Green Afterglow of Undoped SrAl(2)O(4)

Undoped SrAl(2)O(4) nanocrystals were obtained via solution combustion using urea as fuel. The afterglow properties of undoped SrAl(2)O(4) were investigated. Green afterglow from undoped SrAl(2)O(4) is visible to the human eye when the 325 nm irradiation of a helium–cadmium laser (13 mW) is ceased. The afterglow spectrum of undoped SrAl(2)O(4) is peaked at about 520 nm. From the peak temperature (321 K) of the broad thermoluminescence glow curve, the trap depth of trap levels in undoped SrAl(2)O(4) is estimated to be 0.642 eV using Urbach’s formula. Based on first-principles density functional calculations, the bandstructures and densities of states are derived for oxygen-deficient SrAl(2)O(4) and strontium-deficient SrAl(2)O(4), respectively. Our results demonstrate that the green afterglow of undoped SrAl(2)O(4) originates from the midgap states introduced by oxygen and strontium vacancies. The observation of green afterglow from undoped SrAl(2)O(4) helps in gaining new insight in exploring the afterglow mechanisms of SrAl(2)O(4)-based afterglow materials.