Efficient Solar Spectrum-Like White-Light Emission in Zinc-Based Zero-Dimensional Hybrid Metal Halides

ADVANCED OPTICAL MATERIALS.27 April 2023.https://doi.org/10.1002/adom.202300218

Organic–inorganic metal halides (OIMHs) with high-efficiency solar spectrum-like emission are attracting broad and current interest. Here, five 0D Zn-based hybrid halides are synthesized based on aromatic organic cations with different carbon-chain lengths: C6H5CH2NH3+ (PMA+) and C6H5(CH2)4NH3+ (PBA+). (PMA)2ZnCl4 exhibits the highest photoluminescence quantum yield of 37.2% of reported Zn-based white-emission OIMHs. The emission spectrum of (PBA)2ZnI4 indicates a color rendering index of 98, which is the highest among single-component white-light-emitting phosphors. Spectral characterizations and density functional theory calculations demonstrate that the extremely broad emission of (PBA)2ZnI4 originates from the synergistic emission of organic cations and self-trapped excitons. The optical properties of the obtained (PMA)2ZnBr4, (PMA)2ZnI4·H2O, and (PBA)2ZnCl4 are also characterized for comparison, and with the same organic cations, the PLQY decreases from chloride to bromide to iodide. This work demonstrates that the selection of appropriate organics and halogens can enable fine tuning of single-component white-light emission, satisfying varying needs for solid-state lighting.

Achieving efficient violet-light-excited blue phosphors by nitridation for violet-chip-based full-spectrum lighting


Inorg. Chem. Front., 2023,10, 2430-2437.https://pubs.rsc.org/en/content/articlelanding/2023/QI/D2QI02489F

With the pursuit of healthy lighting, full-spectrum white light-emitting diodes (WLEDs) fabricated with violet chips and tri-color phosphors have been put forward. However, the excitation bands of most reported blue phosphors are located in the ultraviolet (UV) region, which hinders the development of full-spectrum lighting. In this work, by partially introducing N3− into a matrix, a series of Ba0.697Al10.914O17.232-3y/2Ny:0.16Eu2+ (BAONy:Eu) blue phosphors with red-shifted photoluminescence excitation (PLE) spectra were synthesized. Under the excitation of 400 nm violet light, the internal/external quantum efficiency (IQE/EQE) values of the optimal sample BAON1.0:Eu were calculated to be 80%/52%, while the retained integrated emission intensity at 150 °C can be 95% of that at room temperature. The WLED device fabricated by coating BAON1.0:Eu and other commercial phosphors on a violet chip achieved an ultra-high color rendering index (Ra = 95.4). These results indicate that our synthesized BAON1.0:Eu can be an excellent candidate blue phosphor for full-spectrum WLED lighting.

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.

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.

Green persistent luminescence and the electronic structure of β-Sialon: Eu 2+

https://pubs.rsc.org/en/content/articlelanding/2019/tc/c9tc03833g/unauth

Graphical abstract: Green persistent luminescence and the electronic structure of β-Sialon:Eu2+

Divalent europium doped aluminum silicate oxy-nitride (β-Sialon:Eu2+) has been widely used in backlights for liquid-crystal displays due to its outstanding green emission properties. Herein, the persistent luminescence (PersL) performance and electronic structure of β-Sialon:Eu2+ with the general formula Eu0.015Si5.5Al0.485O0.515N7.485 are first reported. The PersL duration is observed to be 400 s after 254 nm irradiation. By virtue of density functional theory (DFT) calculations, we verify that the trap levels responsible for PersL are impurity levels induced by Si–O bonds located below the bottom of the conduction band (CB) on random substitution of Al–O for Si–N in β-Si3N4. The trap depth and density are estimated through experimental data. The charging process for PersL is clarified by the thermoluminescence excitation (TLE) spectrum. The electronic structure diagrams (host referred binding energy, HRBE and vacuum referred binding energy scheme, VRBE) of β-Sialon:Eu2+ are constructed to deeply understand the PersL mechanism and luminescence behavior. We propose a novel strategy to construct the HRBE schemes, i.e. using the onset energy of the thermoluminescence excitation (TLE) spectrum as the energy difference between the 4f ground state and the bottom of the CB to pinpoint the 4f energy level location of Eu2+. This work would allow more rational design of luminescent materials.