Zhenyue Wu

A semi-conductive organic–inorganic hybrid emits pure white light with an ultrahigh color rendering index

White-light emission has evoked great attention as one of the most promising technologies in the applications of solid-state lighting devices, light emitting diodes, and flat-panel displays. However, up to now, pure white-light emitting materials have rarely been reported. Here, we present a single-component white-light emitting semiconductor, [C5H9–NH3]4CdBr6, which exhibits CIE chromaticity coordinates of (0.33, 0.33). Notably, this value is the same as that of the standard pure white-light emission. Remarkably, it shows an ultrahigh color rendering index of 92.5, which exceeds that of mixed-phosphor light sources and is comparable to the recently reported highest one among single-component materials. Mechanistic studies indicate that the white-light emission originates from the synergetic effect of deep defects coupled with the organic component. Such an organic–inorganic hybrid with outstanding color characteristics will pave a new approach in the development of white-light emitting materials with practical applications.

[C5H12N]CdCl3: an ABX3 perovskite-type semiconducting switchable dielectric phase transition material

A new organic–inorganic ABX3 perovskite-type semiconducting hybrid, N-methylpyrrolidinium trichlorocadmate (MPCC), has been synthesized. It is found that MPCC exhibits semiconducting behaviour with an optical bandgap of ∼4.65 eV, as well as remarkable dielectric switching properties. It displays a structural phase transition (SPT) at Tc = 254 K, being confirmed by DSC and specific heat measurements. Dielectric measurements display distinct step-like anomalies around Tc, suggesting MPCC as a switchable dielectric material. Variable temperature single-crystal X-ray diffraction reveals that symmetry-breaking occurs from Pnma (at 280 K, >Tc) to P21/c (at 230 K, <Tc), which is attributed to the ordering of the disordered N-methylpyrrolidinium (MP) cation. The most distinct difference between its low- and high-temperature structures is the order–disorder dynamics of the MP cation, which mainly contribute to the SPT and switchable dielectric activities of MPCC. This finding paves a new way for designing multi-featured ABX3-type SPT hybrids by choosing disordered cationic moieties.

N-Methylpyrrolidinium hydrogen tartrate (NMPHT): an above-room-temperature order–disorder molecular switchable dielectric material

A novel molecular switchable dielectric material N-methylpyrrolidinium hydrogen tartrate (NMPHT) has been synthesized, which undergoes above room temperature phase transition. Thermal measurements, e.g. differential scanning calorimetry and specific heat, confirm the presence of a phase transition around 317.5 K. The dielectric measurement displays a distinct step-like anomaly around Tc, showing two different dielectric states, which reveals that NMPHT is a switchable dielectric material. The single-crystal X-ray diffraction analyses at variable temperatures demonstrate that the phase transition emerges from the severe disordering of the N-methylpyrrolidinium (NMP) cation, and during the transition the symmetry of NMPHT is transformed from higher (C2/c) to lower (P21/n). These findings will provide a new horizon to design smart dielectric structural phase transition materials by incorporating a flexible NMP based scaffold.

Broadband white-light emission with a high color rendering index in a two-dimensional organic–inorganic hybrid perovskite

Two-dimensional (2D) organic–inorganic hybrid layered perovskites have attracted increasing attention as promising candidates in optoelectronics, due to their excellent physical attributes. However, although great efforts have been made, broadband white-light emission with a high color rendering index based on 2D hybrid perovskites still remains rare. Here, we report a broadband white-light emissive 2D organic–inorganic hybrid (110)-oriented perovskite, N-(3-aminopropyl)imidazole tetrachloro-lead (1), in which the 2D corrugated layered inorganic framework is formed by corner-shared highly distorted lead chloride octahedra. Remarkably, the color rendering index of 1 is up to 93, which is superior to that of previously reported broadband white-light emission in 2D organic–inorganic hybrid perovskites. Such a 2D hybrid layered perovskite material with a high color rendering index may provide potential applications in white light-emitting diodes.

Broad-Band-Emissive Organic–Inorganic Hybrid Semiconducting Nanowires Based on an ABX3-Type Chain Compound

Organic-inorganic hybrid lead halide (e.g., CH3NH3PbX3, where X = CI, Br, and I) nanowires (NWs) with remarkable electric and optical properties have recently garnered increasing attention, owing to their structural flexibility and tunability compared to inorganic semiconducting NWs. While most recently reported NWs are limited to methylammonium/formamidinium three-dimensional lead halide perovskites, it is urgent to develop new organic-inorganic hybrid semiconducting NWs. Here, broad-band-emissive single-crystal semiconductive NWs based on a new ABX3-type organic-inorganic chain hybrid, (2-methylpiperidine)lead tribromide, are reported. It is believed that this work will enrich the organic-inorganic hybrid semiconducting NWs and may provide potential applications for LED displaying.

(2-Methylpiperidine)PbI3: an ABX3-type organic–inorganic hybrid chain compound and its semiconducting nanowires with photoconductive properties

Organic–inorganic hybrid semiconducting nanowires have recently been widely regarded as promising candidates for electric and optical applications due to their faster carrier separation and low charge recombination. Here, we reported organic–inorganic hybrid semiconducting nanowires with photoconductive properties based on a one dimensional ABX3-type compound, (2-methylpiperidine)PbI3 (1). In 1, one dimensional infinite double chains are surrounded by protonated organic 2-methylpiperidine cations to form a quantum wire structure, which has been thought to be favorable for carrier transport. Furthermore, the prepared semiconducting nanowires of 1 display obvious photoconductive properties, which have been verified using I–V and time-dependent photoresponse measurements. All the results indicate that such semiconducting nanowires based on low dimensional organic–inorganic hybrid materials have potential photoelectric applications.

Switchable behaviors of quadratic nonlinear optical properties originating from bi-step phase transitions in a molecule-based crystal

Solid-state nonlinear optical (NLO) switches are recently emerging as a new class of promising stimuli-responsive materials for photoelectric application. Herein, we report an organic molecular crystal, N- methylcyclohexylamine picrate (1), which exhibits remarkable switching behaviors of quadratic NLO properties with a large contrast of ∼20 between its NLO-on and NLO-off states. This is almost comparable with the conventional photochromic counterparts, and suggests the great potential of 1 as a quadratic NLO-switching candidate. It is noteworthy that 1 undergoes bi-step structural phase transitions at T1 = 240 K and T2 = 285 K, which are closely associated with its NLO-switching activities. Above T1, disordering of anionic and cationic moieties leads to vanishing of the NLO effect, (i.e. NLO-off state). In contrast, below T1, stepwise frozen ordering of the structural moieties generates strong NLO activities, with the NLO response being ∼0.9 times that of KH2PO4. Such an order–disorder transformation accounts for the high-contrast NLO switching of 1. It is believed that this finding affords an effective strategy for designing new stimuli-responsive materials.

(C6H13N)2BiI5: A One-Dimensional Lead-Free Perovskite-Derivative Photoconductive Light Absorber

Lead-free organic-inorganic hybrid perovskites have recently attracted intense interest as environmentally friendly, low-cost, chemically stable light absorbers. Here, we reported a new one-dimensional (1D) zigzag chainlike light-absorbing hybrid material of (C6H13N)2BiI5, in which the corner-sharing octahedral bismuth halide chains are surrounded by organic cations of tetramethylpiperidinium. This unique zigzag 1D hybrid perovskite-derivative material shows a narrow direct band gap of 2.02 eV and long-lived photoluminescence, which is encouraging for optoelectronic applications. Importantly, it behaves as a typical semiconducting material and displays obvious photoresponse in the visible-light range. This work opens a potential pathway for the further application of 1D lead-free hybrids.

Li8NaRb3(SO4)6·2H2O as a new sulfate deep-ultraviolet nonlinear optical material

Sulfates have long been ignored as nonlinear optical materials over the past decades. Here we report a new sulfate deep-ultraviolet nonlinear optical material Li8NaRb3(SO4)6·2H2O synthesized by the facile water solution method. It crystallizes in the asymmetric monoclinic space group C2 (No. 5). Its single-crystal structure features a three-dimensional framework made up of SO4 and LiO4 tetrahedra. Powder second-harmonic generation tests demonstrate that Li8NaRb3(SO4)6·2H2O is phase-matchable with a second-harmonic generation response of about 0.5 × KH2PO4. Ultraviolet-visible-near-infrared diffuse reflectance spectra illustrate that the ultraviolet cutoff edge of Li8NaRb3(SO4)6·2H2O may be as low as λ < 190 nm. Theoretical calculations reveal that the optical properties of Li8NaRb3(SO4)6·2H2O are mainly attributed to S–O groups. All these results reveal that Li8NaRb3(SO4)6·2H2O may possess potential use in the deep-ultraviolet nonlinear optics field. We believe that the discoveries in our work will attract scientists’ attention to sulfate systems for their potential as deep-ultraviolet nonlinear optical materials.

Above-room-temperature switching of quadratic nonlinear optical properties in a Bi–halide organic–inorganic hybrid

Organic–inorganic hybrid nonlinear optical (NLO) switches have recently attracted intensive attention as potential candidates for optical applications. Herein, by introducing an organic triamine cation, we obtain a lead-free Bi-based organic–inorganic hybrid, (C4H16N3)BiBr6 (1), which behaves as a promising above-room-temperature modulator of quadratic NLO responses. More importantly, 1 possesses a remarkable NLO switching contrast of up to ∼35 and a notable switching repeatability. Additionally, microscopic single-crystal structural analyses reveal that the coordinated distortion of inorganic [BiBr6]3− octahedra and the order–disorder transformation of the flexible organic triamine cations synergistically contribute to its NLO switching behavior. We believe that this work will promote the development of high-performance NLO switching materials based on devisable organic–inorganic metal–halide hybrids.