Synchrotron radiation spectroscopy of rare earth doped persistent luminescence materials

The electronic structure of the polycrystalline CaAl2O4:Eu2+,Ce3+ persistent luminescence materials were studied with X-ray absorption (XANES) and UV–VUV emission and excitation spectroscopy by using synchrotron radiation. Theoretical calculations using the density functional theory (DFT) were carried out simultaneously with the experimental work. The experimental band gap energy (Eg) value of 6.7 eV agrees very well with the DFT value of 6.4 eV. From the 4f7→4f65d1 excitation bands of Eu2+, the positions of the 4f7 ground as well as the 4f65d1 excited levels were established. The excitonic fine structure which could act as trap levels close to the bottom of the conduction band could not be observed, however. The different processes contributing to the mechanism of persistent luminescence from CaAl2O4:Eu2+ were constructed and discussed.