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All-inorganic lead-free luminescent metal halides have attracted considerable interest for their special optical properties in various optoelectronic applications. Among them, lanthanide-based Cs3LnCl6 metal halides, with low phonon energies and suitable crystallographic features, have been in the spotlight due to their appealing optical properties. However, it remains challenging for us to know how to simply and efficiently synthesize lanthanide-based Cs3LnCl6 metal halides, and how to optimize their low absorption and emission efficiencies owing to the parity-forbidden f–f transitions. In this minireview, we summarized several synthesis approaches towards both Cs3LnCl6 polycrystals and nanocrystals. The association of the crystal/electronic structure, optical properties and applications is discussed in three sections: self-trapped emission, down-conversion luminescence, and upconversion luminescence. We provide not only the synthesis strategies and recent progress in the luminescence properties of Cs3LnCl6, but also their promising future as alternatives to their toxic and poorly stable lead-based counterparts. [ABSTRACT FROM AUTHOR]

An ultrawide-color-gamut backlight is crucial for achieving ultrahigh definition and ultrahigh resolution liquid crystal displays (LCDs), where green-emitting phosphors with narrow spectral emission are the decisive factors. However, the key green-emitting phosphors currently used in light-emitting diode (LED) backlights, such as commercial β-SiAlON:Eu2+, have the disadvantages of a wide emission band and large particles. In order to display more colorful and vivid photographs, there is an urgent need to accelerate the development of narrow-band green-emitting phosphors with independent intellectual property rights and high quantum efficiency. This article outlines the design of green-emitting phosphors and the improvement of their luminescent properties. From a design perspective, an optimal phosphor must consider the host material and the activator. The emission bands of Tb3+, Mn2+, Ce3+ and Eu2+ are usually located in the visible region, and the short luminesence decay time of Eu2+/Ce3+ makes it a potential activator for high-quality displays. In the exploration and selection of hosts for novel phosphors, approaches such as single-particle diagnosis, high-throughput density functional theory (DFT) calculations and mineral-inspired prototype evolution are commonly employed. Thermal stability and quantum efficiency (QE) are critical properties for phosphors, and various strategies to enhance these characteristics are discussed herein. Moreover, the color gamuts of various green-emitting phosphors are presented, highlighting their applications in green-emitting phosphor-based WLEDs used in LCD screens and projectors. These WLEDs display more vivid image quality than the conventional commercial WLEDs. Finally, the future outlook on exploring and developing green-emitting phosphors with enhanced performance is discussed. [ABSTRACT FROM AUTHOR]

Low dimensional organic‐inorganic hybrid metal halide materials have attracted extensive attention due to their superior optoelectronic properties. However, low photoluminescence quantum yields (PLQYs) caused by parity‐forbidden transition hinder their further application in optoelectronic devices. Herein, a novel yellow‐emitting PMA4Na(In,Sb)Cl8 (C7H10N+, PMA+) low‐dimensional OIMHs single crystal with a PLQY as high as 88 % was successfully designed and synthesized, originating from the fact that the doping of Sb3+ effectively relaxes the parity‐forbidden transition by strong spin‐orbit (SO) coupling and Jahn‐Teller (JT) interaction. The as‐prepared crystal shows an efficient dual emission peaking 495 and 560 nm at low temperature, which are ascribed to different levels of 3P1→1S0 transitions of Sb3+ in [SbCl6]3− octahedral caused by JT deformation. Moreover, wide‐range luminescence tailoring from cyan to orange can be achieved through adjusting excitation energy and temperature because of flexible [SbCl6]3− octahedral in the PNIC lattice. Based on a relative stiff lattice environment, the 560 nm yellow emission under 350 nm light excitation exhibits abnormal anti‐thermal quenching from 8 to 400 K owing to the suppression of non‐radiative transition. The multimode luminescence regulation enriches PMA4Na(In,Sb)Cl8 great potential in the field of optoelectronics such as temperature sensing, low temperature anti‐counterfeiting and WLED applications. [ABSTRACT FROM AUTHOR]

Development of ultra‐broadband visible‐to‐near‐infrared (VIS‐NIR) luminescent materials is a challenging but rewarding endeavor, as they are highly desirable for a number of applications in photonics, optoelectronics, and biological sciences. Nevertheless, to date, rare earth‐doped phosphors that can be efficiently excited by blue light and produce broadband emission in the VIS‐NIR regions remain scarce. In this study, a series of Ce3+‐doped Ba3M4O9 (M = Sc, Lu, Y) broadband luminescent materials are designed based on low‐coordination crystallographic lattice engineering. Among these materials, Ba3Y4O9:Ce3+ produces a continuous ultra‐wide VIS‐NIR emission (λem = 660 nm) in the range of 500–950 nm under 410 nm light excitation. This emission wavelength is the longest among those observed in Ce3⁺‐doped oxide materials. Structural refinement, theoretical calculation, and spectral analysis demonstrate that this VIS‐NIR broadband emission is attributed to the occupying multiple distorted octahedral lattice sites by Ce3+ in Ba3Y4O9. Several strategies are employed to enhance the luminescence intensity and thermal stability of this material, including the use of carbon paper coating, the incorporation of co‐solvents, and the addition of GeO₂ or ZrO₂. Furthermore, the as‐prepared materials demonstrate multifunctional applications in white light‐emitting diodes (WLED), night vision, and fluorescent thermometers. This study offers insights into the design of Ce3+‐doped ultra‐wide VIS‐NIR light‐emitting materials. [ABSTRACT FROM AUTHOR]

Narrow‐band cyan‐emitting materials for white light‐emitting diode (wLED) application have shown great potential in increasing the maximum accessible display gamut and improving the color rendering of full‐spectrum healthy lighting. However, the discovery of novel narrow‐band cyan emitters with excellent luminescence performances remains challenging. Here, an ultra‐narrow‐band cyan‐emitting Na5K3(Li3SiO4)8:Eu2+ (N5K3:Eu2+) phosphor (λem = 483 nm) with full width at half maximum (FWHM) of only 18 nm is developed from some typical UCr4C4 frameworks phosphors by slightly modifying crystal structure and symmetry. Through controllable regulation of the ratio of Na and K from Na4K4(Li3SiO4)8:Eu2+ (N4K4:Eu2+) and Na6K2(Li3SiO4)8:Eu2+ (N6K2:Eu2+) to N5K3:Eu2+, the lattice sites forming shoulder peaks are further squeezed to generate the narrowest cyan emission. Moreover, the N5K3:Eu2+ exhibits low photoluminescence thermal quenching (90%@150 °C) and high internal quantum efficiency (IQE) of 50%. The color rendering index of wLED for full‐spectrum health lighting is enhanced from 92 to 94. Using this short‐wavelength cyan emission instead of a part of the emission from a blue chip can effectively prevent "blue hazard". This work provides basic principles for the design of ultra‐narrow‐band phosphors, thus achieving their applications in the fields of healthy lighting and eye‐friendly display. [ABSTRACT FROM AUTHOR]

Even though there have been significant advancements in the development of Cr3+‐activated near‐infrared (NIR) phosphors, the challenge still remains to develop highly efficient and thermally stable NIR phosphors. Here, the Ca4‐xZnxHfGe3O12:0.03Cr3+ solid solution phosphors with 834–806 nm NIR emission are constructed by substituting Zn2+ for Ca2+, thereby facilitating the formation of [ZnO6] luminescence site. The coexistence of [HfO6] and [Zn/CaO6] luminescence centers is confirmed through DFT calculation, time‐resolved photoluminescence (TRPL) spectroscopy, and low‐temperature‐photoluminescence (77 K) spectroscopy. The formation of [ZnO6] effectively resolves the issue of lattice mismatch between Cr3+ and Ca2+. Furthermore, the simultaneous enhancement of luminescence intensity and thermal stability is realized through a synergistic combination of lattice distortion and rigidity enhancement. By optimizing the substitution concentration of Cr3+, the internal quantum efficiency (IQE) of 92% and an external quantum efficiency (EQE) of 29% are finally achieved. Meanwhile, the thermal stability is also enhanced from 59%@400 K (x = 0) to 81%@400 K (x = 0.8). The developed NIR phosphor‐converted light‐emitting diodes (pc‐LEDs) exhibit promising prospects in the fields of security, biomedicine, non‐destructive testing and rapid identification. [ABSTRACT FROM AUTHOR]

Mn2+‐doped metal halide perovskites present remarkable optical properties in optoelectronic applications, although the realization of high efficiency and stability is still a challenge. In this work, a series of highly efficient and stable orange‐emitting Mn2+ alloyed Cs4Cd1‐xMnxBi2Cl12 single crystals are successfully synthesized via a hydrothermal reaction. Combined with the crystal structure and spectral characterization at 7 K, the site occupation of Mn2+ and defect emission are systematically discussed. Benefiting from the effective [BiCl6]3−→[MnCl6]4− energy transfer and lattice distortion, these single crystals exhibit a maximum internal and external quantum yield of ≈97% and ≈65% at 35% heavy doping level. Interestingly, these Mn2+‐alloyed single crystals exhibit remarkably waterproof stability, no decrease in emission intensity is observed after immersion in deionized water for 4 h. After soaking in deionized water for 100 days, the internal quantum yield can still maintain 44%, implying good chemical stability and moisture resistance due to the formation of protective BiOCl layer. This work provides new insights into the optimization mechanism for Mn2+ luminescence and overcoming the downside of their waterproofing in humid conditions. [ABSTRACT FROM AUTHOR]

Visible‐to‐near‐infrared (VIS‐NIR) luminescent materials are in great demand in the field of non‐destructive testing such as component determination and hyperspectral imaging. Although Cr3+‐activated phosphors are widely reported, controllable tailoring ultra‐wide VIS‐NIR luminescence excited by blue light is still a challenge. The strategies of cationic substitution and energy transfers are effective for adjusting the luminescence of Cr3+‐activated phosphors. In this work, a series of Cr3+‐doped Sc‐based solid solution phosphors (Ba3‐mSrmSc4O9:Cr3+) are reported. Under the excitation of blue light, these phosphors exhibit broadband emission due to the different luminescence centers induced by Cr3+ occupying different cationic sites. Because of the weaker crystal field strength, Cr3+ realizes a broadband emission with a longer peak position (λem = 820 nm) and broader full width at half maximum (FWHM≈182 nm) in Ba2SrSc4O9. Furthermore, Ce3+/Yb3+ ions are introduced into Ba2SrSc4O9:Cr3+, achieving an ultra‐wide VIS‐NIR luminescence (460–1200 nm) by the Ce3+→Cr3+→Yb3+ multiple energy transfers. Designing energy transfers is beneficial to improve the quantum efficiency and weaken the thermal quenching. Finally, the NIR phosphor‐converted light‐emitting diode (pc‐LED) fabricated by Ba2SrSc4O9:Cr3+ demonstrates great potential in night‐vision and water component detection. This work provides an effective design idea for controllable tailoring ultra‐wide VIS‐NIR luminescence by chemical substitution and energy transfer. [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]

Zero‐dimensional (0D) lead‐free metal halides with efficient photoluminescence (PL) have wide application prospects in the optoelectronics field due to their unique structures and physicochemical properties. However, thermal quenching seriously hinders the practical applications of metal halide materials. Herein, this challenging effort is spearheaded to design novel lead‐free 0D indium‐based chloride K3InCl6:Sb3+ single crystals with zero‐thermal quenching and a near‐unity PL quantum yield based on an effective strategy to suppress non‐radiative transitions. Experimental and computational studies indicate that the intense PL emission originates from self‐trapping excitons (STEs). The extremely low temperature of 7 K and time‐resolved spectra reveal the existence of two individual STEs emissions induced by the distinguished octahedrons in K3InCl6:Sb3+ crystals. Meanwhile, the K3InCl6:Sb3+ crystals can maintain PL stability without thermal quenching over a wide temperature range. Furthermore, the phosphor‐converted light‐emitting diodes can stably operate in the long term, benefitting from the significant structural and PL stability of Sb3+‐doped 0D indium‐based chlorides. Therefore, this work not only presents new 0D metal halides with high efficiency and remarkable stability, but also provides insights into designing high‐performance optoelectronic materials. [ABSTRACT FROM AUTHOR]

Recently, an optical thermometer based on the dual‐emitting fluorescent intensity ratio (FIR) in the visible light (VIS) region has achieved great development. However, there is very little progress in thermometers from NIR light. In this work, a novel optical thermometer based on highly efficient NIR dual‐emission of Cr3+ and Ni2+ in LaZnGa11O19 (LZG) with a magnetoplumbite structure is designed. Utilizing energy transfer from Cr3+ to Ni2+, the dual‐emission shows a wide coverage in the 650–1600 nm region, covering the NIR I and II windows, respectively. The as‐reported LZG:0.3Cr3+ and LZG:0.3Cr3+,0.01Ni2+ phosphors can reach internal/external quantum efficiency (IQE/EQE) of 94%/64% and 77%/53%, respectively. The electroluminescence property and potential applications in spectroscopic analysis, night‐vision, and bioimaging of fabricated NIR‐LED with LZG:0.3Cr3+,0.01Ni2+ have also been investigated. In addition, the designed ratiometric optical thermometer responds to wide temperature ranges (100‐175 K, 200–475 K) and shows a maximum relative sensitivity value (Sr) of 2.4% K−1 at 475 K. The optical performance of absorption in the red region and emission in the NIR region enables the LZG:0.3Cr3+,0.01Ni2+ to become a candidate for NIR optical thermometers in biotechnological applications. [ABSTRACT FROM AUTHOR]

Porous covalent organic frameworks (COFs) have been widely used for the efficient removal of iodine from solution due to their abundance of electron-rich sites. In this study, two kinds of ketoenamine-based COFs, TpBD-(OMe)2 and TpBD-Me2, are successfully synthesized via Schiff base reaction under solvothermal conditions using 1, 3, 5-triformylphoroglucinol as aldehyde monomer, o-tolidine and o-dianisidine as amino monomers. The ability of TpBD-(OMe)2 and TpBD-Me2 to adsorb iodine in cyclohexane or aqueous solutions has been quantitatively analyzed and interpreted in terms of adsorption sites. TpBD-Me2 possesses two adsorption sites, -NH- and -C=O, and exhibits an adsorption capacity of 681.67 mg/g in cyclohexane, with an initial adsorption rate of 0.6 g/mol/min with respect to COF unit cell. The adsorption capacity of TpBD-(OMe)2 can be as high as 728.77 mg/g, and the initial adsorption rate of TpBD-(OMe)2 can reach 1.2 g/mol/min in the presence of oxygen atoms between the methyl group and the benzene ring. Compared with TpBD-Me2, the higher adsorption capacity and adsorption rate of TpBD-(OMe)2 towards iodine are not only reflected in organic solvents, but also in aqueous solutions. It is proven through X-ray photoelectron spectroscopy and Raman spectroscopy that iodine exists in the form of I2, I3−, and I5− within TpBD-(OMe)2 and TpBD-Me2 after adsorption. This work not only expands the application of COFs in the field of iodine adsorption, but also provides research ideas and important an experimental basis for the optimization of iodine adsorption sites. [ABSTRACT FROM AUTHOR]

Lead‐free halide double perovskites are currently gaining significant attention owing to their exceptional environmental friendliness, structural adjustability as well as self‐trapped exciton emission. However, stable and efficient double perovskite with multimode luminescence and tunable spectra are still urgently needed for multifunctional photoelectric application. Herein, holmium based cryolite materials (Cs2NaHoCl6) with anti‐thermal quenching and multimode photoluminescence were successfully synthesized. By the further alloying of Sb3+ (s‐p transitions) and Yb3+ (f‐f transitions) ions, its luminescence properties can be well modulated, originating from tailoring band gap structure and enriching electron transition channels. Upon Sb3+ substitution in Cs2NaHoCl6, additional absorption peaking at 334 nm results in the tremendous increase of photoluminescence quantum yield (PLQY). Meanwhile, not only the typical NIR emission around 980 nm of Ho3+ is enhanced, but also the red and NIR emissions show a diverse range of anti‐thermal quenching photoluminescence behaviors. Furthermore, through designing Yb3+ doping, the up‐conversion photoluminescence can be triggered by changing excitation laser power density (yellow‐to‐orange) and Yb3+ doping concentration (red‐to‐green). Through a combined experimental‐theoretical approach, the related luminescence mechanism is revealed. In general, by alloying Sb3+/Yb3+ in Cs2NaHoCl6, abundant energy level ladders are constructed and more luminescence modes are derived, demonstrating great potential in multifunctional photoelectric applications. [ABSTRACT FROM AUTHOR]

Metal halide perovskites (MHPs) have shown great application prospects in the field of optoelectronics owing to their superior optical and optoelectronic properties. Bandgap engineering and impurity doping are effective ways to achieve regulation of luminous properties in the visible light region. However, realizing efficient deep red and wide‐range tunable near‐infrared (NIR) emission remains a challenge. Here, a series of rare earth (RE3+) ions (RE = Nd, Dy, Ho, Er, Tm, Yb) doped Cs4Cd1−xMnxSb2Cl12 (0 ≤ x ≤ 1) quadruple perovskites are designed. An efficient tunable luminescence from red to NIR light is achieved based on the energy transfer (ET) from Mn2+ to RE3+ by building the Mn2+ energy bridge, which covers the NIR‐I (650–900 nm) and NIR‐II (900–1700 nm) regions. Moreover, the ET efficiency is availably influenced by the doping concentration of Mn2+. Interestingly, the energy bridge from Mn2+ to RE3+ is cut off because of the increased bandgap when Bi3+ is introduced into the RE3+‐doped Cs4Cd0.4Mn0.6Sb2−yBiyCl12 (0 ≤ y ≤ 2) lattice. Through bandgap engineering, the ET from Mn2+ to RE3+ resembles an "optical energy shutter" which quenches the NIR emission of RE3+ owing to the mismatched energy level but enhances the emission of Mn2+. [ABSTRACT FROM AUTHOR]