Unveiling the microstructures and electronic features of a trivalent chromium-doped yttrium oxide crystal: a...

Transition-metal-doped yttrium oxide is highly efficient in generating light from the visible to near-infrared region with excellent physical stability. Thus, it is a significant activator in various solid-state laser materials. However, we still lack a first-principles study on the microstructures and electronic features of the complexes. To address this gap, here, we provide a detailed theoretical analysis of the Cr³⁺-doped Y₂O₃ (Y₂O₃:Cr) crystal. Based on the density functional theory combined CALYPSO structural search method, the stable structures of the Y₂O₃:Cr system are successfully identified, including the ground-state structure and the first four metastable isomers. A novel cage-like configuration of Y₂O₃:Cr is reported for the first time. The good agreement between the simulated and experimental X-ray diffraction patterns demonstrates the reliability of the structure. The results of the electronic band structure calculations reveal that the band gap of Y₂O₃:Cr decreases to 3.23 eV compared to that of pure Y₂O₃. This is caused by introducing the 3d states of the impurity Cr³⁺ ion in electronic density of states. By calculating the electron localization function (ELF), we find that the Cr-O bonds in the Y₂O₃:Cr crystal are conclusively ionic. These results could provide important information for understanding the microstructures of transition-metal-doped materials.