Remarkable near-infrared emission enhancement of Cr3+-activated BaGe4O9: the role of lithium ions

Abstract

Driven by the demand for miniaturized broadband near-infrared (NIR) light sources, considerable effort has been dedicated to developing Cr³⁺-activated phosphors. However, in many cases, the multivalent nature of the Cr ion is adverse to achieving highly efficient emission of Cr³⁺. Herein, strategic Li⁺ co-doping was employed to boost the NIR emission of BaGe₄O₉:Cr³⁺. In the phosphor, Li⁺ ions play a pivotal role in the distribution of Cr³⁺ on the two octahedral sites and the elimination of Cr⁴⁺ and crystal defects, leading to a 42.9-fold enhancement of Cr³⁺ emission. The obtained BaGe₄O₉:Cr³⁺,Li⁺ exhibited broadband emission centered at 808 nm, with an FWHM of 177 nm and an internal quantum efficiency of 61.3%. A fabricated pc-LED device utilizing the phosphor showcased an NIR radiant flux of 24.8 mW and a photoelectric efficiency of 8.9% at 100 mA. Furthermore, the application of the pc-LED in bio-imaging, night vision and information encryption was successfully demonstrated.