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Nanocomposites based on crystalline carbon nitride (CGCN) and cobalt titanate (CoTiO3) have been synthesized and characterized by a number of physico-chemical methods (electron microscopy, electron and IR spectrophotometry, luminescence spectroscopy, and X-ray diffraction). It is concluded based on the analysis of the obtained results, in particular, the luminescence characteristics and Mott–Schottky dependences, that the S-scheme of separation of photogenerated charges between components is realized during the formation of CGCN/CoTiO3 composites. This leads to a decrease in the recombination of electron–hole pairs and an increase in the efficiency of hydrogen evolution from water–ethanol solutions when compared to the presence of CGCN. The effective quantum yield of hydrogen formation is ~90% under light irradiation at λ = 405 nm with the participation of the composite of the optimal composition. [ABSTRACT FROM AUTHOR]

The structural and electrical characteristics of (Mg, Zn)O ceramics produced using the solid state reaction at 1100 °C for 3 hours were studied applying X-ray diffraction and IR reflection spectroscopy as well as means of direct current measurements versus MgO content in initial charge (varied from 0 to 100 mol.%). It has been shown that electrical conductivity extracted from the IR reflection spectra corresponds to that of hexagonal phase in a solid solution, while plasmon in cubic phase was not observed. The electron concentration in the hexagonal grains of solid solution prepared with MgO content below 30 mol. % in the charge was found to be close to that of ZnO grains. It shows the tendency to decrease with further growth of the MgO content, which was explained by extraction of zinc interstitials, responsible for ZnO conductivity, from ZnO under formation of the MgZnO cubic phase. The direct current measurements have shown the lower conductivity as compared to the value estimated from IR reflection spectra. This fact along with the superlinearity of current-voltage characteristics has been explained by the presence of intergranular barriers, which does not allow obtaining information on the concentration of free electrons in the grain by this method. The possible nature of intergranular barriers as well as the role of grain boundaries in the DC conductivity of samples has been discussed. [ABSTRACT FROM AUTHOR]

The samples ZnO:Mn were prepared using the conventional solid-state technique. To dope them with manganese, we used water solutions of MnSO4 and MnCl2. The properties inherent to both types of the obtained ceramics have been compared. It was found that the former demonstrated nonlinear current-voltage characteristics, whereas those of the latter were, in fact, linear. The analysis of EPR, diffuse reflectance and Raman spectra obtained for prepared ceramics allowed concluding that, in the samples doped with MnSO4, formation of Mn-related phase, namely, ZnMn2O4 spinel occurred at ZnO grain boundaries under sintering. It has been ascertained that a thin layer of this substance separates adjacent ZnO grains, which provides appearance of the back-to-back Schottky barriers at grain boundaries and “varistor behavior” of current-voltage characteristics. [ABSTRACT FROM AUTHOR]

Defect related emission in undoped and doped with manganese ZnO ceramics was investigated. Mn concentration NMn was varied from 1019 to 1021 cm-3.The samples were sintered for 3 hours in air at 1100 °C. The color of ZnO:Mn ceramics changed from yellow to reddish-brown with increasing the Mn content. Photoluminescence (PL) spectra of prepared samples were measured at room temperature and analyzed by Gaussian fitting. PL of undoped ceramics exhibited itself as intense broad band peaking at about 550 nm. Two effects were shown to occur as a result of Mn doping: i) drastic quenching of self-activated PL accompanied by gradual red-shift of spectral boundary of the quenching with increasing the Mn content; ii) appearance of a new emission band peaking at 645 nm that becomes dominant in the PL spectrum at Nmn = 1020 cm-3. The observed effects were believed to be due to re-absorption of self-activated ZnO emission by Mn-related centers. The following recombination in excited centers was supposed to occur by both radiative and nonradiative ways, the former being responsible for 645 nm PL band. [ABSTRACT FROM AUTHOR]

InSb wafers of n-type conductivity were annealed at 300, 370 and 400 °C for 30 min in an open tube system under flowing argon ambient. The conductivity type conversion are revealed for the first time in samples with the electron concentration ~1.0·1014 cm-3 for all annealing temperatures. Experimental evidences have been obtained that this phenomenon has a bulk character. In annealed samples the spectral response exhibits pronounced increase in the short-wave region. The effect of annealing on electrical and photoelectrical properties of n-InSb has been explained by formation of InSb antisites. [ABSTRACT FROM AUTHOR]

Undoped as well as Li-, Ag-, Cu- and Zn-doped MgxZn1-xO ceramics with x = 0-0.20 were sintered at 1000 °C. Defect-related photoluminescence (PL) and PL excitation spectra were measured at room temperature in 400-800 nm and 250-400 nm spectral ranges, accordingly. Two types of PL bands were observed: i) the bands, spectral positions of which were not influenced by the Mg content (Cu-related as well as selfactivated orange and red ones); ii) the bands, spectral positions of which exhibited some blueshift with increasing Mg content (Li- and Ag-related and self-activated green ones). It has been shown that used doping gives the possibility to obtain the phosphor with intense visible emission within the blue-yellow spectral range. [ABSTRACT FROM AUTHOR]

Nominally undoped ZnO ceramics were sintered in air and N2 flow at 1000 °C. Room temperature photoluminescence (PL) spectra of the samples were measured and analyzed using Gaussian fitting. The self-activated orange PL band peaking at 610 nm was separated by Gaussian deconvolution. Based on the obtained results compared with some literature data, it has been concluded that the defects responsible for self-activated orange emission in ZnO are zinc vacancies. [ABSTRACT FROM AUTHOR]

Here we report on the effect of post-growth thermal annealing at 200-440 °C on the photoluminescence (PL) characteristics of CdSe/ZnSe quantum dot (QD) and CdZnSe/ZnSe quantum well (QW) heterostructures grown by molecular beam epitaxy. After heat treatment at temperatures lower than 270 °C, the PL intensity from both type of structures increases, while at temperatures above 270-340 °C it decreases. A blue shift of the excitonic band position caused by Cd out-diffusion from the QDs (QWs) is observed above 320-340 °C and is five times larger for the QD-related PL band than for the QW one. It is found that the energy of the excitonic transitions in the wetting layers does not change upon annealing. Lower thermal stability of the QDs as compared to that of the wetting layer and of the QW is explained by lateral Cd/Zn interdiffusion in the wetting layers via column II vacancies (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The photoluminescence spectra of porous silicon at 77 and 300 K and their transformation during aging were investigated. The competition of two radiative recombination channels that have a common excitation mechanism was observed. It is shown that only one of them, which causes infrared emission band and is present in as-prepared samples, is connected with excitonic recombination in Si nanocrystals. The second one that causes red emission band appears during aging is supposed to be connected with carrier recombination through oxide-related defects. It is shown that this channel dominates in aged samples. [ABSTRACT FROM AUTHOR]