Effect of Al/Sr ratio on the luminescence properties of SrAl2O4:Eu2+, Dy3+ phosphors

Recent studies have brought out many phosphors like Eu2+, Dy3+-doped alkaline earth aluminates. The trivalent Dy3+ ions as co-dopants greatly enhance the duration and intensity of persistent luminescence. These phosphors show excellent properties, such as high quantum efficiency, long persistence of phosphorescence, good stability and suitable color emission. In this work the effect of Al/Sr ratio on the afterglow and phosphorescence decay properties of Eu2+ and Dy3+ co-activated strontium aluminates synthesized by a solid-state process has been investigated. The luminescence properties of samples were investigated by means of excitation spectra, emission spectra and X-ray diffraction analysis. A variety of strontium aluminates, such as SrAl2O4, Sr4Al2O7, Sr3Al2O6, Sr3Al2(Eu, Dy, Y)O7.5, Al5(Eu, Dy, Y)O12, Sr4Al14O25, SrAl12O19 and (Eu, Dy, Y)AlO3 have been identified in the samples prepared from starting precursors with Al/Sr mole ratios ranging from 0.44 to 5. The afterglow decay rate was found to be the fastest for sample with Al/Sr ratio of 4.18, in which SrAl4O7 phase was dominant. The afterglow decay rate for phosphor with Al/Sr ratio of 2, in which SrAl2O4 phase was dominant, was detected to be slow. Moreover, the emission spectra of the samples shift to yellow-green long wavelength from bluish-green-ultraviolet short wave with the increase of Al/Sr ratios resulting from the change in the composition.