Optical Quantum Yield in Plasmonic Nanowaveguide.

We have developed a theory of the quantum yield for plasmonic nanowaveguide made from an ensemble of a quantum dots layer as the cladding and a metallic nanoparticles layer as the core. The bound states of the confined probe photons in the plasmonic nanowaveguide are calculated using the transfer matrix method based on the Maxwell equations. It is shown that the number of bound states in the nanowaveguide depends on the dielectric properties of metallic nanoparticles. The probe field induces dipoles in quantum dots and metallic nanoparticles which interact with each other via the dipole-dipole interaction. The nonradiative decay linewidths due to dipole-dipole coupling are calculated using the quantum mechanical perturbation theory. An analytical expression of the quantum yield is obtained. We have predicted that the quantum yield decreases as the concertation of metallic nanoparticles increases. We have also calculated the photoluminescence of the nanowaveguide and found that the enhancement in photoluminescence is due to the surface plasmon polariton coupling with exactions. On the other hand, the quenching in the photoluminescence is due to the quantum yield which is inversely proportional to the nonradiative linewidth. Further, we have predicted that the nonradiative linewidth appearing in the quantum yield decreases as the width of the core in the plasmonic nanowaveguide increases. This is because the nonradiative linewidth directly depends on the density of states of bound photons and it decreases with the increase of the width. We also compared our theory with experiments of a nanowaveguide where the core is fabricated from Ag- nanoparticles and the cladding is fabricated from the perovskite quantum dots. A good agreement between theory and experiments is found. Our analytical expressions of the quantum yield and photoluminescence can be used by experimentalists to proforma new types of experiments and for inventing new types of nanosensors and nanoswitches.