Annealing temperature dependent photoluminescence and afterglow of undoped CaAl2O4

Abstract

Undoped CaAl2O4 nanocrystals were synthesized via sol–gel combustion technique, and the effects of subsequent thermal annealing on the photoluminescence (PL) and afterglow of undoped CaAl2O4 nanocrystals were investigated by means of X–ray diffractometry, PL spectroscopy and afterglow dosimetry, respectively. As the annealing temperature increases from 200 to 750 °C, the PL spectrum of undoped CaAl2O4 consists of one blue PL subband and one violet PL subband with their peak energies varying in the range of 2.67–2.86 eV and 3.12–3.31 eV, respectively. It is found that annealing CaAl2O4 can generate significant impacts on the PL and afterglow properties of undoped CaAl2O4. On one hand, the integrated PL intensity of undoped CaAl2O4 decreases with the annealing temperature. On the other hand, the blue afterglow intensity of undoped CaAl2O4 varies with the annealing temperature. More importantly, the duration of the blue afterglow can be extended seven times from 1.98 to 14.25 s when CaAl2O4 is annealed at 600 °C for 2 h. On the basis of density functional calculations, our work demonstrates that oxygen vacancies in CaAl2O4 are the luminescence center of the blue afterglow. In addition to providing valuable insight toward rational development of more efficient afterglow materials, these results are helpful for promoting our fundamental understanding of the afterglow mechanisms of Eu2+ doped CaAl2O4.