Electronic Structure of the $SrAl_2O_4$:$Eu^{2+}$ Persistent Luminescence Material

Abstract

he electronic structure of the strontium aluminate ($SrAl_{2}O_{4}:Eu^{2+}$) materials was studied with a combined experimental and theoretical approach. The UV-VUV synchrotron radiation was applied in the experimental study while the electronic structure of the non-optimized and optimized crystal structure were investigated theoretically by using the density functional theory. The structure of the valence and conduction bands as well as the band gap energy of the material together with the position of the $Eu^{2+} 4f^{7}$ $^{8}S_{7/2}$ ground state were calculated. The calculated band gap energy (6.4 eV) agreed well with the experimental value of 6.6 eV. The valence band consisted mainly of oxygen states whereas the bottom of the conduction band of strontium states. In agreement with the experimental results, the calculated $4f^{7}$ $^{8}S_{7/2}$ ground state of $Eu^{2+}$ lies in the energy gap of the host. The position of the $4f^{7}$ ground state depended on the Coulomb repulsion strength. The position of the $4f^{7}$ ground state with respect to the valence and conduction bands was discussed using theoretical and experimental evidence available