Abstract
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.
Highlights
Phosphorescent materials have attracted considerable attention with respect to a wide range of applications in organic light emitting devices (OLEDs) and glow-in-the-dark materials, which are charged with bright light such as room light
We characterized the effect of activator and co-activator composition on the phosphorescence intensity
When the Dy3+/ Eu2+ ratio is greater than 2.4, the amount of Eu2+ contributing to phosphorescence characteristics becomes less than the amount of Dy3+ contributing to afterglow characteristics; the doi:10.1371/journal.pone.0145434.g001
Summary
Phosphorescent materials have attracted considerable attention with respect to a wide range of applications in organic light emitting devices (OLEDs) and glow-in-the-dark materials, which are charged with bright light such as room light. Phosphorescence of Green-Emitting Alkaline Earth Aluminate Phosphor but it does not maintain its phosphorescence for more than a few hours, and is not bright and chemically stable enough for many applications. Many recent studies have improved the phosphorescence quantum yield of strontium aluminates by the use of activators and coactivators [7,8,9,10,11,12], it is challenging to develop long and enhanced afterglow phosphors. We have investigated the effects of various doping compositions and impurities on the phosphorescence of green-emitting alkaline earth aluminate phosphor (SrAl2O4:Eu2+,Dy3+) and improved its phosphorescence characteristics. We compared various compositions of the activator (Eu2+) and coactivator (Dy3+), and impurities to find optimal conditions for improving the brightness and decay time of the green-emitting alkaline earth aluminate phosphor. We succeeded in developing a new phosphor, SrAl2O4:Eu2+,Dy3+, which shows extremely bright and long-lasting phosphorescence
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