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

Fe³⁺-doped near-infrared (NIR) phosphors have received a lot of interest because they are nontoxic, inexpensive, and ecologically benign. In this work, Fe³⁺-activated Li₂ZnAO₄ (A = Si, Ge) phosphors were synthesized by solid-phase reactions, in which Fe³⁺ entered the Zn²⁺ tetrahedral site. When excited by 300 nm UV light, broad NIR emission bands at 750 nm (Li₂ZnSiO₄: Fe³⁺) and 777 nm (Li₂ZnGeO₄: Fe³⁺) were observed, with internal quantum efficiencies (IQE) of 62.70% (Li₂ZnSiO₄: Fe³⁺) and 30.57% (Li₂ZnGeO₄: Fe³⁺). The thermal stability was increased from 35.43 to 49.79% at 373 K via cationic regulation. The combination of activation energy, electron-phonon coupling, and Debye temperature explained the improved thermal stability of Li₂ZnGeO₄: Fe³⁺ phosphor. Besides, the as-synthesized phosphor demonstrated sensitive and selective Cu²⁺ ion detection.