Tuning size and up-conversion luminescence of CeO2:Yb3+/Er3+ nanoparticles through lanthanide doping

Abstract

Particle size is a critical parameter in up-conversion luminescence tuning and application research. In this study, CeO2:Yb3+/Er3+ nanospheres were synthesized via coprecipitation. The average size of these nanospheres gradually decreased as the Yb3+ doping concentration increased, which might be attributed to the influence of Yb3+ doping on the growth rate of nanospheres by surface charge repulsion. Upon exciting these nanospheres using a 980-nm laser, the corresponding up-conversion red-green emission intensity ratio gradually increased as the Yb3+ doping concentration increased, which might be ascribed to two reasons: the strengthened 4S3/2 → 4F9/2 nonradiative relaxation process and the enhanced Er3+ → Yb3+ energy back-transfer process. To assess the influence of the nonradiative relaxation process on the up-conversion emission red-green ratios, the down-conversion emission spectra and decay curves of CeO2:x%Yb3+/2%Er3+ nanospheres that were excited by a 520 nm laser were investigated. To validate how the particle size affects the up-conversion emission, CeO2:x%Lu3+/2%Yb3+/2%Er3+ nanospheres of various sizes were synthesized by substituting optically active Yb3+ using optically inert Lu3+. The corresponding up-conversion emission spectra and decay curves were investigated. The experimental results enhanced our understanding of how lanthanide doping affects the up-conversion luminescence tuning of Er3+, offering great potential to regulate the morphology and optical properties of the up-conversion luminescence nanoparticles.