Achieving Broadband NIR-I to NIR-II Emission in Layer-Structured Mg4Nb2O9:Cr3+,Yb3+ Phosphor for Multifunctional Applications

Broadband near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) have garnered unprecedented attention in photonic, optoelectronic and biological applications. Here, an efficient broadband NIR phosphor Mg4Nb2O9:Cr3+ was achieved. Excited by 455 nm blue light, the Mg4Nb2O9:Cr3+ phosphor exhibited a maximum peak at 863 nm with a relatively wide full width at half maximum (FWHM) of approximately 178 nm and the internal quantum efficiency (IQE) was measured to be 94%. The observed broadband emission in the NIR range can be attributed to two distinct Cr3+ centers within the Mg4Nb2O9 structure, namely Mg2+ and Mg2+-Mg2+ dimer, which was confirmed through luminescence, decay kinetic analysis and density function theory (DFT) calculations. To further broaden the NIR emission, Yb3+ was co-doped with Cr3+ in Mg4Nb2O9. Benefited from the efficient energy transfer from Cr3+ to Yb3+, the codoped Mg4Nb2O9:Cr3+, Yb3+ shows a bandwidth of 223 nm and IQE of 86.4%. The pc NIR-LED device incorporating this phosphor achieved a NIR output power of 131.6 mW at input current of 400 mA, with a photoelectric conversion efficiency of 44.2%. Finally, the constructed NIR-LED demonstrated multifunctional applications in non-destructive detection and information encryption.