The colored component of several important ancient pigments, including Egyptian blue and Han blue, are based on alkali earth copper tetrasilicate materials. In recent work, we have found that these layered materials can be chemically exfoliated into their constituent monolayers to provide alkali earth copper tetrasilicate nanosheets—defined by nanometer thickness and lateral dimensions that are on the order of several microns. The facile exfoliation of these materials into nanosheets is especially surprising in view of their long history on artifacts under a variety of environmental conditions, and we have examined the issue of whether archaeological samples are affected by this exfoliation mechanism. We have characterized the properties of these nanosheets by an array of analytical techniques, including powder x-ray diffraction, photoluminescence measurements, and Raman spectroscopy. In all cases, we observe differences between nanosheet and bulk samples that originate from the loss of coupling between layers when going from three-dimensional to two- dimensional structures. Both CaCuSi4O10 nanosheets (derived from Egyptian blue) and BaCuSi4O10 nanosheets (derived from Han blue) have strong near-infrared luminescence properties like their bulk counterparts, yet they are amenable to modern solution processing methods. We have demonstrated ink jet printing with CaCuSi4O10 nanosheet inks, as well as the fabrication of nanosheet-based papers. Potential applications for these materials include NIR-based biomedical imaging and security inks.
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