(328b) Cation Effect to the Luminescence Performance and Temperature Sensitivity of Rare-Earth Doped Complex Metal Oxide

Rare earth (RE) based phosphor materials are widely used as luminescent probes in high temperature optical thermometry where the traditional contact thermometers are unsuitable. The current generation of luminescent thermometers, such as Y stabilized ZrO₂ and NaYF₄, lack stability and energy transport within the working temperature ranges. As such, the challenge is to develop an oxide-based material with high luminescence intensity and thermal sensitivity/stability, which is suitable for an optical temperature sensor/thermal barrier coating. The goal for this work is to develop a fundamental understanding of the local environment surrounding RE dopants in metal oxide hosts to engineer their luminescence property. To maximize the luminescence, local symmetry, doping concentration, and radiative/non-radiative relaxation pathways need to be simultaneously optimized. This interaction between the dopant ions and host matrices, and the resulting impact on the luminescent signal, is the focus of this work and is critical for engineering the application dependent luminescent properties.

In this work, Sc³⁺ is substituted in RE doped Y₂O₃ lattices to generate smaller cation sites, enhancing the crystal field, and modifying the allowed optical transitions. Er³⁺ is used as a photoluminescent probe to study the effect of site position and symmetry on the upcpnversion (UC) performance. In comparison with traditional hydrothermal method, Sc³⁺ is successfully incorporated into Y₂O₃ lattice via the co-precipitation/molten salt method without segregating observed. The doping improved UC luminescent efficiency, stemming from the decreased site symmetry found in the YScO hosts due to Er preferential occupancy at the C₂ sites. Meanwhile, the YScO oxide was found to significantly improve the luminescence intensity and red-to-green ratio at a lower Yb³⁺ concentration (5 mol%) instead of a higher concentration (20 mol%) commonly used. This was attributed to an increased energy transfer between the closer Yb³⁺-Er³⁺ pairs. Next, same host materials were doped with Eu³⁺ to develop high performance optical thermometry at high temperature. It was found that the sensitivity was affect by both host crystal structure and phonon energy. Phonon energy determines the possibility of the temperature dependent transitions, while the crystal structure is applied to estimate the temperature sensitivity. It was found that the Judd-Ofelt parameters, calculated based on Er³⁺ excitation, can be used to estimate the absolute sensitivity of Eu³⁺ doped YScO NPs. The Ω₂ values from Judd-Ofelt analysis and asymmetry ratio based on Eu magnetic dipole (MD) and electric dipole (ED) transitions follow a similar trend as the Sc concentration increasing. This work reveals the application of Judd-Ofelt analysis of other RE ion in predicting the temperature sensitivity of Eu doped materials based on the hypersensitive transitions.