The synthesis of epitaxially grown, wurtzite CdSe/CdS core/shell nanocrystals is reported Shells of up to three monolayers in thickness were grown on cores ranging in diameter from 23 to 39 A Shell growth was controllable to within a tenth of a monolayer and was consistently accompanied by a red shift of the absorption spectrum, an increase of the room temperature photoluminescence quantum yield (up to at least 50%), and an increase in the photostability Shell growth was shown to be uniform and epitaxial by the use of X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and optical spectroscopy The experimental results indicate that in the excited state the hole is confined to the core and the electron is delocalized throughout the entire structure The photostability can be explained by the confinement of the hole, while the delocalization of the electron results in a degree of electronic accessibility that makes these nanocrystals

Epitaxial Growth of Highly Luminescent CdSe/CdS Core/Shell Nanocrystals with Photostability and Electronic Accessibility

A review was presented to demonstrate a historical description of the synthesis of light-emitting conjugated polymers for applications in electroluminescent devices. Electroluminescence (EL) was first reported in poly(para-phenylene vinylene) (PPV) in 1990 and researchers continued to make significant efforts to develop conjugated materials as the active units in light-emitting devices (LED) to be used in display applications. Conjugated oligomers were used as luminescent materials and as models for conjugated polymers in the review. Oligomers were used to demonstrate a structure and property relationship to determine a key polymer property or to demonstrate a technique that was to be applied to polymers. The review focused on demonstrating the way polymer structures were made and the way their properties were controlled by intelligent and rational and synthetic design.

Synthesis of Light-Emitting Conjugated Polymers for Applications in Electroluminescent Devices

Antifouling technology—past, present and future steps towards efficient and environmentally friendly antifouling coatings

We have studied the influence of piezoelectric fields on luminescence properties of GaInN strained quantum wells. Our calculation suggests that an electric field of 1.08 MV/cm is induced by the piezoelectric effect in strained Ga0.87In0.13N grown on GaN. The photoluminescence peak energy of the Ga0.87In0.13N strained quantum wells showed blue shift with increasing excitation intensity. Moreover, the well-width dependence of its luminescence peak energy was well explained when the piezoelectric fields were taken into account. These results clearly showed that the piezoelectric field induced the quantum-confined Stark effect.

https://iopscience.iop.org/article/10.1143/JJAP.36.L382/pdf

Quantum-Confined Stark Effect due to Piezoelectric Fields in GaInN Strained Quantum Wells

We have identified piezoelectric fields in strained GaInN/GaN quantum well p-i-n structures using the quantum-confined Stark effect. The photoluminescence peak of the quantum wells showed a blueshift with increasing applied reverse voltages. This blueshift is due to the cancellation of the piezoelectric field by the reverse bias field. We determined that the piezoelectric field points from the growth surface to the substrate and its magnitude is 1.2 MV/cm for Ga0.84In0.16N/GaN quantum wells on sapphire substrate. In addition, from the direction of the field, the growth orientation of our nitride epilayers can be determined to be (0001), corresponding to the Ga face.

Determination of piezoelectric fields in strained GaInN quantum wells using the quantum-confined Stark effect

Polarized Electroluminescence from an Anisotropic Nematic Network on a Non‐contact Photoalignment Layer

Donor-acceptor recombination has been investigated in ZnS by optically detected magnetic resonance (ODMR). Resonances due to both donors and A-centre acceptors have been observed in hexagonal and cubic ZnS containing group IIIB and group VIIB dopants. Spectral dependence measurements show that both resonances are associated with the blue self-activated emission, which lies at 2.70 eV in ZnS:Cl and 2.60 eV in ZnS:Al,I. The resonances are observed as increases of order 0.4% in the total emission intensity and are accounted for in terms of a donor-acceptor recombination process. It is found that the signals are predominantly from donor-acceptor pairs that are sufficiently close for recombination to occur before thermalisation is achieved but which are sufficiently well separated for the exchange interactions and associated line broadening to be small. The investigation confirms that the self-activated emission is due to radiative recombination of an electron from a shallow donor with a hole on an A-centre.

http://iopscience.iop.org/article/10.1088/0022-3719/12/2/023/pdf

Spin-dependent donor-acceptor pair recombination in ZnS crystals showing the self-activated emission

Optically detected electron spin resonance in amorphous silicon

Photocurrent time-of-flight experiments are used to study the transport properties of hole-conducting nematic liquid crystals. Nondispersive transients are observed and a value of $4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}{\mathrm{cm}}^{2}{\mathrm{V}}^{\ensuremath{-}1}{\mathrm{s}}^{\ensuremath{-}1}$ is found for the hole mobility of a chiral nematic glass at room temperature. The hole mobility of a reactive mesogen in the nematic glass phase is increased by photopolymerization of its reactive end chains to form an insoluble network. The mobility of the network shows a weak field dependence over the temperature range 295--373 K. The experimental data can be explained by hopping between the nematic cores using a Gaussian disorder model that includes spatial correlations in the carrier energy. The density-of-state distribution obtained from the model agrees with that measured spectroscopically.

J.E. Nicholls

Papers

Polarized Electroluminescence from an Anisotropic Nematic Network on a Non‐contact Photoalignment Layer

Spin-dependent donor-acceptor pair recombination in ZnS crystals showing the self-activated emission

Optically detected electron spin resonance in amorphous silicon

Nondispersive hole transport of liquid crystalline glasses and a cross-linked network for organic electroluminescence

Donor-acceptor nature of the blue self-activated emission in ZnS crystals