Synthesis, photoluminescence and thermostimulated-luminescence properties of novel red long-lasting phosphorescent materials β-Zn3(PO4)2:Mn2+,M3+ (M = Al and Ga)

Abstract

Novel red long-lasting phosphorescent materials β-Zn₃(PO₄)₂:Mn²⁺,M³⁺ (M = Al and Ga) were synthesized by means of high-temperature solid-state reaction. Photoluminescence (PL) excitation and emission, long-lasting phosphorescent (LLP) emission, decay curves, brightness and chromaticity coordination, and thermostimulated-luminescent (TSL) spectra were used to characterize the powder phosphors. The emissions for both PL and LLP are due to the ⁴T_1g(⁴G) → ⁶A_1g(⁶S) transition of Mn²⁺ ions in β-Zn₃(PO₄)₂. The incorporation of trivalent ions M³⁺ decreases the PL intensity and contrarily improves the LLP properties including brightness and duration with increasing ionic radius. After irradiation with ultraviolet light peaking at 254 nm, Zn₃(PO₄)₂:Mn²⁺,Ga³⁺ shows the initial intensity of the red phosphorescence at 460 mcd m⁻² with the chromaticity coordinates x = 0.6679, y = 0.3321 after the removal of the excitation source. Its red phosphorescence lasts no less than 2.5 h. The results of TSL show that some intrinsic defects associated with peaks at 381, 450 and 510 K appear in Zn₃(PO₄)₂:Mn²⁺ whereas a novel compensating defect V^″_Zn for the substitution of Zn²⁺ by Al³⁺and Ga³⁺ is associated with peaks at 380 K for Zn₃(PO₄)₂:Mn²⁺,Al³⁺ and 377 K for Zn₃(PO₄)₂:Mn²⁺,Ga³⁺. The negative defect V^″_Zn serves as an efficient hole-trapping center. The density of the trapped-charges for the TSL peaks at 380 and 377 K is respectively 1.2 and 2.7 times more intensive than that for the peak at 381 K. The TSL intensity is strongly dependent on the density of the trapped charges. An electron–hole recombination model is proposed to interpret the mechanism for the red LLP of Mn²⁺. Based on this model, the improvement of red LLP performance of Mn²⁺ is strongly related to the density of the trapped charges, which can be modified by the added ions. It demonstrates that the red LLP performance of Mn²⁺ can be controlled by the species of the auxiliary ions.