Fluorescence model for multi-layer papers using conventional spectrophotometers

We present an extension of a Kubelka-Munk based fluorescence model in which we introduce an apparent scattering (SUV) and absorption (KUV) coefficient for all wavelengths below 400 nm. We describe a method for modelling the total radiance factor of multi-layer papers and for estimating the optical parameters (S, K and Q) of each layer. Assuming that the fluorescent whitening agent only absorbs below 400 nm, we are able to determine SUV, KUV and the apparent quantum efficiency, Q(UV,l) for 400 nm<l<700 nm, from spectral radiance measurements in the visual part of the electromagnetic spectrum. We test the proposed method on different layered constructions made of three individual pilot paper layers. The proposed method allows the papermaker to determine the illumination independent fluorescence characteristics of single- and multilayer paper layers using a conventional single-monochromator spectrophotometer operating in the visible part of the electromagnetic spectrum, and also to predict the radiance factor of fluorescing layered papers.PaperOp