Small Stokes Shift and Two‐Site Occupation in the ANb₂O₆:Cr³⁺ (A = Zn/Mg) Phosphors Toward Highly Efficient Ultra‐Broadband Near‐Infrared Emission for Multifunctional Applications

Abstract The development of the new generation of smart near infrared (NIR) light sources is a problem demanding prompt solution with the increasing role of NIR spectroscopy in security, food, medical treatment, agriculture, and other fields. In this work, Cr³⁺ doped ANb₂O₆ (A = Zn/Mg) phosphors are successfully developed, which generate a NIR emission with a peak at 930 nm covering 750–1300 nm under excitation of 515 nm light. Thanks to the small Stokes shift, the internal quantum efficiency (IQE) values of the optimal samples of ZnNb₂O₆:Cr³⁺ and MgNb₂O₆:Cr³⁺ reach up to 70% and 62%, respectively. This ultra‐broadband NIR emission originates from the simultaneous occupation of [AO₆] and [NbO₆] octahedrons by Cr³⁺, which is confirmed by the excitation wavelength‐dependent emission spectra, low‐temperature photoluminescence spectra (77 K), time‐resolved photoluminescence (TRPL) spectra, and density functional theory (DFT) calculation. The thermal quenching mechanism of ANb₂O₆:Cr³⁺ (A = Zn/Mg) is revealed from the aspects of thermal cross and thermal ionization. Benefiting from the excellent performance of ANb₂O₆:Cr³⁺ (A = Zn/Mg) NIR phosphors, the combination of 520 nm LED chips, and as‐prepared phosphors demonstrate the dramatic potential applications in night vision, non‐destructive testing, biological tissue imaging, and spectral analysis.