Additive manufacturing has attracted recent attention for glass fabrication due to its advantages to manufacture parts with complex geometries. In 3D printing, various techniques such as fused deposition modeling, selective laser melting, direct ink writing, and stereolithography are developed for glass fabrication. For its high printing accuracy, fast speed, and excellent surface quality, stereolithography shows a great potential in fabricating fused quartz glass with intricate structures and optical lenses. This paper was to enhance the optical performance of fused quartz glass including optical absorption, photoluminescence and light scattering properties via infusing metal ions into the glass. We investigated the metal salt solution immersion, debinding and sintering processes based on liquid crystal display 3D printing technology. We fabricated a fused silica glass doped with Cr³⁺ and Co²⁺ metal ions.

A homogeneous solution of photopolymer was prepared via mixing 60% 2-hydroxyethyl methacrylate, 10% triethylene glycol diacrylate, and 30% phenoxyethanol. 2,4,6-trimethylbenzoyldiphenyl phosphine oxide, Sudan orange G, and diethyl phthalate were added to the solution and dispersed for 5 min. Silica nanoparticles of 53% (in mass fraction) were then added and dispersed by a dissolver for 10 min. The photosensitive paste was cured using an LCD 3D printer. Subsequently, the printed parts were heated at 600 ℃ for 2 h, and then soaked in a metal ions solution for 1 h. After being air-dried at 50 ℃ for 1 h, the doped debinding part was sintered at 1 280 ℃ for 2 h. Metal ion-doped glass in the furnace can be obtained after cooling to room temperature.

After debinding and sintering, the printed fused quartz glass parts are densified. The removal of organic binder from the debinding parts causes a contraction of the parts. The micropores disappear after the sintering process, resulting in dense parts that are colorless and transparent. Furthermore, a high concentration of the doped mental ions leads to an extensive crystallization and reduces the transparency of the samples.

Based on the Raman spectra of parts doped with Cr³⁺ and Co²⁺ and commercial glass KN7980, four characteristic peaks of fused silica glass appear, confirming that the finished parts are fused silica glass. In the Raman spectra of the fused silica, the characteristic peaks at 896 cm^-1 and 985 cm^-1 doped with Cr³⁺ correspond to the polymerized chromate species and the Cr—O stretching vibration of discrete chromate species (CrO₄^2-), respectively. This indicates that chromium oxide crystallization occurs in fused silica glass doped with a certain concentration of Cr³⁺. The XRD patterns show that Cr³⁺ induces a crystal precipitation in the fused silica glass, for characteristic peaks of quartz at 2θ of 26.43° and cristobalite at 2θ of 63.56° and 67.91° in the glass doped with Cr³⁺. The characteristic diffraction peaks in the glass doped with Co²⁺ appearing at 2θ of 32.2°, 47.7° and 57.4° are consistent with those of CoO.

The absorption spectra of the glass doped with 2.042 μmol/cm³ concentration of Cr³⁺ reveal that the bands at 471 nm and 660 nm are due to the spin-allowed transition A_2g(F)→⁴T_1g(F) and ⁴A_2g(F)→⁴T_2g(F), respectively. Consequently, Cr³⁺-doped fused silica glass can absorb blue light at 471 nm and red light at 660 nm. The absorption spectra of the parts doped with 12.249 μmol/cm³ concentration of Co²⁺ indicate that the bands at 597 nm and 662 nm result from the spin-allowed transition ⁴T_1g(F)→⁴T_1g(P) and ⁴T_1g(F)→⁴A_2g(F), respectively. Co²⁺-doped fused silica glass shows absorption of blue light at 597 nm and red light at 662 nm. Doping the glass with metal ions imparts unique optical and structural properties to the glass, so that chromium- and cobalt-containing glasses have applications in industries, such as Integrated optics, filters, fiber lasers and near-infrared laser materials.

LCD 3D printing technology was used to produce optical components of fused silica glass doped with Cr³⁺ and Co²⁺ metal ions, having the superior properties, compared with commercial glass KN7980. The Cr³⁺-doped green fused silica glass had a great filtering ability for blue light (471 nm) and red light (660 nm). The Co²⁺-doped blue fused silica glass had a great filtering ability for yellow light (597 nm) and red light (662 nm). The filtering performance of multilayered silica glass could be deliberately tailored to enhance its performance since the filtering ability of silica glass was correlated to the metal ion doping concentration.