Surface Plasmon Enhanced Photoluminescence of Carbon Dots Formed In Situ on Silver Gratings

We report the enhanced photoluminescence of carbon dots formed in situ on silver gratings via plasmonic reduction of a carbonaceous seed layer. This layer transforms into photoluminescent carbon dots in a non-oxygenated environment, catalyzed by surface plasmon polaritons (SPPs) excited on the grating by a pump laser, as monitored in real-time via Raman scattering. Pump SPPs subsequently excite the carbon dots, which emit at longer wavelengths into the local electromagnetic environment, which is dominated by SPPs propagating on and diffracting from the grating. We experimentally observe SPP-enhanced photoluminescence as a significant reduction in the lifetime of the emitters, and as induced coherence in far-field emission. Purcell factors of ∼70 are deduced from lifetimes of ∼30 ps for carbon dots measured using time-correlated single-photon counting. SPPs accelerate radiative decay and produce polarized directional free-space emission via grating diffraction, conferring characteristics of coherence to a random arrangement of luminescent carbon dots. A method for modeling an ensemble of random, incoherent emitters using finite-difference time-domain (FDTD) simulations is proposed, and the results agree with observed far-field images and measured Purcell factors. Our results provide insight into carbon dot - SPP interactions and have implications for cavity-enhanced biosensors, quantum emitters, and carbon-based light sources.