Tetracoordinate Fe 3+ Activated Li 2 ZnAO 4 (A = Si, Ge) Near-Infrared Luminescent Phosphors.

Fe 3+ -doped near-infrared (NIR) phosphors have received a lot of interest because they are nontoxic, inexpensive, and ecologically benign. In this work, Fe 3+ -activated Li 2 ZnAO 4 (A = Si, Ge) phosphors were synthesized by solid-phase reactions, in which Fe 3+ entered the Zn 2+ tetrahedral site. When excited by 300 nm UV light, broad NIR emission bands at 750 nm (Li 2 ZnSiO 4 : Fe 3+ ) and 777 nm (Li 2 ZnGeO 4 : Fe 3+ ) were observed, with internal quantum efficiencies (IQE) of 62.70% (Li 2 ZnSiO 4 : Fe 3+ ) and 30.57% (Li 2 ZnGeO 4 : Fe 3+ ). 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 Li 2 ZnGeO 4 : Fe 3+ phosphor. Besides, the as-synthesized phosphor demonstrated sensitive and selective Cu 2+ ion detection.