Silica-Encapsulated Germania Colloids as 3D-Printable Glass Precursors

Core–shell colloids make attractive feedstocks for three-dimensional (3D) printing mixed oxide glass materials because they enable synthetic control of precursor dimensions and compositions, improving glass fabrication precision. Toward that end, we report the design and use of core–shell germania–silica (GeO2–SiO2) colloids and their use as precursors to fabricate GeO2–SiO2 glass monoliths by direct ink write (DIW) 3D printing. By this method, GeO2 colloids were prepared in solution using sol–gel chemistry and formed oblong, raspberry-like agglomerates with ∼15 nm diameter primary particles that were predominantly amorphous but contained polycrystalline domains. An ∼15 nm encapsulating SiO2 shell layer was formed directly on the GeO2 core agglomerates to form core–shell GeO2–SiO2 colloids. For glass 3D printing, GeO2–SiO2 colloidal sols were formulated into a viscous ink by solvent exchange, printed into monoliths by DIW additive manufacturing, and sintered to transparent glasses. Characterization of the glass components demonstrates that the core–shell GeO2–SiO2 presents a feasible route to prepare quality, optically transparent low wt % GeO2–SiO2 glasses by DIW printing. Additionally, the results offer a novel, hybrid colloid approach to fabricating 3D-printed Ge-doped silica glass.