Eu 2+ Stabilized at Octahedrally Coordinated Ln 3+ Site Enabling Red Emission in Sr 3 LnAl 2 O 7.5 (Ln = Y or Lu) Phosphors

Red spectrum loss in phosphor‐converted light‐emitting diodes (pc‐LEDs) restricts high‐quality warm‐white lighting. Herein, two blue‐light excitable red‐emitting Sr 3 LnAl 2 O 7.5 :Eu (Ln = Y or Lu) phosphors are reported, and red emission originating from an unprecedented substitution model, with Eu 2+ occupied sixfold octahedrally coordinated lanthanide (Ln 3+ ) sites is demonstrated. Site occupancy identification reveals that three different sites are occupied by Eu 2+ and one distinct site is occupied by Eu 3+ , and the Eu 2+ stabilized at Ln 3+ site accompanied by Eu 3+ selectively occupies at Sr 2+ site as a charge compensator. An anomalous prolonged Eu 2+ ‐photoluminescence decay emission with increasing temperature in the low‐temperature region is demonstrated. This accounts for the trapped electrons, which are thermally released from shallow traps and eventually populate the Eu 2+ 5d level to form an excited‐state Eu 2+ . The findings help better understand Eu 2+ occupancy and luminescence. These also provide a new perspective for the exploration of novel Eu 2+ activated oxide‐based red phosphor for pc‐LEDs.