Spontaneous and stimulated emission from dyes. Spectroscopy of the neutral molecules of acridine orange, proflavine, and rhodamine B

The absorption and fluorescence spectra of acridine orange, proflavine, and rhodamine B have been studied with particular attention being paid to the acid-base properties of these dyes in polar and non-polar solvents. These studies show that the neutral acridine dyes do not form dimers but they are readily protonated even in non-polar solvents due to traces of water which are difficult to remove. Attempts to achieve laser emission form the acridine dyes were unsuccessful, probably because of their low fluorescence quantum yields. Suggestions are made for optimizing the laser efficiency of rhodamine B in various alcohol solutions at low temperatures.