A photoluminescence study of the changes induced in the zinc white pigment by formation of zinc complexes

It is known that oil paintings containing zinc white are subject to rapid degradation. This is caused by the interaction between the active groups of binder and the metal ions of the pigment, which gives rise to the formation of new zinc complexes (metal soaps). Ongoing studies on zinc white paints have been limited to the chemical mechanisms that lead to the formation of zinc complexes. On the contrary, little is known of the photo-physical changes induced in the zinc oxide crystal structure following this interaction. Time-resolved photoluminescence spectroscopy has been applied to follow modifications in the luminescent zinc white pigment when mixed with binder. Significant changes in trap state photoluminescence emissions have been detected: the enhancement of a blue emission combined with a change of the decay kinetic of the well-known green emission. Complementary data from molecular analysis of paints using Fourier transform infrared spectroscopy confirms the formation of zinc carboxylates and corroborates the mechanism for zinc complexes formation. We support the hypothesis that zinc ions migrate into binder creating novel vacancies, affecting the photoluminescence intensity and lifetime properties of zinc oxide. Here, we further demonstrate the advantages of a time-resolved photoluminescence approach for studying defects in semiconductor pigments

Integrated Imaging and Spectroscopic Analysis of Painted Fresco Surfaces Using Terahertz Time-Domain Technique

Terahertz time-domain (THz-TD) imaging plays an increasingly significant role in the study of solid-state materials by enabling the simultaneous extraction of spectroscopic composition and surface topography in the far-infrared region (3–300 cm^-1). However, when applied to works of art in reflection configuration, significant challenges arise, including weak signal intensity, multiple signal losses, and surface distortion. This study proposes a practical solution to overcome these limitations and conducts an integrated imaging and spectroscopic analysis on painted fresco surfaces, allowing for the retrieval of surface thicknesses, material distribution, and pigment spectroscopic signals. The study addresses the issue of surface geometrical distortion, which hampers the accurate determination of the THz phase signal. By tackling this challenge, this work successfully determines the absorption coefficient for each point on the surface and retrieves spectroscopic signatures. Additionally, the temporal deconvolution technique is employed to separate different layers of the sample and differentiate between outer and inner surface topography. The objective of this study is to demonstrate the advantages and limitations of THz-TD imaging in determining surface thicknesses, material distribution, and pigment spectroscopic signals. The results obtained highlight the potential of THz-TD imaging in investigating painted works of art, offering new possibilities for routine analysis in the field of cultural heritage preservation

Time-resolved photoluminescence microscopy for the analysis of semiconductor-based paint layers

In conservation, science semiconductors occur as the constituent matter of the so-called semiconductor pigments, produced following the Industrial Revolution and extensively used by modern painters. With recent research highlighting the occurrence of various degradation phenomena in semiconductor paints, it is clear that their detection by conventional optical fluorescence imaging and microscopy is limited by the complexity of historical painting materials. Here, we illustrate and prove the capabilities of time-resolved photoluminescence (TRPL) microscopy, equipped with both spectral and lifetime sensitivity at timescales ranging from nanoseconds to hundreds of microseconds, for the analysis of cross-sections of paint layers made of luminescent semiconductor pigments. The method is sensitive to heterogeneities within micro-samples and provides valuable information for the interpretation of the nature of the emissions in samples. A case study is presented on micro samples from a painting by Henri Matisse and serves to demonstrate how TRPL can be used to identify the semiconductor pigments zinc white and cadmium yellow, and to inform future investigations of the degradation of a cadmium yellow paint

Chemical analysis and computed tomography of metallic inclusions in Roman glass to unveil ancient coloring methods

This paper describes the analysis of two near-spherical metallic inclusions partially incorporated within two Roman raw glass slags in order to elucidate the process that induced their formation and to determine whether their presence was related to ancient glass colouring processes. The theory of metallic scraps or powder being used in Roman times for glass-making and colouring purposes is widely accepted by the archaeological scientific community, although the assumption has been mainly based on oral traditions and documented medieval practices of glass processing. The analysis of the two inclusions, carried out by X-ray computed tomography, electrochemical analyses, and scanning electron microscopy, revealed their material composition, corrosion and internal structure. Results indicate that the two metallic bodies originated when, during the melting phase of glass, metal scraps were added to colour the material: the colloidal metal–glass system reached then a supersaturation condition and the latter ultimately induced metal expulsion and agglomeration. According to the authors’ knowledge, these two inclusions represent the first documented and studied finds directly associated with the ancient practise of adding metallic agents to colour glass, and their analysis provides clear insights into the use of metallic waste in the glass colouring process.This paper describes the analysis of two near-spherical metallic inclusions partially incorporated within two Roman raw glass slags in order to elucidate the process that induced their formation and to determine whether their presence was related to ancient glass colouring processes. The theory of metallic scraps or powder being used in Roman times for glass-making and colouring purposes is widely accepted by the archaeological scientific community, although the assumption has been mainly based on oral traditions and documented medieval practices of glass processing. The analysis of the two inclusions, carried out by X-ray computed tomography, electrochemical analyses, and scanning electron microscopy, revealed their material composition, corrosion and internal structure. Results indicate that the two metallic bodies originated when, during the melting phase of glass, metal scraps were added to colour the material: the colloidal metal-glass system reached then a supersaturation condition and the latter ultimately induced metal expulsion and agglomeration. According to the authors' knowledge, these two inclusions represent the first documented and studied finds directly associated with the ancient practise of adding metallic agents to colour glass, and their analysis provides clear insights into the use of metallic waste in the glass colouring process

On the photoluminescence changes induced by ageing processes on zinc white paints

Recent research is focusing on the study of interaction mechanisms between pigments and binders, as they are crucial for understanding paint ageing and conservation issues. In this work, we investigate these mechanisms and follow the changes induced by ageing on zinc white paint by employing Fourier Transform Infrared (FTIR) and Time-Resolved Photoluminescence (TRPL) spectroscopies. The two techniques, applied on thermally aged mock-up samples and on a 19th oil painting, provide complementary information on the effect of the binder on the ZnO pigment particles. The characterization of the infrared absorption spectra confirms the well-known tendency of amorphous metal carboxylate formation in zinc white paint following ageing. At the same time, the ageing of paint film produces significant changes in the photoluminescence emission from defect centres of ZnO. The emission that is mostly affected by the changes of the micro-environment is the blue band (430 nm) – associated with surface defects – whereas the green emission (530 nm) is stable. The results demonstrate that the evolution of the pigment-binder system has detectable consequences on the crystalline structure of the pigment particles and we speculate that the main cause of these modifications is the functionalization of the pigment particle surfaces. The possibility to follow crystal structure changes with time-resolved photoluminescence can thus support chemical studies on metal carboxylate formation and paint deterioration by providing information about pigment-binder interactions

Self-Referenced Method for Geometrical Distortion Removal in THz Time-Domain Reflection Imaging

In this article, we develop a method for removing the phase drift induced by physically distorted object in terahertz time-domain reflection imaging (THz-TDRI). The proposed approach is defined as self-referenced, as it does not rely on any numerical parameter optimization nor extra instrumental components, and it is based on the unique manipulation of time-domain imaging data. In fact, we demonstrate that the problem can be solved assuming a linear contribution of the temporal shift induced by surface curvature. We illustrate how the self-referenced method is modeled and implemented, and we report the results obtained on two objects with different characteristics: a tilted and highly reflective surface, and a warped and heterogeneous surface. The proposed method demonstrates how to successfully remove the phase alterations induced on the reflected electric field, and how to repair the heavily corrupted images in the frequency-domain

Empowering PET: harnessing deep learning for improved clinical insight

Abstract This review aims to take a journey into the transformative impact of artificial intelligence (AI) on positron emission tomography (PET) imaging. To this scope, a broad overview of AI applications in the field of nuclear medicine and a thorough exploration of deep learning (DL) implementations in cancer diagnosis and therapy through PET imaging will be presented. We firstly describe the behind-the-scenes use of AI for image generation, including acquisition (event positioning, noise reduction though time-of-flight estimation and scatter correction), reconstruction (data-driven and model-driven approaches), restoration (supervised and unsupervised methods), and motion correction. Thereafter, we outline the integration of AI into clinical practice through the applications to segmentation, detection and classification, quantification, treatment planning, dosimetry, and radiomics/radiogenomics combined to tumour biological characteristics. Thus, this review seeks to showcase the overarching transformation of the field, ultimately leading to tangible improvements in patient treatment and response assessment. Finally, limitations and ethical considerations of the AI application to PET imaging and future directions of multimodal data mining in this discipline will be briefly discussed, including pressing challenges to the adoption of AI in molecular imaging such as the access to and interoperability of huge amount of data as well as the “black-box” problem, contributing to the ongoing dialogue on the transformative potential of AI in nuclear medicine. Relevance statement AI is rapidly revolutionising the world of medicine, including the fields of radiology and nuclear medicine. In the near future, AI will be used to support healthcare professionals. These advances will lead to improvements in diagnosis, in the assessment of response to treatment, in clinical decision making and in patient management. Key points • Applying AI has the potential to enhance the entire PET imaging pipeline. • AI may support several clinical tasks in both PET diagnosis and prognosis. • Interpreting the relationships between imaging and multiomics data will heavily rely on AI. Graphical Abstrac