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 Mg ₄Nb ₂O ₉:Cr ³⁺ was achieved. Excited by 455 nm blue light, the Mg ₄Nb ₂O ₉:Cr ³⁺ 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 Cr ³⁺ centers within the Mg ₄Nb ₂O ₉ structure, namely Mg ²⁺ and Mg ²⁺-Mg ²⁺ dimer, which was confirmed through luminescence, decay kinetic analysis and density function theory (DFT) calculations. To further broaden the NIR emission, Yb ³⁺ was co-doped with Cr ³⁺ in Mg ₄Nb ₂O ₉. Benefited from the efficient energy transfer from Cr ³⁺ to Yb ³⁺, the codoped Mg ₄Nb ₂O ₉:Cr ³⁺, Yb ³⁺ 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.