PHOTOELECTRIC PROPERTIES OF MnIn2S4 SINGLE CRYSTALS

The spectral distribution of the photoconductivity and the temperature dependence of the photocurrent of MnIn2S4 single crystals are investigated. The intrinsic, impurity photoconductivity and a maximum at an energy of 2.69 eV, which is associated with the intracenter transition of Mn2+ ions (6A1→4A1), are revealed in the photoconductivity spectrum. The region of the wavelengths of 600–1000 nm appears with an excess of manganese in the crystals and is caused by a donor defect. At temperatures of 80—145 K, the increase in the photocurrent is associated with the thermal depletion of the adhesion levels. The activation energy of the adhesion levels is determined.

INFLUENCE OF THE THICKNESS OF THE n-Si SUBSTRATE AND ITS DOPING LEVEL ON THE ABSORBING PROPERTIES OF SILICON PLASMON STRUCTURES IN THE INFRARED RANGE

The absorption spectra of Si/SiO2/Si3N4/Si+ and Si/SiO2/Si+ structures with an island surface layer are calculated using the finite difference time domain method. The absorption spectra were modeled depending on the thickness of the substrate and its doping level. It was found that the thickness of the i-Si substrate does not affect the overall absorption of the structure. At the same time, an increase in the thickness of the n-Si substrate leads to an expansion of the absorption band with an intensity of more than 70%. It is established that the doping level of the substrate affects the absorption value of the structures and bandwidth with an absorption value above 80%. It is shown that a wide absorption band with intensity of more than 80% occurs at the doping level of the substrate in the range of 2 . 1019—5 . 1019 cm–3. Dispersion relations in the Si+/SiO2/Si+ structure with an unstructured surface layer are obtained. These dispersion relations may indicate the existence of plasmon oscillations in the system. It is established that a violation of the phase synchronization of the modes at both Si/dielectric interfaces at a significant difference between the doping levels of the substrate and the surface layer can lead to a decrease in the absorption.

INFLUENCE OF THE COMPOSITION OF THE RADIO-FREQUENCY SPUTTERING ATMOSPHERE ON THE DENSITY OF STATES AND INTERBAND LIGHT ABSORPTION IN THIN Y2O3 FILMS

The long-wavelength edge of the fundamental absorption band of thin Y2O3 films obtained by radiofrequency ion-plasma sputtering is investigated. The edge of interband absorption after annealing of the films in an atmosphere of argon, oxygen, or a mixture of these gases is shown to be approximated well by the Urbach empirical rule. Diffractograms of the obtained films were studied and a model of a heavily doped or defective semiconductor in the quasi-classical approximation was used to analyze the experimental results. This model allows determining the radius of the basic electronic state, the screening radius, and the rootmean-square potential depending on the sputtering atmosphere.

MANIFESTATION IN IR-LUMINESCENCE OF THE CROSS RELAXATION PROCESSES BETWEEN NV CENTERS IN WEAK MAGNETIC FIELDS

We present a combined experimental and theoretical study of the effect of magnetic field on the luminescence from an ensemble of NV centers in diamond. It was found that the intensity of infrared luminescence associated with transitions between singlet levels of NV centers shows a pronounced increase of a near-zero magnetic field. The influence of the power and polarization of laser radiation on the amplitude and shape of the revealed local maximum in IR-luminescence of NV centers is investigated. An eight-level photophysical model of an NV center in the presence of an arbitrarily directed magnetic field has been constructed and on its basis the calculation has been performed of the luminescence intensity emitted by an ensemble of NV center, both in the visible and infrared regions of the spectrum. It is shown that the phenomenological allowance for the cross-relaxation of NV centers between each other and with other paramagnetic centers in a diamond within the framework of this model allows describing the experimentally observed fluorescence features of an ensemble of NV centers in the presence of weak magnetic fields.

ANALYTICAL REPRESENTATIONS FOR THE TRUNCATED SPECTRAL CHARACTERISTICS OF THE FOUR-POINT COHERENCE FUNCTION OF A LASER BEAM IN A TURBULENT MEDIUM

New analytical representations for the truncated spectral characteristics of the four-point coherence function of a laser beam propagating in a turbulent medium are obtained. These representations are valid for any level of fluctuations of the refractive index in air. For two particular cases they turn into exact analytical representations previously derived by the authors with using of an integro-functional equation for truncated spectral characteristic of the four-point coherence function. A constructive procedure for obtaining approximate analytical expressions of the four-point coherence function of a laser beam propagating in a turbulent medium is proposed.

SPECTRAL PROPERTIES OF A BENZOTHIAZOLE DYE MODIFIED WITH POLYETHYLENE GLYCOL

The spectral properties of a new benzothiazole dye modified with polyethylene glycol have been investigated. A strong dependence of the fluorescence quantum yield on the viscosity and polarity of the medium has been shown, i.e. the conjugation of the dye with polyethylene glycol does not lead to the loss of the properties of the molecular rotor, while significantly reduces its aggregation. When incorporated into amyloid fibrils, the quantum yield of the dye increases by more than 40 times; the new dye can be regarded as an efficient fluorescent probe for amyloid fibrils detection and research. In this case, not only the intensity, but also the position of the absorption spectrum can be used as a sensitive parameter. The presence of blood plasma proteins (albumins) in the solution has practically no effect on the position of the absorption spectrum and has little effect on the fluorescence intensity of the probe.

ANALYSIS OF THE COMPOSITION OF WATER-ALCOHOL MIXTURES USING THE INFRARED ABSORPTION SPECTRA OF THEIR VAPORS

The article presents the results of studies of infrared absorption spectra of saturated vapors of alcohols and alcohol-containing mixtures in the range of 1.3—1.5 μm. A method was developed for the quantitative determination of the composition of water-alcohol mixtures based on the use of multiple linear regression, and a range of methanol concentrations was determined, in which the nonlinearity of the dependence of the concentration of alcohols in saturated vapors over a liquid mixture on the concentration of alcohols in this liquid mixture does not significantly affect the results of analysis of the mixture composition. A method for optimizing a set of wavelengths for multiple linear regression, based on minimizing the mean-square error in determining the concentration is proposed and implemented. The developed methods make it possible to determine the presence of small (<1%) amounts of methanol against the background of large amounts of ethanol and water using relatively inexpensive and accessible spectroscopic equipment.

EXPRESS ANALYSIS OF TRIETHOXYSILANE AND TETRAETHOXYSILANE USING THE RAMAN SPECTROSCOPY METHOD FOR OPTIMIZATION OF THE TECHNOLOGICAL PROCESS OF MONOSILANE SYNTHESIS

A technique for the express analysis of the products of technological processes is described, which was developed using the Raman spectroscopy method. The analysis of the Raman spectra includes the interpretation of the spectral bands, taking into account the values of the characteristic frequencies of the vibrational spectra of organic compounds, as well as the determination of the integral intensities of the corresponding spectral ranges. By example of the real time control procedure for the technological process of monosilane synthesis, the express analysis of tetraethoxysilane, which is a by-product of this technological process, is carried out. Significant advantages of using the express analysis method are demonstrated, which provide control over the normal course of the technological process and obtaining results that allow making adjustments to the process flow diagram in order to optimize it.

EFFECT OF THE DENSITY OF SURFACE V-DEFECTS ON LASER PROPERTIES OF InGaN/GaN HETEROSCTRUCTURES WITH MULTIPLE QUANTUM WELLS GROWN ON SILICON SUBSTRATES

We investigated the radiative properties of InGaN/GaN heterostructures with multiple quantum wells (MQWs) grown on silicon substrates with different thicknesses of quantum wells at optical excitation. The correlation of laser and photoluminescent properties with the surface morphology of the gallium nitride coating layers and the density of V-defects has been established. It is shown that, with a growth in the density of V-defects, the threshold power density of the excitation of the generation of InGaN/GaN heterostructures with MQWs increases.

APPLICATION OF ATOMIC SPECTROSCOPY TO MEASURING STRONG INHOMOGENEOUS MAGNETIC FIELDS

Using the spectrum of selective reflection (SR) of laser radiation from the boundary of the surface of the dielectric window of the spectroscopic nanocells – pairs of rubidium atoms, the value of the magnetic field applied to the nanocell is measured. A method is proposed for calculating the magnetic induction B in the range of 0.1–6.0 kG based on the ratio of the frequency intervals between atomic transitions, which greatly simplifies the determination of B, particularly, there is no need for a reference spectrum at B = 0. To implement the SR process a 300-nm column of vapors of Rb atoms is used, and atomic transitions with a sub- Doppler spectral width of 80–90 MHz are formed. This leads to frequency separation of transitions in SR spectrum that is important for the proposed method. SR spectrum can be analyzed using a specially designed computer program that accelerates the data processing. The small thickness of the vapor column allows high spatial resolution, which is important in the case of inhomogeneous magnetic fields.