Figure 1:

Schematic description of the effects of red-edge excitation on emission spectra. The term λ_c indicates excitation which is central in the last absorption band of the fluorophore. The term λ_R indicates excitation on the red edge of the absorption band. The solid lines represent the observed spectra, and the dashed lines represent the emission spectra of either the F or the R state. The dotted line represents a possible consequence of reverse relaxation (see the text).