Crystal structure and luminescence mechanism of novel Fe³⁺‐doped Mg_0.752Al_2.165O₄ deep red‐emitting phosphors

Abstract

Nonstoichiometric alumina‐rich spinel provides diverse and changeable local environments for transition‐metal dopants. In this contribution, novel Mg0.752Al2.165−xO4:xFe3+ 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 Fe3+‐doped MgAl2O4. The excitation spectrum of Mg0.752Al2.165−xO4:xFe3+ 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 Al3+ entering the spinel crystal lattice. According to the results of EPR, NMR, and PL/PLE measurements, it was proposed that the Fe3+ ions locate at the distorted octahedral coordination. The changes of the local structure of Fe3+ ions promote the doublet state's involvement in the d−d transition. It was proposed that the new excitation peak at 320 nm in Mg0.752Al2.165−xO4:xFe3+ is associated with the transitions from the ground state 6A1g(6S) to the 4A2g(4F)/T1g(4P) and doublet states. The transition between the lower energy excited state of 2T2g(2I) and 6A1g(6S) mainly contributes to the deep red emission and the red‐shifting effect.

Structural confinement toward suppressing concentration and thermal quenching for improving near-infrared luminescence of Fe3+

“…It can be seen that the absorption bands are mainly located in the UV region (270-400 nm), which can be attributed to the host absorption of SGP (300 nm) as well as the charge transfer (CT) transition between ligand O 2− ions and central metal Fe 3+ ions (330 nm). 26 Compared with the Fe 3+ -free sample, in addition to the absorption band from O 2− -Fe 3+ CT transitions, there exist three other absorption bands peaking at about 425, 550 and 750 nm in Fe 3+ -doped phosphors originating from 6 A 1 ( 6 S) → 4 T 2 ( 4 D), 6 A 1 ( 6 S) → 4 T 2 ( 4 G) and 6 A 1 ( 6 S) → 4 T 1 ( 4 G) transitions of Fe 3+ ions, 27 respectively. When enhancing the Fe 3+ dopant concentration from 5% to 100%, the absorption intensity gradually increases.…”

“…2d, an additional excitation peak at 383 nm appears when the PLE spectrum is recorded at 77 K, and this peak originates from the 6 A 1 ( 6 S) → 4 E( 4 D) transition of Fe 3+ ions. 26 Fig. S5 † shows the magnified PLE spectrum recorded at 77 K and the DR spectrum ranging from 450 to 800 nm of SGP:0.2Fe 3+ .…”

Tetracoordinate Fe3+ Activated Li2ZnAO4 (A = Si, Ge) Near-Infrared Luminescent Phosphors

“…Unfortunately, Fe 3+ in an octahedral environment may suffer from poor IQY because the symmetry of the octahedral crystal field is higher than that of the tetrahedral crystal field. Fe 3+ in a tetrahedral environment may exhibit improved luminescence performances owing to the readily broken-down electric selection rules . Besides, Fe 3+ in the tetrahedron shows a blue shift in emission due to the decrease in the crystal field strength.…”

“…Fe 3+ in a tetrahedral environment may exhibit improved luminescence performances owing to the readily broken-down electric selection rules. 20 Besides, Fe 3+ in the tetrahedron shows a blue shift in emission due to the decrease in the crystal field strength. To obtain a longer NIR emission, cationic engineering has usually been used.…”

Broadband emitting Fe3+‐doped double perovskite‐type antimonates phosphors for NIR spectroscopy applications

“…23,24 On the one hand, tetrahedrally coordinated Fe 3+ ions emit in the 650−750 nm range, such as Mg 2 SnO 4 : Fe 3+ , Li 2 ZnSiO 4 : Fe 3+ , and LiAl 5 O 8 : Fe 3+ . [25][26][27] On the other hand, sixcoordinated Fe 3+ ions are expected to exhibit longer NIR emission wavelengths by adjusting the symmetry of the octahedra lower, such as MgAl 2 O 4 : Fe 3+ and MgGa 2 O 4 : Fe 3+ , 28,29 especially Sr 2−y Ca y (InSb) 1−z Sn 2z O 6 : Fe 3+ phosphors can achieve unprecedented long-wavelength NIR emission tuning from 885 to 1005 nm. 30 Moreover, double perovskite type antimonates (A 2 BSbO 6 ) are preeminent NIR host materials due to the abundant [BO 6 ]/[SbO 6 ] octahedra availing transition metal ions to incorporate.…”