Modification of radiative rates of molecules coated on a single microcavity by evanescent coupling of whispering gallery modes (WGMs)

Dye-coated single microspheres exhibit whispering gallery modes (WGMs) within the spontaneous emission bandwidth of the dye spectrum. These modes are extremely sensitive to the size, shape and the refractive index besides their coating thickness. Aden and Kerker theory has been used to simulate the WGMs. The effect of refractive index of the medium and the microsphere on WGMs has been studied. Variations are observed in the decay rates of the excited state with the size of the microspheres on varying the refractive index of the medium surrounding the microcavity. It is found that (i) the observed quality factors (Q-values) are smaller by several orders of magnitude than those expected theoretically and (ii) the radiative rates are enhanced for Q-values > 3 × 103.