Such radiation has a long-lived 4f-4f transition, observed when evaluating lanthanides resulting in sharp narrowband emission. This light emission can be supported even when incorporating the lanthanide ion in a dispersion medium that acts as a host matrix with diverse functionalities. [7,9] Two host matrix types for lanthanide ions are identified, namely, organic [10] and inorganic materials. [7,11] Inorganic materials have high lattice-binding energy combined with rigidness; thus, in most cases, they show greater chemical and thermal resistance and photostability against continuous excitation than organic materials. [1,8] Highly crystalline inorganic host matrices are typically preferred to reduce point defects emissions. Hence, attention should be given to the crystallinity of the host material and the nonradiative multiphonon relaxation caused by the crystal lattice. [9] In practice, low phonon energy hosts are preferred to utilize the luminescent activator effectively. [7] However, the commonly used SiO 2 (≈1100 cm −1 stretching vibration) presents low lanthanide solubility, [12,13] leading to cluster formation at high dopant contents (10 18 cm −3 ), [14] quenching the lanthanide emission. [13] In photonics, a substitute for SiO 2 is ZrO 2 , which has relatively good transparency in the visible and infrared range and low phonon energy (≈470 cm −1 ). [12] ZrO 2 occurs in three polymorphs, tetragonal, monoclinic, and cubic, denoted t-ZrO 2 , m-ZrO 2 , and Implementation of more refined structures at the nano to microscale is expected to advance applications in optics and photonics. This work presents the additive manufacturing of 3D luminescent microarchitectures emitting light in the visible range. A tailor-made organo-metallic resin suitable for two-photon lithography is developed, which upon thermal treatment in an oxygen-rich atmosphere allows the creation of silicon-free tetragonal (t-) and monoclinic (m-) ZrO 2 . The approach is unique because the tailor-made Zrresin is different from what is achieved in other reported approaches based on sol−gel resins. The Zr-resin is compatible with the Eu-rich dopant, a luminescent activator, which enables to tune the optical properties of the ZrO 2 structures upon annealing. The emission characteristics of the Eu-doped ZrO 2 microstructures are investigated in detail with cathodoluminescence and compared with the intrinsic optical properties of the ZrO 2 . The hosted Eu has an orange−red emission showcased using fluorescence microscopy. The presented structuring technology provides a new platform for the future development of 3D luminescent devices.
