Synthesis and Upconversion Luminescence Fine-tuning of Yb/Ho-Doped Indium and Gallium Oxide Nanoparticles.

Rare earth (RE) dopants can modulate the bandgap of oxides of indium and gallium and provide extra upconversion luminescence (UCL) abilities. However, relevant UCL fine-tuning strategies and energy mechanisms have been less studied. In this research, InGaO, Ho monodoped and Yb/Ho codoped InO, and Ho monodoped YbGaO nanoparticles (NPs) were synthesized by a solvothermal method. The effects of Yb and Ho dopants on the crystal structures, UCL properties, and optical bandgaps of the oxides were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UCL spectroscopy, and measurements of decay times, pump power dependence, and transmittance spectra. The crystal structures of oxide products of indium and gallium were significantly modified with RE dopants. InO and YbGaO were selected as the host materials. For Yb/Ho codoped InO NPs, there existed energy transfers from the defect states of InO to Ho and from Yb to Ho. With a fixed Ho concentration, InO:0%Yb,2%Ho NPs showed the optimal UCL properties mainly due to InO-Ho energy transfer and Ho-Yb energy-back-transfer, while with a fixed Yb concentration, InO:5%Yb,3%Ho NPs with a slight YbO impurity and YbGaO:2%Ho NPs did mainly due to Ho-Ho cross-relaxation. Besides, the optical bandgaps of InO and YbGaO were noticeably broadened with RE dopants. These findings can offer feasible directions for the synthesis and UCL fine-tuning of RE-doped oxides of indium and gallium and improve their multifunction application prospects in the fields of semiconductor and UCL nanomaterials.