MOLECULAR RADIATIVE TRANSPORT .2. MONTE-CARLO SIMULATION

The theory of radiative transport allows in principle the accurate cal culation of the fluorescence intensity and anisotropy decays. and of t he fluorescence spectrum and macroscopic quantum yield, under given co nditions. However, most of the coefficients of the theoretical express ions: are in general not amenable to analytic form, and even their num eric computation is quite difficult. Given the probabilistic nature of the underlying processes of absorption and emission. a Monte-Carlo (M C) simulation built upon the basic theoretical equations is particular ly well suited for the Cask. In this work, we discuss and carry out de tailed simulations for a realistic system (rhodamine 101 in ethanol) i n a finite three-dimensional volume that reproduces a common fluoresce nce cell. The two usual geometries of detection are considered: front face and right angle. The MC simulation method developed allows, for t he first time, the accurate calculation of the effect of radiative tra nsport on fluorescence intensity and anisotropy decays, time-resolved and steady-state spectra, ns;well as on the values of the macroscopic quantum yield and steady-state anisotropy. Because the spatial distrib ution of each generation of excited molecules can also be obtained wit h this method, a direct and clear picture of the spatial evolution of the excitation is also obtained. (C) 1996 American Institute of Physic s.