  Frequency shifts, radiative decay rates, the Ohmic loss contribution to the
nonradiative decay rates, fluorescence yields, and photobleaching of a
two-level atom radiating anywhere inside or outside a complex spherical
nanoshell, i.e. a stratified sphere consisting of alternating silica and gold
concentric spherical shells, are studied. The changes in the spectroscopic
properties of an atom interacting with complex nanoshells are significantly
enhanced, often more than two orders of magnitude, compared to the same atom
interacting with a homogeneous dielectric sphere. The detected fluorescence
intensity can be enhanced by 5 or more orders of magnitude. The changes
strongly depend on the nanoshell parameters and the atom position. When an atom
approaches a metal shell, decay rates are strongly enhanced yet fluorescence
exhibits a well-known quenching. Rather contra-intuitively, the Ohmic loss
contribution to the nonradiative decay rates for an atomic dipole within the
silica core of larger nanoshells may be decreasing when the silica core - inner
gold shell interface is approached. The quasistatic result that the radial
frequency shift in a close proximity of a spherical shell interface is
approximately twice as large as the tangential frequency shift appears to apply
also for complex nanoshells. Significantly modified spectroscopic properties
(see computer program (pending publication of this manuscript) freely available
at http://www.wave-scattering.com) can be observed in a broad band comprising
all (nonresonant) optical and near-infrared wavelengths.
