Crystal structure and luminescence mechanism of novel Fe <sup>3+</sup> ‐doped Mg <sub>0.752</sub> Al <sub>2.165</sub> O <sub>4</sub> deep red‐emitting phosphors
Fei Qi, Guangsheng Tu, Bingtian Tu, Hao Wang, Jian Zhang, Weimin Wang, Zhengyi Fu
Abstract
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.