Spectroscopic study of chromophores in ancient HIMT glass

We have studied a series of Late Roman glass fragments belonging to the peculiar group called HIMT (High Iron Magnesium Titanium glass), characterized by different color nuances, and previously chemically characterized [1-3]. XANES, UV-VIS and luminescence spectroscopies [4-6] are exploited for determining the distribution of the oxidation states of the two chromophores Fe and Mn in the ancient finds and in two synthetic glass specifically prepared with selected chemically compositions. Fe and Mn K-edge XANES spectra were collected in fluorescence mode at the GILDA-CRG beamline (ESRF, Grenoble, France). A dynamically and sagittally focussing monochromator with Si (311) crystals was used. Energy calibrations were achieved using Fe and Mn foils as references and the position of the first inflection point was taken at 7112.0 and 6538.0 eV respectively. The pre-edge region was extracted from the normalized spectra and analysed by least-square fitting of pseudo-Voight functions of equal width to the pre-edge spectral envelope. For each sample, the pre-edge centroid was calculated from the average position of the pseudo-Voigt functions, weighted by their respective integrated areas. UV-VIS absorption spectra were measured on a Varian Cary 100 double-beam spectrophotometer operated between 900 and 200 nm. Luminescence emission and excitation spectra were collected in a Spex Jobin-Yvon FluoroMax3 spectrofluorometer. On the basis of both XANES and UV-VIS results, in all the ancient glass samples Fe results to be mostly in its oxidate state 3+. XANES data indicate that the prevalent Mn oxidation state is 2+, however the presence of minor amounts of Mn3+ has been proved by UV-VIS and luminescence spectroscopy. The different spectroscopic techniques, used in a combined approach, are able to interpret the apparent anomalous colour of some of the ancient glass samples.