Abstract

The influence of medium on the photophysical properties of a fluorinated coumarin (coumarin 485, C485) is studied in detail. The absorption and fluorescence characteristics of coumarin 485 dye doped poly(methyl methacrylate) modified with various additives (1,4-dioxane, chloroform, n-butyl acetate, acetonitrile and ethanol) are studied and the results are compared with the respective liquid mixtures. The fluorescence lifetime, fluorescence quantum yield, radiative and the non-radiative decay constants of C485 in polymer and corresponding monomer compositions are obtained. The gain characteristics of C485 in various modified poly(methyl methacrylate) (MPMMA) matrices are studied at various nitrogen laser powers in a transverse pumping configuration and the results are compared with the gain characteristics in the corresponding liquid mixtures. It is found that the gain of C485 in MPMMA increases with the increase in the dielectric constant of the medium while in the liquid medium, the reverse effect is observed. It is also found that the gain coefficient of C485 in a solid matrix shows 90% reduction when compared to the liquid medium. The photobleaching effect of this dye is also studied for a fixed nitrogen laser power and it is found that the photobleaching effect decreases with the increase in the dielectric constant of the medium. A significant improvement in the photostability was achieved from coumarin 485 doped PMMA modified with ethanol. The number of pumping pulses needed for 80% reduction of the initial output is 13 600 pulses for the input power of 10 kW and the repetition rate of 2 Hz.