Green Afterglow of Undoped SrAlO.

Undoped SrAlO nanocrystals were obtained via solution combustion using urea as fuel. The afterglow properties of undoped SrAlO were investigated. Green afterglow from undoped SrAlO 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 SrAlO 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 SrAlO 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 SrAlO and strontium-deficient SrAlO, respectively. Our results demonstrate that the green afterglow of undoped SrAlO originates from the midgap states introduced by oxygen and strontium vacancies. The observation of green afterglow from undoped SrAlO helps in gaining new insight in exploring the afterglow mechanisms of SrAlO-based afterglow materials.