Spontaneous emission of dye molecules as a function of the surrounding dielectric medium

We study the spontaneous emission of sulforhodamine B and sulforhodamine 101 molecules solved in water droplets (reversed micelles) that are stabilized by a surfactant and suspended in various mixtures of heptane and toluene. The experimental characterization includes measurements of absorption spectra, luminescence spectra and luminescence decay times. The various experimental results can be used to compute the radiative lifetimes of the dyes in the various solvents: (i) from the variation of the luminescence decay time, (ii) from the absorption spectra using the Strickler-Berg formula, and (iii) from the variation of the intensity of luminescence as a function of the luminescence decay time. An excellent agreement between the three methods is found for the sulforhodamine 101 molecule. For the sulforhodamine B molecule, all but the Strickler Berg formula agree very well.