A Cr3+-doped halide double perovskite Cs2AgInCl6:Cr3+ is first reported which exhibits a broad near-infrared emission ranging from 850 to 1350 nm centered at 1010 nm with a FWHM of 180 nm.

Cr3+/Cr4+‐activated near‐infrared (NIR) luminescent materials have attracted extensive attention owing to their tunable emission wavelength and widespread applications in plant growth, food analysis, biomedical imaging, night vision, and so on. Plenty of excellent NIR materials are developed by introducing Cr3+/Cr4+ ion to various inorganic hosts. Herein, the effect of crystal field on Cr3+/Cr4+ luminescence by combining the Tanabe–Sugano energy level diagram and configuration coordinate model is discussed. Research progress of Cr3+/Cr4+‐doped NIR luminescent materials, including the phosphors designed from structural models with octahedral, tetrahedral, and other coordination types, is then outlined. The luminescence properties of more than 200 kinds of Cr3+/Cr4+‐doped materials are summarized. In particular, several strategies for tuning emission wavelength, broadening emission band, enhancing NIR luminescence efficiency, and improving thermal stability, are listed. Finally, the current challenges and future prospects in the research of Cr3+/Cr4+‐doped NIR luminescent materials are presented. This review will contribute to a deeper understanding of not only Cr3+/Cr4+ luminescence mechanism but also the current research progress of chromium‐doped luminescent materials, so as to develop more Cr3+/Cr4+‐activated NIR luminescent materials with better performance and explore more applications.

Trivalent chromium ion-doped near-infrared (NIR) phosphors have been widely studied due to their tunable emission wavelengths and broad applications. High Cr 3+ concentration can improve absorption efficiency but generally results in low emission intensity due to the concentration quenching effect. Herein, we report a series of efficient NIR phosphors with suppressed concentration quenching, Sr 9 M 1−x (PO 4 ) 7 :xCr 3+ (M = Ga, Sc, In, and Lu), showing a broadband NIR emission ranging from 700 to 1100 nm peaking at 850 nm upon the 485 nm light excitation. The emission peak position is almost independent of the type of M ion and the Cr 3+ dopant content, and the type of M ion has little influence on the luminescence thermal quenching, indicating that [MO 6 ] octahedra are rigid enough to keep octahedral volumes and average M 3+ −O 2− distances nearly constant owing to the formation of the framework structure on Cr 3+ substitution. The NIR emission intensities monotonously increase with the Cr 3+ content increasing from 0 to 80% with suppressed concentration quenching, the intensity of Sr 9 Cr(PO 4 ) 7 still maintains 84.23% of Sr 9 Ga 0.2 (PO 4 ) 7 :0.8Cr 3+ phosphor, and the thermal quenching behavior is slightly dependent on x; these effects can be attributed to the suppressed energy transfer due to the structural confinement effect. The optimal sample, Sr 9 Ga 0.2 (PO 4 ) 7 :0.8Cr 3+ , has an internal/external quantum efficiency of 66.3%/29.9%. Finally, we fabricate a NIR phosphor-conversion light-emitting diode and demonstrate its applications in nondestructive examination and medical fields.

Energy transfer (ET) between optically active ions usually leads to luminescent concentration quenching and thermal quenching. Toward luminescence enhancement, it is very challenging to control the ET path. Herein, we demonstrated a strategy for selectively controlling ET pathway through the structural confinement effect for activated ions. In the Yb 3+ -doped Sr 9 Cr(PO 4 ) 7 (SCP) compound, Cr 3+ ions are well separated from each other (≥8.97 Å), but they are close to Yb 3+ ions (3.70−5.29 Å) due to structural confinement. Therefore, ET is depressed between Cr 3+ ions but induced from Cr 3+ to Yb 3+ ions. On increasing Yb 3+ concentration, the thermal stability of near-infrared emission is significantly improved. The emission intensity of the SCP:0.15Yb 3+ phosphor at 375 K can keep 100% of that at 80 K. Finally, we show the potential applications of SCP:Yb 3+ phosphor in food analysis and nondestructive examination fields. This study provides a new strategy for enhancing luminescence.

For healthy lighting, daily lighting that considers both visible light and near-infrared (NIR) light is necessary. However, at~900 nm, the extensively used solar-like phosphor-converted light-emitting diodes (pc-LEDs) are limited by a lack of high-performance NIR luminescent materials. We report a broadband NIR phosphor Sr 2 ScSbO 6 :Cr 3+ with a double perovskite-type structure, thus simultaneously demonstrating high luminescence efficiency and good thermal stability. Under 550-nm excitation, Sr 2 ScSbO 6 :Cr 3+ demonstrates broadband NIR emission centered at~890 nm with luminescence internal/external efficiencies of 82.0%/35.7%, respectively. Furthermore, the luminescence integrated intensity at 430 K remains at~66.4% of the initial intensity. We successfully fabricated pc-LED devices using a 465-nm-sized blue chip and other commercial phosphors, presenting a relatively complete solar-like spectrum from blue to NIR light and is expected to be used in solar-like lighting.

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Cr3+-activated near-infrared (NIR) materials have currently attracted extensive attention owning to emerging NIR spectroscopic applications. One promising strategy to tuning the excitation and emission spectra is to modulate compositions and...