Transient absorption study on Red Vermilion darkening in presence of chlorine ions and after UV exposure

The application of no destructive techniques in the field Cultural Heritage is becoming fundamental to understanding degradation phenomena. In this study, Transient Absorption (TA) spectroscopy was exploited explain process which causes darkening Red Vermilion, a famous pigment known also as cinnabar. optical properties involved are studied pure HgS and chlorine doped samples, before after exposure UV light (365 nm). study carried out with particular attention on ground state bleaching signals, directly connected formation intra-gap trap levels responsible for degradation. First derivative reflectance spectra reveal presence these defectivities, while analysis Tauc plots from Kubelka Munk function confirms reduction energy band gap due exposure. With help Density Functional calculations, we simulated role S vacancies producing defective alpha-phase, consequent and, finally, progressive phase transformation cubic metacinnabar. turns be an important tool diagnosis about conservation pigments applied Heritage.