Mechanistic insights into energy transfer in highly doped upconversion nanoparticles

Highly doped upconversion nanoparticles (UCNPs) feature complex energy transfer dynamics that enable strong luminescence but also introduce significant challenges such as cross-relaxation and concentration quenching. This thesis presents a comprehensive investigation into the underlying mechanisms of energy transfer in highly doped UCNPs and explores strategies to enhance their upconversion luminescence (UCL). Cryogenic temperature conditions are employed to effectively suppress non-radiative losses in Er³⁺-rich systems, leading to pronounced luminescence enhancement. Additionally, modulation of cross-relaxation channels enables finely tuned temperature-dependent emission, allowing these materials to function as highly sensitive luminescent thermometers. To further improve excitation efficiency and mitigate photothermal effects, Er-rich systems are integrated with Nd³⁺ sensitization, enabling effective 808 nm excitation and enhanced UCL output compared to conventional 980 nm systems. Beyond mechanistic studies, the practical versatility of highly doped UCNPs is demonstrated in two light-driven systems: near-infrared-triggered photoclick reactions and optically powered rotary molecular motors. Together, these results provide deep mechanistic insights into lanthanide-doped nanomaterials and establish a versatile platform for next-generation UCNPs with enhanced performance in photochemistry, biomedical imaging, optical sensing, and nanoscale photonic applications.