Molecular radiative transport. II. Monte-Carlo simulation

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Abstract
The theory of radiative transport allows in principle the accurate calculation of the fluorescence intensity and anisotropy decays, and of the fluorescence spectrum and macroscopic quantum yield, under given conditions. However, most of the coefficients of the theoretical expressions are in general not amenable to analytic form, and even their numeric computation is quite difficult. Given the probabilistic nature of the underlying processes of absorption and emission, a Monte-Carlo (MC) simulation built upon the basic theoretical equations is particularly well suited for the task. In this work, we discuss and carry out detailed simulations for a realistic system (rhodamine 101 in ethanol) in a finite three-dimensional volume that reproduces a common fluorescence cell. The two usual geometries of detection are considered: front face and right angle. The MC simulation method developed allows, for the first time, the accurate calculation of the effect of radiative transport on fluorescence intensity and anisotropy decays, time-resolved and steady-state spectra, as well as on the values of the macroscopic quantum yield and steady-state anisotropy. Because the spatial distribution of each generation of excited molecules can also be obtained with this method, a direct and clear picture of the spatial evolution of the excitation is also obtained.