Mario Piacentini

Photostimulated desorption studies on potassium iodide

Abstract In this work we present the results of photostimulated desorption measurements obtained on KI under excitation in the fundamental absorption region. Yield curves of both potassium and iodine desorbed atoms are reported at several sample temperatures. We discuss the experimental results in terms of the optical constants and of the production efficiency of F and H centers in KI.

Spectral Behavior of White Pigment Mixtures Using Reflectance, Ultraviolet—Fluorescence Spectroscopy, and Multispectral Imaging

Reflectance spectroscopy, ultraviolet (UV)—fluorescence spectroscopy, and multispectral imaging have been widely employed for pigment identification on paintings. From ancient times to the present, lead white, zinc white, and titanium white have been the most important white pigments used for paintings and they are used as pigment markers for dating a work of art. The spectral behavior of these pigments is reported in several scientific papers and websites, but those of their mixtures are quite unknown. We present a combined nondestructive approach for identifying mixtures of lead white, zinc white, and titanium white as powder and dispersed in two different binder media (egg yolk and linseed oil) by using reflectance spectroscopy, spectrofluorimetry, multispectral reflectance and UV-fluorescence imaging. We propose a novel approach for mapping the presence of white pigments in paintings by false color images obtained from multispectral reflectance and UV-fluorescence images. We found that the presence of lead white mixed with either zinc white or titanium white is highly detectable. Zinc white mixed with lead white or titanium white can be identified due to its UV-fluorescence emission, whereas titanium white in association with lead white or zinc white is distinguishable by its reflectance spectral features. In most cases, the UV-fluorescence analyses also permit the recognition of the binder media in which the pigments are dispersed.

Application of near infrared spectroscopy (NIR), X-ray fluorescence (XRF) and chemometrics to the differentiation of marmora samples from the Mediterranean basin

Abstract Near-infrared (NIR) and X-ray fluorescence spectra were recorded for 15 different samples of marmora, from the Mediterranean Basin and of different colours. After appropriate pretreatment (SNV transform + second derivative), the results were subjected to principal component analysis (PCA) treatment with a view to differentiating them. The observed differences among the samples were chemically interpreted by highlighting the NIR wavelengths and minerals, respectively, contributing the most to the PCA models. Moreover, a mid-level data fusion protocol allowed integrating the information from the different techniques and, in particular, to correctly identify (based on the distance in the score space) three test samples of known type. Moreover, it should be stressed that positive results on the differentiation and identification of marmora were obtained using two completely non-invasive, non-destructive and relatively inexpensive techniques, which can also be used in situ.

Delayed emission in photon stimulated desorption of alkali halides

Abstract Photon stimulated desorption of KI has been measured at several temperatures between 300 K and 485 K using photons in the energy region around the fundamental absorption threshold of KI. The yield spectra vs photon energy of the emission of potassium and iodine atoms are very similar to each other and show a weak structure near threshold, in correspondence of the main exciton absorption peak, followed by a smooth exponential increase, unrelated with the higher energy absorption features of KI. The time dependence of the desorption signal of potassium atoms, measured after turning either on or off the radiation beam, shows the existence of two simultaneous processes with completely different time constants: a ‘fast’ process with a time constant shorter than our time resolution of 0.5 s, and a ‘slow’ process with a time constant of several seconds. The intensity of the slow process is strong at low temperatures and in the region of the main exciton absorption peak, and becomes negligeable at high t...

Desorption Induced by Electronic Transitions: Application to Ionic Compounds

The ejection of atoms and molecules from the surface of solids subject to the bombardment of energetic particles is a well known phenomenon that is employed routinely in laboratories and industrial plants for cleaning a surface, determining surface composition or ejecting material from a solid for deposition on adjacent targets. This emission, called sputtering, is the result of a direct momentum transfer from the incident particles to the atoms of the solid.

B and C band excitation and emission spectra in KI:T1

Abstract We present the excitation spectra of KI:T1 measured in the region of the B and C absorption bands at several emission wavelengths and at 20 K, 80 K and 300 K. An accurate analysis of these spectra shows new properties of the excitation spectra, that we relate to the non radiative relaxation of the excited electrons towards the luminescent states.