Thermodynamic stability and multifunctionality of Eu and Er-codoped AlN: Toward biomedical sensing, imaging and spintronic devices

Rare-earth (RE) dopants such as Europium (Eu) and Erbium (Er) impart distinctive optical and magnetic functionalities to host semiconductors, making them attractive for biomedical applications. In this work, we investigate Eu and Er co-doped wurtzite (WZ) AlN using density functional theory within LSDA+U and mBJ+U frameworks. The calculations revealed that the incorporation of Eu and Er atoms modified the electronic structure of AlN by narrowing the band gap and enhancing the hybridization between RE-5d and N-2p states, thereby establishing strong ferromagnetic interactions among the localized magnetic moments. A total magnetic moment of ∼9μB, mainly localized on RE atoms, confirmed robust ferromagnetism. Optical spectra indicated strong luminescence in the visible and NIR regions, enabling applications in deep-tissue imaging and biosensing. Thermodynamic analysis further showed high Debye temperatures and pressure-dependent thermal stability, suggesting excellent mechanical rigidity and resilience under biomedical operating conditions. Overall, these findings establish Eu/Er co-doped AlN as a multifunctional material platform for next-generation biomedical imaging, sensing, and implantable device technologies.