Mechanism of the prolongation of the green afterglow of SrAl2O4:Dy3+ caused by the use of H3BO3 flux

Significant prolongation in the green afterglow of SrAl2O4:Dy3+ was achieved by adding 10 mol% H3BO3 into the starting material. The surface morphology, crystalline structure, chemical composition, photoluminescence, afterglow and decay characteristics of the phosphor were characterized by scanning electron microscopy, X-ray diffractometry, energy-dispersive X-ray spectroscopy, transmission electron microscopy, photoluminescence and photoexcitation spectroscopy, respectively. It was found that the afterglow time constant of the green afterglow from SrAl2O4:Dy3+ phosphor could be enhanced over 100 folds from 53 to 5538 s after the addition of 10 mol% H3BO3 flux. No traces of Eu were found in the phosphors within the 1 μg/g detection limit of the inductively coupled plasma atomic emission spectrometry. By employing meta generalized gradient approximation to describe the exchange-correlation functional, the band structures of SrAl2O4:Dy3+ were calculated within the framework of density functional theory. The ground state of Dy3+ ions and the defect levels of VO
-
- , VSr″ and VAl″′ were quantitatively determined in the band gap of SrAl2O4. A possible afterglow mechanism was proposed to shed fresh light on the green afterglow of SrAl2O4:Dy3+. The significant prolongation in the afterglow of SrAl2O4:Dy3+ can be attributed to the H3BO3 flux introduced VAl″′ in the host lattice.