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