(219c) The Influence of Compositions and Defects on Vibrational and Optical Properties of Sodalite through Density Functional Theory

Zeolites are well-known for their applications in processes such as catalysis, adsorption, and ion-exchange. Recently, zeolites have been explored for applications in optoelectronics due to their uniform micropores (< 2nm) and regular arrays of defined channels. For example, different types of extra-framework charge- compensating cations have been shown to have different external quantum efficinecies. In addition, the water content can also have dynamical emission color change in some silver-exchanged zeolites. These intriguing optical properties, which can be tailored by changing the composition and synthesis conditions, are typically poorly interpreted. Understanding and characterizing the relationships between chemical composition, synthesis conditions, and the resulting structural, vibrational, and optical properties are important to utilizing these materials more efficiently in optoelectronics. Among the characterization tools available for zeolitic materials, vibrational spectroscopy (infrared and Raman) and photoluminescence spectroscopy have been used extensively. Sodalite (framework code SOD) is a relatively simple framework that can be used as a model system to explore optical and ifrared behavior. We explore the effects of compositional variation on the vibrational properties of sodalite through density functional theory (DFT) calculations with periodic boundary condintions (PBC). DFT and experiments are in good agreement in terms of predicting the characteristic vibrational modes of sodalite. However, in our experimental IR, we observed substantial peak broadening in the asymmetric stretching region and additional peaks between the bending mode and symmetric/asymmetric stretching regions. We hypothesize that this comes from the existence of hydroxyl groups and/or water content. This suggests that we should work toward determining the effects of other types of defects (e.g., hydroxyl groups, water, charge-compenstating cations). The response of zeolites to adsorbates may expand their utility to humidity sensors and other applications.