Eu2+ Stabilized at Octahedrally Coordinated Ln(3+) Site Enabling Red Emission in Sr(3)LnAl(2)O(7.5) (Ln = Y or Lu) Phosphors

Hu, T ; Gao, Y ; Molokeev, MS ; Xia, ZG; Zhang, QY. ADVANCED OPTICAL MATERIALS. DOI: 10.1002/adom.202100077

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 Eu2+ occupied sixfold octahedrally coordinated lanthanide (Ln(3+)) sites is demonstrated. Site occupancy identification reveals that three different sites are occupied by Eu2+ and one distinct site is occupied by Eu3+, and the Eu2+ stabilized at Ln(3+) site accompanied by Eu3+ selectively occupies at Sr2+ site as a charge compensator. An anomalous prolonged Eu2+-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 Eu2+ 5d level to form an excited-state Eu2+. The findings help better understand Eu2+ occupancy and luminescence. These also provide a new perspective for the exploration of novel Eu2+ activated oxide-based red phosphor for pc-LEDs.