Porous materials may find a wide range of applications in the optical and photonics fields in the near future, including filtration and separation systems capable of providing real-time information about the efficacy of such processes through opto-electronic transduction mechanisms, entrapment of optically active molecules (e.g., lasing polymers and fluorescent dyes), and sensor coatings that possess size- and shape-selectivity. Crystalline, porous materials, such as zeolites, exhibit such selectivity through their molecular-sieving abilities. Additionally, zeolites have other highly-desirable properties for commercial opto-electronic applications, including high surface area, high pore volume, excellent thermal and chemical stability, and innate long-range order. However, current challenges in this area include the difficulty of scaling up zeolite synthesis from laboratory to industrial scale, particularly for zeolites synthesized as thin films and coatings; the small number of successful designs that take full advantage of the properties of zeolites, such as pore size and shape; and, most importantly, the lack of specific knowledge about the optical properties (refractive indices, vibrational modes, absorbance and emission bands, etc.) of zeolitic materials. We have begun a systematic effort to characterize and catalog such properties. Understanding the intricate relationships between synthesis parameters and final optical properties will provide system designers with the ability to fine-tune zeolite synthesis to suit particular applications. Moreover, unusual and heretofore unknown material properties may come to light during this process. For example, we have recently demonstrated that some zeolites are capable of producing photoluminescence if synthesized under the correct conditions [1]. As part of an ongoing, systematic effort to understand and predict the fundamental interactions between infrared light and zeolitic structures, the goal of this study is to examine the complex interrelationships among composition, structure, crystallization parameters, and the vibrational spectra of pure-silica and aluminosilicate sodalite (zeolite framework code
SOD).
We report the synthesis and optical characterization of these materials with varying crystallization times and temperatures, and varying aging times. A software-aided design of experiments was applied to assist in the statistical analysis of the samples, and to determine the most important synthetic factors that impact their infrared and Raman spectra. These experimentally-determined spectra will be assisted by Density Functional Theory (DFT) calculations to interpret the vibrational spectra of a zeolite framework with any composition. Together, computational models and experimental data will assist the design of optoelectronic systems utilizing zeolites and their special optical properties.
References:
1. Planells, A., et al., Investigation of the photoluminescence of microporous silicalite-1 (MFI) films. Microporous and Mesoporous Materials, 2016. 220: p. 73-80.
