Photoluminescence properties of zinc white: an insight into its emission mechanisms through the study of historical artist materials
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While the photophysical properties of ZnO nanostructures have been widely explored, less research has focused on the bulk material present in artist pigments. This study is based on the analysis of historical pastels, representative of artist materials available at the turn of the twentieth century, and of the pure powder pigment as the control sample. The study of the intensity of the photoluminescence emission as a function of the fluence and of the nanosecond and microsecond emission decay kinetic properties allows the elucidation of the emission mechanisms in control ZnO and historical samples containing ZnO. Data suggest that in historical samples the near-band-edge free-exciton photoluminescence emission, typically occurring in the pure semiconductor, is influenced by the interaction of the pigment with surrounding organic binding material. Conversely, crystal defects, typically expected in historical samples following the imperfect synthesis process available at the beginning of the twentieth century, introduce minor modifications to the photoluminescence emission. The study further suggests that zinc carboxylates, detected in all historical samples and known to introduce characteristic groups on the surface of ZnO, could be responsible for changes in emission mechanisms. Research demonstrates how photoluminescence decay kinetics and the study of the dependence of the emission intensity on the fluence are powerful methods for elucidating the nature of the mechanism processes in luminescent semiconductor pigments.
KeywordsZinc Oxide Green Emission Emission Mechanism Historical Sample Effective Lifetime
Authors wish to thank the Central European Research Infrastructure Consortium (CERIC-ERIC) for measurements and analyses of FE-SEM and Francesca Gherardi from Chemistry Department of Politecnico di Milano for measurements and analyses of FTIR spectroscopy. We are grateful to Lucia Toniolo from Chemistry Department of Politecnico di Milano for providing us historical samples. Research was partially funded by the Italian Ministry of Education, Universities and Research within the framework of the JPI Cultural Heritage JHEP Pilot call through the LeadART project ‘Induced decay and ageing mechanisms in paintings: focus on interactions between lead and zinc white and organic material’.
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