Luminescent YAG:Ce³⁺ 3D micro-structures via multi-photon laser lithography

This work addresses the challenge of fabricating crystalline single-phase luminescent 3D microstructures by demonstrating a fabrication process of yttrium aluminum garnet doped with cerium (YAG:Ce³⁺) 3D micro-objects. Precursors were synthesized via a sol-gel method and characterized by refractive index (RI) measurements, Fourier-transform infrared spectroscopy (FT-IR), and thermogravimetric (TG) analysis to verify chemical composition changes during photopolymerization and thermal treatment. Multiphoton laser 3D lithography (MP3DL) was employed to produce hybrid metal-organic 3D structures, which were subsequently converted into crystalline ceramics through controlled 3-step annealing. Structural analysis by X-ray diffraction (XRD) confirmed the formation of single-phase cubic YAG across Ce³⁺ concentrations up to 5 mol-% in 3D objects, while scanning electron microscopy (SEM) revealed isotropic shrinkage (ca. 39%) and well-preserved geometries with sub-micrometer features after pyrolysis. The smallest feature of a crystalline 3D object achieved was 0.48 μm with a spatial resolution down to 2.4 μm. Luminescence measurements showed characteristic Ce³⁺ emission centered at 558 nm, with maximum intensity at 2 mol-% doping. These findings establish a reliable pathway to fabricate thermally stable, high-resolution, luminescent single-phase YAG:Ce³⁺ 3D micro-objects, enabling their integration into optoelectronic and photonic applications.