Self-trapped exciton (STE) emissions derived from inorganic octahedral units make metal halide perovskites promising photoluminescence materials for light-emitting applications. However, there is still little understanding of the intrinsic STE emissions in metal halide perovskites or derivatives with nonoctahedral units. In this work, via high pressure compression, remarkable STE emission enhancement is, for the first time, realized in one-dimensional CsCu 2 I 3 crystals with {CuCl 4 } tetrahedral units. The intertetrahedral distortion is believed to induce the slight emission enhancement of the ambient phase under initial compression. Notably, the obvious structural distortions of both inter-and intratetrahedra are responsible for the significant emission enhancement of the high pressure phase. This work not only sheds light on the structure−optical property relationships of tetrahedron-based halide complexes, but also may provide guidance for the design and fabrication of highly luminescent metal halides.

Solution‐processed metal‐based halide perovskites have taken a dominant position for perovskite optoelectronics including light emission and X‐ray detection; however, the toxicity of the included heavy metals severely restricts their applications for wearable, lightweight, and transient optoelectronic devices. Here, the authors describe investigations of large (4 × 6 × 2 mm3) 3D metal‐free perovskite MDABCO‐NH4I3 (MDBACO = methyl‐N′‐diazabicyclo[2.2.2]octonium) single crystal and its charge recombination and extraction behavior for light emission and X‐ray detection. Unlike conventional 3D metal‐based perovskites, this lightweight and biocompatible perovskite large crystal is processed from aqueous solution at room temperature, and can achieve both an extremely long carrier lifetime up to ≈1.03 µs and the formation of self‐trapped excited states for luminescence. These features contribute to a photoluminescence quantum yield (PLQY) as high as ≈53% at room temperature and an X‐ray sensitivity up to 1997 ± 80 μC Gy cm−2 at 50 V bias (highest among all metal‐free detectors). The ability to tune the perovskite band gap by modulating the structure under high pressure is also demonstrated, which opens up applications for the crystal as colored emitters. These attributes make it a molecular alternative to metal‐based perovskites for biocompatible and transient optoelectronics.

A lead-free piezoelectric material with ultra-high properties, Ba(Ti0.8Zr0.2)O3-x(Ba0.7Ca0.3)TiO3(BZTxBCT) nanocrystals was synthesized via a sol-gel method, and the corresponding thin films were also deposited on Pt/Ti/SiO2/Si substrates by a spin-coating approach. The BZT-xBCT thin film exhibited a high remnant polarization of 22.15 mC cm2 with a large coercive field of 68.06 kV cm1. The resultant gel is calcined at various elevated temperatures and studied with FTIR/XRD/Raman/DSC-TGA/AFM/SEM techniques for gel composition, crystallization, phase transition, thermochemistry and the morphology of the film. Although the room temperature crystal structure of the BZT-xBCT nanocrystals appears to be a standard perovskite structure by conventional X-ray diffraction (XRD), Raman spectroscopy demonstrates the presence of non-centrosymmetric regions arising from the off-centering of the titanium (zirconium) atoms.The Raman spectra findings demonstrate the degree by which the tetragonal phase grows with the increase of calcining temperature in BZT-0.5BCT, and the characteristic ferroelectric-ferroelectric phase transition in BZT-xBCT while going through the MPB process. The structural and constituent evolution for the conversion process from gel to ceramic, as well as the formation mechanism of the BZT-0.5BCT crystallite, were also elucidated.Keywords gel, synthesized, ba, ti0, 8zr0, 2, crystallization, o3, ferroelectric, x, ba0, 7ca0, 3, tio3, thin, films, evolution, phase, properties, sol Disciplines Engineering | Physical Sciences and Mathematics Publication DetailsWang, Z., Zhao, K., Guo, X., Sun, W., Jiang, H., Han, X., Tao, X., Cheng, Z., Zhao, H., Kimura, H., Yuan, G., Yin, J. & Liu, Z. (2013). Crystallization, phase evolution and ferroelectric properties of sol-gel-synthesized Ba(Ti0.8Zr0.2)O3-x(Ba0.7Ca0.3)TiO3 thin films. Journal of Materials Chemistry C, 1 522-530. AuthorsZeng-mei Wang, Kuan Zhao, Xin-li Guo, Wei Sun, Hua-long Jiang, Xue-qin Han, Xu-tang Tao, Zhen-xiang Cheng, Hong-yang Zhao, Hideo Kimura, Guo-liang Yuan, Jiang Yin, and Zhi-guo Liu nanocrystals was synthesized via a sol-gel method, and the corresponding thin films were also deposited on Pt/Ti/SiO 2 /Si substrates by a spin-coating approach. The BZT-xBCT thin film exhibited a high remnant polarization of 22.15 mC cm À2 with a large coercive field of 68.06 kV cm À1 . The resultant gel is calcined at various elevated temperatures and studied with FTIR/XRD/Raman/DSC-TGA/AFM/SEM techniques for gel composition, crystallization, phase transition, thermochemistry and the morphology of the film. Although the room temperature crystal structure of the BZT-xBCT nanocrystals appears to be a standard perovskite structure by conventional X-ray diffraction (XRD), Raman spectroscopy demonstrates the presence of non-centrosymmetric regions arising from the off-centering of the titanium (zirconium) atoms. The Raman spectra findings demonstrate the degree by which the tetragonal phase grows with the increase of calcining temperature in BZT-0.5BCT, and the...

Zero‐dimensional (0D) hybrid metal halides are promising light emitters. However, it is still challenging to accurately design their structures with targeted photoluminescence properties. Herein, high pressure is used to change the self‐trapped exciton (STE) emission of 0D (bmpy)9[ZnBr4]2[Pb3Br11] (bmpy: 1‐butyl‐1‐methylpyrrolidinium). Under initial compression, the simultaneous contraction and distortion of photoactive [Pb3Br11]5− vary the equilibrium of STE emissions between different excited states, tuning the emission color from yellow green to cyan. Notably, sufficient structural distortion under continuous compression leads to the formation of more and deeper STE states, exhibiting an unprecedented broadband white‐light emission. This study reveals the structure‐dependent optical properties of 0D hybrid metal halides, providing novel insights into the mechanism of STE emission.

Self-trapped exciton (STE) emission of low-dimensional metal halides has witnessed explosive developments in both display and illumination, due to its intriguing photoluminescence properties. As one typical feature, STE emission energy is commonly independent of excitation wavelength. Herein, a rare phenomenon of inverse excitation-dependent dual-band emission is achieved on 0D Cs 2 InBr 5 •H 2 O. Under initial compression, the contraction of inhomogeneously coordinated InBr 5 O octahedra gives rise to blue-shifted STE emission with the decreased Stokes shift. As the phase transition occurs under higher pressure, considerable octahedral distortions generate a new defect-related localized exciton emission. Notably, the high-energy emission from the intrinsic STE state is only observed under the low-energy excitation, which is believed to originate from the excitation-dependent multiple excited states in high-pressure Cs 2 InBr 5 •H 2 O.