Near-IR Emission and upconversion luminescent properties of Tb3+/Yb3+ Co-doped HfO2/SiO2 nanoparticles

The luminescent characteristics of spherical hafnia/silica (HfO₂/SiO₂) nanoparticles (NP?s) co-doped with Tb³⁺/Yb³⁺ were analysed. These NP?s were synthesized using the spray pyrolysis technique. The addition of SiO₂ and Tb³⁺/Yb³⁺ was found to induce a cubic phase in HfO₂. The luminescent spectra presented the characteristic emission peaks for inter-electronic energy levels transitions of the Tb³⁺ and Yb³⁺ ions, with an excitation band centred at 270 nm. Under solid-state laser excitation at 980 nm an upconversion emission related to the Tb³⁺ ion was observed. The maximum emission peak in the visible region was at 543 nm, associated with ⁵D₄ → ⁷F₅ transitions of the Tb³⁺ ions and an IR emission peak at 970 nm (²F_5/2 → ²F_7/2) pertaining to Yb³⁺, with irradiation at 270 nm (UV). The energy transfer mechanism from Tb³⁺→Yb³⁺ (excitation at 270 nm), is discussed based on the time decay of the luminescence intensity analysis and the energy transfer efficiency (η_ET) and was determined to be in the range of 29.2% to40.8%.