Giant Improvement on the Afterglow of Sr 4 Al 14 O 25 :Eu 2+ ,Dy 3+ Phosphor by Systematic Investigation on Various Parameters

Abstract

Highly intense, long persistent Sr 4 Al 14 O 25 :Eu 2+ ,Dy 3+ blue-green phosphor with different B 3+ , Eu 2+ , Dy 3+ , and Ag + contents was prepared by solid-phase reaction at various temperatures in reductive atmosphere of 10% H 2 in N 2 . The effects of synthesis parameters like calcination temperature and time, calcination environment, effect of stoichiometry of the host composition, and additives like addition of boron and rare earth ions (Eu, Dy) were studied in detail. Results revealed that the phosphor containing ~40 mol% H 3 BO 3 showed dense and pure Sr 4 Al 14 O 25 phase with higher emission intensity, but in the samples containing less than 20 mol% H 3 BO 3 mixed phases consisting of Al 2 O 3 , SrAl 12 O 19 and SrAl 2 O 4 were observed, while in higher H 3 BO 3 content, SrAl 2 B 2 O 7 phases predominated. When the stoichiometry of Al/Sr was 3.7, the best phosphorescence and afterglow were noted. The phosphor containing 4 at.% of Eu and 8 at.% of Dy, and 3 at.% Ag exhibited the maximum initial intensity of 5170 mcd·m −2 and the longest persistency of greater than 30 hours over the value of 5 mcd·m −2 , higher than the commercial products and applicable for various display applications involving indoor as well as outdoor uses.