Whispering gallery modes in photoluminescence of ruthenium bipyridine in coated microcavities

We used the charge transfer (CT) complex of tris (2,2′ bipyridyl) dichloro ruthenium (II) hexahydrate (Ru(bpy)₃Cl₂.6H₂O) (RuCOM), well- characterised in water and in microcrystalline state, to dope or coat the microspheres and study the effect of whispering gallery modes (WGMs) on photoluminescence (PL) spectra and radiative lifetimes. Interestingly, in presence of dissipative quality factor, RuCOM broadens the WGMs when coated than when doped. Theoretical simulations for electric field for a coating of RuCOM on glass microspheres shows evanescent field extending in to the coated layer. The decay rates of RuCOM embedded or coated on microspheres are considerably different from the rates in crystalline RuCOM and the decay has an additional component of short lifetime. The enhancement of decay rate in small microcavities has been assigned to a weak Purcell's effect due to presence of microcrystals.