Three pairs of dyes which operate as efficient energy transfer dye lasers in ethanol have been investigated to understand the dominant energy transfer mechanisms taking place in them. Special attention is given to the experimental configuration which is expected to influence the energy transfer rate constants over an order of magnitude or two. Fluorescence lifetimes have also been studied using time correlated single photon counting technique. It is found that apart from the excitation source and the concentration of dyes, the experimental configuration has a crucial role to play in determining the dominant energy transfer mechanism.

Rotation-free transmission measurements governed by ground-state recovery of coumarin 102, coumarin 138 and coumarin 339 dyes in ethanol solutions were performed for the first time by pump-probe technique using 35 ps pulses of Nd:YAG laser at 355 nm. Recovery of absorption is characterized by simple exponential behaviour with relaxation times of 4.0, 3.7 and 3.0 ns respectively for C 102, C 138 and C 339. These values are comparable to the lifetimes of the first excited singlet states.

The time-resolved laser emission of coumarin 102 was investigated in various aprotic and protic solvents at picosecond resolution by frequency upconversion technique. The spectral shift of the transient emission spectrum is attributed to solvent reorientation and the results are discussed.