Structural Design of Cr³⁺-Activated Hexaaluminate Phosphors with High Quantum Efficiency and Cr³⁺–Cr³⁺ Exchange Coupling Pairs

Introducing large-radius cations usually causes structural relaxation, leading to a spectral redshift and low optical performance in Cr 3+ -activated phosphors. Here, MNAl 10 O 17:Cr 3+ phosphors are synthesized, and the substitution of large-radius cations induces the abnormal lattice shrinkage of the N site and atomic site splitting of the M site due to the unique hexaaluminate structure, further distinctly improving luminescent properties. To investigate the university of atomic site splitting, a series of phosphors, Na 2(1– m ) K 2 m Al 10.8 O 17:0.2Cr 3+ and Gd 1– n La n MgAl 10.8 O 19:0.2Cr 3+, are synthesized, and the variation of their luminescent properties conforms to the expected rule. Finally, Ga 3+ ions are introduced to improve the luminescence efficiency. Internal/external quantum efficiencies of the optimal sample are 98.1 and 65.8%, respectively. Meanwhile, an anomalous spectral blueshift indicates the existence of Cr 3+ –Cr 3+ exchange coupling pairs, and a comparative analysis of similar cases is conducted to provide some insights into the luminescence of coupling pairs.