Tuning the photoluminescence of Eu2+ and Eu3+ co-doped SrSO4 through post annealing technique

Eu2+ and Eu3+ co-doped SrSO4 microcrystals were synthesized by employing Eu3+ as the sole doping source in the precipitation synthesis. As the annealing temperature increases from 200 to 1000 °C, it is found that the broad photoluminescence (PL) band of Eu2+ peaking at 378 nm is dramatically enhanced in intensity as the cost of the narrowband emissions of Eu3+ at 584, 591 and 612 nm, respectively. Moreover, Two broad PL bands, one of which is centered at 500 nm while the other is centered at 625 nm, are recorded upon post annealing. On the basis of density functional calculations, post annealing introduced oxygen vacancy is proposed to play critical roles in tuning the PL of Eu2+ and Eu3+ co-doped SrSO4. On one hand, the oxygen vacancy is responsible for the enhanced emission of Eu2+ at 378 nm by reducing Eu3+ to Eu2+. On the other hand, the oxygen vacancy acts as electron trap and luminescence center in SrSO4 with the result of the broad PL band centered at 500 nm. Our results have demonstrated that the PL of Eu2+ and Eu3+ co-doped SrSO4 microcrystals can be tuned by simply varying the post annealing temperature.