[Resonance light scattering of rhodamine B]

The characteristic and mechanism of resonance light scattering (RLS) of Rhodamine B (RhB) were studied. In acidic solutions with pH from -0.38 to 4.10, the intensity of RLS increases with an increase in pH and reaches a maximum at nearly neutral pH. The change in RLS intensity with the wavelength was not accordant with Rayleigh scattering law. The fluorescence excitation and emission spectra of RhB overlap partly, and the RLS peak lies between the fluorescence excitation and emission peaks. In the three-dimensional fluorescence contour spectra of RhB, Rayleigh scattering line intersects fluorescence contour. In light polarization experiment, the polarization of RLS was measured to be P approximately = 0.1. All the above experimental facts reveal that the RLS of RhB is mainly resonance fluorescence. The mechanism of RLS enhancement by the increase in pH is that the formation of fluorescence species occurs in acid-base equilibrium. The RLS peak of RhB appears within the envelope of absorption, and light scattering is affected by light absorption, so, the relationship between RLS intensity and RhB concentration is not strictly linear.