Defect-Rich Wide Bandgap Li₂ZrO₃ Engineered for Multiple Functionalities through a Cation Doping Scheme

In light of the growing demand for multifunctional materials in contemporary advanced technologies, this study examines cation-induced electronic structure modulation in defect-rich Li₂ZrO₃ by introducing Tb⁴⁺/Eu³⁺ dopants. A ceramic method involving the high-temperature solid-state reaction of reactants was adopted to generate the samples. The crystal and chemical structure analyses were performed using powder X-ray diffraction (PXRD) and Raman spectroscopy. Combining absorption/emission spectroscopy, electron paramagnetic resonance (EPR), and X-ray photoelectron spectroscopy (XPS), we mapped defect-related electronic states and demonstrated the redistribution of energy levels by doping. Tb⁴⁺ incorporation introduced an intense yellow color to the samples and caused a reduction in the optical bandgap from 5.45 to 2.46 eV, accompanied by intrinsic luminescence. Notably, 10 mol % Tb-doped Li₂ZrO₃ exhibited remarkable photocatalytic activity, efficiently degrading crystal violet (CV) under visible light. The reactive oxygen species involved in the photocatalytic process were determined. In Eu³⁺-doped samples, excitation-dependent tunable emissions (in red, blue, and white regions) were observed. Lithium in Eu- and Tb-doped Li₂ZrO₃ samples could be exchanged with protons, causing a partial reduction of Tb⁴⁺ → Tb³⁺. These findings have established that defect-rich Li₂ZrO₃ can be engineered as a versatile, multifunctional optical material by an appropriate cation doping scheme.