Synthesis and Upconversion Luminescence Fine-tuning of Yb3+/Ho3+-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 3+ monodoped and Yb 3+ /Ho 3+ codoped In 2 O 3, and Ho 3+ monodoped Yb 3 Ga 5 O 12 nanoparticles (NPs) were synthesized by a solvothermal method. The effects of Yb 3+ and Ho 3+ 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. In 2 O 3 and Yb 3 Ga 5 O 12 were selected as the host materials. For Yb 3+ /Ho 3+ codoped In 2 O 3 NPs, there existed energy transfers from the defect states of In 2 O 3 to Ho 3+ and from Yb 3+ to Ho 3+ . With a fixed Ho 3+ concentration, In 2 O 3:0%Yb 3+,2%Ho 3+ NPs showed the optimal UCL properties mainly due to In 2 O 3 –Ho 3+ energy transfer and Ho 3+ –Yb 3+ energy-back-transfer, while with a fixed Yb 3+ concentration, In 2 O 3:5%Yb 3+,3%Ho 3+ NPs with a slight Yb 2 O 3 impurity and Yb 3 Ga 5 O 12:2%Ho 3+ NPs did mainly due to Ho 3+ –Ho 3+ cross-relaxation. Besides, the optical bandgaps of In 2 O 3 and Yb 3 Ga 5 O 12 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.