Electronic structure and photoluminescence properties of Eu3+-activated KMPO4 (M = Sr, Ba)

The electronic structures of KMPO4 (M = Sr, Ba) were calculated by the density functional theory with the local-density approximation. The calculated result shows that KSrPO4 and KBaPO4 are direct-band gap materials with direct energy gaps of 4.52 and 4.35 eV, respectively. Meanwhile, by analyzing the valence band structures of KMPO4 (M = Sr, Ba), the strength of binding of valence band electrons of KBaPO4 is stronger than that of KSrPO4. In addition, the photoluminescence (PL) properties of the intense red-emitting phosphors KM1–xPO4:Eu3+x (M = Sr, Ba) were investigated. The PL emission spectra excited at 393 nm are dominated by the peak at 611 nm due to the forced electric dipole 5D0–7F2 transition of Eu3+ ions, which is attributed to low local symmetry sites occupied by Eu3+ ions in these hosts. And the optimum integrated intensities for KSr1–xPO4:Eu3+x and KBa1–xPO4:Eu3+x are 1.3 times and 1.1 times of that for commercial Y2O3:Eu3+, respectively.