Interactions in Rare-Earth-Doped Nanoparticles: A Multi-Transition, Concentration, and Excitation Path Analysis

Understanding and modeling energy transfer mechanisms in rare-earth-doped nanomaterials are essential for advancing luminescent technologies used in bioimaging, optical thermometry, and solid-state lasers. In this work, we investigate the photoluminescence dynamics of Yb³⁺ and Er³⁺ ions in Y₂O₃ nanoparticles over a wide concentration range (0.5-17%), using both direct and up-conversion excitation. Luminescence decays of green, red, and near-infrared transitions were measured and analyzed using a single rate equation model incorporating radiative and non-radiative processes, energy transfer mechanisms, and defect-related quenching. Using specific measurements to determine each model parameter in a reliable way, we successfully reproduce experimental trends across most concentrations and excitation paths. This unified approach thus provides a sound and predictive framework for modeling energy transfer in rare-earth-doped materials and offers valuable insights for optimizing photoluminescent properties in nanostructured systems.