Enhanced VK3+ center afterglow in MgAl2O4 by doping with Ce3+

Ceramic samples of Ce3+-doped and undoped MgAl2O4 have been prepared and studied. Persistent phosphorescence of lifetime longer than 10 h has been observed at 520 nm in the Ce3+-doped sample. We have identified the long persistence as arising from VK3+ centers in MgAl2O4. The VK3+ center is a hole trapped at a divalent site. The VK3+ emission results from the recombination of electrons from the conduction band with holes located at the VK3+ centers 2.4 eV below the MgAl2O4 conduction band. Thermoluminescence spectra of the two samples have also been studied. Thermoluminescence peaks in the undoped MgAl2O4 sample are found at 41°C (0.43 eV) and 238°C (0.92 eV), and have been identified as arising from an electron and a hole trap, respectively. Doping with Ce3+ leads to the formation of two additional thermoluminescence peaks, at 14°C (0.3 eV) and 131°C (0.45 eV), both related to electron traps. The Ce3+ ions greatly enhance the afterglow by increasing the population of trapped electrons and holes.