We report on the photoluminescence properties of Sr4Al14O25:Eu2+,Dy3+ (SAED) phosphors modified by adding Ho3+ in excess and partially substituting Dy3+ with Ho3+ (SAEDHs). Samples were produced using an established solid-state synthesis method known to consistently yield long-persistent afterglow phoshors. Substitutions were performed in stoichiometrically modified host lattices (Al/Sr = 3.2, 3.5, 3.7). Partially substituting Dy3+ with Ho3+ resulted in a remarkable increase in photoluminescence (PL) intensity, Ho3+ co-doping caused a shift in the main emission peaks between 494 and 497 nm and introduced new peaks as well. Important from the security application point of view, the PL intensity was significantly improved under both purple (400 nm) and blue (445 nm) illumination. Color shift of the powders from green to a yellowish and pale pink shade resulted from the Ho3+ addition. Afterglow (AG) properties and thermoluminescence (TL) response decreased non-gradually as Dy3+ was substituted by Ho3+, due to possible charge transfer effects caused by Ho3+. AG and TL properties remained more intact in the presence of Ho3+ when the Al/Sr ratio differed from the ideal 3.5 ratio. Rearrangements of trap energy levels, and energy transfer induced by Ho3+ co-doping were analysed by TL. Dy3+/Ho3+ co-dopants and Al/Sr stoichiometric ratios asymmetrically influenced the trapping/detrapping and energy transfer processes of the SAEDH phosphors. The developed new materials meet the general characteristics of long-persistent phosphors: charging by sunlight, efficient light conversion, chemical stability, all-night afterglow observable by the human eye.
- Long-persistent phosphor
- Multiple co-activation
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics
- Condensed Matter Physics