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 KM_1–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 KSr_1–xPO₄:Eu³⁺_x and KBa_1–xPO₄:Eu³⁺_x are 1.3 times and 1.1 times of that for commercial Y₂O₃:Eu³⁺, respectively.