The effect of varying concentrations on the photophysical properties of the laser dye Rhodamine B (RB) in ethanol was studied both experimentally and theoretically. The fluorescence spectrum of these concentrations (1 × 10–2, 1 × 10–3, 1 × 10–4 and 1 × 10–5mol/litre) was taken experimentally. Pure tuning of RB in ethanol was obtained. Red shifting of about 20 nm to longer wavelengths was achieved by varying the concentration from 1 × 10–5 mol/litre to 1 × 10–2 mol/litre. The theoretical modelling equation for the effect of concentration on the fluorescence spectrum of RB solution in ethanol was achieved using the program Table Curve 2D, version 5.01. The best theoretical equation for the concentration profile was the Gauss mod function reported in the following equation:
|y = a + b * exp (-5 * (lx-cl/d)e)|
The equation was applied to two concentration profiles, 0.5 × 10–3 and 0.5 × 10–4 mol/litre. The experimental fluorescence spectrum of RB in ethanol was plotted against the theoretical fluorescence spectrum. There is good consistency between the behaviour of the experimental and theoretical fluorescence spectra, specifically for intensity and wavelength fluorescence. This equation allows us to plot the fluorescence spectrum for any concentration of RB in ethanol that was not measured experimentally.