Measurement of Vibrational Modes in Single SiO2 Nanoparticles Using a Tunable Metal Resonator with Optical Subwavelength Dimensions

Using a tunable optical subwavelength microcavity, we demonstrate controlled modification of the vibronic relaxation dynamics in a single SiO2 nanoparticle. By varying the distance between the cavity mirrors we change the electromagnetic field mode structure around a single nanoparticle and the radiative transition probability from the lowest vibronic level of the electronically excited state to the progression of phonon levels in the electronic ground state. We demonstrate redistribution of the photoluminescence spectrum between zero-phonon and phonon-assisted bands and modification of the excited state lifetime of the same individual SiO2 particle measured at different cavity lengths. By comparing the experimental data with a theoretical model, we extract the quantum yield of a single SiO2 nanoparticle.