The optimum concentration technique for increasing the intensity of the Raman spectrum of a colored substance has been considered in detail. Intensity-concentration data are given for a number of Raman lines. An optimum concentration for a maximum in observed Raman intensity is shown to exist for each of the Raman lines examined. An expression has been derived relating the observed Raman intensity with the molar concentration of a solution of absorbing substance in a transparent solvent by consideration of the absorption of both the exciting radiation and the scattered radiation. The agreement between the theoretical curves and the experimental points is good. More experimental data are necessary to check further the theoretical expression. The best technique for obtaining the Raman spectra of colored substances is to use excitation radiation which will not be absorbed and which will not cause photochemical decomposition. When light sources which emit such radiation are not available, the optimum-concentration technique has been shown to be a possible alternative method for obtaining a Raman spectrum.
ELLIS R. LIPPINCOTT, JOHN P. SIBILIA, and ROBERT D. FISHER, "Optimum Concentration Effect in Raman Spectroscopy," J. Opt. Soc. Am. 49, 83-89 (1959)