Fig. 2: FRET determines R6G lasing.

a Absorption and emission spectra of DG and R6G show a strong overlap of DG emission and R6G absorption spectra, indicating good energy conservation. b Time-resolved fluorescence decay of DG in the absence (green) and presence (pink) of R6G. The shorter fluorescence lifetime of DG in the presence of R6G indicates FRET from DG to R6G. c Schematic illustration of energy transfer via FRET at the interface of the microcavity.