Photophysical parameters and lasing properties of Coumarin 540A dye molecules are studied in solutions of increasing viscosity, from liquid solutions in 1,4-dioxane to solid solutions in poly͑methyl methacrylate͒. The fluorescence quantum yield and lasing efficiencies decrease as the viscosity of the solution increases, reflecting the strong influence of the rigidity of the medium on the radiative processes. The photodegradation mechanisms acting on the fluorophores are analyzed by following

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... dependence of laser induced fluorescence and laser output on the number of pump laser pulses. The fluorescence redistribution after pattern photobleaching technique is used, and Fick's second law is applied to study the diffusion of dye molecules in the highly viscous polymer solutions. The diffusion coefficients of the dye molecules as a function of the increased viscosity of the medium are determined.