Intrinsic- and Rare Earth Ion-Activated Luminescence in NbAlO₄ with Wide Structure Channels

Compounds with ordered and interconnected channels have versatile multifunctional applications in technological fields. In this work, we report the intrinsic- and Eu³⁺-activated luminescence in NbAlO₄ with a wide channel structure. NbAlO₄ is an n-type semiconductor with an indirect allowed transition and a band-gap energy of 3.26 eV. The conduction band and valence band are composed of Nb 3d and O 2p states, respectively. Unlike the common niobate oxide Nb₂O₅, NbAlO₄ exhibits efficient self-activated luminescence with good thermal stability even at room temperature. The AlO₄ tetrahedron effectively blocks the transfer/dispersion of excitation energy between NbO₆ chains in NbAlO₄, allowing for effective self-activated luminescence from NbO₆ activation centers. Moreover, Eu³⁺-doped NbAlO₄ displayed a bright red luminescence of ⁵D₀ → ⁷F₂ transition at 610 nm. The site-selective excitation and luminescence of Eu³⁺ ions in a spectroscopic probe were utilized to investigate the doping mechanism. It is evidenced that Eu³⁺ is doped in the structure channel in NbAlO₄ lattices, not in the normal cation sites of Nb⁵⁺ or Al³⁺. The experimental findings are valuable in developing new luminescent materials and improving the understanding of the material’s channel structure.