Physics of color centers

At the doping level of 1 mol%, Tb3+ doped CaAl2O4 (Tb–doped CaAl2O4) nanocrystals were synthesized via the sol–gel combustion technique. Green afterglow was recorded for the as–prepared Tb–doped CaAl2O4. The effects of subsequent annealing on the green afterglow of Tb–doped CaAl2O4 were investigated by means of X–ray diffractometry, scanning electron microscopy, transmission electron microscopy, photoluminescence spectroscopy, afterglow spectroscopy, and thermoluminescence dosimetry, respectively. Both the intensity and duration of the afterglow of Tb–doped CaAl2O4 are found to decrease with the increase in the annealing temperature when annealing temperature is lower than 600 °C. Afterglow of Tb–doped CaAl2O4 is completely quenched as annealing temperature is over 700 °C. In combination with annealing temperature dependent photoluminescence and thermoluminescence of Tb–doped CaAl2O4, our results indicate that the degradation of the afterglow can be linked to the oxidation of Tb3+ into Tb4+ at high annealing temperatures.