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 R₂PbBr_4−xCl_x (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.

Sci. China Mater. 2019, 62, 1013–1022. https://link.springer.com/article/10.1007/s40843-018-9404-4

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 (Mn^II) 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)₂Pb_1–xMn_xCl₄ band-edge emission and the T₁→⁶A₁ 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.

Adv. Opt. Mater. 2019, 7(10). https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.201900139

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 Cs₂SnCl_6−xBr_x are reported, as well as their use as photodetector materials. Millimeter-sized Cs₂SnCl_6−xBr_x 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 Cs₂SnCl_6−xBr_x 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.

https://pubs.acs.org/doi/abs/10.1021/acs.inorgchem.8b03295

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.

https://pubs.rsc.org/en/content/articlehtml/2019/qi/c9qi00777f

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.