On the effects of milling and thermal regeneration on the luminescence properties of Eu2+ and Dy3+ doped strontium aluminate phosphors

This paper reports a comparison of luminescence, particle size and crystallinity reduction of SrAl2O4: Eu2+, Dy3+ (SA2) and Sr4Al14O25: Eu2+, Dy3+ (SA14) phosphors by ball milling. In addition, the regeneration possibilities of rare earth metal doped strontium aluminate phosphors (SAEDs) were investigated. The crystallinity degradation and particle size reduction were characterized by powder X-ray diffraction, and scanning electron microscopy (SEM) techniques respectively. Afterglow (AG), photo- (PL) and thermoluminescent (TL) properties of SAEDs were followed in parallel. The trap level shifts during the degradation and regeneration process were calculated from the TL data. The oxidation and reduction of Eu2+/3+ luminescence centre was followed by X-ray photoelectron spectroscopy (XPS). Luminescence degradation became significant after 2 mu m avg. particle diameter reached, for both SAEDs. Considerable differences were found in their stress durabilities. The SA2 and SA14 characteristics are largely influenced by the details of the mechanical energy investment method, in reached crystallinity, particle diameter, and the Eu2+/3+ state, besides the total amount of energy transferred. The reversibility of the Eu2+/3+ ratio, PL and afterglow performance of the milled phosphors could be restored to some extent, by similar to synthesis annealing. The SA14 and SA2 phosphors responded differently to the regeneration process.