Multisite occupation mechanism and near-infrared luminescence characteristics of Cr3+ ions in Na-β"-Al2O3

Taking inspiration from multiple luminescence sources, Cr³⁺-doped Na-β"-Al₂O₃ fluorescent powder was synthesized through high-temperature solid-state method. The results show that Cr enters the Na-β"-Al₂O₃ lattice in the form of trivalent ions and occupies the Al³⁺ lattice within a limited concentration range. Phosphors are composed of submicrometer flake particles with good dispersion, and the concentration difference has little effect on the morphology and size of the particles. It is worth mentioning that by controlling the multisite occupation of Cr³⁺ in the matrix, spectral regulation can be realized in the near-infrared region, that is, the increase of Cr³⁺ concentration helps to broaden the emission peak at 709 nm (x = 0.13). Furthermore, the results of the energy transfer analysis show that there is energy transfer between Cr³⁺. More importantly, the band gap energy level provided by oxygen vacancies in the matrix leads to excellent thermal quenching resistance of the fluorescent powder between 378 and 428 K, and the luminescence intensity of the material can still maintain 60 % of that at room temperature when the temperature rises to 428 K. The phosphors with good microscopic morphology and thermal stability have application value in biological imaging, food safety detection, and other fields.