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The poly(p-phenylenevinylene)/polyurethane(PPV/PU)composite films obtained from water-borne PU system with PPV precursor(PrecPPV)were investigated. UV-VIS absorption, photoluminescence(PL), thermoluminescence(TL)spectra and dynamic mechanical analysis(DMA)results of pure PPV and its composite are reported and analysed. The conversion of the PrecPPV/PU into PPV/PU composite was confirmed also by mean of dielectric spectroscopy. It was concluded from the UV-VIS absorption and PL spectra at room temperature that the conjugation length of the PPV chains in this composite and in pure PPV is similar. In the PL spectra at low temperatures positions of the peaks are the same in the pure PPV and in the composite. Upon cooling all peaks shift towards longer wavelengths and change their relative intensities. The TL spectra show that in these materials relatively shallow traps dominate, yielding TL maximum at ca. 70  K. The composite films cast from water suspension are flexible in contrast to pure PPV which forms rigid film. In DMA it is reflected by lower values of the storage modulus E' and of the amplitude of tanδin the composites compared to pure PPV film. [ABSTRACT FROM AUTHOR]

Abstract CdTe/CdS core-shell quantum dots were synthesized and implemented into a light emitting device resulting in multi-channel electroluminescence with a light-green emission color. The main electroluminescence band at about 530 nm corresponds to the emission by the CdTe core (type I core/shell structure), while the next emission band at 595 nm is assigned to the crossed recombination of electrons from the conduction band of the CdS shell and holes from the valence band of the CdTe core (type II core/shell structure). At the same time, the photoluminescence spectrum of the synthesized CdTe/CdS core-shell quantum dots contains only one emission band distinctive for type II structures. This behavior of CdTe/CdS core-shell quantum dots upon the electroexcitation allows the extension of the electroluminescence spectrum in the optical region in a way that is useful for lighting-source applications. Such multi-channel electroluminescence can most probably also be reproduced in related core-shell systems accounting for size-confinement between the core size and shell thickness. Graphical abstract Image 1 Highlights • The CdTe/CdS core-shell quantum dots based QLED was fabricated. • This QLED demonstrates multi-channel electroluminescence. • The quantum dots demonstrate the mixed electroluminescence typical for type I and type II core-shell systems. • The strain-induced band shift effect was observed for the 1 s -1 s transition in CdTe core in the presence of CdS shell. [ABSTRACT FROM AUTHOR]

Three new bipolar star-shaped derivatives of 2,4,6-triphenyl-1,3,5-triazine containing carbazolyl groups were designed, synthesized and characterized. All the materials possess high thermal stability and high glass transition temperatures ranging 97–226 °C. Photophysical study of the dilute solutions and neat films of the synthesized compounds was performed. Lippert–Mataga plots revealed linear dependence of Stokes shifts on the orientation polarizability for all the compounds. The dilute solutions of the triazine derivatives exhibited high photoluminescence quantum yields reaching 0.85, while for the neat films photoluminescence efficiency of 0.20–0.33 was observed. Ionization potentials of the solid layers of carbazole-triazine adducts estimated by photoelectron spectroscopy were found to be in the range of 5.49–5.97 eV. Hole drift mobility of the materials well exceeded the magnitude of 10 −3 cm 2 V −1 s −1 at an electric field of 6.4 · 10 5 V/cm. The selected compounds were tested as light emitting materials in organic light emitting diodes based on host-guest systems. [ABSTRACT FROM AUTHOR]