Abstract
We perform Monte Carlo light scattering simulations to study the angular distribution of the fluorescence emission from turbid media and compare the results to measured angular distributions from fluorescing white paper samples. The angular distribution of fluorescence emission is significantly depending on the concentration of fluorophores. The simulations show also a dependence on the angle of incidence that is however not as evident in the measurements. A detailed analysis of the factors affecting this angular distribution indicates that it is strongly correlated to the mean depth of the fluorescence process. The findings can find applications in fluorescence spectroscopy and are of particular interest when optimizing the impact of fluorescence on e.g. the appearance of paper as the measured values are angle dependent.
Highlights
Fluorescent dyes are widely used to improve or affect the appearance of textiles and paper products
In order to study the impact of fluorophore concentration on the angular distribution of the fluorescence emission, we measure the angle-resolved radiance in the emission wavelength band of paper samples of different fluorescent whiteness agents (FWAs) concentrations when illuminated with monochromatic UV excitation at two different angles of incidence
We have measured the angular distribution of the fluorescence from paper samples with different amount of fluorescing whitening agents (FWA)
Summary
Fluorescent dyes are widely used to improve or affect the appearance of textiles and paper products. Daylight fluors are typically used for attention-grabbing applications, whereas a special type of fluorescent dyes is used to increase the whiteness of paper and textiles. These dyes are referred to as fluorescent whiteness agents (FWAs) or optical brightening agents (OBAs). In order to predict the appearance in different illuminations, bispectral radiance data relating spectral radiance to individual excitation wavelengths is required. This matrix of bispectral radiance factors is known as the Donaldson matrix [2] and can be determined with the double monochromator method [3, 4]. Extension to other measuring geometries or viewing environments relies on the assumption of a Lambertian distribution of the luminescent radiance factor
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