NIR photoluminescence of ZSM-5 and mordenite zeolites, containing low-valence bismuth exchange cations

Low valence bismuth cationic centers were introduced into hydrogen forms of ZSM-5 and mordenite zeolites via impregnation of zeolites in aqueous solution of bismuth salts and subsequent reductive solid state ion exchange (SSIE). It has been found that Near IR photoluminescent bismuth monocations Bi+ and cluster ions are formed in the exchange positions and their optical properties in ZSM-5 and mordenite depend mainly on a zeolite Si/Al ratio and, to a lesser extent, on the amount of loaded bismuth. The photoluminescence emission and excitation spectra of bismuth cationic species (monocations or clusters) are markedly different in ZSM-5 and mordenite. This difference can be explained, taking into the account, that extraframework (exchanged) cations in mordenite zeolite, unlike ZSM-5, can occupy only several distinct positions relative to the mordenite framework structure.