Photoluminescence (PL) spectra of ZnO:Ag highly dispersed powders obtained by chemical deposition from aqueous solution are investigated in the wavelength range between 360 and 750 nm at room temperature under excitation between 250 and 350 nm. Before starting the synthesis, the Ag dopant was introduced into the initial solution in the form of AgNO3 silver nitrate in the amount of 12, 102, and 252 mg. The PL spectra consist of an ultraviolet emission (380 nm) attributed to AgZn acceptor-bound exciton, a short-wavelength violet emission (400 – 450 nm) and a wide long-wavelength yellow-orange emission (560 – 600 nm). With decreasing excitation energy, the violet emission decreases in intensity, while the yellow-orange emission increases. This is caused by the phenomenon of self-absorption of the short-wavelength emission and energy transmission to the centers of the long-wavelength emission. A rapid decrease in intensity of all the PL bands is found for the sample with maximum Ag concentration. This fact is due to the appearance of the second phase in the form of silver oxide and, consequently, a decrease in the concentration of AgZn point defects responsible for the bands.
Satyendra Nath (S.N.) Bose is one of the great Indian scientists. His remarkable work on the black body radiation or derivation of Planck’s law led to quantum statistics, in particular, the statistics of photon. Albert Einstein applied Bose’s idea to a gas made of atoms and predicted a new state of matter now called Bose-Einstein condensate. It took 70 years to observe the predicted condensation phenomenon in the laboratory. With a brief introduction to the formative period of Professor Bose, this research survey begins with the founding works on quantum statistics and, subsequently, provides a brief account of the series of events terminating in the experimental realization of Bose-Einstein condensation. We also provide two simple examples to visualize the role of synthetic spin-orbit coupling in a quasi-one-dimensional condensate with attractive atom-atom interaction.
Herein we report on the structural and optical properties of pure and Eu-doped (3% at.) ZnO aerogels nanostructures (ZnO-ans) synthesized by sol-gel associated with drying at supercritical conditions of isopropanol (254 °C, 54 bars). The samples were investigated using X-ray diffraction (XRD), SEM, UV-visible spectroscopy, FTIR and photoluminescence (PL). XRD studies exhibit the formation of a high crystal quality ZnO wurtzite hexagonal structure. The UV-visible measurements point out that the absorption intensity and the band gap energy increase after Eu-doping. FTIR analysis confirms the formation of ZnO phase and reveals a shift toward longer wavenumber of the Zn-O absorption band after Eu -doping. SEM images show that Eu3+ ions lead to change the morphology of ZnO crystalline from pastille to sphere. PL measurements reveal a decrease of UV luminescence intensity and an increase of the visible one due to Eu-doping.
By encouraging girls and women to develop and maintain an interest in STEM subjects, we are preparing the next generation of researchers, engineers, scientists and programmers to meet the growing demand for skilled STEM professionals. Current and future jobs and societal challenges require and will increasingly require a wide range of skills such as teamwork, intercultural competence, empathy, creativity, problem solving and independent non-linear thinking. Accordingly, we must ensure that women and girls are widely represented at all levels as we move forward. It is more important than ever that we eliminate stereotypes and biases and promote women and girls who want to pursue STEM careers.
The sol-gel process was employed to successfully synthesize ZnO nanostructures in isopropanol, employing various subcritical temperature and pressure conditions: (90°C, 2 bar), (120°C, 6 bar), (160°C, 14 bar), and (200°C, 30 bar). The resulting products were subsequently annealed at 500°C for 2 hours and subjected to characterization using different analytical techniques, including X-ray diffraction (DRX), infrared (ATR), UV-Visible, and photoluminescence (PL) spectroscopies. The DRX measurements confirmed that the ZnO nanostructures exhibited a polycrystalline structure of the hexagonal wurtzite type. The cell parameters and stresses within the crystallites were found to be influenced by the synthesis conditions (temperature and pressure), in contrast to the particle size. ATR spectra indicated high purity of the produced nanostructures, and it was observed that the position of the absorption band associated with the Zn-O vibrational bond of ZnO shifted towards lower wavenumbers as the temperature increased. UV-Visible spectra demonstrated that the absorption band shifted towards shorter wavelengths with increasing temperature and pressure. The optical gap displayed a similar trend to the lattice parameters and strain within the nanoparticles. PL measurements revealed that the processing temperature and pressure resulted in increased UV emission and decreased visible emission. However, the positions of the UV emission bands were independent of the synthesis parameters.
The paper describes a software design for a 42-kHz ultrasonic transmitter based on the 32bit timer of a TMS320C6713B processor.
The paper describes results of experimental studies of the dependence of the resistance, transverse and longitudinal magnetoresistance, as well as the Shubnikov–de Haas (SdH) oscillations of Bi0.83Sb0.17 semiconductor single-crystal wires with diameters of (75–1100) nm, as a function of the thickness, in a temperature range of (3.1–300) K at magnetic fields of up to 14 T. The wires were prepared by liquid-phase casting. It has been found that the temperature dependences of the resistance of wires with d < 0.5 m have two regions exhibiting a semiconductor and a metallic behavior of the resistance, the two regions being separated by a maximum, which is shifted to the high-temperature region with a decrease in the wire diameter d. It has been revealed that the energy gap E increases by a factor of 2 with a decrease in wire diameter d, due to the occurrence of the quantum size effect. The “metallic” behavior of conductivity is attributed to surface states characteristic of topological insulators, which is most clearly evident in thin wires at temperatures of T < 50 K. It has been shown that, in the presence of a uniform magnetic field H, the field dependences of the longitudinal and transverse magnetoresistance in quasi-one-dimensional systems can undergo a significant change depending on the ratio of quantum wire radius to the magnetic length R = (ch/eH)1/2, as well as on the decrease in the mean free path of carriers due to scattering on the wire surface. The SdH oscillation periods exhibit anomalies that are typical neither to bulk Bi1xSbx samples nor to semimetallic wires based on Bi1xSbx alloys. This fact points to the essential role of surface states of topological insulators in 1D-systems, which lead to the occurrence of new effects that are not characteristic of other systems.
A brief review of our recent research on preparation and characterization of oxide nanoparticles and their derivatives by hydrothermal growth is presented. A series of Ga2O3 , ZnO, and TiO2 nanoparticles, as well derivative nanomaterials including GaN nanowires and ZnO/TiO2 nanocompostes have been prepared. Ga2O3 and ZnO nanopowders have been produced using metal nitrate hydrates as precursors, while Titanium isopropoxide was used for preparation of TiO2 nanopowders. GaN nanowires have been produced by nitridation of Ga2O3 nanomaterials. The produced nanomaterials have been characterized scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis and Fourier transform infrared (FTIR) spectroscopy. Ga2O3 nanoparticles doped with Eu3+ ions have been characterized by photoluminescence spectroscopy in order to assess their prospects in developing nanophosphors materials.
An analytical solution for the Gibbs–Tolman–Koenig–Buff equation for microwire and nanowire surfaces has been obtained. Analysis has been performed for a cylindrical surface in terms of the linear and nonlinear Van der Waals theory.
This study presents a brief analysis of Zn1-xMgxO and (GaxIn1-x)2O3 thin films deposited on Si substrates by the spin coating method. The morphology and chemical composition of the prepared thin films were studied by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis. The evolution of the crystal structure with a change in the film composition and the technological conditions for annealing after spin coating was studied by X-ray diffraction (XRD) analysis. The annealing atmosphere and temperature were optimized in terms of producing films with a stoichiometric composition and a high crystalline quality.
In this paper results of studying CdS/ZnTe heterostructures synthesized by the quasi-closed space sublimation method on glass substrates coated with an ITO layer are described. The electrical and photoelectric properties of the structures are studied using current–voltage and capacitance–voltage characteristics in a temperature range of 30–100 °C. Analysis of the experimental data shows that the main specific feature of CdS/ZnTe structures is the formation of a high-resistance transition layer, which affects the separation of carriers at the barrier contact. The current carrier concentration in the space charge region, which is determined from the capacitance–voltage characteristics, is 1 x 1015 cm-3; this fact suggests that one of the contacting materials—ZnTe—exhibits a high resistivity. Measurements of current–voltage characteristics in the solar cell mode give the following photoelectric parameters: open circuit voltage (UOC = 0.53 V, JSC = 27–30 A/cm2, and FF = 0.25.
The role of infrared radiation in stimulating cellular metabolism can be dual. Firstly, the energy of light quanta is used by the cell instead of the energy of adenosine triphosphate hydrolysis. Secondly, light absorption cannot replace this hydrolysis. However, it can accelerate its rate and thus the productivity of metabolic reactions associated with it. This process is significantly enhanced by the use of terahertz modulation of infrared radiation, which is manifested, for example, in optically stimulated transport of ions through biological membranes. For therapeutic effects on the above-described processes in biological tissues, a device has been developed that generates infrared radiation with wavelengths in the range of maximum transparency of biological tissues modulated in amplitude in a frequency range of 1011–1012 Hz. The modulation of radiation has been produced by the method of interference.
Low-temperature photoluminescence (PL) is used to study defects evolution via immersion technique and annealing in vacuum of ZnTe thin films. In this paper we studied how copper doping from solutions of different molar concentrations affects PL of ZnTe thin films grown by close space sublimation (CSS) method. Undoped ZnTe thin films showed PL emission in the (520-680) nm wavelength region. The incorporation of copper in ZnTe produce a number of broad emission bands that correspond to an electron transition from the conduction band to spin-orbit states of the localized level of Cu2+ ions. All the studied samples had variable concentrations of oxygen and the possibility of the formation of auxiliary oxides is discussed.
This paper reports the luminescence spectra of YTaO4 activated with rare-earth ions, such as Eu3+ and Tb3+. The effect of these rare-earth ions on the luminescence of yttrium tantalate phosphors is studied. The luminescent properties are studied under X-ray and electron beam excitations. It is found that, under these excitations, the emission centers of the rare-earth activators (Eu3+, Tb3+) efficiently contribute to the overall luminescence. Color cathodoluminescence images clearly show the dependence of chromaticity on the different activators. These rare-earth activated phosphors exhibiting various luminescence chromaticities are promising materials for optoelectronic applications and for X-ray intensifying screens in medical diagnosis, because they provide a broad variation of visible photoluminescence from blue to red.
Experimental results on the bis[(μ 2 -etoxi)(benzoyl trifluoroacetonato)(nitrato)(1,10- phenantroline)europium(III)]1,10-phenantroline europium(III) coordination complex (hereafter, [Eu(μ 2 -OC 2 H 5 )(btfa)(NO 3 )(phen)] 2 ·phen) are described. The complex is characterized by photoluminescence (PL) and infrared spectroscopy. Photoluminescence spectra of the complex exhibit strong emission with specific narrow emission bands associated with the 5 D 0 → 7 F j (j = 0–4) transitions. The pattern of emission band splitting and the luminescence time decay suggest the presence of at least two different sites of the Eu 3+ ion in a low-symmetry environment. The absolute PL quantum yield of the complex is determined to be 49.2%.
In this paper, the design of a system for the control of a solar panel motion by means of a servomotor based on an Arduino board is described. The system calculates optimum tracks and position of the sun to ensure that the solar panel is always directed to the sun in order to increase the amount of energy generated by the solar panel. The device makes use of four solar modules for detection and a servomotor to automatically rotate the solar panel to adjust it to the sun position
In this paper, solutions for two problems are proposed. One of the problems is associated with increasing the strength of objects, for instance, the strength of windows in industrial buildings and dwelling houses. The other problem is related to electromagnetic shielding. Both of these problems are related to the protection form terrorist acts, since terrorists make use of concentrated electromagnetic pulses to destroy computers or other electronic equipment. The proposed solutions are based upon the manufacturing of glass windows reinforced with cast glass-coated amorphous micro- and nanowires (CGCAMNWs) having a special composition and structure, which increases their tensile strength against mechanical destruction, on the one hand, and imparts them with shielding properties against electromagnetic radiation, on the other hand. The CGCAMNW materials are of interest from both theoretical and practical points of view.
The characteristics of transient photocurrent in amorphous heterostructures Al-As0.40S0.30Se0.30/Ge0.09As0.09Se0.82/Ge0.30As0.04S0.66–Al in the case of the positive polarity of the applied voltage at the top illuminated Al electrode are presented and discussed in this paper. The complex structure of the spectral distribution of the stationary (Fig. 1) and the transient (Fig. 3) photocurrent characteristics can be assigned to the different values of the optical band gap Eg of the involved amorphous layers (about Eg ~ 2.0 eV for As0.40S0.30Se0.30 and Ge0.09As0.09Se0.82; about Eg ~ 3.0 eV for Ge0.30As0.04S0.66). It is found that the dependence of photocurrent on light intensity has a power-law behavior Ipc ~ Fα(1.0 ≤ α ≤ 0.5), which is characteristic of amorphous semiconductors with an exponential distribution of localized states in the band gap.
The conventional measurement signal sample-and-hold amplifier comprising a sample and hold circuit in the form of a sample switch, a voltage hold capacitor, and a voltage repeater further includes two similar sample-and-hold circuits of reference voltages. The idea of the proposed amplifier is that hold capacitors are equally discharged in all three sample-and-hold circuits. Therefore, an affine ratio for the stored three voltage samples does not change the intrinsic value over a long discharge time. Then, this invariant affine ratio is taken as the measuring signal. A reproducing (recovery) unit, which is also included, calculates this affine ratio. In turn, the included information signal former shaper pre-converts (prepares) the initial measurement signal using reference voltages. Thus, the hold time is significantly increased, while maintaining a short sample time for the given hold capacitor. On the other hand, the affine ratio uses differences and voltage ratios. Therefore, offset errors are mutually reduced. It is possible to implement the proposed sample-and-hold amplifier in the form of an analog chip based on a multiplier and the known multi-channel sample-and-hold amplifier.
