3.1.2. LuminesceFig. 3A compares the emission features of the uncoated andcoated paper sheets under UV excitation. For all of them, the spectra displayed a main broad band with two components peakingaround 430 nm, attributed to the optical brighteners agents present in the paper sheets. For the FITC–CH-coated sheets, an additional emission band peaking at higher wavelengths was detected.This coating-related emission was in tune with that of the fluores-cein moiety, known to occur around 510–540 nm (Guan et al.,2007). Increasing the excitation wavelength from 350 to 500 nm(Fig. 3B), no change in the energy of the emission bands was mea-sured, but only an enhancement in the relative intensity of thehigh-wavelength component. As the number of FITC–CH depositedlayers increased from 1 to 5, the fluorescein-related emissionexhibited a bathochromic shift from 531 nm to 538 nm (Figs 3Aand B), attributed to the increase in the fluorescein concentration,as already observed for other dye compounds (Anedda et al., 2005;Canham, 1993)