The photoluminescence of isolated and paired Bi ions in layered LnOCl crystals: a first-principles study.

Luminescent s centers have shown great potential for applications as phosphors and scintillators. First-principles calculations based on density functional theory are performed to systematically analyze the luminescent centers of isolated and paired Bi(6s) ions in layered LnOCl (Ln = Y, Gd, La) crystals. The spin-orbit coupling and orbital hybridization both show important effects on the luminescence properties. The luminescence of the isolated Bi ion is confirmed as the interconfigurational transition of P → S. For the Bi pair, the adiabatic potential energy surfaces are calculated and the charge transfer excited state is the most stable, which accounts for the visible emission of a large Stokes shift. Furthermore, the electron-hole pair separation, absorption, excitonic state and emission of the material with fully-concentrated Bi, BiOCl, are discussed. This study shows that the first-principles calculations can serve as an effective tool for the photoluminescence analysis and engineering of materials activated with isolated, paired and even fully-concentrated s ions.