Eu +3 5 D Resonance Quenching to the Charge-Transfer States in Y2O2S, La2O2S, and LaOCl

Abstract

The ${}^{5}D$ emissions of Eu³⁺ in Y₂O₂S, La₂O₂S, and LaOCl quench sequentially with increasing temperature in the simple order ${}^5{D}_3{,}^5{D}_2{,}^5{D}_1{,}^5{D}_0$ . These ${}^{5}D$ quenchings are attributed to thermally activated resonance crossovers from the ${}^{5}D$ states to the charge‐transfer states (CTS). The activation energies for the ${}^{5}D$ quenching place the CTS relative to the ${}^{5}D$ states. The ${}^7\mathrm{F\to }\mathrm{CTS}$ absorption bands also place the CTS relative to the ${}^{7}F$ states. The agreement between these two independent CTS placements supports the model of ${}^5\mathrm{D-}\mathrm{CTS}$ resonance transitions. Thermally activated ${}^5\mathrm{D\to }\mathrm{CTS}$ crossovers also account for the two‐step ${}^5{D}_2$ quenching observed in LaOCl and La₂O₂S.