Tailoring the competition between electric dipole and magnetic dipole emission in $\mathrm{Eu}$-doped cubic sesquioxide $M_2{O}_3$ ($M$ = $\mathrm{Sc},Y,\mathrm{La}$)

With an explosive increase in demand for efficient luminescent materials in integrated optical systems, research on lanthanide ion-doped cubic sesquioxide ceramics has become important and attractive. Because of the large doping capability of lanthanide atoms and a low preparation temperature that is much lower than the melting point, sesquioxides have demonstrated promising potential as a host matrix in solid-state laser gain media. Here, for the first time, we demonstrate that two types of cation sites with different symmetries in cubic sesquioxides could empower effective manipulation of the luminescence properties of lanthanide dopants, leading to either magnetic dipole (MD) or electrical dipole (ED) emission, respectively. Using rigorous first-principle calculations, the luminescence properties of $\mathrm{Eu}$-doped sesquioxide $M_2{O}_3$ ($M$ = $\mathrm{Sc},Y,\mathrm{La}$) are systematically investigated, unveiling the underlying competition mechanisms between MD and ED spontaneous emission. Through analyzing the formation energies of $\mathrm{Eu}$ dopants and intrinsic defects, the impact of strain and temperature on the doping concentration and dopant sites of $\mathrm{Eu}$ in sesquioxide is unambiguously elucidated, facilitating effective and selective manipulation of MD and ED emission.