Novel Cr3+-activated far-red emitting phosphors with β-Ca3(PO4)2-type structure for indoor plant cultivation

Int. J. Miner. Metall. Mater., 29(2022), No. 6, pp. 1286-1294. http://ijmmm.ustb.edu.cn/article/doi/10.1007/s12613-021-2363-6

Cr3+-activated far-red and near-infrared phosphors have drawn considerable attention owing to their adjustable emission wavelengths and wide applications. Herein, we reported a series of Cr3+-doped phosphors with β-Ca3(PO4)2-type structure, of which Ca9Ga(PO4)7:Cr3+ possessed the highest far-red emission intensity. At an excitation of 440 nm, the Ca9Ga(PO4)7:Cr3+ phosphors exhibited a broad emission band ranging from 650 to 850 nm and peaking at 735 nm, and the broadband superimposed two sharp lines centering at 690 and 698 nm. The optimal sample Ca9Ga0.97(PO4)7:0.03Cr3+ had an internal quantum efficiency of 55.7%. The luminescence intensity of the Ca9Ga0.97(PO4)7:0.03Cr3+ phosphor obtained at 423 K could maintain 68.5% of that at room temperature, demonstrating its outstanding luminescence thermal stability. A phosphor-conversion light-emitting diode was fabricated, indicating that the Ca9Ga(PO4)7:Cr3+ phosphor has potential applications in indoor plant cultivation.

Efficient broadband near-infrared phosphor Sr2ScSbO6:Cr3+ for solar-like lighting

Sci. China Mater. 65, 748–756 (2022).https://doi.org/10.1007/s40843-021-1785-6

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 Sr2ScSbO6:Cr3+ with a double perovskite-type structure, thus simultaneously demonstrating high luminescence efficiency and good thermal stability. Under 550-nm excitation, Sr2ScSbO6:Cr3+ demonstrates broadband NIR emission centered at ∼890nm 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.

Structural Confinement toward Controlling Energy Transfer Path for Enhancing Near-Infrared Luminescence

Chem. Mater. 2021, 33, 21, 8360–8366 https://pubs.acs.org/doi/10.1021/acs.chemmater.1c02734

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 Yb3+-doped Sr9Cr(PO4)7 (SCP) compound, Cr3+ ions are well separated from each other (≥8.97 Å), but they are close to Yb3+ ions (3.70–5.29 Å) due to structural confinement. Therefore, ET is depressed between Cr3+ ions but induced from Cr3+ to Yb3+ ions. On increasing Yb3+ concentration, the thermal stability of near-infrared emission is significantly improved. The emission intensity of the SCP:0.15Yb3+ phosphor at 375 K can keep 100% of that at 80 K. Finally, we show the potential applications of SCP:Yb3+ phosphor in food analysis and nondestructive examination fields. This study provides a new strategy for enhancing luminescence.

Octahedron-dependent near-infrared luminescence in Cr3+-activated phosphors

https://doi.org/10.1016/j.mtchem.2021.100704

Searching for broadband near-infrared (NIR) materials with high efficiency and excellent thermal luminescence stability is of great significance because of their widespread spectroscopic applications. Different element substitution can modulate the structure and crystal field of host lattice so as to regulate the luminescent properties. Herein, we report the octahedron-dependent NIR luminescence in Cr3+-doped KMP2O7 (M = Ga, Sc, In, and Lu) phosphors and investigate the effect of octahedral environment on luminescent properties, aiming to provide guidance for host material selection. The decreased crystal field strength leads to the apparent spectral red shift from 815 to 900 nm for the samples of M = Ga to Lu. The small Stokes shift as well as weak electron–phonon coupling effect decreases the non-radiative transition probability and thus gives rise to the highest emission intensity and excellent thermal stability of Cr3+-doped KGaP2O7. The optimal sample, KGa0.89P2O7:0.11Cr3+, possesses an internal/external quantum efficiency of 55.8%/36.6%, and its integrated emission intensity at 423 K can maintain 68% of that at room temperature. Finally, we investigate the potential applications in non-destructive examination field by manufacturing a NIR phosphor-conversion light-emitting diode device.

Temperature-driven n–p conduction type switching without structural transition in a Cu-rich chalcogenide, NaCu5S3


Chem. Commun., 2020,56, 4882-4885. https://doi.org/10.1039/D0CC01429J

We report for the first time the discovery of reversible n–p conduction type switching in a chalcogenide, NaCu5S3, without structural transition. AC impedance and first-principles simulations of the ionic migration confirmed the local melting trends of the hexagonal copper lattice at high temperatures, which could result in superionic conductivity within NaCu5S3.

Hybrid Metal Halides with Multiple Photoluminescence Centers

Angewandte Chemie., 2019, 58(51), 18670-18675. https://onlinelibrary.wiley.com/doi/abs/10.1002/anie.201911419

Very little is known about the realm of solid-state metal halide compounds comprising two or more halometalate anions. Such compounds would be of great interest if their optical and electronic properties could be rationally designed. Herein, we report a new example of metal halide cluster-assembled compound (C9NH20)9[Pb3Br11](MnBr4)2, featuring distinctly different anionic polyhedra, namely, a rare lead halide cluster [Pb3Br11]5− and [MnBr4]2−. In accordance with its multinary zero-dimensional (0D) structure, this compound is found to contain two distinct emission centers, 565 nm and 528 nm, resulting from the formation of self-trapped excitons and 4T1–6A1 transition of Mn2+ ions, respectively. Based on the high durability of (C9NH20)9[Pb3Br11](MnBr4)2 upon light and heat, as well as high photoluminescence quantum yield (PLQY) of 49.8 % under 450 nm blue light excitation, white light-emitting diodes (WLEDs) are fabricated, showcasing its potential in backlight application.

Single‐Component White‐Light Emission in 2D Hybrid Perovskites with Hybridized Halogen Atoms

Adv. Opt. Mater., 2019, 7(24), 1901335. https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.201901335

With single-component photoinduced white-light (WL) emission, low-dimensional hybrid halide perovskites have emerged as a new generation of luminescent materials; however, the effect of halogens on the intrinsic light emissions and the corresponding mechanisms is still unknown. Herein, the investigation of a family of two-dimensional (2D) hybrid perovskites R2PbBr4−xClx (R = BA+, PMA+, PEA+; x = 0, 1, 2, 3, 4) highlights the influence of halogens on intrinsic emission to reveal the dependence of the photoluminescence on the nature and contribution of the halogens. Ultrabroad emissions covering the entire visible-light region are achieved in the halogen hybrid systems with the stoichiometry of R2PbBr2Cl2 (R = BA+, PMA+, PEA+), showing their potential as single-component WL phosphors in solid-state lighting devices. The origin of the WL emissions is the synergistic recombination emission of free excitons and self-trapped excitons. The ratio of halogens (Br/Cl) is confirmed to be a critical factor to fine-tune the intrinsic emission properties. This work provides a feasible strategy to achieve single-component WL emission in 2D hybrid perovskites, and proposes a method for regulating halogen contents for optimizing luminescent properties.

Crystal structure and luminescence properties of lead-free metal halides (C6H5CH2NH3)3MBr6 (M = Bi and Sb)


J. Mater. Chem. C, 2020,8, 7322-7329. https://doi.org/10.1039/D0TC00562B

Organic–inorganic hybrid metal halides have received extensive attention owing to their versatile structures and optoelectronic properties. Herein, we report two lead-free metal halides, (PMA)3BiBr6 and (PMA)3SbBr6 [PMA+: (C6H5CH2NH3)+, as the abbreviation of phenylmethylammonium], which possess iso-structural zero-dimensional structures and crystallize in the monoclinic space group P21/c. (PMA)3BiBr6 and (PMA)3SbBr6 exhibit optical band gaps of ∼3.50 and 3.40 eV, respectively, and density functional theory calculations reveal their indirect bandgap behaviors. Upon 350 and 425 nm excitation, (PMA)3BiBr6 and (PMA)3SbBr6 exhibit broadband emission peaking at 510 nm and 625 nm with wide full-widths at half-maximum of ∼153 and 175 nm, respectively. The emission mechanism of the metal halides is attributed to self-trapped exciton emission. The relationship between the crystal structure and luminescence intensity is also discussed. Finally, both metal halides have high decomposition temperatures and are stable for long-term storage under ambient conditions, demonstrating their potential for optoelectronic applications.

Sb3+ Doping-Induced Triplet Self-Trapped Excitons Emission in Lead-Free Cs2SnCl6 Nanocrystals

J. Phys. Chem. Lett., 2019, 10, 23, 7439–7444 https://pubs.acs.org/doi/abs/10.1021/acs.jpclett.9b03035

Doped halide perovskite nanocrystals (NCs) have opened new opportunities for the emerging optical and optoelectronic applications. Here, we describe a hot-injection synthesis of all-inorganic lead-free Cs2SnCl6 and Sb3+ doped Cs2SnCl6 NCs. Cs2SnCl6 NCs present a blue emission peak at 438 nm, whereas a new broad-band emission peak appears at 615 nm for the Sb3+ doped NCs. Comparative structural and spectral characterizations of Sb3+ doped Cs2SnCl6 NCs with micrometer-sized undoped and Sb3+ doped crystals show that the formation of broad-band orange emission is originted from triplet self-trapped excitons, attributed to the 3Pn–1S0 transitions (n = 0, 1, 2). Our results in Sb3+ doped Cs2SnCl6 materials provide insights into the machanisms of doping-induced emission centers, and it extends the existing knowledge of optical properties of doped halide NCs for further studies.

Lead-Free Hybrid Metal Halides with a Green-Emissive [MnBr4] Unit as a Selective Turn-On Fluorescent Sensor for Acetone

Inorg. Chem. 2019, 58, 19, 13464–13470.https://pubs.acs.org/doi/abs/10.1021/acs.inorgchem.9b02374

Abstract Image

Organic–inorganic hybrid metal halides with zero-dimensional (0D) structure has emerged as a new class of light-emitting materials. Herein, a new lead-free compound (C9NH20)2MnBr4 has been discovered and a temperature-dependent phase transition has been identified for two phases (space group P21/c and C2/c) in which individual [MnBr4]2– anions connect with organic cations, (C9NH20+) (1-buty-1-methylpyrrolidinium+), forming periodic structure with 0D blocks. A green emission band, peaking at 528 nm with a high photoluminescence quantum efficiency (PLQE) of 81.08%, has been observed at room temperature, which is originated from the 4T1(G) to 6A1 transition of tetrahedrally coordinated Mn2+ ions, as also elaborated by density functional theory calculation. Accordingly, a fast, switchable, and highly selective fluorescent sensor platform for different organic solvents based on the luminescence of (C9NH20)2MnBr4 has been developed. We believe that the hybrid metal halides with high PLQE and the exploration of these as a fluorescence sensor will expand the applications scope of bulk 0D materials for future development.