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Transition metal ions, such as Cr3+, Fe3+, and Ni2+, are widely recognized activators for efficient broadband near‐infrared (NIR) phosphors. However, the potential of Mn2+ ions as NIR‐emitting activators is relatively overlooked due to their typically narrowband emission in the visible spectral region and relatively weak absorption. Herein, a heavy Mn2+‐doped Zn1‐xAl2O4: xMn2+ (ZAO: xMn2+) phosphor is presented that exhibits a single NIR emission band peaked at 830 nm with a bandwidth of 135 nm under excitation at 450 nm. Through comprehensive structural and spectral analysis, this NIR band is attributed to the emission originating from Mn2+ ions within the MnO6 octahedra. Importantly, the formation of Mn2+–Mn2+ dimers breaks the spin‐forbidden rule and significantly enhances the transition probability, as supported by the excited state dynamic analysis. Consequently, the optimal ZAO: 0.70Mn2+ sample shows high internal/external photoluminescence quantum yields of 85.8%/36.9%, along with good thermal stability demonstrated by the emission intensity at 423 K retains 60% of that at 298 K. Finally, a prototype NIR pc‐LED device is fabricated by combining ZAO: 0.70Mn2+ phosphor with a 450 nm blue diode chip, generating an NIR output power of 28.84 mW at 100 mA. This study provides novel insights into high‐performance Mn2+‐activated NIR phosphors. [ABSTRACT FROM AUTHOR]

The strategy of heavily doping Mn2+ not only enhances light-absorption intensity, but also sometimes induces the production of unique long-wavelength luminescence. However, the understanding of the luminescence mechanism remains limited. Herein, we investigated the Mn2+ concentration-dependent luminescence behavior of LaMgAl11O19: xMn2+ (LMAO : xMn2+) phosphors. Upon an excitation of 450 nm, the PL spectra of LMAO : xMn2+ transitioned from single green emission to dual-wavelength green/far-red emission, ultimately evolving into pure far-red emission by gradually increasing Mn2+ concentration. The green emission was attributed to tetrahedrally coordinated Mn2+, whereas the far-red emission originated from octahedral Mn2+ owing to its significantly prolonged lifetime. Notably, an energy transfer occurred between neighboring tetrahedral and octahedral Mn2+, resulting in their similar excitation spectra. Additionally, when the concentration of Mn2+ was further increased, the far-red emission spectrum underwent a sustained redshift, and broadband NIR luminescence peaking at 830 nm with a shortened lifetime emerged, suggesting its luminescence originates from Mn2+–Mn2+ dimers. Finally, leveraging the similar excitation spectra and distinct thermal quenching behaviors of the green and far-red emissions, we developed a novel FIR thermometer LMAO : 0.54Mn2+ demonstrating excellent temperature-sensing capability and repeatability. This study provides new insights into the heavily Mn2+-doped materials and advanced optical applications. [ABSTRACT FROM AUTHOR]

Synthesis of a Mn4+‐activated fluoride red‐emitting phosphor combining high efficiency, excellent thermal stability, and outstanding moisture resistance still remains a challenge. Herein, this work synthesizes a red‐emitting phosphor Cs2NbF6: Mn4+ (CNF: Mn4+) based on the cation‐exchange method. Interestingly, as a result of the redox reaction between Mn3+ (Mn2+) and Nb5+ ions during the exchange reaction, the real Mn4+ concentration is remarkably increased, while Nb5+ ions are reduced to Nb4+. The obtained optimum CNF: Mn4+ phosphor shows high internal and external photoluminescence (PL) quantum yield (QY) of 92% and 58%, respectively. Moreover, the CNF: Mn4+ exhibits excellent thermal stability (I@150 = 105%) and moisture resistance. A white light‐emitting diode (LED) packaged by combining blue diode chips, Y3Al5O12:Ce3+ yellow phosphor, and CNF: Mn4+ red phosphor demonstrates a low correlated color temperature (CCT) of 3872 K, high color rendering index (CRI) of Ra = 88, and a luminous efficacy of 105 lm W−1. The high‐performance of the white LED suggests the great potential of the CNF: Mn4+ narrowband red phosphor in display and lighting fields. [ABSTRACT FROM AUTHOR]

Phosphor-converted light-emitting diodes (pc-LEDs) have important applications in security surveillance and food testing. However, developing new broadband near-infrared phosphors remains an important issue. Herein, the high-temperature solid-state reaction method was applied to synthesize a new type of Cr3+ doped Mg2Al4Si5O18 broadband NIR phosphor which matches a blue LED chip. It exhibits a broadband near-infrared (NIR) phosphor emission with a focus of 856 nm and a full width at half maximum >200 nm after excitation at 453 nm. The optimum concentration of Cr3+ was established to contain 2 mol%. At 398 K, the luminescence intensity is 45.2% of that at 298 K. The power output of NIR pc-LEDs fabricated by incorporating a 450 nm chip and the Mg2Al4Si5O18:0.02 Cr3+ phosphor is 19.69 mW at 300 mA current. Finally, the developed NIR pc-LED shows significant potential for use in night-vision imaging. [ABSTRACT FROM AUTHOR]

With the rapid development of NIR pc-LEDs, the development of a novel NIR phosphor with broadband emission, strong luminescence and high thermal stability is urgent. Here, three isotypic garnet fluorides Na3X2Li3F12 (X = Al, Ga, or In) (NXLF) activated by Cr3+ were synthesized. The emission peak shifts from 752 to 778 nm and FWHM expands from 101 to 121 nm. The values of Dq/B indicate that Cr3+ ions undergo a weak crystal field. Among them, NInLF:Cr3+ has the highest IQE of 87.2% and NAlLF:Cr3+ exhibits the best thermal stability, which maintains 82% of its initial intensity at 423 K. The Huang–Rhys factor of NAlLF:Cr3+ exhibits a rather low EPC. The output power and photoelectric conversion efficiency of the packaged NIR pc-LEDs could achieve 149 mW and 14.3% at 350 mA. Under the irradiation of NIR light, clear images of blood vessel distribution of palm and arm were obtained, implying that these phosphors have great application potential in the biomedical field. [ABSTRACT FROM AUTHOR]

Near-infrared (NIR) phosphor-converted light emitting diode (pc-LED) light sources have broad application prospects in environmental science, biomedical and plant growth fields. However, NIR phosphors still suffer from narrowband emission and low thermal stability. Here, we prepared a novel Lu2CaMg2−xSi3O12:xCr3+ (LCMS:xCr3+, x = 0.005–0.06) phosphor with broadband emission by a high-temperature solid state reaction. Under excitation at 450 nm, the emission spectrum of the LCMS:0.05Cr3+ phosphor shows a broadband emission in the range of 650–1000 nm with a large full width at half maximum (FWHM) of 125 nm and an R-line emission of 692 nm. In addition, the LCMS:0.05Cr3+ phosphor has good thermal stability and can maintain 70% emission intensity at 150 °C relative to that at room temperature. The LCMS:0.05Cr3+ phosphor exhibits a high internal quantum efficiency (IQE) of ∼76%. Using this phosphor, a NIR pc-LED with photoelectric efficiencies of 14.8% at 100 mA and 6.0% at 320 mA and NIR output powers of 59.5 mW at 100 mA and 181.0 mW at 320 mA was obtained. The broadband LCMS:0.05Cr3+ phosphor with a NIR emission peaked at 750 nm can serve as a light source for plant cultivation and has superior application prospects in the agriculture field. [ABSTRACT FROM AUTHOR]

Recent decades have witnessed a major development in broadband near-infrared (NIR)-emitting phosphors because of their potential applications in real-time nondestructive examination. These applications require the emission spectra of phosphors to be as broad as possible for efficient performance. Therefore, a blue-light excited LiInF 4 : Cr 3+ phosphor with a NIR emission covering 700-1400 nm is successfully synthesized. Under 470 nm excitation, it shows broadband emission peaked at 980 nm with the full-width at half maximum of 210 nm. The structure and crystal field environment are investigated in detail, and the LiInF 4 : Cr 3+ possesses a weak crystal field strength and strong electron-phonon coupling. An efficient NIR phosphor-converted light-emitting diode (pc-LED) is fabricated by the prepared LiInF 4 : Cr 3+ phosphor and commercial blue diode chip, generating a NIR radiant flux of 5.54 mW at 150 mA drive current. Finally, the NIR pc-LED is successfully applied to identify the blood vessel distribution of the hand. This work suggests the potential of LiInF 4 : Cr 3+ phosphor in applications.

Phosphor-converted light-emitting diodes (pc-LEDs) have important applications in security surveillance and food testing. However, developing new broadband near-infrared phosphors remains an important issue. Herein, the high-temperature solid-state reaction method was applied to synthesize a new type of Cr 3+ doped Mg 2 Al 4 Si 5 O 18 broadband NIR phosphor which matches a blue LED chip. It exhibits a broadband near-infrared (NIR) phosphor emission with a focus of 856 nm and a full width at half maximum >200 nm after excitation at 453 nm. The optimum concentration of Cr 3+ was established to contain 2 mol%. At 398 K, the luminescence intensity is 45.2% of that at 298 K. The power output of NIR pc-LEDs fabricated by incorporating a 450 nm chip and the Mg 2 Al 4 Si 5 O 18 :0.02 Cr 3+ phosphor is 19.69 mW at 300 mA current. Finally, the developed NIR pc-LED shows significant potential for use in night-vision imaging.

Near-infrared (NIR) phosphor-converted light emitting diode (pc-LED) light sources have broad application prospects in environmental science, biomedical and plant growth fields. However, NIR phosphors still suffer from narrowband emission and low thermal stability. Here, we prepared a novel Lu2CaMg2-xSi3O12:xCr3+ (LCMS:xCr3+, x = 0.005-0.06) phosphor with broadband emission by a high-temperature solid state reaction. Under excitation at 450 nm, the emission spectrum of the LCMS:0.05Cr3+ phosphor shows a broadband emission in the range of 650-1000 nm with a large full width at half maximum (FWHM) of 125 nm and an R-line emission of 692 nm. In addition, the LCMS:0.05Cr3+ phosphor has good thermal stability and can maintain 70% emission intensity at 150 °C relative to that at room temperature. The LCMS:0.05Cr3+ phosphor exhibits a high internal quantum efficiency (IQE) of ∼76%. Using this phosphor, a NIR pc-LED with photoelectric efficiencies of 14.8% at 100 mA and 6.0% at 320 mA and NIR output powers of 59.5 mW at 100 mA and 181.0 mW at 320 mA was obtained. The broadband LCMS:0.05Cr3+ phosphor with a NIR emission peaked at 750 nm can serve as a light source for plant cultivation and has superior application prospects in the agriculture field.