The refractive index of agZIF-62 determined by ellipsometry, was found to be nD (589.3 nm) = 1.5802 (Figure ), which is noticeably higher than previously reported (~1.55 for the same ratio of linkers ; noteworthy, the glass used in this previous report was prepared by hotpressing, which would -assumedly -lead to enhanced densification, too). In addition, we also find a higher Abbe number (lower optical dispersion) of 32.8 (SI) as compared to that previous work (~31 ) (Figure ); although the Abbe number remains on a relatively low level, placing agZIF-62 to within the group of plastic materials in terms of optical refraction). As a perspective, future optical materials based on agZIF-62 and similar MOF-derived glasses could exploit the porous structure to generate optical breathing effects , based on the reversible incorporation of guest molecules. Moreover, the glassy nature offers tunable porosity. Aside affecting gas permeation performance, this would also enable tailoring of the optical properties to an extent beyond the typical cooling-rate dependence of inorganic glasses.