Center for Molecular Spectroscopy and Dynamics

2020 KECS Spring Meeting

The chromogenic material, which have various applications in smart windows and glasses, reversibly change their color when electrons and cations are injected by applied voltage or absorption of light. Especially, electrochromic devices (ECDs) have been studied in many studies to utilize as switchable windows, however, it is difficult to make them on a large scale due to the technical requirements for ECDs. This problem does not occur in photochromic devices (PCDs), but the studies on the mechanism of PCDs are still insufficient. In a PCD, the intercalation/deintercalation of Li ions during the coloring/bleaching process plays an important role in the device’s color-switching performance. In this study, we propose a plausible mechanism for the PCD using in-operando Raman spectroscopy. The time resolved Raman spectra of PCD was measured under illumination and in the dark. Through the spectral shift of characteristic peaks of WO₃, we propose a Li⁺ insertion/extraction mechanism into specific sites within the tunnels that exist in the hexagonal WO₃ units during PCDs coloring/self-bleaching.