Application of the Kubelka—Munk Correction for Self-Absorption of Fluorescence Emission in Carmine Lake Paint Layers

Abstract

The variations of the fluorescence emission of carmine lake travelling through an absorbing and scattering medium, such as a paint layer, were investigated by ultraviolet (UV)-visible absorption, fluorescence spectroscopy, and imaging techniques. Samples of the lake were studied in dilute and saturated solutions, on a reference test panel and a real case study. Relevant spectral modifications have been observed as a function of the lake concentration mainly consisting of a fluorescence quenching, red shift of emission maxima, and deformation of emission band. The application of a correction factor based on the Kubelka-Munk model allowed fluorescence spectra obtained in solution and on painted samples of known composition to be compared and correlated, highlighting that the fluorescence of the lake within paint layers is affected by both self-absorption and aggregation phenomena. This approach has been successfully applied on a painting by G. Vasari for the noninvasive identification of carmine lake. The results reported here emphasize the necessity of taking physical phenomena into account in the interpretation of the fluorescence spectra for a proper and reliable characterization and identification of painting materials in works of art.

Synthesis of Pt/BiFeO3 heterostructured photocatalysts for highly efficient visible-light photocatalytic performances

“…With the increase of Pt loading, the SPR peak of Pt/BFO became broader and a little stronger due to a higher distribution of Pt nanoparticles on the surface of BFO. Moreover, based on these diffuse reflection spectra, the band gaps can be calculated from the plot of the KubelkaMunk function [16,43] ((αhν) 2 ) vs photon energy (hν)) for direct band gap semiconductors, as presented in the inset of Fig. 6.…”

Strong room-temperature blue-violet photoluminescence of multiferroic BaMnF4

“…Till now, the supposed self-absorption has been conformed rationally. Self-absorption is a common case for solid luminescent 7 materials, and has been researched for many years [31,[33][34][35][36][37]. In some solid state, physical phenomena such as multiple scattering and self-absorption of the emitted light may occur, leading to the distortion or split of the luminescence features, thus compromising the data interpretation [31,38].…”

A technical step forward in the integration of visible-induced luminescence imaging methods for the study of ancient polychromy

“…For madder lakes this is centred at c. 455-540 nm, depending on their preparation procedure [38], the blue LED (λ max = 465 nm) is an optimal excitation wavelength for these coloured species whilst avoiding the excitation of binders, varnishes or resins that preferentially absorb UV wavelengths. This not only increases the emission signal from the species of interest but the narrow emission band also minimises the effects of distortion of the emission features, such as self-absorption, multiple scattering and inner filter effects, produced by interference from other excited species [21,39,40]. Evidence of this can be seen by comparing the area of pink pigment under the belly of the duck in the UVL and VIVL (Lee No 21 filter) images of Terracotta A (Fig.…”

“…5b-d) record the colour information for the emitted luminescence in each case, as detected by the camera, but as discussed, the presence of stray light from the excitation source distorts the information and colour of the luminescence displayed in these images. Removal of the stray light can be carried out following previously published procedures, where the contribution of stray light on photo-induced luminescence images (ambient light, light emitted by other materials present in the room, parasitic light coming from the irradiation source), is appraised and taken into account by using the Spectralon ® 99% reflectance standard [15,24,39]. This yields images which are very similar in terms of the luminescence observed from the areas of pink/purple pigment.…”