Influence of Nano Filler (ZrO2) on Optical and Thermal Studies of Potassium Doped Polyethylene Oxide Solid Polymer Electrolytes

Solid polymer electrolyte films made with potassium doped Polyethylene oxide using ZrO2 as nanofiller (70PEO-30KBF4-x ZrO2 where x = 1, 2.5, 5, 7.5, & 10 wt% ­­) were prepared by solution casting technique. Optical and thermal properties of polymer electrolyte films were studied by using Optical absorption and DSC techniques. From Optical absorption spectra, it is observed that fundamental absorption edge is shifted towards the higher wavelength side (range 259- 297 nm) with increase of nano filler (ZrO­2) concentration (1-10 wt %). Optical band gap for all electronic transitions (p=1/2, 2, 2/3 and 1/3) are found to be increased as incorporation of nano filler (ZrO2) which confirms the structural rearrangements takes place in polymer electrolyte films. Optical band gap for indirect allowed transitions (p=1/2) are found to be in the range of 1.93-3.34eV. Decrease in Urbach energy (4.8eV- 1.4eV) is associated with decrease in defect formation in host polymeric matrix (PEO-KBF4) as a result of embedded nano filler (ZrO2). DSC spectra analysis of polymer electrolytes has showed melting temperatures in the range 63.63-73.71°C and highest crystallinity is found to be 85 % (10 wt % ZrO­2). Enthalpy values are elevated with increase in nanofiller composition (ZrO2) in the present polymer electrolyte films.Keywords: PEO based polymer electrolytes, Solid polymer electrolytes, Optical and Thermal studies.

Спектры пропускания монокристаллов гибридных перовскитов MAPbI-=SUB=-3-=/SUB=- вблизи края фундаментального поглощения

The paper presents the transmission spectra of hybrid perovskite MAPbI3 single crystals near the fundamental absorption edge in a wide temperature range. The absorption coefficient α of the single crystal samples is estimated at a temperature T = 150 K for the light with a photon energy E = 1.6 eV and at T = 40 K for E = 1.8 eV. The obtained values turned out to be several orders of magnitude smaller than the values of α for thin-film samples known from the literature. A sharp shift of the fundamental absorption edge by ~ 100 meV was observed at a temperature T1 = 160 K of the structural phase transition from the tetragonal to the orthorhombic phase. The temperature hysteresis of the shift of the fundamental absorption edge near T1 was recorded, which is characteristic of a first-order phase transition.

Optical Properties of Rare Earth Nitrides

<p>This experimental thesis uncovers the fundamental optical features of rare earth nitride compounds and relates them to their electronic structure. Experimental observations for the optical energy gaps for thin films of GdN, DyN, SmN and EuN are made for the first time. Thin films are grown by thermal evaporation in ultra high vacuum environment and are passivated by MgF₂ layers. Initial characterizations indicate the polycrystalline thin films of RENs are strongly textured along [111] direction. Optical characterization techniques, Fourier transform infrared and conventional UV/Vis spectrometers are used in conjunction with SQUID magnetometer and DC electrical resistivity. Transmission and reflection spectra for rare earth nitride thin films were obtained in the photon energy range 0.5 – 5.5 eV in their paramagnetic and ferromagnetic phases. Paramagnetic GdN has a direct energy gap of 1.30±0.05 eV which coincides well with theoretically predicted energy gap. A red-shift in the fundamental absorption edge of ferromagnetic GdN is observed along with onset of absorption at higher energy attributable to the exchange splitting of conduction and valence bands of GdN. The spin split joint density of states is in remarkable agreement with theoretically calculated spin polarized band structure of GdN. Similarly for DyN a consensus is found between theory and experiment on the energy gap of 1.20±0.05 eV at room temperature. However, in the case of SmN, an energy gap of 1.30±0.1 eV is underestimated by theory to 0.81 eV. For EuN, the experimentally determined value of energy gap is 0.97±0.05 eV. This value is used to tune the band structure calculation by QSGW theory which returns a ferromagnetic semiconducting solution for EuN.</p>

Optical Properties of Rare Earth Nitrides

<p>This experimental thesis uncovers the fundamental optical features of rare earth nitride compounds and relates them to their electronic structure. Experimental observations for the optical energy gaps for thin films of GdN, DyN, SmN and EuN are made for the first time. Thin films are grown by thermal evaporation in ultra high vacuum environment and are passivated by MgF₂ layers. Initial characterizations indicate the polycrystalline thin films of RENs are strongly textured along [111] direction. Optical characterization techniques, Fourier transform infrared and conventional UV/Vis spectrometers are used in conjunction with SQUID magnetometer and DC electrical resistivity. Transmission and reflection spectra for rare earth nitride thin films were obtained in the photon energy range 0.5 – 5.5 eV in their paramagnetic and ferromagnetic phases. Paramagnetic GdN has a direct energy gap of 1.30±0.05 eV which coincides well with theoretically predicted energy gap. A red-shift in the fundamental absorption edge of ferromagnetic GdN is observed along with onset of absorption at higher energy attributable to the exchange splitting of conduction and valence bands of GdN. The spin split joint density of states is in remarkable agreement with theoretically calculated spin polarized band structure of GdN. Similarly for DyN a consensus is found between theory and experiment on the energy gap of 1.20±0.05 eV at room temperature. However, in the case of SmN, an energy gap of 1.30±0.1 eV is underestimated by theory to 0.81 eV. For EuN, the experimentally determined value of energy gap is 0.97±0.05 eV. This value is used to tune the band structure calculation by QSGW theory which returns a ferromagnetic semiconducting solution for EuN.</p>

Optically Active TiO2:Er Thin Films Deposited by Magnetron Sputtering

Titanium dioxide photoanodes for hydrogen generation suffer from a profound mismatch between the optical absorption of TiO2 and the solar spectrum. To solve the problem of low solar-to-chemical efficiency, optically active materials are proposed. In this work, TiO2 thin films containing erbium were deposited by radio frequency RF magnetron sputtering under ultrahigh vacuum conditions UHV. Morphology, structural, optical and electronic properties were studied. TiO2:Er thin films are homogenous, with uniform distribution of Er ions and high transparency over the visible VIS range of the light spectrum. However, a profound 0.4 eV blue shift of the fundamental absorption edge with respect to undoped TiO2 was observed, which can be attributed either to the size effect due to amorphization of TiO2 host or to the onset of precipitation of Er2Ti2O7 nanocrystals. Near-infrared NIR to VIS up-conversion is demonstrated upon excitation at 980 nm, while strong green photoluminescence at 525 and 550 nm occurs upon photon absorption at 488 nm.

Закономерности температурных изменений спектров отражения инфракрасного излучения кристалла Bi-=SUB=-0.8-=/SUB=-Sb-=SUB=-1.2-=/SUB=-Te-=SUB=-3-=/SUB=- в области возбуждения плазменнных колебаний свободных носителей заряда и межзонных переходов

The regularities of the temperature behavior of the reflection spectra of the Bi0.8Sb1.2Te3 crystal obtained in the range of the plasma resonance of free charge carriers and the fundamental absorption edge allow us to trace the changes in the plasmon energy Ep and the optical band gap Eg opt. The observed decrease in Eg opt with increasing temperature corresponds to the existing ideas about the redistribution of holes between the nonequivalent extremes of the valence band in (Bi2-xSbx)Te3 (0<x<1) crystals. The dominance of this process in a certain temperature range contributes to the change in plasma frequencies. Keywords: reflection spectra, plasma oscillations, electron-plasmon interaction, dielectric functions.

Effect of thickness on optoelectronic properties of ITO thin films

Purpose Indium tin oxide (ITO) is a material belonging to the group of transparent conductive oxides, which are widely used in many fields of technology including optoelectronics and photovoltaics. However, the properties of ITO thin films depend on many factors. Therefore, the aim of the study was thorough investigation of the properties of sputtered ITO thin films of various thicknesses. Design/methodology/approach ITO coatings were deposited by magnetron sputtering in pure argon atmosphere using ceramic ITO target. Various deposition times resulted in obtaining thin films with different thickness, which had significant influence on the optoelectronic properties of deposited coatings. In this work the results of investigation of structural, surface, optical and electrical properties were presented. Findings Increase of the coating thickness caused change of the microstructure from amorphous to nanocrystalline and occurrence of grains with a size of 40 to 60 nm on their surface. Moreover, the fundamental absorption edge was red-shifted, whereas the average transmission in the visible wavelength range remained similar. Increase of the thickness caused considerable decrease of the sheet resistance and resistivity. It was found that even thin films with a thickness of 10 nm had antistatic properties. Originality/value The novelty and originality of presented work consists in, among other, determination of antistatic properties of ITO thin films with various sheet resistances that are in the range typical for dielectric and semiconducting material. To date, there are no reports on such investigations in the literature. Reported findings might be very helpful in the case of, for example, construction of transparent antireflective and antistatic multilayers.

Photoluminescence and features of the defective structure of nominally pure lithium niobate single crystals.

The photoluminescence intensity in lithium niobate crystals close to the stoichiometric composition being lower than in a congruent crystal was established. The increase of Li / Nb ratio leads to shifting the photoluminescence bands to the short-wavelength region of the spectrum and changing the fundamental absorption edge of the crystals under study. It was shown that, in addition to point defects in the cationic sublattice, complex defects due to the presence of OH groups and compensation defects (VLi / VNb) in the structure can also contribute to photoluminescence.