I. P. Shcherbakov

Emission kinetics of light, sound, and radio waves from single-crystalline quartz after impact on its surface

A steel striker impacting the surface of single-crystalline quartz generates strain waves and their related acoustic and electromagnetic emissions. Simultaneously, microcracks with free excited SiO• radicals at their edges appear in the single crystal. The relaxation of the electronic excitation causes bursts of fractoluminescence. The intensity of the bursts is proportional to the microcrack surface area. It is found that the linear sizes of microcracks vary from 15 to 70 μm. Cracking changes the slope of the time dependences of the acoustic and electromagnetic emission intensities. The microcrack size distribution obeys a power law with an exponent of about two.

Fractoluminescense of crystalline quartz upon an impact

The kinetics of fractoluminescence of quartz single crystals subjected to an impact with a steel striker is investigated. It is established that, within several tens of microseconds after an impact, there appear two to three tens of fractoluminescence flashes. An analysis of the luminescence spectra demonstrates that fractoluminescence arises upon the transition from an excited electron level to the ground electron level in SiO. radicals formed as a result of the breaking of the Si-O-Si bonds. Acoustic emission signals are detected simultaneously with fractoluminescence. It is revealed that all except the first of the fractoluminescence flashes arise from vibrations of the crystal-striker system after the impact. Approximately ten cracks with linear sizes of several millimeters are observed on the surface of the plate. The SiO· radicals are assumed to be located at the surface of these cracks. The time of fractoluminescence excitation is determined by the growth rate of cracks and amounts to ≈1–3 μs. After the growth of the cracks is terminated, the fractoluminescence intensity decreases exponentially with a mean time of ≈12 μs, which does not depend on the temperature. This makes it possible to attribute the observed luminescence to fluorescence, i.e., to a singlet-singlet transition.

Emission processes accompanying deformation and fracture of metals

Present-day physical methods of investigation reveal that the fracture and plastic deformation of metals is accompanied by emission processes, in particular, by luminescence and emission of electrons. All the metals studied thus far exhibit a capability of luminescence. The intensity, duration, and spectrum of mechanoluminescence are different for different metals. The intensity is determined by the mechanical and thermal characteristics. For a given metal, the intensity depends on dislocation density in the structure and the sample loading rate. The spectrum of noble metals is governed by the electronic structure of surface states. The dynamics of mechanoluminescence and electron emission (exoemission) depends on the rate of stress variation in the sample under study. This permits one to consider the mechanoluminescence and exoemission not only as physical characteristics but also as a potential tool for probing surface states in metals and the kinetics of emergence of mobile dislocations on the surface with a high time resolution.

Effect of the microstructure of a metal on the emission spectrum excited during destruction of current-carrying conductors by an MHD instability

The spectral characteristics of the radiation emitted during the destruction of copper conductors with different microstructures by a high-density current are investigated experimentally. The proposed mechanisms leading to radiation generation and the experimental results corresponding to these mechanisms are discussed.

Organic light-emitting diodes based on polyvinylcarbazole films doped with polymer nanoparticles

The optical and electrical properties of light-emitting diode structures with an active layer based on nanocomposite polyvinylcarbazole (PVK) films doped with nanoparticles of another light-emitting polymer, MEH-PPV, have been studied. It has been established that the size of MEH-PPV particles in the PVK matrix is of the order of 100 nm. The spectral range of photoluminescence of such structures can be changed by varying the ratio of PVK to MEH-PPV. The current-voltage characteristics of composite light-emitting diodes based on PVK: MEH-PPV films indicate p-type conductivity. It has been shown that a decrease in the MEH-PPV nanoparticle concentration in the PVK matrix shifts the threshold values of the bias for the onset of electroluminescence toward smaller values and makes the photoluminescence and electroluminescence spectra more similar to the spectrum of the white light-emitting diode. The influence of the form of the polymer and polymer nanoparticles on the mechanisms of injection and transport of charge carriers and the radiative recombination in the studied structures has been discussed.

Dynamics of microcracks and time dependences of surface deformation of a heterogeneous body (granite) under an impact

The dynamics of fractoluminescence flashes and the time dependences of surface deformation of granite with different sizes of feldspar grains under an impact on samples by a metal pin have been studied with a 10 ns resolution. A band at ∼1.9 eV has been observed in the fractoluminescence spectra, which means that, under the influence of mechanical stresses, Si-O-Si bonds are broken and ≡ SiO⊙ free radicals are formed. The fractoluminescence has the form of flashes with a duration of ∼10 ns. It has been assumed that each of them corresponds to the nucleation of a microcrack. From the flash intensities and the elastic wave velocity, the linear size of microcracks has been estimated to be from ∼8 to 30 μm. Microcracks are mainly generated during passage of a deformation wave through feldspar grains. An impact causes the appearance of eigenvibrations of the entire sample, and cracking of grains gives rise to eigenvibrations of grains.

Luminescence of quartz under the action of a shock wave

Upon fracture of quartz under the action of a shock wave caused by an electric explosion, a plasma jet is formed. An analysis of the luminescence spectra shows that the jet consists of atoms and cations of the elements contained in quartz and impurities in it.

Structural changes in the surface of a heterogeneous nanocrystalline body (sandstone) under the friction

The structure of a ~30 nm thick surface layer of a heterogeneous nanocrystalline solid body (sandstone) before and after the friction was investigated using photoluminescence and Raman spectroscopy. Before the friction, this layer contained nanocrystals of quartz, anatase, feldspar, and montmorillonite. The friction caused a sharp decrease in the concentration of nanocrystals of quartz and feldspar.

Emission of plasma escaping from a heterogeneous solid (granite) under an electric discharge near its surface

The electrical breakdown of air near a granite plate causes sequential release of several hundred plasma jets consisting of electrons, positively charged ions, and Si, O, and other atoms. The release duration of each jet does not exceed ∼10 ns, and the interval between them varies from ∼10 to ∼300 μs. It is assumed that the shock wave increases the lattice strain in dislocation pile-ups to such values at which the ground and excited state levels begin to cross. This leads to transitions between electronic levels, breaking of interatomic bonds, and emission of positively charged ions and electrons.

Dynamics of the deformation and destruction of a heterogeneous body (granite) under the influence of an electric discharge

The device is constructed, which makes it possible to simultaneously detect, with a time resolution of 10 ns, fractoluminescence as well as electromagnetic emission and surface deformation observed in a solid during its destruction under the effect of a shock wave. Using this device, time dependences of deformation and destruction of the granite plate caused by an electric breakdown with an energy of 0.2 J in air near its surface are investigated. It is found that the breakdown causes the appearance of a shock wave in granite, the velocity of which is ∼5 km/s. The shock wave stimulates emission of a plasma consisting of atoms and ions, which enter into the graphite composition, from the granite surface. It is assumed that the appearance of the plasma is caused by cumulation of the shock wave energy in micropores contained in graphite.