M. Romčević

Raman spectroscopy of impurity states in gallium-doped PbTe

We present Raman spectra and results of galvanomagnetic measurements of PbTe single crystals, doped with gallium, between 10 and 300 K. The effect of persistent photoconductivity depends on the gallium concentration. In all samples well-resolved peaks were observed at about 104 cm-1 (impurity-induced PbTe LO mode) and 166 cm-1 at all temperatures. Another mode appears at about 117 cm-1 at temperature below 250 K. One additional mode, at about 188 cm-1, is observed in PbTe + 0.4 at% Ga. These modes are discussed in terms of local vibrations of impurities corresponding to different Ga charge states.

Far-infrared study of impurity local modes in gallium-doped PbTe

Abstract We present far-infrared reflection spectra and results of galvanomagnetic measurements of PbTe single crystals doped with gallium between 10 and 300 K. The analysis of the far-infrared reflection spectra was made by a fitting procedure based on the model of coupled oscillators. Together with the strong plasmon–phonon coupling we obtain three local modes of gallium at about 122, 166 and 192 cm −1 . The position of these modes depends of impurity center charge, and their intensity depends of temperature and of gallium concentration. Persistent photoconductivity effect was registered in the sample with 0.4 at.% Ga by galvanomagnetic and far-infrared measurements.

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 .

Study of NiFe2O4 and ZnFe2O4 Spinel Ferrites Prepared by Soft Mechanochemical Synthesis

Two types of ferrites, NiFe2O4 and ZnFe2O4 were prepared by soft mechanochemical synthesis. XRD and Raman spectroscopy were used to characterize the ferrite samples. On the basis of magnetic measurements was confirmed that the degree of inversion changes after sintering. The conduction activation energy, ΔE was determined by fitting the DC conductivity data with the Arrhenius relation. The effect of temperature on impedance parameters was studied using an impedance analyzer in a wide frequency range (100 Hz - 10 MHz). It was observed that the impedance spectra of NiFe2O4 and ZnFe2O4 ferrites include both grain and grain boundary effects.

Raman spectroscopy of bismuth silicon oxide single crystals grown by the Czochralski technique

In this work, single crystals of bismuth silicon oxide (BSO; Bi12SiO20) have been grown by the Czochralski method. The growth conditions were studied. The critical diameter and the critical rate of rotation were calculated. Suitable polishing and etching solutions were determined. The structure of the Bi12SiO20 has been investigated by x-ray diffraction (XRD), and Raman and Fourier transform infrared spectroscopy (FTIR) spectroscopy. The results obtained are discussed and compared with the published data. The pale yellow Bi12SiO20 single crystals prepared were without cores. Using spectroscopic measurements 19 Raman and 5 IR modes were observed.

Spectroscopic characterization of YAG and Nd:YAG single crystals

In this paper, we used the Czochralski method to obtain good quality yttrium aluminium garnet (YAG, Y3Al5O12) and yttrium aluminium garnet doped with neodymium (Nd:YAG) crystals. The investigations were based on the growth mechanisms and the shape of the liquid/solid interface crystallization front on the crystal properties and incorporation of Nd3+ ions. The obtained single YAG and Nd:YAG crystals were studied by use of x-ray diffraction, Raman and IR spectroscopy. There are strong metal oxygen vibrations in the region of 650–800 cm−1 which are characteristics of Al-O bond: peaks at 784/854, 719/763 and 691/707 cm−1 correspond to asymmetric stretching vibrations in tetrahedral arrangement. Peaks at 566/582, 510/547 and 477/505 cm−1 are asymmetric stretching vibrations and 453/483 cm−1 is the symmetric vibration of the Al-O bond in octahedral arrangements of the garnet structure. Lower energy peaks correspond to translation and vibration of cations in different coordinations—tetrahedral, octahedral and dodecahedral in the case of the lowest modes.

Far-infrared spectra of Pb1−xMnxTe alloys

Abstract Far-infrared reflectivity spectra of Pb1−xMnxTe (0.0001⩽x⩽0.1) single crystals were measured in the 10–250 cm−1 range at room temperature. 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 long wavelength optical phonon modes of these mixed crystals showed an intermediate one–two mode behavior.

Raman Spectra of Bismuth Titanate Ceramics

Bismuth titanate is a typical layer-structured ferroelectric material and belongs to the Aurivilius type-structure compounds family. A bismuth titanate ceramic material could be obtained by mechanically activated synthesis after thermal treatment at a temperature slightly lower than in conventional solid-state reaction. In this case bismuth titanate was prepared through mechanochemical synthesis starting from bismuth oxide and titanium oxide in rutile form. The mixture of oxides was milled in a zirconium oxide jar in a planetary ball-mill in intervals from 1 to 12 hours. The ratio of powders to zirconium oxide balls during milling was 1:20. Bismuth titanate was formed after 1 h. The Raman spectroscopy analysis was performed.

Cd1-xMnxS Nanoparticles: Far-Infrared Phonon Spectroscopy

Phonon spectra of Cd1-xMnxS (x = 0; 0.01; 0.05; 0.1; 0.15; 0.3) nanoparticles (d ~ 4.5 nm) have been investigated by far-infrared reflection (FIR) (spectral range 40 - 600 cm-1, temperature range 80 – 300 K) and Raman spectroscopy (100 – 700 cm-1, 300 K). Cd1-xMnxS nanoparticles have been synthesized by using aqueous solution precipitation. We obtained interesting features in FIR spectra: there are expected modes of bulk CdS (240 cm-1, 300 cm-1), new modes connected with nano-size of CdS (130 cm-1, 170 cm-1) and additional mode at 120 cm-1 in Cd1-xMnxS nanoparticles which can be assigned to the presence of Mn. The position of obtained modes is discussed in the frame of the linear chain model with both mass and force constant defects. Raman spectroscopy gives us only the mode at 300 cm-1 and its second harmonic.

Influence of Preparation Method on SOP Modes in ZnO Doped with CoO Nanoparticles

The aim of the present work is to study influence of preparation method on samples characteristics, creation and behavior of surface optical phonons (SOP) modes with change of concentration of doping elements by micro Raman spectroscopy. Nanocrystalline samples of ZnO(Co) were prepared by use of traditional wet chemistry method followed by calcinations and the microwave assisted hydrothermal synthesis. The phase composition of the samples (ZnO, Co3O4, ZnCo2O4) and the mean crystalline size (14–300 nm) were determined using X-ray diffraction measurements. In this paper we report the experimental spectra of Raman scattering (from 100 to 1600 cm−1) for both type of samples. Main characteristic of experimental Raman spectrum are: sharp peak at 436 cm−1 and broad multi phonon structure at ~1150 cm−1, typical for ZnO; sharp peaks at 194, 482, 521, 618 and 691 cm−1 typical for Co3O4 and sharp peaks at 185, 475, 520, 610 and 690 cm−1 typical for ZnCo2O4 nanoparticles. The phonon of registered phase’s exhibit effects connected to phase concentration, while the SOP phonon mode exhibit significant confinement effect.