Study the Effect of PH on Absorption and Fluorescence Spectra of Eosin Y Dye in Ethanol

The excitation wavelength (λex= 490 nm) at room temperature was determined to examine the impact of pH on the absorption and emission spectra of an eosin y compound dissolved in ethanol at a concentration of 1×10-5 M. The relative fluorescence intensity of eosin in ethanol at the concentration of 1×10-5 M was decreasing with the increasing of acidity (pH < 7) and the red shift of fluorescence was decreasing by adding a few drops of 1N solution of HCl, (pH normal = 7.26). However when a few droplets of NaOH were added, it was observed that the opposite, the relative fluorescence intensity was increasing with increasing basicity (pH > 7) and the red shift of fluorescence was decreasing with increasing basicity. Characteristics like fluorescence and absorption wavelength were further measured, along with graphical correlations like the one between pH and the relative fluorescence intensity. The relative fluorescence intensity of eosin in ethanol at the concentration of 1×10-5 M was decreasing with increasing acidity and the red shift of fluorescence was decreasing with increasing acidity (pH 7). However when a few droplets of NaOH were added, it was observed that the opposite was true: the relative fluorescence intensity was increasing with increasing basicity and the red shift of fluorescence was decreasing with increasing basicity.