Enhanced fluorescence yields through cavity quantum-electrodynamic effects in microdroplets

Measurements of the integrated fluorescence yield per molecule of Rhodamine 6G (R6G) in 4–16-μm-diameter levitated microdroplets show a size dependence that is attributed to a net increase in the fluorescence decay rate for the smaller (4–5-μm) droplets. The average fluorescence yield in 4-μm droplets (for which we have previously observed emission-rate enhancement) is approximately a factor of 2 larger than the yield measured for larger droplets for which emission-rate enhancement does not occur. These results suggest that there is little emission-rate inhibition in this system, even though the fluorescence emission spectrum overlaps several cavity resonances. A mechanism based on spectral diffusion is postulated for the apparent absence of cavity-inhibited emission and is illustrated by Monte Carlo calculations using time-dependent line-shape functions.