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

Adv. Opt. Mater., 2019, 7(24), 1901335.

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.

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

Inorg. Chem., 2019, 58, 22, 15602–15609.

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.

Unraveling the mechanochemical synthesis and luminescence in MnII-based two-dimensional hybrid perovskite (C4H9NH3)2PbCl4

Sci. China Mater. 2019, 62, 1013–1022.

The mechanochemical route is a facile and fast way and has received much attention for developing versatile advanced functional materials. Herein, we reported a mechanochemical synthesis for incorporating divalent manganese ions (MnII) into a two-dimensional (2D) hybrid perovskite (C4H9NH3)2PbCl4. The mild external stimuli originating from the grinding at room temperature enabled the formation of MnII-doped 2D hybrid perovskites, and rapidly changed the luminescence characteristics. The photoluminescence analyses show that the violet and orange emissions are attributed to (C4H9NH3)2Pb1–xMnxCl4 band-edge emission and the T16A1 transition of Mn2+ resulting from an efficient energy transfer process, respectively. Site preference and distribution of the doped Mn2+ cations on the locations of Pb2+ were analyzed. The formation energy calculated by the density functional theory (DFT) indicates that the Mn2+ ions can rapidly enter the crystal lattice due to the unique 2D crystal structure of the hybrid perovskite. Such a case of mechanochemical synthesis for the 2D hybrid perovskite motivates many novel emerging materials and the related applications.

Lead‐Free Perovskite Derivative Cs2SnCl6−xBrx Single Crystals for Narrowband Photodetectors

Adv. Opt. Mater. 2019, 7(10).

Lead-free and stable Sn halide perovskites demonstrate tremendous potential in the field of optoelectronic devices. Here, the structure and optical properties of the “defect” perovskites Cs2SnCl6−xBrx are reported, as well as their use as photodetector materials. Millimeter-sized Cs2SnCl6−xBrx single crystals are grown by the hydrothermal method, with the body color continuously changing from transparent to yellow and finally to dark red. Narrowband single-crystal photodetectors using Cs2SnCl6−xBrx crystals are presented, which show a high detectivity of ≈2.71 × 1010 Jones, with narrowband photodetection (full-width at half-maximum ≈45 nm) and high ion diffusion barriers. Moreover, the response spectra are continuously tuned from near violet to orange depending on the variation of the bandgap of the single crystals by changing the halide compositions. The strong surface charge recombination of the excess carriers near the crystal surfaces produced by short wavelength light elucidates the narrowband photodetection behavior. This work provides a new paradigm in the design of lead-free, stable, and high-performance perovskite derivatives for optoelectronics applications.

Synthesis and Luminescence Properties of CsPbX3@Uio-67 Composites toward Stable Photoluminescence Convertors

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All-inorganic halide perovskite (CsPbX3, X = Cl, Br, or I) nanocrystals (NCs) have been widely studied due to their outstanding optoelectronic properties. However, some inevitable factors like light, heat, and moisture affected the stability of CsPbX3 NCs and further limited their practical application. In this work, the stability of all-inorganic halide perovskite NCs can be improved by integrating them in the stable Zr-based metal–organic frameworks (Uio-67). Compared to pristine perovskite NCs, typical CsPbBr3@Uio-67 composites display a stable photoluminescence property that can be maintained for 30 days under ambient atmospheric conditions. Due to the proposed confinement effects of CsPbX3 NCs coordinated with the pore structures of Uio-67, the related structural model of CsPbX3@Uio-67 composites was elucidated. White LED device was further fabricated by combining CsPbBr3@Uio-67 composites and commercial K2SiF6:Mn4+ red phosphors with a blue-emitting chip, which demonstrated a wide color gamut (138% of National Television Standards Committee color space). The strategy on encapsulation of CsPbX3 NCs into Uio-67 will open up a stable platform for optoelectronic applications.

Luminescent perovskites: recent advances in theory and experiments

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Perovskites form an important and enormous class of inorganic compounds. Recently, perovskite materials have attracted extensive research interest owing to their excellent optoelectronic properties. Deep insights into the relationships between the crystal structure, electronic structure and properties play an important role in the development of new functional materials and high-performance devices. In this review, after a brief introduction, we first discuss the crystal structure and crystal chemistry of perovskites according to their three classes: standard perovskites, low-dimensional perovskites and perovskite-like halides. Next, the electronic structure and luminescence from different physical origins are presented. Then, we present a survey on the design, synthesis and luminescence properties of different perovskites, including halide perovskites, oxide perovskites, and lanthanide- or transition metal-doped perovskites, also including dimension-different perovskites (3D, 2D, 1D and quantum dots). We also summarize the strategies for improving the photoluminescence quantum yield (PLQY) and chemical stability, including by surface passivation, encapsulation and doping. Finally, we review their applications and give a brief outlook.

Double perovskite Cs2AgInCl6:Cr3+: broadband and near-infrared luminescent materials

Inorg. Chem. Front., 2019,6, 3621-3628

Searching for high performance and broader applications of inorganic halide perovskites has drawn extensive attention. In this work, a Cr3+-doped halide perovskite, Cs2AgInCl6:Cr3+, which exhibits broadband near-infrared (NIR) emission is first obtained via the traditional high temperature solid-state reaction. A broad emission band ranging from 850 to 1350 nm centered at 1010 nm with a full-width at half-maximum (FWHM) of 180 nm is assigned to the spin-allowed 4T2 → 4A2 transition of octahedrally coordinated Cr3+ ions in a very weak crystal-field environment. The excitation bands centered at 353, 565 and 800 nm can be attributed to the absorption of the Cs2AgInCl6 host, the Cr3+ d–d transitions of 4A2 → 4T1 and 4A2 → 4T2, respectively. Upon 760 nm excitation, the photoluminescence quantum yield (PLQY) of Cs2AgIn0.9Cl6:0.1Cr3+ is about ∼22.03%. Cs2AgInCl6:Cr3+ phosphors with such broadband NIR emission have potential in phosphor converted light emitting diodes (pc-LEDs) which have applications in bioimaging and biomonitoring.