Molecular radiative transport. III. Experimental intensity decays

Abstract

A critical experimental test of a previously developed theory of molecular radiative transport is described. It is concluded that the theory gives an accurate description of the effect of radiative transport on fluorescence observables. The numerical coefficients of the fluorescence decay are computed from a Monte Carlo integration procedure that mimics the photon trajectories inside a realistic sample cell, and is carried out only using known molecular and geometrical parameters. The predicted parameters are confronted with the experimental observables accessible in a typical single-photon timing experiment, rhodamine 101 in ethanol being the system studied. The theoretical predictions quantitatively describe the effects of concentration and excitation and emission wavelengths experimentally observed in optical dense nondiffusing media for the two most common geometric arrangements: front-face and right-angle detection. It is shown that radiative transport leads to spatially heterogeneous fluorescence kinetics, as a direct consequence of the existence of a spatial distribution function of electronic excitation inside the sample cell. The agreement between theory and experimental results is good, with the average decay times predicted within ≃3% accuracy for front-face detection.