Visible upconversion of erbium oxide and their correlation with crystalline defects

Abstract

We present the synthesis of erbium oxide (Er2O3) by chemical bath deposition technique at ~ 60 ± 2 °C for a prolonged period of 60 hr and subsequently thermally treated at ~1000 °C in an air atmosphere. The morphology of samples is analyzed by Scanning Electron Microscopy. The crystalline phase is explored by X-Ray Diffraction, identifying the cubic-bixyite phase of Er2O3 and grain size that ranges between ~7.9 nm to ~10.9 nm. The calculated bandgap energy is found of ~4.5 eV and ~3.8 eV when using the Tauc equation and the Effective mass approximation model, respectively. We consider that vacancies, interstices, grain boundaries, and stacking faults present a corpuscular behavior. In this regard, the Maxwell-Boltzmann statistics is applied as an original approach considering the crystalline native defects associated with vacancies and interstices. We discuss the photoluminescence dependence with the trap density and the surface recombination velocity in the light of the Maxwell-Boltzmann theoretical results associated with the electronic transitions related to the native intrinsic defects situated at the Vis-region. The photoluminescence spectrum shows two strong emission bands in Vis-region that correspond to 4S3/2 and 4I15/2 electronic transitions. Upconversion-emission consists of blue, green, and weak red bands originated from the 4 f→4 f intra-transitions.