Quantification of Emission Efficiency in Persistent Luminescent Materials

Accurate quantification of efficiency enables rigorous comparison between different photoluminescent materials, providing an optimization path critical to the development of next-generation light sources. Persistent luminescent materials exhibit delayed and long-lasting luminescence due to the temporary storage of optical energy in engineered structural defects. Standard characterization methods do not provide a universal comparison of phosphor performance, hindering the evaluation of the efficiency of the various processes involved in afterglow. Here, a protocol is established to determine the quantum yield of persistent phosphors by considering the ratio of photons emitted in the afterglow and during charging to those absorbed. The method is first applied to transparent single crystals of the most common persistent phosphors, such as SrAl2O4:Eu2+,Dy3+ and Y3Al2Ga3O12:Ce3+,Cr3+. The versatility of the methodology is demonstrated by quantifying the quantum yield of a ZnGa2O4:Cr3+ thin film, a material widely used in in vivo imaging. The high efficiency of strontium aluminate is confirmed, and a strong dependence of the obtained values on the illumination conditions is revealed, highlighting a trade-off between efficiency and brightness. The results contribute to the development of standardized protocols for analyzing afterglow mechanisms and assessing overall efficiency, facilitating rigorous comparison and optimization of persistent materials beyond trial-and-error approaches.