Eu<sup>2+</sup> Stabilized at Octahedrally Coordinated Ln<sup>3+</sup> Site Enabling Red Emission in Sr<sub>3</sub>LnAl<sub>2</sub>O<sub>7.5</sub> (Ln = Y or Lu) Phosphors
Tao Hu, Yan Gao, Мaxim S. Моlokeev, Zhiguo Xia, Qinyuan Zhang
Abstract
Abstract 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.