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.

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.

Infrared-photostimulable and long-persistent ultraviolet-emitting phosphor LiLuGeO4:Bi3+,Yb3+ for biophotonic applications

Mater. Chem. Front., 2021,5, 1468-1476 https://pubs.rsc.org/en/content/articlelanding/2021/qm/d0qm00932f/unauth

Photodynamic therapy needing ultraviolet (UV) in deep tissue is hindered due to the low biological tissue penetration ability of UV light. Here, we demonstrate a persistent ultraviolet-emitting phosphor, LiLuGeO4:Bi3+,Yb3+, which can be re-stimulated by near infrared (NIR) light. Yb3+-doping significantly enhances the trap density without changing the thermoluminescence peak positions. The phosphor can be effectively activated by a 254 nm lamp and exhibits prominent persistent luminescence peaking at 350 nm. The decay time can be recorded much longer than 15 h. This phosphor exhibits simulated in vivo photostimulated persistent luminescence after a longtime decay by using in vitro NIR light penetrating biological tissue. Combined with CaAlSiN3:Eu2+, red persistent luminescence from Eu2+ is obtained. LiLuGeO4:Bi3+,Yb3+ makes up the shortage of excellent UVA persistent phosphors. It is expected to have potential applications as an in vivo renewable excitation source to trigger photosensitizers or fluorescent probes when used for biophotonic applications.

Crystal-field splitting of Ce3+ in narrow-band phosphor SrLiAl3N4

J. Rare Earths., 2021, 39(4), 386-389https://www.sciencedirect.com/science/article/abs/pii/S1002072120300053

As a promising narrow-band phosphor, SrLiAl3N4 has a seemingly ultra-small total crystal-field splitting of only 2400 cm−1 with Ce3+ as dopant ions. This paper is devoted to unravel this anomalous phenomenon based on semi-quantitative crystal-field calculations. The results show that there may exist undetected excitation peaks immersed in the host excitation band, and the calibrated crystal-field splitting is 27000 cm−1, comparable to those of other Ce3+ doped phosphors. In the end the effect of polyhedral deformation on energy level is briefly discussed.

Efficiency-Tunable Single-Component White-Light Emission Realized in Hybrid Halides Through Metal Co-Occupation

ACS Appl. Mater. Interfaces 2021, 13, 25, 29835–29842 https://pubs.acs.org/doi/abs/10.1021/acsami.1c07636

Organic–inorganic hybrid metal halides have attracted widespread attention as emerging optoelectronic materials, especially in solid-state lighting, where they can be used as single-component white-light phosphors for white light-emitting diodes. Herein, we have successfully synthesized a zero-dimensional (0D) organic–inorganic hybrid mixed-metal halide (Bmpip)2PbxSn1–xBr4 (0 < x < 1, Bmpip+ = 1-butyl-1-methyl-piperidinium, C10H22N+) that crystallizes in a monoclinic system in the C2/c space group. Pb2+ and Sn2+ form a four-coordinate seesaw structure separated by organic cations forming a 0D structure. For different excitation wavelengths, (Bmpip)2PbxSn1–xBr4 (0 < x < 1) exhibits double-peaked emission at 470 and 670 nm. The emission color of (Bmpip)2PbxSn1–xBr4 can be easily tuned from orange-red to blue by adjusting the Pb/Sn molar ratio or excitation wavelength. Representatively, (Bmpip)2Pb0.16Sn0.84Br4 exhibits approximately white-light emission with high photoluminescence quantum yield up to 39%. Interestingly, the color of (Bmpip)2PbxSn1–xBr4 can also be easily tuned by temperature, promising its potential for application in temperature measurement and indication. Phosphor-converted light-emitting diodes are fabricated by combining (Bmpip)2PbxSn1–xBr4 and 365 nm near-UV LED chips and exhibit high-quality light output.

Lead-Free Broadband Orange-Emitting Zero-Dimensional Hybrid (PMA)3InBr6 with Direct Band Gap

Inorg. Chem., 2019, 58, 22, 15602–15609. https://pubs.acs.org/doi/abs/10.1021/acs.inorgchem.9b02669

Low-dimensional organic–inorganic hybrid metal halides have emerged as broadband light emitters for phosphor-converted white light-emitting diodes (WLEDs). Herein, we report a new zero-dimensional (0-D) lead-free metal halide (PMA)3InBr6 [PMA+: (C6H5CH2NH3)+] that crystallizes in the monoclinic system with P21/c space group. The structure consists of slightly distorted [InBr6]3– octahedra surrounded by organic PMA+ cations. The direct band gap characteristic of (PMA)3InBr6 was demonstrated by density functional theory calculation, and its relatively wide band gap of 3.78 eV was experimentally determined. Upon 365 nm ultraviolet light excitation, (PMA)3InBr6 exhibited strong broadband orange luminescence with a full-width at half-maximum of ∼132 nm resulting from self-trapped exciton emission, and the photoluminescence quantum yield was determined to be ∼35%. A WLED fabricated by combining the orange-emitting (PMA)3InBr6, a green phosphor Ba2SiO4:Eu2+, and a blue phosphor BaMgAl10O17:Eu2+ exhibited a high color-rendering index of 87.0. Our findings indicate that the organic–inorganic hybrid (PMA)3InBr6 may have potential for luminescence-based applications.

Luminescent thermal stability and electronic structure of narrow-band green-emitting Sr-Sialon: Eu2+ phosphors for LED/LCD backlights

J. Alloys Compd., 2019, 805, 1246-1253. https://www.sciencedirect.com/science/article/abs/pii/S092583881932715X

Stable and high-efficiency narrow-band green phosphor is a key component for wide color gamut liquid crystal display (LCD) backlights. In this paper, narrow-band green-emitting Sr3-3xSi13Al3O2N21:3xEu2+ (0.001 ≤ x ≤ 0.09) (Sr-Sialon:Eu2+) phosphor with a full-width at half maximum of 66 nm has been successfully synthesized by using the solid-state reaction method. All the samples are the pure phase with Sr3Si13Al3O2N21-type structure. Their emission band maximum can be tuned from 495 to 523 nm by increasing Eu2+ content. The compound with x = 0.03 possesses the highest luminescence intensity with the peak position around 510 nm. Luminescent thermal stability gets better with Eu2+ concentration decreasing. The integrated intensity of the sample with x = 0.01 at 425 K remains about 80% of the intensity at room temperature. The host referred binding energy (HRBE) and vacuum referred binding energy (VRBE) schemes are constructed to further explain its luminescent thermal quenching mechanism. White light-emitting-diode (w-LED) device using optimized Sr2.91Si13Al3O2N21:0.09Eu2+ phosphor demonstrates its potential application for LCD backlights.

Tolerance factor and phase stability of the garnet structure

Acta Cryst., 2019. C75, 1353-1358. https://scripts.iucr.org/cgi-bin/paper?qp3034

We introduce a structural descriptor, the tolerance factor, for the prediction and systematic description of the phase stability with the garnet structure. Like the tolerance factor widely adopted for the perovskite structure, it is a com­positional parameter derived from the geometrical relationship between multi-type polyhedra in the garnet structure, and the calculation only needs the information of the ionic radius. A survey of the tolerance factor over 130 garnet-type com­pounds reveals that the data points are scattered in a narrow range. The tolerance factor is helpful in understanding the crystal chemistry of some garnet-type com­pounds and could serve as a guide for predicting the stability of the garnet phase. The correlation between the tolerance factor and the garnet-phase stability could be utilized by machine learning or high-throughput screening methods in material design and discovery.