Mg<sub>4</sub>InSbO<sub>8</sub> Spinel: Double 2:1 Ordering in Tetrahedral and Octahedral Sublattices and Perspective Application as an Optical Thermometer via Mn<sup>2+/4+</sup> Doping
Zien Cheng, Jinmei Huang, Guangxiang Lu, Yuhan Wu, Maxim Avdeev, Tao Yang, Pengfei Jiang
Abstract
AB 2 O 4 -type spinel oxides were extensively investigated as prospective magnetic, photocatalytic, cathode, and host materials. Herein, a new Mg 4 InSbO 8 spinel was rationally designed and structurally characterized by high-resolution X-ray powder diffraction (XRPD) in combination with neutron powder diffraction. Mg 4 InSbO 8 crystallizes in the Imma -superstructure with lattice dimensions of a = √2/2· a C, b = 3√2/2· a C, and c = a C, where a C is the lattice parameter of the cubic ( Fd 3̅ m ) archetype spinel. The formation of this hitherto unreported Imma -spinel superstructure is a result of 2:1 Mg 2+ /Sb 5+ ordering in the octahedral sublattice, which further creates two crystallographically independent tetrahedral sites with distinctive sizes and thereby resulting in a site-selective 2:1 occupation for the Mg 2+ and In 3+ cations. Mg 4 InSbO 8 is the first spinel superstructure exhibiting double 2:1 cationic ordering in both octahedral and tetrahedral sublattices. Compared with other ordered spinel structures, we found that the ionic radius and charge differences, coordination geometry preference, and chemical bonding character are all responsible for the formation of this unique doubly ordered spinel superstructure of Mg 4 InSbO 8 . Theoretical calculations, together with diffuse reflectance spectroscopy, revealed that Mg 4 InSbO 8 is an indirect semiconductor. Moreover, the multiple tetrahedral and octahedral sites in Mg 4 InSbO 8 are appropriate for green- and deep-red-emitting Mn 2+ and Mn 4+ activators, respectively. Tunable color emission from green to white and then to deep red can be achieved for Mg 4 InSbO 8 /Mn 2+/4+ phosphors by adjusting the excitation energy. More importantly, Mn 2+ and Mn 4+ activators experience distinctive thermal quenching responses, thereby resulting in a vivid color change from green to red for Mg 4 InSbO 8 /Mn 2+/4+ upon heating. The highest sensitivity for color change is S r = 2.10% at 453 K, manifesting potential applications in temperature sensing. Our findings pave the way to designing cation-ordered spinel superstructures and exploring and expanding their prospective applications.