Temperature Promotes Photoluminescence in Lanthanide-Doped 3D Ceramic Microarchitectures

Two-photon lithography (TPL) is a powerful technique for creating 3D microarchitectures. Applied to high-refractive-index materials like ZrO₂, it promises advanced optics. This is the case of ZrO₂ host matrixes in combination with luminescent dopants. However, due to the nonideal crystallinity attained to the TPL pre-ceramic replica from a custom-made photoresin, the emission of lanthanide (Ln) dopants in ZrO₂ microarchitectures can be suboptimal. However, crystallinity exacerbated by annealing can promote Ln-emission, thereby enabling the integration of ceramic micro-optic into a low-temperature process. This work presents a photoresin containing a metal-organic monomer tailored for TPL, enabling the fabrication of Ln-doped tetragonal ZrO₂ (t-ZrO₂) microarchitectures. The emission properties of Ln-doped microarchitectures with trivalent Ln ions (Ln³⁺), i.e., Yb³⁺ (2.5 mol%), Er³⁺ (0.35 mol%), and Tm³⁺ (0.35 mol%) are studied. The results demonstrate that Ln emission is absent when annealing the microarchitectures at 600 °C. Annealing at 750 °C activates Ln³⁺ emissions, including ²F_5/2–²F_7/2 (infrared), ⁴S_3/2–⁴I_15/2 (green), and ³H₄–³F₆ (near-infrared) transitions corresponding to Yb, Er, and Tm species. Transmission electron microscopy (TEM) confirms that t-ZrO₂ crystallinity becomes more prominent at 750 °C, demonstrating the promotion of Ln emissions upon thermal treatment and underscoring the role of crystalline in TPL micro-optical ceramics.