Kарактеризација наночестица кобалт ферита добијених различитим методама синтезе и поређење са Рамановим спектрима других ферита и неких кубичних оксидних спинела

ingle phase cobalt ferrite (CoFe2O4) with nanoparticles of similar sizes (15.7-19 nm) was obtained by different synthesis methods: coprecipitation, ultrasonically assisted coprecipitation, coprecipitation followed by mechanochemical treatment, microemulsion and microwave assisted hydrothermal synthesis. The obtained CoFe2O4 samples have been studied using a variety of characterization techniques: X-ray diffraction (XRD), Raman spectroscopy, far infrared (FIR) reflectivity and attenuated total reflectance (ATR) in combination with Fourier-transform infrared (FTIR) spectroscopy in mid IR spectra. Different methods of synthesis produced nanoparticles with different lattice constants, internal stresses and different cation inversion values. This is confirmed in the subtle changes in the Raman and IR spectra of different CoFe2O4 nano-powders. The Raman spectra of CoFe2O4 were compared with the spectra of other ferrites and some cubic oxide spinels in an attempt to evaluate the contribution of tetrahedral and octahedral oscillations in certain Raman modes.Монофазни кобалт ферит са наночестицама сличних величина (15,7-19 нанометара) добијен је различитим методама синтезе: копреципитацијом, ултразвучно потпомогнутом копреципитацијом, копреципитацијом праћеном механохемијском синтезом, микроемулзијом и микроталасном хидротермалном синтезом. Добијени узорци кобалт ферита су проучавани коришћењем различитих техника карактеризације: дифракцијом рендгенских зрака на праху, Раман спектроскопијом, рефлексијом у далекој инфра-црвеној области (ИЦ) и методом апсорпције при вишеструкој тоталној рефлексији у комбинацији са инфра-црвеном спектроскопијом (АТР-ИЦ) у средњој инфра црвеној области. Различитим методама синтезе добијене су наночестице са различитим константама решетке, унутрашњим напрезањима и различитим вредностима инверзије катјона. Ово је потврђено у суптилним променама у Раман и ИЦ спектрима различитих нано-прахова кобалт ферита. Раман спектри кобалт ферита упоређени су са спектрима других ферита и неких кубних оксидних спинела у покушају да се процени утицај удела тетраедарских и октаедарских осцилација у одређеним Раман модовима

Photoluminescence Spectroscopy of CdTe/ZnTe Self-Assembled Quantum Dots

We present photoluminescence (PL) measurements of two different, 3 monolayers and 12 monolayers (ml), CdTe self-assembled quantum dot (SAQD) samples. The spectra were recorded in the temperature range 20 K–300 K, with photoexcitation over the ZnTe barrier layer. PL spectra displayed two main emission bands. High-energy PL emission (E1) is ZnTe LO like phonon- (ωLO = 204.2 cm−1 (3 ml), ωLO = 207.3 cm−1 (12 ml)) assisted deexcitation. Dominant low-energy band (E2) presents the direct deexcitation to ground state of the CdTe quantum dots

Vibrational and magnetic properties of nano-sized CoFe2O4 obtained by various synthesis techniques: a comparative study

Nanocrystalline CoFe2O4 has been synthesized by various synthesis methods. The obtained monodomain nanoparticles are similar in sizes (15.8-19 nm), but with different internal stresses, size distributions and cation inversion coefficients (0.51 - 0.90) due to different synthesis routes. The structure and cation distribution are investigated by XRD diffraction analysis, Raman and FIR spectroscopy. Measurement of magnetization, i.e. coercivity, enable the calculation of the anisotropy coefficient K1 = (3.6-5.12)·105 J cm-3, which is very high in cobalt ferrite. The anisotropy coefficient directly depends on the nanoparticle size. It has been shown that magnetization linearly depends on the cation inversion, except in the sample with the largest nanoparticles (19 nm), where the more regular crystal structure prevails and higher values of magnetization were obtained. The average magnetic moments at 300 K are: μFe = 3.6μB and μCo = 2.5μB. It is obvious that with small adjustments in the synthesis, desirable nanoparticle properties can be obtained

Optical properties of CuSe thin films - band gap determination

Copper selenide thin films of three different thicknesses have been prepared by vacuum evaporation method on a glass substrate at room temperature. The optical properties of the films were investigated by UV-VIS-NIR spectroscopy and photoluminescence spectroscopy. Surface morphology was investigated by field-emission scanning electron microscopy. Copper selenide exhibits both direct and indirect transitions. The band gap for direct transition is found to be ~2.7 eV and that for indirect transition it is ~1.70 eV. Photoluminescence spectra of copper selenide thin films have also been analyzed, which show emission peaks at 530, 550, and 760 nm. The latter corresponds to indirect transition in investigated material. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. III45003

Far-infrared spectra of mesoporous ZnS nanoparticles

ZnS nanoparticles were synthesized mechanochemically by high-energy milling, with three different milling times (5 min, 10 min and 20 min). Nitrogen adsorption method was used for examining specific surface area and texture of obtained powders. It was found that all samples are completely mesoporous. The optical properties were studied by far-infrared spectroscopy at room temperature in spectral region of 50-600 cm(-1). The analysis of the far-infrared reflectivity spectra was made by the fitting procedure. The dielectric function of ZnS nanoparticles is modeled as a mixture of homogenous spherical inclusions in air by the Maxwell-Garnet formula. In the analysis of the far-infrared reflection spectra, appearance of combined plasmon-LO phonon modes (CPPMs) with high phonon damping are observed, which causes decrease of coupled plasmon-phonon frequencies. (C) 2016 Elsevier B.V. All rights reserved

Kарактеризација наночестица кобалт ферита добијених различитим методама синтезе и поређење са Рамановим спектрима других ферита и неких кубичних оксидних спинела

Single phase cobalt ferrite (CoFe2O4) with nanoparticles of similar sizes (15.7-19 nm) was obtained by different synthesis methods: coprecipitation, ultrasonically assisted coprecipitation, coprecipitation followed by mechanochemical treatment, microemulsion and microwave assisted hydrothermal synthesis. The obtained CoFe2O4 samples have been studied using a variety of characterization techniques: X-ray diffraction (XRD), Raman spectroscopy, far infrared (FIR) reflectivity and attenuated total reflectance (ATR) in combination with Fourier-transform infrared (FTIR) spectroscopy in mid IR spectra. Different methods of synthesis produced nanoparticles with different lattice constants, internal stresses and different cation inversion values. This is confirmed in the subtle changes in the Raman and IR spectra of different CoFe2O4 nano-powders. The Raman spectra of CoFe2O4 were compared with the spectra of other ferrites and some cubic oxide spinels in an attempt to evaluate the contribution of tetrahedral and octahedral oscillations in certain Raman modes.Монофазни кобалт ферит са наночестицама сличних величина (15,7-19 нанометара) добијен је различитим методама синтезе: копреципитацијом, ултразвучно потпомогнутом копреципитацијом, копреципитацијом праћеном механохемијском синтезом, микроемулзијом и микроталасном хидротермалном синтезом. Добијени узорци кобалт ферита су проучавани коришћењем различитих техника карактеризације: дифракцијом рендгенских зрака на праху, Раман спектроскопијом, рефлексијом у далекој инфра-црвеној области (ИЦ) и методом апсорпције при вишеструкој тоталној рефлексији у комбинацији са инфра-црвеном спектроскопијом (АТР-ИЦ) у средњој инфра црвеној области. Различитим методама синтезе добијене су наночестице са различитим константама решетке, унутрашњим напрезањима и различитим вредностима инверзије катјона. Ово је потврђено у суптилним променама у Раман и ИЦ спектрима различитих нано-прахова кобалт ферита. Раман спектри кобалт ферита упоређени су са спектрима других ферита и неких кубних оксидних спинела у покушају да се процени утицај удела тетраедарских и октаедарских осцилација у одређеним Раман модовима

Spectroscopy study of Bi12GeO20 single crystals

In this work single crystals of bismuth germanium oxide (Bi12GeO20) have been grown by the Czochralski method. 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 Bi12GeO20 has been investigated by X-ray diffraction, Raman and FTIR spectroscopy. The obtained results are discussed and compared with published data. On the basis of the measurements by Raman spectroscopy, we observed 15 modes

Growth, characterization and optical quality of calcium fluoride single crystals grown by the Bridgman method

Calcium fluoride - CaF2 single crystals were grown using the Bridgman technique. By optimizing growth conditions, lt 111 gt -oriented CaF2, crystals up to 20 mm in diameter were grown. Number of dislocations in CaF2 crystals which were made by the method of Bridgman was 5x10(4) - 2x10(5) per cm(2). In this paper we used XRD, Raman spectroscopy and the measurement of transmission in the mid IR-range to investigated structural and optical properties of obtained CaF2 single crystals

Surface optical phonon – Plasmon interaction in nanodimensional CdTe thin films

Structural and optical properties of CdTe thin films were investigated applying atomic force microscopy (AFM), XRD powder technique, Raman spectroscopy and far–infrared spectroscopy. CdTe thin films were prepared by using thermal evaporation technique. In the analysis of the far – infrared reflection spectra, numerical model for calculating the reflectivity coefficient for system which includes films and substrate has been applied. Effective permittivity of film mixture (CdTe and air) was modeled by Maxwell – Garnet approximation. We reveal the existence of surface optical phonon (SOP) mode and coupled plasmon-SOP modes (CPSOPM). © 2018 Elsevier B.V

Raman spectroscopy of ZnS quantum dots

ZnS nanoparticles were synthesized mechanochemically by high-energy milling. In order to investigate influence off milling time to sample properties, samples were produced in three different milling times (5 min, 10 min and 20 min). The morphology of samples has been investigated by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). X-ray diffraction (XRD) investigation of synthesized nanocrystals identified cubic structure. From XRD, ZnS size of crystallites was estimated as 1.9 nm (after 5 min milling time), 2.3 nm (10 min) and 2.4 nm (20 min), implying that we are in strong confinement regime. The optical properties were studied by Raman spectroscopy, in spectral region 100-500 cm(-1), excitation source was 514.5 nm (E-L = 2.41 eV), which means that we are in off resonant regime. Dominant spectral structures, of comparable intensity, are registered in spectral region 130-180 cm(-1), around 265 cm(-1) and around 345 cm(-1). First two are assigned as second-order ZnS modes. A theoretical model of continuum medium was used to calculate frequencies of the confined optical phonons in ZnS. Satisfactory agreement with experimental results was found and mode at 345 cm(-)1 is assigned as LO type phonon confined in ZnS nanocrystal. (C) 2015 Elsevier B.V. All rights reserved