the sustained phosphorescence also can last approximately 19 h above the recognizable intensity level (0.32 mcd m⁻²). In order to study the trapping process and explain the mechanism of long afterglow, a schematic model is also proposed and discussed in detail.