Reversible Interconversion between Ag₂ and Ag₆ Clusters and Their Responsive Optical Properties

The exploration of structural interconversion in clusters triggered by external stimuli has attracted significant interest due to its potential to elucidate structure-property relationships of metal clusters. In this study, two types of silver clusters, Ag₂ and Ag₆, are synthesized. Interestingly, the clusters exhibit reversible transformations in response to changes in the solvent conditions. The structures and optical properties of these clusters are thoroughly characterized using techniques such as mass spectrometry, single-crystal X-ray diffraction, photoluminescence, and radioluminescence spectroscopy. While both Ag₂ and Ag₆ display excellent photoluminescence properties, Ag₂ demonstrates superior performance in X-ray radioluminescence compared to Ag₆. Flexible scintillator films fabricated from Ag₂ clusters exhibit outstanding X-ray imaging capabilities, achieving a spatial resolution of 15.0 lp/mm and an impressive detection limit for an X-ray dose of 0.58 μGy s^-1. This detection limit is nearly 10 times lower than the typical dose rate used in X-ray diagnostics (5.5 μGy s^-1). This work introduces a novel approach for designing thiol-free silver clusters capable of solvent-dependent reversible interconversion, offering new insights into the development of silver clusters for advanced X-ray imaging applications.