Co-existence of Bi with multiple valence states in zeolites – Controlling the optical properties by annealing atmosphere

Abstract We investigate the effect of annealing atmosphere on the optical properties of Bi doped zeolites by diffuse reflectance, steady state and time-resolved photoluminescence (PL), and PL excitation measurements. The results reveal that zeolites can be used as an excellent host material to stabilize multiple Bi centers (Bi 3+ , Bi 2+ , and Bi-related near-infrared (NIR) active centers) in the framework, which shows ultra-broadband emission from visible to NIR range. Annealing in N 2 leads to the partial conversion of Bi 3+ ions into Bi 2+ and Bi-related NIR active centers. Our results demonstrate that the broadband NIR emission may be attributed to the electronic transition of Bi low valence state, rather than a higher valence state.