Plasmon-enhanced up-conversion luminescence in multiple Cu2-xS@SiO2-embedded Er(OH)CO3 composites

Abstract Cu2-xS nanocrystals have great potential to enhance the up-conversion luminescence of rare earth materials. In this work, monodispersed Cu2-xS (Cu8S5 and Cu9S5) nanocrystals and Cu2-xS@SiO2 composited nanoparticles were synthesized by the hot-injection method and reverse micro-emulsion method, respectively. A more efficient semiconductor based plasmonic hybrid structure that Er(OH)CO3 was embedded with multiple Cu2-xS@SiO2 nanoparticles was prepared. Hotspots between Cu2-xS@SiO2 composited nanoparticles were constructed and employed to enhance the excitation photon absorption in Er(OH)CO3. Under the excitation of 980 nm light, due to the localized surface plasmon resonance (LSPR) characters of Cu2-xS nanoparticles, the UC luminescence of the multiple Cu2-xS@SiO2-embedded Er(OH)CO3 composites was obviously enhanced in both the green and red emission bands compared with that of the SiO2@Er(OH)CO3 particles. The UC fluorescence intensity of Cu8S5@SiO2 and Cu9S5@SiO2-embedded Er(OH)CO3 was increased by 45.0 and 15.2 times, compared with that of SiO2@Er(OH)CO3, respectively. We provide a clear experimental evidence that proves that the UC luminescence properties of rare earth doped phosphors are significantly reinforced by engineering localized surface plasmon resonances of Cu2-xS based plasmonic semiconductors. Finite-difference time-domain (FDTD) calculations were carried out and confirmed the effect of the reinforcement of the excitation light field. The UC enhancement mechanisms based on Cu2-xS based plasmonic semiconductor structures were discussed.