Fabrication of Ruby by 3D printing of transparent salt solutions

A novel method is presented for fabricating 3D-printed Cr³⁺-doped α-Al₂O₃ complex structures, known as Ruby, using digital light processing (DLP) 3D printing and sol-gel reactions based on solutions only. The aqueous printing solution comprises aluminum and chromium chloride as the sol-gel precursor and acrylic acid (AA) as the polymerizable component. After photopolymerization, aging, and sintering at 1150°C, structures shrink up to 28±7 %, achieving a final printing resolution of 55.7±0.7 μm, surpassing the nominal printer's resolution of 200 μm. Characterization includes X-ray diffraction, scanning electron microscopy, UV-Vis, and fluorescence measurements, revealing crystalline Cr:α-Al₂O₃ composition emitting at 693 nm. The structures exhibit maximum compression stress of 89±3 MPa and microhardness of 340–500 HV, showcasing potential applications in thermal insulation, jewelry, and mechanical uses.