A First-Principles Explanation of the Luminescent Line Shape of SrLiAl₃N₄:Eu²⁺ Phosphor for Light-Emitting Diode Applications

The red phosphor SrLiAl₃N₄:Eu²⁺ is among the first promising phosphors with a small bandwidth for next-generation lighting [1], but the microscopic origin of this narrow emission remains elusive. In the present work [2], density functional theory, the ΔSCF-constrained occupation method, and a generalized Huang–Rhys theory are used to provide an accurate description of the vibronic processes occurring at the two Sr²⁺ sites that the Eu²⁺ activator can occupy. The emission band shape of Eu(Sr1), with a zero-phonon line at 1.906 eV and a high luminescence intensity, is shown to be controlled by the coupling between the 5d_z²–4f electronic transition and the low-frequency phonon modes associated with the Sr and Eu displacements along the Sr channel, as already observed in the similar SrLi₂Al₂O₂N₂:Eu²⁺ [3]. The good agreement between our computations and experimental results [4] allows us to provide a structural assignment of the observed total spectrum. These results highlight the importance of the Sr channel in shaping the narrow emission of SrLiAl₃N₄:Eu²⁺, and they shed new light on the structure–property relations of such phosphors.

[1] Pust, P., Weiler, V., Hecht, C, et al. Nat. Mater. 13(9), 891-896 (2014)

[2] Bouquiaux, J., Poncé, S., Jia, Y., et al. Chem. Mater., 35(14), 5353–5361 (2023)

[3] Bouquiaux, J., Poncé, S., Jia, Y., et al. Adv. Opt. Mater. 9(20), 2100649 (2021)

[4] Tsai, Y., Nguyen, H. D., Lazarowska, A., Angew. Chem. Int. Ed. 55(33), 9652-9656 (2016)