No abstract

This paper reports on the intense blue afterglow from undoped CaAl2O4 nanocrystals in an attempt to achieve a clear understanding of the afterglow mechanism of Eu2+-doped CaAl2O4. Undoped CaAl2O4 nanocrystals were obtained via solution combustion technique. Intense blue afterglow, which is quite similar to that of Eu2+-doped CaAl2O4, is observed with naked eyes for undoped CaAl2O4 regardless of no Eu2+ species in the phosphors. Based on density functional calculations, the electronic structures of oxygen-deficient CaAl2O4 are given, and the mechanism of the blue afterglow from undoped CaAl2O4 is discussed in terms of the oxygen vacancy introduced midgaps. The recorded blue afterglow from undoped CaAl2O4 nanocrystals leads to significant progress in our fundamental understanding of the afterglow mechanisms of Eu2+-doped CaAl2O4.

No abstract

Undoped SrAl2O4 nanocrystals were obtained via solution combustion using urea as fuel. The afterglow properties of undoped SrAl2O4 were investigated. Green afterglow from undoped SrAl2O4 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 SrAl2O4 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 SrAl2O4 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 SrAl2O4 and strontium-deficient SrAl2O4, respectively. Our results demonstrate that the green afterglow of undoped SrAl2O4 originates from the midgap states introduced by oxygen and strontium vacancies. The observation of green afterglow from undoped SrAl2O4 helps in gaining new insight in exploring the afterglow mechanisms of SrAl2O4-based afterglow materials.

No abstract