Decoding theSynergy-Competition of Plasmonic Fieldand Thermal Effects for Level-Selective Rare-Earth Luminescence

Abstract Surface plasmons modulate rare-earth luminescence via local field enhancement and photothermal effects, yet the synergy-competition between these inherently coupled effects remains to be decoded, impeding precise level-selective control. Herein, we construct a Yb3+, Er3+ upconversion system with different metals (Au/Ag nanoislands) and host morphologies (prism/plate), and combine steady-state spectroscopy, fluorescence lifetime dynamics, and multiphysics simulations to decode their interplay. We unveil pronounced level selectivity: the 2H11/2→4I15/2 transition is dominated by field enhancement, whereas the 4S3/2→4I15/2 and 4F9/2→4I15/2 transitions exhibit a synergy-competition between field enhancement and nonradiative processes. Ag nanoislands, owing to dense coverage, create strong near-field coupling that boosts 520 nm emission but simultaneously introduce additional nonradiative decay channels, limiting lifetime extension. Dispersed Au nanoparticles, by contrast, form weaker coupling that suppresses nonradiative losses, resulting in a markedly prolonged excited-state lifetime. Host morphology further governs the field–thermal balance: plate-like crystals realize tighter plasmon coupling and higher enhancement under single-wavelength excitation, yet their smaller volume and reduced heat capacity lead to more pronounced thermal quenching under dual-wavelength coexcitation. Prism-like crystals, benefiting from larger metal-ion separation and greater thermal mass, achieve superior net enhancement at 520 nm. Simulations corroborate the near-field and thermal origins of these behaviors. This work decodes the synergy-competition landscape, establishing a design framework for level-selective rare-earth luminescence and tunable photonic devices.