Single-Site Occupancy of Eu2+ in Multiple Cations Enables Efficient Ultra-Broadband Visible to Near-Infrared Luminescence

An important challenge in the research and development of compact near-infrared (NIR) light sources is the discovery of new efficient ultra-broadband NIR luminescent materials to replace the conventional Cr 3+ -doped compounds. Herein, this work reports a divalent europium-doped Ba 3 GeO 4 Br 2 phosphor that exhibits a high photoluminescence quantum yield of 48.8% and an ultra-broad emission band ranging continuously from 500 to 1100 nm (full width at half maximum = 202 nm) under near-ultraviolet or blue light excitation. A strategy of embedding alumina crucible in high purity graphite crucible is devised and deployed during solid-state sintering to facilitate the conversion of Eu 3+ into Eu 2+ . Theoretical calculations, structural refinement, and spectral analysis demonstrate that the visible to NIR emission in Ba 3 GeO 4 Br 2 :Eu 2+ originates from the Eu 2+ ions occupying the distorted Ba3O 3 Br 4 polyhedra in the lattice. The as-prepared phosphor-converted light-emitting diode device achieves an optical output power of 30.1 mW@100 mA (520–1100 nm) and a photoelectric efficiency of 22%@100 mA (350–1100 nm). Experiments on tissue penetration and NIR imaging illustrate its application in spectral detection and food quality testing appears promising.