Phase evolution in Bi2O3:Yb3+/Er3+ nanoparticles with nearly single-band red upconversion luminescence

Abstract

Bi2O3:Yb3+/Er3+ nanoparticles with flower-like morphology were easily synthesized by urea-assisted coprecipitation reactions. The influences of calcination temperature and doping concentration on the crystal phase structures of Bi2O3 and Bi2O3:x%Yb3+/2%Er3+ (x = 0–30) were systematically investigated by XRD analysis. The experimental results revealed that lanthanide doping could effectively improve the thermal stability of Bi2O2CO3 samples, and the monoclinic-to-tetragonal-to-cubic phase transitions of Bi2O3 were implemented by controlling calcination temperatures and introducing smaller lanthanide ions (Ln3+) into the host lattices. Based on the analysis of TG and DSC curves, we found that the fundamental reason for this phase transition was the different stabilities of each crystalline phase under different doping conditions. Upon 980 nm laser excitation, Bi2O3:x%Yb3+/2%Er3+ samples presented near single-band red upconversion emission owing to the efficient energy reabsorption of the Bi2O3 host to Er3+ emission.