Abstract
X-ray, UV−vis, FT-infrared, Raman, continuous wave, and pulsed ESR spectroscopy were applied to characterize pigments prepared at 500 °C under vacuum or in air from mixtures of zeolite A (LTA) with sulfur (40 wt %) and anhydrous sodium sulfide (Na2/S = 0.1−0.4). The samples maintained the LTA structure. Sample color results from an S3− absorption band and the shoulder of a UV band. The fingerprint and asymmetric stretch region of the IR spectra show that the pigments synthesized in air have more disordered structures. The S2−/S3−ratio was estimated from Raman spectra. The ESR spectra of S3− radicals show the existence of several phases visible as five different ESR components. Two components dominate: ideal [Na4S3−]3+ clusters and clusters existing in a disordered environment. The samples synthesized in air show a substantial distortion of local structure. Synthesis in vacuum leads to products containing about 20% of the ordered crystalline phase.
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