Breaking Spin-Forbidden Transition by an Antisite Defect Strategy for Enhancing Far-Red Emission of Cr ³⁺ -Activated Phosphors

Cr³⁺-activated phosphors have recently attracted significant research interest because their excellent luminescence properties are comparable to those of lanthanides, enabling diverse applications in modern optical devices. However, Cr³⁺ ions often encounter a spin-forbidden ²E→⁴A₂ transition in a strong crystal field, such as AB₂O₄-type spinel oxides, causing a significant limited far-red-emitting performance. Herein, we adopted an effective antisite defect strategy for reducing the local lattice symmetry and breaking the forbidden transition of Cr³⁺ by constructing antisite defects based on ingenious Al-by-Zn substitution within the ZnAl₂O₄ matrix, thus converting harmful lattice defects into beneficial luminescence elevations. As a result, the emissive intensity of the Cr³⁺-activated phosphors was increased by 2.5-fold, while the internal quantum efficiency (IQE) increased from 46.40% to 73.74%. Moreover, rational ion doping of nonmetallic B³⁺, rare earth-based Y³⁺, and Lu³⁺ further reinforced the absorption and luminescence of phosphors by intensifying lattice distortion, which actualized diverse applications of plant lighting devices, light-converted films, and night vision. This antisite defect strategy provides a fresh perspective for an in-depth understanding of intrinsic structure-property relationships and the design of high-performance phosphors.