PHYSICAL REVIEW A 89, 063817 (2014) Spontaneous emission and energy transfer rates near a coated metallic cylinder Vasilios Karanikolas, Cristian A. Marocico, and A. Louise Bradley * Semiconductor Photonics Group, School of Physics and CRANN, Trinity College Dublin, College Green 2, Dublin, Ireland (Received 13 March 2014; published 19 June 2014) The spontaneous emission and energy transfer rates of quantum systems in proximity to a dielectrically coated metallic cylinder are investigated using a Green’s tensor formalism. The excitation of surface plasmon modes can signiﬁcantly modify these rates. The spontaneous emission and energy transfer rates are investigated as a function of the material and dimensions of the core and coating, as well as the emission wavelength of the donor. For the material of the core we consider gold and silver, whose surface plasmon wavelengths lie in the visible part of the electromagnetic spectrum. The spontaneous emission rate is enhanced by several orders of magnitude when the emission wavelength is close to the surface plasmon wavelength. The energy transfer rate enhancement is found to be concentrated in hot spots around the circumference of the coated cylinder. Introducing the energy transfer efﬁciency as a parameter, we ﬁnd that, when the donor emission and acceptor absorption spectra are resonant with the surface plasmon modes excited on the coated cylinder, the energy transfer efﬁciency can be signiﬁcantly enhanced compared to the off-resonance situation. Tuning the surface plasmon wavelength to the emission wavelength of the donor via the geometrical and material parameters of the coated cylinder allows, therefore, control of the energy transfer efﬁciency. DOI: 10.1103/PhysRevA.89.063817 PACS number(s): 33.80.−b, 42.50.−p, 73.20.Mf I. INTRODUCTION In 1946 Purcell showed that a quantum system’s intrinsic properties, such as its spontaneous emission (SE) or decay rate, can be modiﬁed by the presence of material bodies in its vicinity [1]. Various structures have been investigated with respect to their role in modifying the SE rate: planar dielectric and metallic interfaces [2–8], spheres [9–13], and dielectric and metallic cylinders [14–22]. The energy transfer (ET) rate between two quantum systems, donor and acceptor, can also be inﬂuenced by the environment. A variety of geometrical arrangements have been considered when investigating the ET rate, e.g., planar geometries [5,8,23,24], dielectric spheres [25–28], photonic crystals [29], microcavities [30–33], etc. These investigations have found that both enhancement and reduction of the ET rate can occur. In particular, the SE and ET rates can be dramatically enhanced when the quantum systems are placed in close proximity to metallic bodies, due to the possibility of exciting surface plasmon modes [34,35]. Surface plasmons (SPs) are collective oscillations of electrons and the electromagnetic ﬁeld that can be excited at the interface between a dielectric and a conductor. Depending on the size and shape of the dielectric and conducting bodies, the SPs can either propagate along the interface or be localized. The frequency at which SP modes can be excited depends on the geometrical and material characteristics of the bodies. The SE and ET rates have been studied extensively for cylindrical geometries during the past decade, the focus being mainly on the SE rate in the presence of dielectric and metallic cylinders. Furthermore, it has been shown that the ET rate between a pair of quantum emitters can be signiﬁcantly enhanced due to coupling to SP modes on a metallic cylinder [19,22]. It is also known that the presence * bradlel@tcd.ie of a metallic coating on a dielectric core can support SP modes [18]. The presence of the dielectric coating will modify the SP dispersion relations as a function of the thickness and refractive index of the coating. This will, in turn, modify the coupling of the quantum systems to the coated cylinder and offer a way to control the SE and ET rates through the optical and geometrical parameters of the dielectric coating. In this contribution we consider a metallic core coated with a dielectric layer and we investigate the inﬂuence of the SP modes on the SE and ET rates of quantum systems placed in proximity to the coated cylinder. These rates are calculated using a semianalytical Green’s tensor method [36,37]. A variety of quantum systems can be investigated this way, e.g., atoms, molecules, quantum dots, and ﬂuorescent dyes. The metallic core will be either Ag or Au, since the SP wavelength of these metals lies in the visible part of the electromag- netic spectrum, making them of signiﬁcant practical interest. Tabulated experimental data are used to describe the optical response of these materials [38]. Top-down techniques, e.g., electron-beam lithography, or bottom-up techniques, e.g., colloidal synthesis, can be used to fabricate hybrid nanostructures with dimensions of a few tens of nanometers. These structures form the building blocks for a variety of potential technological applications. Nanowires and coated nanowire structures can be used in light har- vesting [39,40] and switching devices [41], imaging [42,43], light conversion [43,44], cloaking [45,46], and quantum optics applications [47]. A good understanding of the SE and ET processes in these environments is important for manipulation of light below the diffraction limit. The paper is structured as follows. In Sec. II we present an outline of the formalism used, while in Sec. III the results of our simulations of the SE and ET rates are presented and discussed. Finally, Sec. IV is reserved for a summary of the results and the conclusions that can be drawn. In addition, the derivations of several expressions are given in two Appendices. 1050-2947/2014/89(6)/063817(13) 063817-1 ©2014 American Physical Society