Mixed Microscopic Eu²⁺ Occupancies in the Next‐Generation Red LED Phosphor Sr[Li₂Al₂O₂N₂]:Eu²⁺ (SALON:Eu²⁺)

Abstract Red‐emitting narrow‐band phosphors are of utmost importance for next‐generation white‐light phosphor‐converted light‐emitting diodes (pc‐wLEDs) for improved efficacy and optimized correlated color temperatures. A promising representative crystallizing in an ordered variant of the UCr 4 C 4 structure type is Sr[Li 2 Al 2 O 2 N 2 ]:Eu 2+ (SALON:Eu 2+ ) emitting at a desirable wavelength of 614 nm. Despite an expected eightfold coordination of the Eu 2+ ions by four N 3− and O 2− ions, respectively, the exact local coordination symmetry and a 1:1 ratio between the two types of ligands is not straightforwardly proven by X‐ray diffraction. Low‐temperature luminescence spectroscopy in conjunction with ligand field theory are powerful alternatives to resolve local features of Eu 2+ as its excited 4f 6 5d 1 configuration reacts sensitively to the polarity of the ligands. The dominant emission at 614 nm shows pronounced vibronic fine structure at 10 K. In addition, weak emission bands can be resolved at 570 and 650 nm even at a low doping concentration of 0.5 mol% and are assigned to Eu 2+ ions being eightfold coordinated by N 3− and O 2− ions in a ratio different from 1:1. Due to the feature of vierer ring‐type channels in SALON:Eu 2+ , those Eu 2+ centers are sufficiently close for mutual energy transfer, which is characterized by time‐resolved luminescence at 10 K.