A. Golubović

Optical properties of PbTe:Mn

Abstract In this paper, we investigate Mn concentration and crystal growth rate influence on optical properties of PbTe:Mn single crystals. We measured far-infrared reflectivity spectra at room temperature in the 10–250 cm −1 spectral range. The analysis of the far-infrared spectra was made by a fitting procedure based on the model of coupled oscillators. In spite of the strong plasmon-LO phonon interaction, we found that the plasma frequency decreases as Mn concentration increases, while the crystal growth rate has the opposite effect. Also, we obtained the Mn impurity in-band mode at about 50 cm −1 .

Boron-content dependence of Fano resonances in p-type silicon

We present a study of Fano-type resonances in high quality boron-doped silicon as a function of boron content. The resonance (antiresonance) in the infrared absorption spectra occurs close to the ≈ 0 optical phonon at 519 cm−1. The interaction between the otherwise infrared-forbidden optical phonon and the continuum states of the acceptor was analysed based on a modified Fano model that involves the interaction of a discrete state with two continua.

Investigation of surface defect states in CeO2-y nanocrystals by Scanning−tunneling microscopy/spectroscopy and ellipsometry

Synthesis process strongly influences the nanocrystalline CeO2-y defective structure. The presence of surface defects, in the form of oxygen vacancies in different charge states (F centers), can change the electronic properties of ceria nanocrystals. Nanocrystalline CeO2-y samples were synthesized using three different methods (precipitation, self-propagating room temperature, and hydrothermal synthesis). Raman spectroscopy was used to identify the presence of oxygen vacancies which presumably were formed at the nanoparticle surface. The defect concentration depended on the crystallite size of differently prepared CeO2-y samples. Scanning tunneling microscopy/spectroscopy and ellipsometry were employed to investigate the electronic band structure of defective CeO2-y nanocrystals. Scanning tunneling spectroscopy measurements demonstrated that inside the band gap of CeO2-y nanocrystals, besides the filled 4 f states, appeared additional states which were related to occupied and empty F center defect states. From the ellipsometric measurements, using the critical points model, the energy positions of different F centers states and the values of the reduced band gap energies were determined. The analysis of obtained data pointed out that depending on the synthesis method, different types of F centers (F+ and F0) can be formed in the CeO2-y nanocrystals. The formation of different F center defect states inside the ceria gap have a strong impact on the electrical, optical, and magnetic properties of ceria nanocrystals.

Structural Properties of Pb1-xMnxTe Alloys

Pb1-xMnxTe crystals were grown by Bridgman method and by molecular beam epitaxy (MBE). Structural properties of bulk crystals were studied both by optical microscopy after chemical polishing and etching, and by X-ray powder diffraction. For chemical polishing the solution of 5 vol.% Br2 in HBr at the room temperature after exposure for 2 minutes was determined A solution of 20g KOH in 1 ml H2O2, 2ml glycerol (C3H8O3), and 20 ml H2O at the room temperature after exposure for 6 minutes was found to be a suitable etching solution. The lattice parameters of samples obtained on different way (Bridgman and MBE) were determined.

Structural, morphological, and optical study of titania-based nanopowders suitable for photocatalytic applications

Systematic investigation of the relationship between structural, morphological, optical and photocatalytic properties of the titania-based nanopowders is presented. A series of pure and doped titania catalysts with various (anatase and brookite) phase compositions have been prepared by sol–gel or hydrothermal route. The crystal structure and composition of the synthesized samples have been extensively characterised by XRD and Raman scattering measurements. The nanopowder morphology has been studied using microscopic methods (SEM, AFM, and STM), whereas the porous structure has been revealed by the analysis of nitrogen sorption data. The optical and electronic properties have been studied by spectroscopic ellipsometry. All investigated properties have been correlated to photocatalytic activity, tested in degradation of the pharmaceutically active substances (such as metoprolol and alprazolam) induced by UVA or visible radiation. Based on this correlation, the physical properties which contribute most to the increase in photocatalytic activity of synthesized nanopowders have been determined, in order to optimize the synthesis conditions which could lead to the maximal efficiency in degradation of particular pollutant.