Diamond

Engineering

Transparent ceramics

Metallurgy

Materials science

Ceramic

Spinel

3D printing

Limit (mathematics)

Optical transparency

Physics

Nanotechnology

Mathematics

Optics

Mathematical analysis

Transmittance

Composite material

Opacity

Optoelectronics

Engineering physics

Advanced Materials

3D printing of transparent ceramics has attracted great attention recently but faces the challenges of low transparency and low printing resolution. Herein, magnesium aluminate spinel transparent ceramics with transmittance reaching 97% of the theoretical limit are successfully fabricated using a stereolithography‐based 3D printing method assisted by hot isostatic pressing and the critical factors governing the transparency are revealed. Various transparent spinel lenses and microlattices are printed at a high resolution of ≈100–200 µm. The 3D printed spinel lens demonstrates fairly good optical imaging ability, and the printed spinel diamond microlattices as a transparent photocatalyst support for TiO 2 significantly enhance its photocatalytic efficiency compared with its opaque counterparts. Compared with other 3D printed transparent materials such as silica glass or organic polymers, the printed spinel ceramics have the advantages of broad optical window, high hardness, excellent high‐temperature stability, and chemical resistance and therefore, have great potential to be used in various optical lenses/windows and photocatalyst supports for application in harsh environments.

3D Printing of Transparent Spinel Ceramics with Transmittance Approaching the Theoretical Limit