Role of oxidative pre-calcination in extending blue emission of Sr4Al14O25 nanophosphors formed with microemulsions

Abstract Here, we report the preparation of a single phase blue emitting long persistence Sr 4 Al 14 O 25 nanophosphors formed in the presence of 5 mol% boric acid at 1100 °C when oxidative pre-calcination was applied to precursors synthesised within microemulsions. This two stage process allowed homogeneous dopant distribution and efficient substitutional incorporation of BO 4 in the aluminate framework, which generated associated defect states providing deep trap levels responsible for long persistence, now confirming the previously proposed mechanisms. In addition, the formation of glassy borate phases were avoided reducing aggregation which resulted in crystallite sizes that spanned 41–52 nm and particle sizes in the range 50–200 nm. This two stage process with calcination at 1100 °C resulted in increased initial emission intensity (12%) as well as enhanced long persistence, with a lifetime of deep trap states ( τ 3 ) of 850 s compared to the range 470–690 s from conventional one stage reductive calcination.