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Near-infrared-II (NIR-II) luminescence, which serves as a promising spectral window for biomedical applications and spectral analysis, has numerous potential applications. In this work, the NIR-II luminescence is realized in Li4SrCa(SiO4)2:Cr4+ phosphors. Under 465 nm excitation, the emission peak of Li4SrCa(SiO4)2:3%Cr4+ is located at 1215 nm and the full width at half maximum (FWHM) is more than 230 nm, covering the ultra-long range of 950–1600 nm. The photoluminescence spectra, diffuse reflectance spectra, Raman spectra and time-resolved emission spectra confirm the NIR-II luminescence mechanism. Furthermore, a novel post-reduction strategy is proposed to realize the leap-forward enhancement of NIR-II luminescence from Cr4+. By mutually substituting Sr2+ and Ca2+, a series of Li4Sr1+zCa1−z(SiO4)2:3%Cr4+ (z = −1 to 1) samples are prepared to investigate the universality and applicable conditions of the post-reduction strategy. Benefitting from the NIR-II emission of Cr4+, it has great application potential in optical temperature measurement and spectral analysis. [ABSTRACT FROM AUTHOR]

Component modulation strategies are widely used to modulate the PL properties of fluorescent materials. Metal halide perovskites (MHPs) have many advantages for optical applications, one of which is the excellent structural tunability. In this work, a series of Cs2InCl5·H2O:xCr3+ phosphors were synthesized by a simple hydrothermal method, obtaining a broadband near-infrared (NIR) emission in the 800–1200 nm range with a peak at 910 nm under 360 nm excitation. Unlike the widely used B-site cation modulation, co doping Rb+/K+ at A sites improves the structural rigidity and thus enhances the emission intensity and luminescence thermal stability of the Cs2InCl5·H2O:Cr3+ phosphor. In particular, the emission intensity of (Cs0.7K0.3)2InCl5·H2O:0.25Cr3+ at 125 °C can retain 52% of that at room temperature. Due to its excellent performance, the (Cs0.7K0.3)2InCl5·H2O:0.25Cr3+ phosphor in combination with 380 nm ultraviolet chips shows potential applications in non-destructive testing and night vision. This strategy provides new ideas for the modulation of MHP-based fluorescent materials in the future. [ABSTRACT FROM AUTHOR]

Most near-infrared (NIR) phosphors suffer from short emission wavelength (<1000 nm) and narrow full width at half maximum (FWHM) values below 200 nm, restricting their broader applications in non-destructive tests, spectral analysis and photovoltaic fields. This study presents the successful synthesis of the wolframite-type compound InNbTiO6:Cr3+, with Cr3+ occupying a single In3+ site. Under green light irradiation, it emits an ultra-broadband NIR spectrum centered at 965 nm with a FWHM of 231 nm. Substituting In3+ with Ga3+ induces a blue shift in the emission peak from 969 nm to 934 nm, concomitant with an enhancement in the optical properties. To be specific, the NIR luminescence intensity of In0.58NbTiO6:0.02Cr3+,0.4Ga3+ is enhanced by a factor of 2.3, and its thermal stability is improved from 22.3%@400 K to 41.3%@400 K compared to In0.98NbTiO6:0.02Cr3+. The NIR pc-LED is fabricated by integrating the In0.58NbTiO6:0.02Cr3+,0.4Ga3+ phosphor with a 520 nm chip, showcasing its potential for multifunctional applications in solar cells, spectral analysis, and night vision technologies. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) are the ideal light source for next-generation NIR spectroscopy, and developing novel NIR phosphors with high performance is crucial to achieve a wide range of NIR pc-LED applications. In this work, NIR luminescent material Y2Mg2Al2Si2O12 (YMAS):2%Cr3+ with good quantum efficiency (79%) and excellent thermal stability (88%@100 °C) is prepared. Under 430 nm light excitation, YMAS:2%Cr3+ emits 620–1100 nm NIR light with a full-width at half maximum (FWHM) of 153 nm. Fluorescence decay curves, photoluminescence (PL) spectra, 7 K PL spectra, the Rietveld refinement, 27Al solid-state nuclear magnetic resonance (ss-NMR) spectra and time-resolved emission spectroscopy (TRS) confirm that Cr3+ has two different luminescence centers in the YMAS lattice. Benefiting from the site elimination strategy, the double luminescence centers are proven to be derived from Cr3+ ions occupying the two sites [Al1O6] and [Al2O4]. The NIR packaging device prepared using YMAS:2%Cr3+ has outstanding NIR output power and photovoltaic conversion efficiency as high as 45.7 mW@100 mA and 16.7%@100 mA, respectively. Owing to the excellent performance of the YMAS:2%Cr3+ sample, it presents excellent practical performance in plant growth, bioimaging, non-destructive testing and night vision. [ABSTRACT FROM AUTHOR]