Crystal structure and luminescence mechanism of novel Fe 3+ ‐doped Mg 0.752 Al 2.165 O 4 deep red‐emitting phosphors

Abstract Nonstoichiometric alumina‐rich spinel provides diverse and changeable local environments for transition‐metal dopants. In this contribution, novel Mg 0.752 Al 2.165− x O 4 : x Fe 3+ deep red‐emitting phosphors were designed and prepared by the solid‐state reaction method. The red emission presents an unexpected shift from 735 to 770 nm by comparing with Fe 3+ ‐doped MgAl 2 O 4 . The excitation spectrum of Mg 0.752 Al 2.165− x O 4 : x Fe 3+ is broadened in the UV region with a new strong peak at 320 nm. The crystal structure refinement and NMR spectra fitting reveal that the cation vacancies and disorder increase with excess Al 3+ entering the spinel crystal lattice. According to the results of EPR, NMR, and PL/PLE measurements, it was proposed that the Fe 3+ ions locate at the distorted octahedral coordination. The changes of the local structure of Fe 3+ ions promote the doublet state's involvement in the d−d transition. It was proposed that the new excitation peak at 320 nm in Mg 0.752 Al 2.165− x O 4 : x Fe 3+ is associated with the transitions from the ground state 6 A 1g ( 6 S) to the 4 A 2g ( 4 F)/T 1g ( 4 P) and doublet states. The transition between the lower energy excited state of 2 T 2g ( 2 I) and 6 A 1g ( 6 S) mainly contributes to the deep red emission and the red‐shifting effect.