The temperature dependence of the fluorescence spectra of coumarin 2, coumarin 10 and coumarin 120 in ethyl alcohol is investigated. A blue-shift of the spectra with increase of temperature is observed. The blue-shift is explained by means of excited and ground Franck-Condon state parameters obtained by the adjustment of analytical shape factors to experimental spectra.
Cyclooctatetraene (COT) as a quencher o f fluorescence o f a series o f Rhodamine solutions was studied. The second order rate constants for the quenching process o f Rhodamine 110, Rhodamine 19 pchl., Rhodamine 6G pchl., R hodam ine 6G, Tetramethylrhodamine, Rhodamine B and Rhodamine 3B pchl. are given. It was found that COT enhances rather intersystem crossing than internal conversion.
The influence of cyclooctatetraene on the dye laser output energy was examined, It was shown that COT acts not only as a first triplet quencher but also effectively stimulates depopulation of higher triplet states. The importance of such a behaviour of COT in laser generation of a mixture of rhodamine -COT in ethanol is confirmed experimentally and theoretically, basing on the solution of a system of rate equations of a six level model of a dye laser.
The main assumptions of the quasi-molecule model of electronic spectra of liquid dye solutions are presented. The derived analytical expressions of the spectra account for the solvatochromic effects present in the solution. Based on the obtained spectral profiles of some coumarins in alcohol, new criteria for the validity of the mirror image rule are formulated.
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