Spectroscopic analysis of Mn4+-activated phosphors: Unveiling the relationship between energy levels and Racah parameters

Mn4+-activated red and deep-red phosphors hold promise for widespread applications in solid-state lighting. A deep understanding of the dependence of the excitation and emission energy levels of Mn4+ on its crystal field environment is essential for guiding the development of Mn4+-activated phosphors. By analyzing the photoluminescence spectral properties of Mn4+ in various hosts, this study investigates the relationship between its energy levels and the crystal-field and Racah parameters (Dq, B, and C), and establishes several universal empirical equations. In particular, equation E(2Eg)ZPL = 7B + 3.1C reveals the decisive role of the nephelauxetic effect on the zero-phonon line (ZPL) emission energy of the 2Eg -> 4A2g transition. This formula, along with E (4T1g,a)ZPL = 10.5Dq + 8.9B, enables the precise prediction of the ZPL energy levels from crystal-field and Racah parameters, and vice versa. Furthermore, drawing attention to difficulty in determining the energy levels, we propose an alternative method to enhance the convenience and precision of estimating the ZPL excitation energies and Racah parameters. These findings provide valuable insights into the electronic structure and photoluminescence properties of Mn4+ ions in solids.