Cationic interactions in flame photometry were investigated to study some of the factors that cause enhancements of spectral lines. Interactions of the alkali and alkaline earth metals in an oxygen-acetylene flame have indicated that several mechanisms may be responsible for enhancement. Where conditions are proper, enhancements of emissions of cations may be a combination of at least three factors. a) the effect of electron concentration from an easily ionized extraneous element on the ground state population of the test element, b) the effect of transfer of energy by radiation and c) the effect of transfer of energy due to collisions with excited atoms The effect of the electron concentration on the suppression of the ionization of the test element was the predominant mechanism by which enhancement occurred in most systems studied. However, in the study of the effect of potassium on rubidium direct evidence was obtained of excitation by transfer of radiant energy Indirect evidence of enhancement due to transfer of energy by collision also was observed in the same system.
Russell W. Johnson and W. G. Schrenk, "Mechanisms of Interactions of Alkali and Alkaline Earth Elements in Flame Photometry," Appl. Spectrosc. 18, 144-148 (1964)