Red persistent luminescent Sr3Al2O5₋xSxCl2:Eu2+, Tm3+ phosphors based on lattice engineering

Research and development of persistent luminous phosphors for longer wavelengths, especially for red, is relatively limited, despite significant achievements in persistent luminescent materials for blue and green afterglow. This study uses high-temperature solid phase reactions to successfully prepare S2− doped Sr3Al2O5Cl2:Eu2+, Tm3+ red phosphors. After incorporating S2− into the original O lattice site, Rietveld's refinement of the prepared samples revealed that the occupancy of Tm3+ in the host lattice was optimized. The photoluminescence spectra of the samples showed that the emission is significantly redshifted from 610 to 630 nm as S2− content increases. The main reason for the redshift behavior is that incorporating S2− into the lattice increases crystal field splitting, positively affecting the centroid shift. Additionally, the afterglow of the S2− doped samples are enhanced, with stronger initial brightness and increased duration. This can be attributed to deeper trap energy levels and higher trap concentrations created after incorporating S2−, as confirmed by thermally stimulated luminescence measurements. Consequently, long-lasting red phosphors with brighter afterglow and longer duration were obtained by S2−doping. Possible mechanisms and detailed processes are presented and explained.