Molecular radiative transport. III. Experimental intensity decays

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 o bservables. The numerical coefficients of the fluorescence decay are comput ed from a Monte Carlo integration procedure that mimics the photon trajecto ries inside a realistic sample cell, and is carried out only using known mo lecular and geometrical parameters. The predicted parameters are confronted with the experimental observables accessible in a typical single-photon ti ming experiment, rhodamine 101 in ethanol being the system studied. The the oretical predictions quantitatively describe the effects of concentration a nd excitation and emission wavelengths experimentally observed in optical d ense nondiffusing media for the two most common geometric arrangements: fro nt-face and right-angle detection. It is shown that radiative transport lea ds to spatially heterogeneous fluorescence kinetics, as a direct consequenc e of the existence of a spatial distribution function of electronic excitat ion inside the sample cell. The agreement between theory and experimental r esults is good, with the average decay times predicted within similar or eq ual to 3% accuracy for front-face detection. (C) 1999 American Institute of Physics. [S0021-9606(99)00202-0].