Secret agent in the secret service: Utilization of Sb(iii)-based complexes’ emission properties for the study of forgery and document authenticity

Abstract

Document forgery, information leaks, and falsifying artworks, certificates, and diplomas have become increasingly sophisticated and challenging to detect. Therefore, designing materials whose response to external stimuli can be a perfect detector of crimes such as artifact forgery is crucial. Consequently, we decided to synthesize a functional material that exhibits strong broadband orange emission when exposed to UV light. This material is derived from organic–inorganic hybrids with the acronym D4SB (D4-dibutylammonium cation, Sb(III), B-ligand bromide). The D4SB crystal with stoichiometry (D4)₃[SbBr₆] undergoes one phase transformation at 166 K (heating cycle) in the solid state. A characteristic and unique property is that the phase transition (PT) changes the emission color to yellow in the low-temperature phase. Returning to the high-temperature phase reverses the light emission back to orange. According to the detailed spectroscopic characterization supported by the theoretical calculations, broadband light emission is associated with self-trapping excitons (STEs), resulting from a strong interaction between an electron and a phonon of the crystal lattice. Another advantage of this crystal is the easy mechanochemical synthesis in the solid, which speeds up the chemical reaction and requires no additional chemical solvents, making the synthesis environmentally friendly. We use this property to create the samples as thin films, which were initially used to confirm the authenticity of artifacts.