An Efficient Synthesis and Photoelectric Properties of Green Carbon Quantum Dots with High Fluorescent Quantum Yield

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/)To greatly improve the production quality and efficiency of carbon quantum dots (CQDs), and provide a new approach for the large-scale production of high-quality CQDs, green carbon quantum dots (g-CQDs) with high product yield (PY) and high fluorescent quantum yield (QY) were synthesized by an efficient one-step solvothermal method with 2,7-dihydroxynaphthalene as the carbon source and ethylenediamine as the nitrogen dopant in this study. The PY and QY of g-CQDs were optimised by adjusting reaction parameters such as an amount of added ethylenediamine, reaction temperature, and reaction duration. The results showed that the maximum PY and QY values of g-CQDs were achieved, which were 70.90% and 62.98%, respectively when the amount of added ethylenediamine, reaction temperature, and reaction duration were 4 mL, 180 °C, and 12 h, respectively. With the optimised QY value of g-CQDs, white light emitting diodes (white LEDs) were prepared by combining g-CQDs and blue chip. The colour rendering index of white LEDs reached 87, and the correlated colour temperature was 2520 K, which belongs to the warm white light area and is suitable for indoor lighting. These results indicate that g-CQDs have potential and wide application prospects in the field of white LEDs.Peer reviewedFinal Published versio

Low efficiency roll-off phosphorescent organic light-emitting devices using thermally activated delayed fluorescence hosts materials based 1, 2, 4-triazole acceptor

The host in phosphrescent organic light emitting devices (PhOLEDs), showing the thermally activated delayed fluorescence (TADF) charateristic, can effectively overcome the efficiency roll-off. Herein, six bipolar compounds with donor-π-acceptor (D-π-A) and D-π-A-π-D structures have been synthesized using 1,2,4-triazole derivative (TAZ) as an acceptor and phenothiazine (PTZ), phenoxazine (PXZ), and 9, 9-dimethylacridane (DMAC) as donors. The molecular structures were confirmed by 1H NMR, 13C NMR and X-ray single-crystal diffractions. The large steric hindrance endows these molecules with typical TADF features, including the small singlet-triplet energy splitting (Delta E-ST) of 0.08–0.30 eV and completely spatially separate highest occupied molecular orbitals (HOMO) and the lowest unoccupied molecular orbitals (LUMO) electron densities. The PhOLEDs hosted by these novel TADF materials display excellent performances with low efficiency roll-off

Synthesis and optical properties of composite films from P3HT and sandwich-like Ag-C-Ag nanoparticles

This document is the Accepted Manuscript of the following article: Lingpeng Yan, Yamin Hao, Xiaoting Feng, Yongzhen Yang, Xuguang Liu, Yongkang Chen, and Bingshe Xu, ‘Synthesis and optical properties of composite films from P3HT and sandwich-like Ag–C–Ag nanoparticles’, RSC Advances, Vol. 5(97): 79860-79867, 2015, DOI: https://doi.org/10.1039/C5RA16854F. Content in the UH Research Archive is made available for personal research, educational, and non-commercial purposes only. Unless otherwise stated, all content is protected by copyright, and in the absence of an open license, permissions for further re-use should be sought from the publisher, the author, or other copyright holder.Sandwich-like Ag-C-Ag nanoparticles (Ag-C-Ag NPs) were synthesized under mild hydrothermal conditions in a one-step method. With this approach, Ag was not only encapsulated in the centre of an individual carbon nanosphere, but was also uniformly dispersed within the carbon matrix up to the sphere's shell. Then, poly(3-hexylthiophene):Ag-C-Ag NPs (P3HT:Ag-C-Ag NPs) composite films were prepared by a spin coating method with a chlorobenzene solution of Ag-C-Ag NPs and P3HT. Both morphology and microstructure of Ag-C-Ag NPs were investigated by field emission scanning electron microscopy and high resolution transmission electron microscopy. The possible formation mechanism was proposed. The results have indicated that the Ag-C-Ag NPs present many functional groups and their energy levels match with those of P3HT. It has been observed that an introduction of Ag-C-Ag NPs to P3HT can induce broad and high-absorbing spectra as well as great photoluminescence quenching of P3HT. It is evident that sandwich-like Ag-C-Ag NPs have a great potential to be a new acceptor material in photovoltaic devices.Peer reviewe

Realizing 18.03% efficiency and good junction characteristics in organic solar cells via hydrogen-bonding interaction between glucose and ZnO electron transport layers

Electron transport layers (ETLs) with excellent electron extraction capability are essential for realizing high efficiency in organic solar cells (OSCs). A sol-gel-processed ZnO ETL is widely used in OSCs due to its high mobility and suitable work function. However, the existence of defects usually results in low photovoltaic performance during the operation of OSCs. In this work, glucose (Gl) was used to passivate free OH traps via hydrogen-bonding interaction and formed ZnO/Gl ETLs with ZnO, which exhibited improved electron extraction capability and reduced trap defect density. Thus, a champion efficiency of 18.03% was obtained in a PM6:Y6 light absorber-based cell, which is >11% higher than that of the reference cell (16.15%) with a pristine ZnO ETL. Impressive enhancements by >11% were also observed in different fullerene and non-fullerene light absorber-based cells relative to that of the reference cell. This study demonstrates a new strategy to design ETLs for realizing high efficiency in OSCs

Novel blue fluorescent emitters structured by linking triphenylamine and anthracene derivatives for organic light-emitting devices with EQE exceeding 5%

Achieving an external quantum efficiency exceeding 5% for traditional blue fluorescent organic light emitting devices (OLEDs) is still a current challenge due to the 25% limit of the radiative exciton yield. Bipolar organic molecules with a special hybrid local-excited and charge-transfer state have showed huge potential to address this issue. Herein, we designed and synthesized two novel bipolar compounds, namely TPA-AN-NA and TPA-AN-TFP, which were structured by simply linking a donor of triphenylamine (TPA) and both acceptors of anthracene derivatives. Both resulting compounds show good blue emission with emission peaks at 468 and 471 nm and photoluminescence quantum yields of 30.68 and 23.96% in thin films for TPA-AN-NA and TPA-AN-TFP, respectively. They also exhibit good solubility and can dissolve in several organic solvents with different polarities. Further, the fabricated blue OLEDs with TPA-AN-NA and TPA-AN-TFP as emitters also realize the corresponding blue emission well with electroluminescence peaks at 464 and 472 nm, respectively. The TPA-AN-NA-based blue device achieves a high external quantum efficiency of 5.44% and a radiative exciton yield of 56.68%, exceeding the theoretical limit

Two novel bipolar hosts based on 1,2,4-triazole derivatives for highly efficient red phosphorescent OLEDs showing a small efficiency roll-off

Achieving high efficiency and small efficiency roll-off simultaneously for red phosphorescent organic light-emitting diodes (PhOLEDs) is still a challenge, which is largely related to the host material used in device fabrication. In this wok, we designed and synthesized two novel bipolar host materials, termed 2Cz-TAZ-2Cz and 3Cz-TAZ-3Cz in which 1,2,4-triazole was introduced at the C-2 and C-3 positions of 9-phenylcarbazole, respectively. The materials\u27 photophysical properties were studied in detail.. It was found that 2Cz-TAZ-2Cz and 3Cz-TAZ-3Cz possess excellent thermal stability with thermal decomposition temperature (Td) of 457 and 432 °C, respectively, and that 2Cz-TAZ-2Cz has a better bipolar carrier transport compared to the typical host 4, 4′-bis(9H-carbazole-9-yl)-biphenyl (CBP). Based on the excellent performance of these materials, red phosphorescent OLEDs with 2Cz-TAZ-2Cz and 3Cz-TAZ-3Cz as hosts and bis(1-phenylisoquinoline)(acetylacetonate)iridium (III) (Ir(piq)2acac) as emitter were fabricated. The optimized 2Cz-TAZ-2Cz-based device achieved a high maximum current efficiency and external quantum efficiency (EQE) of 12.4 cd/A and 16.60%, respectively. Moreover, this device also exhibits a small efficiency roll-off, i.e., the EQE is lowered by only 12.0% and 29.4% at a brightness of 1000 cd/m2 and 10,000 cd/m2, respectively, which is superior to CBP-based device, indicating a potential far-reaching application

Surface Morphology Evolution Mechanisms of InGaN/GaN Multiple Quantum Wells with Mixture N2/H2-Grown GaN Barrier

This is an Open Access article distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.Surface morphology evolution mechanisms of InGaN/GaN multiple quantum wells (MQWs) during GaN barrier growth with different hydrogen (H2) percentages have been systematically studied. Ga surface-diffusion rate, stress relaxation, and H2 etching effect are found to be the main affecting factors of the surface evolution. As the percentage of H2 increases from 0 to 6.25%, Ga surface-diffusion rate and the etch effect are gradually enhanced, which is beneficial to obtaining a smooth surface with low pits density. As the H2 proportion further increases, stress relaxation and H2 over- etching effect begin to be the dominant factors, which degrade surface quality. Furthermore, the effects of surface evolution on the interface and optical properties of InGaN/GaN MQWs are also profoundly discussed. The comprehensive study on the surface evolution mechanisms herein provides both technical and theoretical support for the fabrication of high-quality InGaN/GaN heterostructures.Peer reviewe

Suppression of AP1 Transcription Factor Function in Keratinocyte Suppresses Differentiation

Our previous study shows that inhibiting activator protein one (AP1) transcription factor function in murine epidermis, using dominant-negative c-jun (TAM67), increases cell proliferation and delays differentiation. To understand the mechanism of action, we compare TAM67 impact in mouse epidermis and in cultured normal human keratinocytes. We show that TAM67 localizes in the nucleus where it forms TAM67 homodimers that competitively interact with AP1 transcription factor DNA binding sites to reduce endogenous jun and fos factor binding. Involucrin is a marker of keratinocyte differentiation that is expressed in the suprabasal epidermis and this expression requires AP1 factor interaction at the AP1-5 site in the promoter. TAM67 interacts competitively at this site to reduce involucrin expression. TAM67 also reduces endogenous c-jun, junB and junD mRNA and protein level. Studies with c-jun promoter suggest that this is due to reduced transcription of the c-jun gene. We propose that TAM67 suppresses keratinocyte differentiation by interfering with endogenous AP1 factor binding to regulator elements in differentiation-associated target genes, and by reducing endogenous c-jun factor expression

Electrochemical Performance of Graphene Oxide/Black Arsenic Phosphorus/Carbon Nanotubes as Anode Material for LIBs

As a new two-dimensional material, black arsenic phosphorus (B-AsP) has emerged as a promising electrode for lithium-ion batteries (LIBs) due to its large theoretical capacity and ability to absorb large amounts of Li atoms. However, the poor electronic conductivity and large volume expansion during the lithiation/delithiation process have largely impeded the development of B-AsP electrodes. In this study, graphene oxide (GO)/B-AsP/carbon nanotubes (CNTs) with remarkable lithium-storage property were fabricated via CVD and ultrasound-assisted method. The electrochemical behavior of the GO/B-AsP/CNTs was investigated as an anode in lithium-ion batteries. From the results, as a new-type anode for LIBs, GO/B-AsP/CNTs composite demonstrated a stable capacity of 1286 and 339 mA h g−1 at the current density of 0.1 and 1 A g−1, respectively. The capacity of GO/B-AsP/CNTs was 693 mA h g−1 after 50 cycles, resulting in capacity retention of almost 86%. In addition, the stable P-C and As-C bonds were formed between B-AsP, GO, and CNTs. Thus, volume expansion of B-AsP was alleviated and the capacity was increased due to the confining effect of GO and CNTs

Ferromagnetic Property and Synthesis of Onion-Like Fullerenes by Chemical Vapor Deposition Using Fe and Co Catalysts Supported on NaCl

Metal-encapsulating onion-like fullerenes (M@OLFs) were synthesized by CVD at relatively low temperature (420C∘) using Fe and Co nanoparticles impregnated into NaCl as catalyst. The morphology and structure of the products were characterized by field emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. The results show that Fe@OLFs and Co@OLFs with stacked graphitic fragments were prepared using Fe/NaCl or Co/NaCl as catalysts; after Co@OLFs were immersed in concentrated HCl for 48 hours, Co nanoparticles encapsulated by carbon shells were not removed, meaning that carbon shells can protect the encapsulated Co cores against environmental degradation. The coercivity value (750.23 Oe) of Co@OLFs showed an obvious magnetic property