Electronic Structure, Bandgap, and Thermal Quenching of Sr[Mg₃SiN₄]:Eu²⁺ in Comparison to Sr[LiAl₃N₄]:Eu²⁺

In this study the band gap and electronic structure of the next‐generation, red phosphor Sr[Mg₃SiN₄]:Eu²⁺ (SMS) are explored through a combination of soft X‐ray spectroscopy, density functional theory calculations, and thermal quenching data for the Eu²⁺ 5d→4f emissions. The results will be compared to those for the high‐efficiency phosphor Sr[LiAl₃N₄]:Eu²⁺ (SLA), which shows different, yet exceptional emission characteristics in the red‐spectral region. It is found that SMS has an indirect band gap of 3.28 ± 0.20 eV, strong uniformity in the density of states of its nonequivalent nitrogen sites, and an estimated energetic separation between the lowest Eu²⁺ 5d state and the conduction band of ≈0.13 eV. The Eu²⁺ 5d–conduction band separation in SLA is found to be ≈0.28 eV, which points to why the visible emissions of SLA, and not SMS, show outstanding thermal stability. A bonding scheme explaining the band gap difference of SMS and SLA is proposed based on the density of states of SMS. Modifications to each lattice are put forward for achieving optimized phosphor characteristics for use in pc‐LEDs.