Abnormal Lattice Shrinkage, Site Occupation, and Luminescent Properties of Cr 3+ ‐Activated β‐Al 2 O 3 Structure Phosphors

β‐Al 2 O 3 phosphors show good optical properties for highly symmetric lattices and dense frameworks. Here, an abnormal lattice shrinkage phenomenon is found in BaMg 1‐x Zn x Al 9.8 O 17 : Cr 3+ (BM 1‐x Z x A: Cr 3+ ) phosphors, which can be attributed to the variation in the covalency of the chemical bond. Accordingly, the denser crystal structure caused by the abnormal shrinkage improves the luminescent intensity (67%↑) and the thermal stability (69%→76%@150 °C). Internal/external quantum efficiency (IQE/EQE) of BZA: 0.2Cr 3+ reaches 95% and 52.7%, respectively. In addition, the preferential occupation of the Cr 3+ ion is discussed through the crystal field strength calculation, low‐temperature spectra, and fluorescent lifetime. The unique spectrum of the phosphor derives from the occupation of Cr 3+ on the octahedral sites (Al4 and Al1) and the formation of Cr 3+ ‐Cr 3+ coupling pairs. Finally, the high matching rate between the absorption curve of plant pigment P fr and the EL spectrum of the as‐prepared pc‐LED expresses that it can be applied in plant lighting.