Spontaneous and stimulated emission spectra of phthalimide solutions

An investigation was made of the spontaneous and stimulated emission spectra of phthalimide derivatives dissolved in a wide range of solvents at different temperatures. The electron level shifts resulting from different causes (change of the solvent or the temperature) and the corresponding shift of the stimulated emission spectra were observed in a fairly wide,but restricted part of the spectrum. Additional electron level shifts due to various factors suppressed stimulated emission in spite of otherwise favorable conditions (high quantum efficiency of the solutions and high-power excitation). The cause of this effect was determined by investigating experimentally the dependence of the stimulated radiation output on the frequency of the exciting light and the changes in the fluorescence spectra resulting from laser-radiation excitation. The experimental results indicated that induced absorption in the emission band region was the most likely cause of the suppression of the stimulated emission from phthalimide solutions as a result of the short-wavelength shift of the fluorescence spectra.