Plasmon-enhanced up-conversion luminescence and oxygen vacancy defect-induced yellow light in annealed Cu₈S₅@SiO₂@Er₂O₃ nanocomposites

Monodispersed Cu₈S₅ nanoparticles were successfully synthesized by modified hot-injection method, and Cu₈S₅@SiO₂@Er₂O₃ core-shell particles were designed and prepared for up-conversion luminescence. Under the excitation of 980 nm laser, the local surface plasmon resonance of Cu₈S₅ nanoparticles coupled with annealed Er₂O₃ crystals to enhance the up-conversion luminescence of Cu₈S₅@SiO₂@Er₂O₃ nanocomposites in the green and red emission bands, compared with that of SiO₂@Er₂O₃ particles. After addition of Cu₈S₅ nanoparticles, the local near-field enhancement of Cu₈S₅@SiO₂@Er₂O₃ nanocomposites was ~36-folds stronger than that of annealed Er₂O₃ crystals under 980 nm incident light, indicating that Cu₈S₅ nanoparticles have excellent potential for enhancing the up-conversion luminescence of rare earth elements. The generation of yellow light at ~610 nm was attributed to oxygen vacancy defects in annealed Er₂O₃. The formation mechanism of oxygen vacancy defects in annealed Er₂O₃ was proposed and investigated. Furthermore, the mechanism of up-conversion luminescence of Cu₈S₅@SiO₂@Er₂O₃ composites and the electronic band structure of annealed Er₂O₃ crystals were also discussed.