Igor’ Shcherbakov

Hybrid active layers from a conjugated polymer and inorganic nanoparticles for organic light emitting devices with emission colour tuned by electric field

We report on the investigation of the electrical and optical properties of hybrid active layers for organic devices consisting of a conjugated polymer MEH-PPV mixed with ZnO and Si nanoparticles. The effect of an electric field on the photoluminescence (PL) from a MEH-PPV : ZnO composite film is studied. We have found that in the absence of an electric field PL emission from the MEH-PPV : ZnO composites have two main maxima in the blue–red regions. Three additional minor PL maxima attributed to the exciplex states were found at ~420–480 nm. Application of a voltage bias to planar electrodes significantly suppresses the blue emission. Generation of excited states in the MEH-PPV : ZnO structures implies the presence of several radiative recombination mechanisms with the formation of polymer–nanoparticle complexes including exciplex states and charge transfer between the polymer and nanoparticles that can be controlled by an electric field. This effect provides the possibility to tune by an electric field the emission colour of organic light emitting diodes by combining an efficient emission from both organic/inorganic materials involved.

A light-emitting field-effect transistor based on a polyfluorene–ZnO nanoparticles film

We report on a light-emitting organic field-effect transistor (LE-OFET) based on a polyfluorene (PFO)–ZnO nanoparticles film. We have analysed the behaviour of absorption, photoluminescence spectra and electroluminescence (EL) intensity of the PFO : ZnO hybrid films with different ZnO concentrations prepared in the FET configuration. We have found that the PFO : ZnO LE-OFET exhibits the current–voltage characteristics of a unipolar FET with saturation behaviour and operates in the hole accumulation mode. The FET mobility values in the PFO : ZnO films with a high ZnO concentration are close to the mobility of polycrystalline ZnO. A significant increase in the EL intensity of the hybrid films has been observed with an increase in the concentration of ZnO nanoparticles and with the application of gate voltages. The working mechanism of the LE-OFET device is discussed.

Effect of electric field on the photoluminescence of polymer-inorganic nanoparticle composites

Abstract We report on the effect of electric field on the photoluminescence (PL) from a composite consisting of a BEHP-co-MEH-PPV conjugated polymer mixed with ZnO nanoparticles. We have found that in the absence of electric field PL emission from the BEHP-co-MEH-PPV-ZnO composite has two maxima in the blue and green-yellow regions. Application of a voltage bias to planar gold electrodes suppresses the green yellow emission and shifts the only PL emission maximum towards the blue region. Current–voltage characteristics of the BEHP-co-MEH-PPV-ZnO composite exhibit the nonlinear behaviour typical of nonhomogeneous polymer-inorganic structures. Generation of excited states in the BEHP-co-MEH-PPV-ZnO structure implies the presence of several radiative recombination mechanisms including formation of polymer-nanoparticle complexes including “exciplex” states and charge transfer between the polymer and nanoparticle that can be controlled by an electric field.

Microcracking in impact-damaged granites heated up to 600 °C

The acoustic emission (AE) technique was applied for monitoring the high-speed cracking process in three kinds of impact-damaged granites at temperatures 20 °C to 600 °C. The analysis of the amplitude-frequency response of the AE time series showed the presence of a few populations of cracks differing in size in the range 0.25 mm to 2.3 mm. The dependence of the appearance/growth/decay of any given population on temperature and physical and mechanical properties of granites evidenced the interplay between inter- and intragranular cracking under various thermal conditions. At room temperature (pure mechanical forcing), the intergranular damages along boundaries between the same minerals prevail; at 200 °C (impact forcing plus thermoelastic stress), the cracking between grains of quartz and feldspar emerge; finally, in the range 500 °C to 600 °C, the intragranular damages appear.

Nanostructural scaling effect in fracturing homogeneous solids

The scaling effect (power law dependence of number of newly-formed damages on damage size) during fracturing is inherent in heterogeneous materials, such as composites, concrete, rocks, etc., in which multi-site damaging takes place. Fracturing brittle homogeneous materials do not exhibit this phenomenon due to the lack of pre-failure damage accumulation at the microscopic scale level. This work is to determine the role of structural heterogeneity in the process of primary defect nucleation occurring in conventional homogeneous materials. We present highly resolved time series of fractoluminescence (FL) emitted during multiple chemical bond breakage in shock-damaged silica glass and single crystals

Damage initiation in brittle and ductile materials as revealed from a fractoluminescence study

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A comparative acoustic emission study of compression and impact fracture in granite

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