A Theoretical Investigation of Decay and Energy Transfer Rates and Efficiencies Near Gold Nanospheres

TL;DR

This theoretical study examines how gold nanospheres influence quantum emitter decay and energy transfer rates, revealing enhanced non-radiative decay and complex distance dependencies, with implications for nanoscale photonic applications.

Contribution

It provides a detailed theoretical analysis of decay and energy transfer near gold nanospheres, highlighting the effects on radiative and non-radiative rates and the distance dependence of energy transfer mechanisms.

Findings

Non-radiative decay rate is greatly enhanced near nanospheres.

Energy transfer exhibits a 1/r^6 F"orster regime with additional distance dependencies.

Largest F"orster radius occurs when donor emission is red-shifted from the plasmon peak.

Abstract

We consider the effect of Au nanospheres of subwavelength sizes on the decay and energy transfer rates of quantum systems placed in the proximity of these nanospheres. We find that, for the sphere sizes considered in this contribution, the radiative decay rate is barely affected by the presence of the nanosphere, whereas the non-radiative decay rate is greatly enhanced due to energy transfer from the quantum system to the nanosphere, leading to a strong quenching of the emission of the quantum system. The emission wavelength of the quantum emitter and its intrinsic quantum yield play an important role and the impact of both has to be considered together when investigating their effect on the non-radiative decay rate. The energy transfer process from the emitter to the nanosphere has a complicated distance dependence, with a 1/r^6 regime, characteristic of the F\"orster energy transfer mechanism, but also exhibiting other distance dependence regimes. In the case of a donor-acceptor pair in the presence of a Au nanosphere, the donor couples strongly to the nanosphere, acting as an enhanced dipole; the donor-acceptor energy transfer rate then follows a F\"orster trend, with an increased F\"orster radius. The angular dependence of the energy transfer efficiency between donor and acceptor has a strong dipole-dipole trend for small spheres and deviates from it for larger spheres, especially when the donor and acceptor are on opposite sides of the sphere. The spectral overlap of the donor emission, acceptor absorption and gold nanosphere extinction shows an interesting trend in that the largest F\"orster radius is obtained when the donor emission and acceptor absorption maxima are somewhat red-shifted from the localized surface plasmon peak in the extinction spectrum of the Au nanosphere, being located between it and the near-field scattering maximum.