Effect of Composition and Impurities on the Phosphorescence of Green-Emitting Alkaline Earth Aluminate Phosphor

Recent improvements to SrAl₂O₄:Eu²⁺, Dy³⁺ phosphors have enabled the use of luminescent hosts with a stable crystal structure and high physical and chemical stability, thus overcoming the bottleneck in the applicability of ZnS:Cu phosphors. However, enhancement of afterglow lifetime and brightness in SrAl₂O₄:Eu²⁺, Dy³⁺ phosphors remains a challenging task. Here, we have improved the afterglow characteristics in terms of persistence time and brightness by a systematic investigation of the composition of Eu-doped alkaline earth aluminate SrAl₂O₄:Eu²⁺, Dy³⁺ crystals. We found that a Dy³⁺/Eu²⁺ ratio of ~2.4 and ~0.935 mol Eu²⁺ (per mol of SrAl₂O₄) gave the brightest and longest emissions (11% and 9% increase for each). Doping with Si⁴⁺ also resulted in a slight increase in brightness up to ~15%. Doping with alkali metal or alkaline earth metal significantly enhanced the phosphorescence intensity. In particular, doping with 0.005 mol Li⁺ (per mol of SrAl₂O₄) alone boosted the phosphorescence intensity to 239% of the initial value, as compared to that observed for the non-doped crystal, while doping with 0.01 mol Mg²⁺ and 0.005 mol Li⁺ (per 1 mol SrAl₂O₄) boosted the phosphorescence intensity up to 313% of the initial value. The results of this investigation are expected to act as a guideline for the synthesis of bright and long persistent phosphors, and facilitate the development of persistent phosphors with afterglow characteristics superior to those of conventional phosphors.