Bidirectional Energy Transfer-Induced Suppression of Thermal Quenching in Nd³⁺ Codoped NaYF₄:Yb³⁺/Er³⁺ Nanoparticles

Thermal quenching, the decrease in up-conversion luminescence (UCL) intensity with rising temperature, severely limits the applications of rare-earth-doped materials in fields such as lighting, displays, and laser technology. This quenching exhibits pronounced susceptibility at high excitation power, presenting a significant challenge for high-power operation. In this study, Nd³⁺ ions were strategically doped into NaYF₄:Yb³⁺/Er³⁺ nanoparticles to efficiently suppress thermal quenching under relatively high excitation power. Notably, when a vacuum optical-tweezer platform was utilized to eliminate environmental interference, zero thermal quenching of luminescence was observed within a specific excitation power range, where the emission intensity remained nearly constant with increasing temperature. The observed suppression is attributed to the bidirectional energy transfer between Er³⁺ and Nd³⁺: At low power, Er³⁺ → Nd³⁺ transfer alleviates excited-state population saturation in Er³⁺ ions and thereby diminishes nonradiative losses. At high excitation power, Nd³⁺ → Er³⁺ reverse transfer dominates, replenishing Er³⁺ excited states and enhancing thermal stability. Power-dependent lifetime measurements confirm this mechanism, showing prolonged emission lifetimes in tridoped systems under high power. These results disclose the mechanism of thermal quenching and provide a novel concept for developing new luminescent materials with superior abnormal thermal quenching characteristics.