Probing Plasmon Induced Cooling in Fluorophore-Plasmonic Systems using Raman Thermometry.
Surface-enhanced Raman spectroscopy (SERS) is a method that allows for up to one billion times enhancement of the otherwise weak phenomena of Raman scattering. We see this increase in scattering due to the use of plasmonic materials, which utilize localized surface plasmon resonance (LSPR), leading to the concentration of electromagnetic radiation into plasmonic “hot spots.” Using SERS and Raman thermometry, we probe the effective temperatures, a quantification of the vibrational energy of Raman-active modes using a Boltzmann distribution, of molecules adsorbed to gold nanoparticle aggregates. Specifically, we examine the effective temperature of plasmonic-fluorophore systems, which undergo an unforeseen mechanism. We observe up to a 100K decrease in the effective temperature of various fluorophore molecules under resonant CW excitation compared to room temperature. We see this plasmonic “cooling” effect regardless of vibrational mode selection and solvating environment. Our work provides new insight into plasmonic-molecular interactions and provides an initial investigation of this occurrence.