Modulation of Raman-Luminescence Thermometry Performance by Au Nanoparticles in PMMA Films Incorporating EuIII complexes

Conventional thermometers are limited in micro- and nanoscale environments, making Raman spectroscopy an attractive non-contact alternative for temperature sensing. In this work, Au nanoparticles (AuNPs) were incorporated into a PMMA film containing the Eu^III complex [Eu(btfa)₃(phen)] to enhance Raman-luminescence thermometry through localized surface plasmon resonance (LSPR). The AuNPs introduce an additional non-radiative deactivation pathway for the Eu^{III 5}D₀ excited state, reducing its lifetime from 0.737 to 0.665 ms at an optimal AuNP volume of 200 μL. This effect improves the temperature-dependent intensity ratio between the PMMA Raman band and the Eu^III luminescence emission, used as the thermometric parameter. Higher AuNP concentrations promote nanoparticle aggregation, weakening the LSPR effect and restoring the original lifetime. As a result, the maximum relative thermal sensitivity increases from 5.39% K⁻¹ in the AuNP-free film to 6.75% K⁻¹ with 200 μL of AuNP suspension, demonstrating that plasmon-assisted deactivation effectively enhances the performance of combined Raman-luminescence thermometers.