Structure of whispering gallery mode spectrum of microspheres coated with fluorescent silicon quantum dots
Abstract
Whispering gallery modes (WGMs) in microspheres containing embedded fluorophores (e.g., organic dyes or quantum dots) may find refractometric sensing or microlasing applications. However, there have been relatively few investigations on the relationship between the intrinsic microsphere resonances and the WGMs observed in fluorescence spectra for emitters coupled to the microsphere.
Here we find that an apparently simple fluorescence WGM spectrum can mask a much more complicated underlying microcavity mode structure and that the observed fluorescence spectra are controlled by the emitter linewidth. By examining the cavity structure, we also verify that an effective ensemble emitter linewidth can be extracted from the fluorescence data.
Finally, spectral diffusion is suggested as a possible origin of the periodic fluorescence WGM spectra observed in many microsphere cavities, without which these resonances might be unobservable. (C) 2013 Optical Society of America