Optical microcavities with at least one axis of symmetry give rise to trapped modes -known as whispering gallery modes (WGMs). WGMs possess high quality factor (Q) values and low mode volumes (Veff). WGM cavity also has an exponentially decaying evanescent field on its surface. This field is sensitive to the geometry of the cavity and the effective refractive index and can sense the external perturbations. When an emitter is coupled to the cavity, its radiative rate gets modified-an effect known as the ‘Purcell effect’. The metal nanoparticles (NPs), on the other hand exhibit localized surface plasmon resonances (LSPRs). LSPRs are the resonating collective oscillations of free electrons with the incident field. When coupled with the WGM cavity, the field strength of the hybrid cavity increases drastically to improve the Purcell effect. These effects are proposed to be studied in the hybrid system of gold NPs-dye doped single microcavities. In addition, the effect of the microcavity on the radiative rates of another nanosystem -fluorescent nanodiamonds (NDs) have also been attempted towards possible applications as a single-photon emitter.