Impact of nanosizing a host matrix based on a metal–organic framework on solid-state fluorescence emission and energy transfer

We demonstrate that the nanosize effect appears to affect the properties of dye molecules encapsulated in the pores of a metal–organic framework (dye@MOF). The emissive properties of the nanosized dye@MOF...

Energy transfer processes in hyperfluorescent organic light-emitting diodes

Hyperfluorescent organic light-emitting diodes (OLEDs) are based on a combination of molecules displaying thermally activated delayed fluorescence (TADF) and of fluorescent emitters embedded into a host matrix; excitons formed on...

Erbium energy bridging upconversion mechanism studies on BAKL: Er3+/Yb3+ glass-ceramics and simultaneous enhancement of color purity of the green luminescence

Borate oxyfluoride glasses are transparent in the infra-red, ultra violet and visible regions and represent an ideal host matrix for optically active dopants. Due to their lower phonon energies compared...

A Porphyrin Pentamer as a Bright Emitter for NIR OLEDs

The luminescence and electroluminescence of an ethyne-linked zinc(II) porphyrin pentamer have been investigated, by testing blends in two different conjugated polymer matrices, at a range of concentrations. The best results were obtained for blends with the conjugated polymer PIDT-2TPD, at a porphyrin loading of 1 wt%. This host matrix was selected because the excellent overlap between its emission spectrum and the absorption spectrum of the porphyrin oligomer leads to efficient energy transfer. Thin films of this blend exhibit intense fluorescence in the near-infrared (NIR), with a peak emission wavelength of 886 nm and a photoluminescent quantum yield (PLQY) of 27% in the solid state. Light-emitting diodes (LEDs) fabricated with this blend as the emissive layer achieve average external quantum efficiencies (EQE) of 2.0% with peak emission at 830 nm and a turn-on voltage of 1.6 V. This performance is remarkable for a singlet NIR-emitter; 93% of the photons are emitted in the NIR (λ > 700 nm), indicating that conjugated porphyrin oligomers are promising emitters for non-toxic NIR OLEDs.

Impedance Analysis and Noise Measurements on Multi Walled Carbon Nanotube Networks

The electrical impedance characteristics of multi-walled carbon nanotube (MWCNTs) networks were studied as a function of CNT concentrations in the frequency range of 1 kHz–1 MHz. The novelty of this study is that the MWCNTs were not embedded in any polymer matrix and so the response of the device to electrical measurements are attributed to the CNTs in the network without any contribution from a polymer host matrix. Devices with low MWCNT packing density (0.31–0.85 µg/cm2) exhibit a frequency independent plateau in the low-frequency regime. At higher frequencies, the AC conductivity of these devices increases following a power law, characteristic of the universal dynamic response (UDR) phenomenon. On the other hand, devices with high MWCNT concentrations (>1.0 µg/cm2) exhibit frequency independent conductivity over the entire frequency range (up to 1 MHz), indicating that conduction in these devices is due to direct contact between the CNTs in the network. A simple single-relaxation time electrical equivalent circuit with an effective resistance and capacitance is used to describe the device performance. The electrical noise measurements on devices with different MWCNT packing densities exhibit bias-dependent low-frequency 1/f noise, attributed to resistance fluctuations.

Investigation of Electrical Properties of TiO2 Nanocomposite Based Polymer

Past research has reported the challenges regarding on degradation and aging due to high localization of electric field at triple point areas of polymeric insulator. The different materials and designs of polymeric insulator have initiated the partial discharge and arching activities which eventually lead to the insulation failures. The compounding of nanomaterials in the polymer shows a promising result to overcome this problem by redistributing the uniformity of electrical field lines on the insulator. In the present work, ethylene-propylene-diene rubber (EPDM) and titanium dioxide (TiO2) is introduced as nano composites that been embedded into insulator’s housing made of 1) silicone rubber (SiR) and 2) Ethylene Propylene Diene Monomer (EPDM) Rubber. Titanium dioxide (TiO2) is a semiconductor material that can be formed in different sizes either micron or nano-sized filler and has high relative permittivity that be able to reduce the high electrical stresses on high voltage equipment. Meanwhile EPDM shows good mechanical profile, excellent resistance properties and low cost. Therefore, it brings to the new opportunity to fabricate the nanocomposite based on both materials which exhibits an improved electrical properties and good distribution of electric field on polymeric outdoor insulators. In depth investigation was carried out to analyze the effect of different nano-filler loading in the compound and behavior of nanocomposites at different polymer base. An 11kV polymeric insulator is modelled to be simulated by using COMSOL Multiphysics software under dry-clean surface conditions to investigate the electric field distribution at terminal ends and along the insulator creepage path. The Electrostatics interface from the AC/DC Module is used in the evaluation of electric field distribution of insulator model correspondingly with the variations in filler percentage in the host matrix.

A Novel Conductive Antibacterial Nanocomposite Hydrogel Dressing for Healing of Severely Infected Wounds

Wound infections are serious medical complications that can endanger human health. Latest researches show that conductive composite materials may make endogenous/exogenous electrical stimulation more effective, guide/comb cell migration to the wound, and subsequently promote wound healing. To accelerate infected wound healing, a novel medical silver nanoparticle-doped conductive polymer-based hydrogel system (Ag NPs/CPH) dressing with good conductivity, biocompatibility, and mechanical and antibacterial properties was fabricated. For the hydrogel dressing, Ag NPs/CPH, polyvinyl alcohol (PVA), and gelatin were used as the host matrix materials, and phytic acid (PA) was used as the cross-linking agent to introduce conductive polyaniline into the matrix, with antibacterial Ag NPs loaded via impregnation. After a series of analyses, the material containing 5 wt% of PVA by concentration, 1.5 wt% gelatin, 600 μL of AN reactive volume, and 600 μL of PA reactive volume was chosen for Ag NPs/CPH preparation. XPS and FTIR analysis had been further used to characterize the composition of the prepared Ag NPs/CPH. The test on the swelling property showed that the hydrogels had abundant pores with good water absorption (≈140% within 12 h). They can be loaded and continuously release Ag NPs. Thus, the prepared Ag NPs/CPH showed excellent antibacterial property with increasing duration of immersion of Ag NPs. Additionally, to evaluate in vivo safety, CCK-8 experiments of HaCat, LO2 and 293T cells were treated with different concentrations of the Ag NPs/CPH hydrogel soaking solution. The experimental results showed the Ag NPs/CPH had no significant inhibitory effect on any of the cells. Finally, an innovative infection and inflammation model was designed to evaluate the prepared Ag NPs/CPH hydrogel dressing for the treatment of severely infected wounds. The results showed that even when infected with bacteria for long periods of time (more than 20 h), the proposed conductive antibacterial hydrogel could treat severely infected wounds.

Unity of Opposite: Highly Emissive Luminogens in both Solution and Aggregate States toward Room Temperature Phosphorescence and Electroluminescence

Organic light-emitting materials, especially those with two-phase high emission, have attracted considerable attention for applications in bioimaging agents, sensors, optoelectronic devices, etc. Many fluorophores applied in such fields either emit brightly in dilute solution or in aggregate state, with the former often suffering from aggregation-caused quenching effect, and the latter falling dark at low concentrations. Herein, we overcame the dilemma by balancing the planar and distorted structures with various side units and achieved bright emission in both dilute solution (e.g., the absolute quantum yields (ФPL) = 90.2% in THF) and in aggregate states (e.g., ФPL=92.7% in powder state, ФPL = 95.3% in crystal). These luminescent mate-rials are demonstrated as promising guests embedded into host matrix to achieve efficient room temperature phosphores-cence, and these host-guest systems could be applied in the information encryption. Moreover, these luminogens could also be used as single-component emitting layers to construct non-doped organic light-emitting diodes, from which a maximum external quantum efficiency up to 4.75% with Commission International de L’Eclairge (CIE) coordinates of (0.15, 0.05), which is neatest to next generation ultra-high definition television (UHDTV) display standard, was realized. This work pro-vides a feasible strategy of balancing the planar and distorted structure of a luminogen toward highly efficient emission in both solution and solid states.