The visual examination of works of art relies on the careful choice of both filtered UV-illumination and high-sensitivity color camera, providing a method for conservators to detect materials which may not be visible under normal lighting conditions. Typically, proper UV excitation is obtained with low-pressure UV lamps shielded with UV filters for suppressing the visible emission from the lighting devices; in these conditions, digital and analogue photography can provide spectacular images, as has recently been demonstrated during the analysis of wall paintings by Giotto in the Peruzzi Chapel (in the Basilica of Santa Croce, Florence, Italy) [11], where traces of original organic materials employed for paint and for gilding were revealed for the first time.

Many applications in the examination of works of art require the analysis of more quantitative parameters of the emission, including the emission spectrum of a material which reflects its chemical composition. The modification of the fluorescence of organic materials has been reported and related to general and more specific molecular changes, including those related to oxidation phenomena: for example, the photooxidation of protein-based binders [12], oils and varnishes [2], or the oxidation of modern polymers and plastics [13]. It is recognized, however, that the discrimination of materials on the basis of fluorescence spectra is often impossible��subtle spectral differences, which may arise from chemical modifications of materials or differences in molecular properties, may be masked by competing effects, auto-absorption phenomena [14], or scattering [15], for example.

Fluorescence emissions may also be weak and thus spectra may be difficult to detect.1.2. Time-Resolved PhotoluminescenceIn addition to the emission spectrum recorded from the surface of an object, the dynamics of the fluorescence, or luminescence, emission can be useful in the analysis and monitoring of cultural heritage and cultural heritage materials, which is the focus of the analysis presented in this article.In simple terms, the emission process consists of the radiative decay from excited states of the chromophore. The emission lifetime can be interpreted as the average time the fluorophore stays in the excited state and hence provides information on the emission dynamics [16]. AV-951 According to the nature of the excited state (singlet or triplet state) the lifetime can be extremely different varying from ps to ms. In the first case we generally refer to the emission process as fluorescence, while in the second case as phosphorescence. Both phenomena are generally summarized under the term luminescence.