Self-reduction-induced Mn heterovalent coexistence for Vis–NIR dual-emission
Yujia Wang, Xin Pan, Zunqi Liu, Zhaojie Wu, Yiren Xiao, Ke Su, Yinghua Rao, Y.X. Jian, Qingfeng Guo, Libing Liao, Lefu Mei
Abstract
To meet the growing demand for stable dual-emission phosphors in optoelectronic applications, this study investigates a self-reduction strategy in Mn-doped Li<sub>2</sub>ZnGe<sub>3</sub>O<sub>8</sub> (LZGO) phosphors. The spinel-structured LZGO lattice enables the coexistence of Mn<sup>2+</sup> and Mn<sup>4+</sup> via oxygen vacancies and lattice defects, achieving visible (Vis) and near-infrared (NIR) dual emission without the need for external reducing agents. Spectroscopic analyses, including X-ray photoelectron spectroscopy (XPS) and diffuse reflectance spectroscopy (DRS), confirm the heterovalent Mn states, with distinct lifetimes of 3.63 ms (Mn<sup>2+</sup>) and 0.32 ms (Mn<sup>4+</sup>) under selective excitation. The LZGO:xMn system thus demonstrates excitation-tunable Vis-NIR luminescence and high stability, making it a cost-effective and environmentally friendly candidate for anti-counterfeiting and bioimaging applications. This work presents a defect engineering driven design concept for developing multifunctional redox-active phosphors with broad application prospects.