Optical Absorption of Dye Molecules in a Spherical Shell Geometry

Dipole–dipole interactions between neighboring dye molecules can cause substantial spectral changes in optical absorption, with a strong dependence on near-neighbors’ relative distances and orientations. Such effects have been previously investigated in dimers, as well as planar arrangements of dipoles, but not to our knowledge in a three-dimensional spherical configuration. This work provides a comprehensive exploration of the effect of dipolar interactions in such a geometry, varying the dye concentration, orientations, and uniformity in coverage. We also contrast this coupled-dipole model to a simpler but often-used homogeneous effective-medium approximation, which ignores effects of orientation and nonuniformity. The results provide a first step toward the full description of light scattering in a complex anisotropic core–shell geometry, which is of strong relevance in surface-enhanced spectroscopy applications, as well as in the strong coupling between molecular emitters and optical nanoresonators.