National Institute Of Materials Physics - Romania

Potassium hydrogen phthalate (KAP) crystals doped with rhodamine 6G (Rh 6G) and polyvinylpyrrolidone (PVP) were grown by solution evaporation technique. Nucleation occurred without the use of seeds and optically transparent crystals were obtained. The grown crystals were characterized by XRD measurements performed on crystals and their powders, optical transmission and photoluminescence measurements. The influence of the dopants on the structural, morphological and optical properties of the KAP crystals was analysed. Dopants do not change the structure of the single crystals while the addition of PVP changes the morphology of crystals from pseudo-hexagonal to rhomb. Three new XRD reflections are observed in all single-crystal and powder XRD spectra and are probably (0 3 0), (0 4 0) and (0 5 0) lines. The UV cut-off and transparency of the crystals are not changed by doping. Dye-doped KAP crystals exhibit a strong emission band centred at 550 nm excited with 480 nm wavelength. For the dye-doped crystals the up-conversion was investigated and its second harmonic origins are proved using photoluminescence measurements. (C) 2010 Elsevier B.V. All rights reserved.

Large and transparent LiF:Pb and LiF:TI crystals were successfully grown by using Kyropoulos method. They were characterized using spectroscopic measurements combined with differential thermal analysis and thermogravimetry (TG) analysis, in order to investigate the effect of dopants upon the optical properties of these crystals. The optical absorption peaks at 278 nm (for Pb) and 273 nm (for TI) have been assigned to the A-type transition of these ions. Photoluminescence spectra have shown bands at 350 nm (for TI) and 375 nm (for Pb), which have been associated to the dopant ions in different configurations in the lattice. (C) 2010 Elsevier B.V. All rights reserved.

Due to their physical and chemical properties (such as suitable band gaps, large absorption coefficients and good chemical stability) CdTe thin films are interesting for electronic and optoelectronic devices, including particularly photovoltaic cells for space technology. For that specific application, it is of prime importance to study in this type of materials the influence of ionizing radiations on their physical (structural, electrical and optical) properties. In this paper, the photovoltaic cells based on CdS/CdTe thin films, produced by thermal vacuum sublimation, were irradiated with 3 MeV protons at room temperature. The effects of irradiation were studied by investigating the changes in the electrical and optical properties of the cells. It was found that proton irradiation in the above mentioned conditions results mainly in the introduction of defects at the CdS/CdTe interface. A discussion about the possible origin of those defects is given.

The synthesis of a new hybrid composite based on PUS nanoparticles and poly( methyl methacrylate-2acrylamido-2-methylpropane sulfonic acid) [P(MMA-AMPSA)] copolymer is reported. The chemical synthesis consists in two steps: (i) a surfactant-free emulsion copolymerization between methyl methacrylate and 2-acrylamido-2-methylpropane sulfonic acid and (ii) the generation of PbS particles in the presence of the P( MMA-AMPSA) latex, from the reaction between lead nitrate and thiourea. The composite was studied by scanning electron microscopy (SEM), X-ray diffraction, FTIR spectroscopy, thermogravimetric analysis and differential scanning calorimetry. The microstructure observed using SEM proves that the PbS nanoparticles are well dispersed in the copolymer matrix. The X-ray diffraction measurements demonstrate that the PbS nanoparticles have a cubic rock salt structure. It was also found that the inorganic semiconductor nanoparticles improve the thermal stability of the copolymer matrix. (C) 2010 Elsevier Ltd. All rights reserved.

A special mechanism of thermoelectric transport is described, consisting of pulses of charge carriers which "fly" periodically through the external circuit from the hot end of the sample to the cold end, with a determined duration of the "on" and "off" times of the electric contacts, while maintaining continuously the thermal contacts. It is shown that such a "resonant" ideal thermogenerator may work cyclically, with the same efficiency quotient as the ideal efficiency quotient of the thermoelectric devices operated in the usual stationary transport regime but the electric flow and power are increased, as a consequence of the concentration of the charge carriers on pulses of small spatial extent. The process is reversible, in the sense that it can be operated either as a thermoelectric generator or as an electrothermal cooler. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3456037]

We address the quantum dot phase measurement problem in an open Aharonov-Bohm interferometer, assuming multiple transport channels. In such a case, the quantum dot is characterized by more than one intrinsic phase for the electrons transmission. It is shown that the phase which would be extracted by the usual experimental method (i.e. by monitoring the shift of the Aharonov-Bohm oscillations, as in Schuster et al., Nature 385 (1997) 417) does not coincide with any of the dot intrinsic phases, but is a combination of them. The formula of the measured phase is given. The particular case of a quantum dot containing a S = 1/2 spin is discussed and variations of the measured phase with