ABSTRACT We report a novel phosphor, Na 0.9 AlS 2 :Eu 2+ with C2/c symmetry, which contains a significant proportion of stacking faults. Despite minimal post‐synthesis processing, this green light‐emitting novel phosphor demonstrates outstanding luminescence efficacy, reaching 80% compared to β‐SiAlON, which is recognized as the world's best commercially available green phosphor in terms of luminescence efficacy. Notably, this remarkable luminescent property is achievable only in non‐stoichiometric compositions, particularly those with Na‐deficient structures. Through comprehensive characterization using HR‐XRD, EXAFS/XANES, FAULTS analysis, time‐resolved photoluminescence, and DFT calculations, we precisely identified the accommodation status of Eu 2+ in the host structure. Our analyses confirm that Na deficiency creates a wider bandgap that prevents thermal ionization from the Eu 2+ 5d level to the conduction band, which is essential for the phosphor's excellent luminescent properties. Additionally, the material exhibits exceptional stability in ambient conditions, maintaining structural integrity and photoluminescence for up to an hour of exposure—a significant improvement over typical sulfide phosphors. This work not only introduces a high‐performance phosphor with practical advantages for LED applications but also provides fundamental insights into how non‐stoichiometry and stacking faults can synergistically enhance luminescence properties in phosphor materials.
Cho et al. (Sat,) studied this question.