Papers by Keyword: Optical Absorption

Abstract: The FeS₂ films were deposited by using the spray pyrolysis method using mixed aqueous solutions of CH₄N₂S and FeCl₃, with different S:Fe molar ratios. The homogeneous FeS₂ nanocrystalline films with good crystallinity were synthesized. The structure, composition, and properties of these films were very sensitive to the S:Fe molar ratios. The direct transition of the pyrite FeS₂ films were about 0.9 - 1.25 eV. High absorption coefficients and suitable band gaps were observed. FeS₂ thin films were synthesized for new biomaterial applications such as glucose.

Abstract: In order to investigate the effects of strain on optical properties of BiFeO₃, electronic structure, dielectric properties and optical properties of BiFeO₃ under different strain conditions were performed by first-principles calculations. Results show that the optical spectra of BiFeO3 is mainly determined by the contributions from transition from valence band O 2p to conduction band Fe 3d levels or even higher conduction band Bi 6s states in the low-energy region. Compared with equilibrium state, state density peaks shift to left side and state density peaks become broader and lower, and band gap becomes smaller under strain states. Furthermore, strain increases optical absorption coefficient peaks, energy loss coefficient peaks and reflectivity coefficient peaks, and extinction coefficient peaks, exhibiting that optical properites of BiFeO₃ is improved under strain states. Our research provides theoretical guidance for future optical applications of BiFeO₃, especially photovoltaic application.

Abstract: Dy³⁺-doped phosphate glasses of the compositions 20Gd₂O₃ : 10CaO : (70-x)P₂O₅ : xDy₂O₃, where x = 0.05, 0.10, 0.50, 1.00 and 1.50 mol% have been prepared by melt quenching technique and characterized by optical absorption, emission spectra and decay curve analysis. All the transitions in the absorption spectra are originated from the ⁶H_15/2 ground level to the various excited states and these are intra configuration (f-f) transitions. The observed twelve absorption bands centered at 349, 362, 387, 425, 451, 473, 750, 800, 895, 1089, 1266 and 1676 nm are assigned to ⁶P_7/2, ⁴P_3/2, ⁴F_7/2, ⁴G_11/2, ⁴I_15/2, ⁴F_9/2, ⁶F_3/2, ⁶F_5/2, ⁶F_7/2, ⁶F_9/2, ⁶H_9/2 and ⁶H_11/2 transitions, respectively. The absorption spectra of glasses increase with increase in Dy³⁺ ion concentrations. The emission spectra of Dy³⁺-doped glasses are observed to be centered at 483, 573, 662 and 752 nm originated from the ⁴F_9/2→⁶H_15/2, ⁴F_9/2→⁶H_13/2, ⁴F_9/2→⁶H_11/2 and ⁴F_9/2→⁶H_9/2 transitions, respectively under excitation at 349 nm. The highest emission intensity of Dy³⁺-doped glass is 0.50 mol% due to concentration quenching effect. The experimental lifetimes are found to decrease when Dy³⁺ ion concentrations increased due to energy transfer process between Dy³⁺ ions.

Abstract: Silver nanoparticles with different radii were synthesized using silver nitrate solution added with sodium borohydride solution at different ratios. The synthesized silver nanoparticles of radii 25.3 nm, 31 nm, 33.6 nm and 37.1 nm were characterized by transmission electron microscopy (TEM) and UV-vis absorption spectroscopy. The synthesized silver nanoparticles exhibit spherical morphology for all radii. The silver nanoparticles exhibit the plasmon resonance band between 390 nm – 400 nm. The optical trapping effect of Gaussian beam acting on a silver nanoparticle in Rayleigh regime was studied. The optical scattering and optical gradient forces were calculated for silver nanoparticles of different radii.

Abstract: Ternary blend film of conjugated polymer, fullerene and inorganic nanoparticles has intensively studied as active material for high power conversion efficiency (PCE) of hybrid organic-inorganic solar cells. The incorporation of two electron acceptor materials of organic fullerene and inorganic nanoparticles into hybrid with electron donor conjugated polymer is strongly believed can improve the PCE of solar cells by increasing exciton dissociation efficiency due to an increase of interface area between donor and acceptor materials where the positive and negative charges dissociated. We studied optical, structural and morphological properties of ternary thin film containing blend of conjugated polymer poly(3-hexylthiophene (P3HT):fullerene derivative PCBM:Zinc oxide nanoparticles (ZnO-NP) by measuring its optical absorption, crystal structure and film surface morphology. Zinc oxide nanoparticle was prepared by sol-gel method. It has optical absorption below 370 nm and average particle size 40 nm as shown by TEM picture. Ternary thin blend films of P3HT:PCBM:ZnO-NP were prepared by use of spin-coating method. The UV-Vis spectrum of thin film contains absorption peaks originated from contribution of P3HT at wavelengths 520 nm, 550 nm and 600 nm, from contribution of PCBM at 260 nm and 330 nm and from ZnO-NP at wavelengths below 370 nm which confirms that these three materials were well mixed in the films. Its XRD pattern also contains the peaks from each of these three-materials. In this report, we compare surface morphology of thin films of pure P3HT, pure ZnO-NP, blend of P3HT:PCBM, blend of P3HT:ZnO-NP and ternary blend of P3HT:PCBM:ZnO-NP.

Abstract: Erbium doped zinc borotellurite glasses were prepared by using melt-quenching method. The structural properties of the glass samples were determined by using x-ray diffraction (XRD) method and was confirmed its amorphous nature. The density and molar volume is shown to be increased with increasing content of erbium. The refractive index is found to be increased with increasing content of erbium.

Abstract: Density functional calculations were performed for the –H, –OH and –F functional groups adsorbed onto the surface of pseudo-spherical 4H-SiC quantum dots with diameters ranging from 10 to 22 Å. We find that for the investigated diameter range, the H-terminated SiC-quantum dots exhibit strong size dependent quantum confinement effects, while for –F and –OH terminations, the optical gap remains largely unchanged. The –H termination shows an optical absorption onset well above that of –F and –OH for a similar cluster size, which is attributed to the localisation of HOMO and LUMO states to the quantum dot core. Based on our calculations, we suggest that the –H functionalisation is a more promising route for engineering the optical properties of SiC-quantum dots, since this could lead to a wider control over the optical absorption onsets, when compared to –OH and –F terminations.

Abstract: The temperature dependence of the dark electrical conductivity of the LiNbO₃ (LN) crystals annealed in saturated H₂O and D₂O vapor in the range 293...400 K is investigated. It is found that the activation energy of the electrical conductivity is equal to (0.71 ± 0.02) eV and is close this value of LN samples, reduced in hydrogen. Annealing in ampoules with H₂O vapor also lead to LN optical spectra changes such annealing in H₂. The nature of this phenomenon is discussed.

Abstract: The lithium lanthanum borate glasses doped with Dy₂O₃ were prepared by the melt quenching technique. The Dy₂O₃ doped concentration has been increased and substituted B₂O₃ from 0.00 to 1.50 mol% in the glasses. The photoluminescence, optical absorption and physical properties of these glasses have been investigated in this work. The experimental results show that, the molar volume of glasses tended to increase with increasing of Dy₂O₃ concentration, but the density were not depending on the concentration of Dy₂O₃. The UV-Vis-NIR spectra, absorption bands at 451, 798, 894, 1085 1264 and 1676 nm have been observed. For Dy³⁺ doped glasses, emission bands centered at 483, 575 and 664 nm have been observed with 388 nm excitation wavelength. The emission spectra have shown the strongest band in the glasses with 0.50 mol% Dy₂O₃ concentration.

Abstract: N-doped Cu₂O (Cu₂O:N) thin films were deposited on glass substrate by reactive pulse magnetron sputtering method using Cu target. Crystalline phases of thin films were controlled by adjusting N₂ / O₂ flow rate ratio and sputtering power precisely during the sputtering process, and the single phase of Cu₂O(111) thin films were obtained at room temperature. The thin films deposited at different sputtering powers were characteristics of 2D growth and the root mean square (RMS) of surface roughness of thin films gradually increased with the increasing of sputtering power. The optical band gap (E_g) of thin films were in the range 2.18-2.35 eV, and slightly decreased with increasing of sputtering power from 45 W to 90 W.