Plasmon Enhancement of the Hot-Band Absorption-Assisted Anti- Stokes Photoluminescence of Near-Infrared Dyes

Plasmon enhancement of the hot-band absorption-assisted anti- Stokes photoluminescence is a nontrivial task because of the specific mechanism of electronic excitation of an emitter that occurs through population of its vibrational energy levels. Here, we compare the interaction of two related near-infrared dyes that possess the same chromophores and terminal groups but different meso-groups, with plasmonic silica-coated gold nanorods (Au@SiO2) and mesoporous silica-coated copper sulfide nanoparticles (Cu2-xS@MSN), respectively, whose near-infrared plasmon bands overlap with the emission band of the dyes. The dye-plasmonic nanoparticle interactions caused the changes in the anti-Stokes emission intensity, resulting from the superposition of the topological factor and the electromagnetic field effect brought by the nanoparticle. First, the emission properties of the dyes were dependent on whether the molecule interacts with the plasmonic particle via terminal sulfonic groups or the phenylamine meso-group. The interaction mediated by terminal groups led to the suppression of both Stokes and anti-Stokes emission due to topological distortion of the dye chromophore, while interaction mediated by the phenylamine meso-group influenced the shape of the emission band owing to the redistribution of electronic density in the dye chromophore. Second, the effect of the plasmon field on the anti-Stokes emission was identified as a function of the excitation wavelength, where an increase in the relative emission was observed upon approaching the surface plasmon resonance. Enhancement of the anti-Stokes emission by 17% upon interaction of the specific dye via its amino-group at the meso-position with Au@SiO2 and that by up to 50% upon interaction with Cu2-xS@MSN have been achieved.