Papers by Keyword: Transition Metal Ions

Abstract: In this work, the optical and structural properties of the modified crystalline structures of the nanostructured cadmium sulphide (CdS) semiconductor caused by doping with (Cu²⁺, Ag⁺, Au⁺) transition metal ions are studied. Using the chemical bath deposition technique, thin CdS films of good crystalline quality were deposited, which were doped in synthesis without the need for additional steps, obtaining thicknesses of around 100 nm. The chemical binding energies and their interactions of the CdS semiconductor compound with the different transition metal ions were determined by X-ray photoelectron spectroscopy. The crystalline and quality phase of the CBD-CdS thin films were determined by X-ray diffraction that were confirmed by Raman scattering, obtaining that the dominant crystalline phase is zinc blende in the (1 1 1) crystalline direction. A change in crystalline quality from monocrystalline to polycrystalline was observed by XRD in the CdS thin films doped with transition metal ions, keeping the crystalline direction (1 1 1) of the zinc blende phase of CdS as the dominant one; this crystalline behaviour was confirmed by HRTEM micrographs, in addition to the different levels of quantum confinement favoured by each transition metal incorporated into the CdS. By Raman scattering measurements, the crystalline zinc blende phase of CdS was confirmed and also allowed the analysis of the phononic interactions of the binary compound, where Raman shifts provided information on the structural quality and also confirm the effects of quantum confinement. UV-visible optical spectroscopy describes the effects of the crystalline structural modifications with blue shifts on the optical band gap energies of the evaluated CdS samples, related with the different levels of quantum confinement given by the (Cu²⁺, Ag⁺, Au⁺) transition metal dopants.

Abstract: Pure TiO₂ , Ti _0.75 Fe_0.25 O₂, Ti_0.75 Ni_0.25 O₂, Ti_0.75 Co_0.25 O₂ nanocrystals were prepared by low temperature sol-gel method. The samples were characterized by using transmission electron microscope, X-ray diffractometer and ultraviolet-visible spectrophotometer to study the effect of transition metal ions on the photocatalytic properties of TiO₂ nanocrystals. The results show that the pure TiO₂ and Ti_0.75 Fe_0.25 O₂, Ti_0.75 Ni_0.25 O₂, Ti_0.75 Co_0.25 O₂ nanocrystals were granular and the size of which is 3.5, 2.9, 3.6, 3.9 nm, respectively. The titania anatase phases appear in the pure TiO₂ , the Ti_0.75 Fe_0.25 O₂, Ti_0.75 Ni_0.25 O₂, Ti_0.75 Co_0.25 O₂. The absorption edge of Ti_0.75 Fe_0.25 O₂occur red shift comparing with that of pure TiO₂ and the absorption edge of Ti_0.75 Fe_0.25 O₂and Ti_0.75 Fe_0.25 O₂occur blue shift comparing with that of pure TiO2. The photocatalytic properties of pure TiO₂, Ti_0.75 Fe_0.25 O₂, Ti_0.75 Fe_0.25 O₂, Ti_0.75 Fe_0.25 O₂nanocrystals synthesized at low temperature by sol-gel method were investigated by degrading the methyl orange solution under ultraviolet irradiation. The degradation rate of Ti_0.75 Fe_0.25 O₂is the highest (60%) and that of Ti0.75Co0.25O2 (10%) is the lowest among these catalysts after degradation for 120min.The result shows that the photocatalytic property ofTi_0.75 Fe_0.25 O₂nanocrystals synthesized at low temperature is obviously better than that of pure TiO₂ and Ti_0.75 Fe_0.25 O₂, Ti_0.75 Fe_0.25 O₂.

Abstract: A system of borate based glass with different modifier but similar dopant was investigated to determine both the structural and photoluminescence properties. The glass sample from the series of x(M):(1-x)B2O3 where 0.2 ≤ x ≤0.7 mole% and M was Li2O and SrO, and the metaborate composition of glass was doped withMn¬¬2+, Fe2+ and Zn2+ ions. The effect of the modifier towards the structural and photoluminescenceproperties in the glass samples was investigated using Fourier-Transfer Infrared (FT-IR) spectroscopy and photoluminescence spectroscopy. Infrared spectrum revealed the traces of BO3 and BO4 units at different modifier and concentration. Significant changes in the host structure showed modification at specific region depending on the type of modifier.The photoluminescence of the samples were studied using the luminescence spectrophotometer. The samples were excited at different emission wavelength to compare the results. This study showed that with the introduce Mn2+, Fe2+ and Zn2+ ions as activators within the host material enhancedphotoluminescence characteristic.

Abstract: A series of Antimony Borate glass samples were investigated to determine the structural feature. The glass samples from the series of xSb2O3:(1-x)B2O3 with composition of 20≤x≤60 mol% and 0.6 Sb2O3:0.4B2O3:y with y is 0.01 mol% of Nb2O5, CuO, ZnO system have been prepared using melt-quenching technique. The structural properties of Sb2O3 host and the introduction of dopents onto the host sample has been investigated using Infrared and RAMAN Spectroscopy. The result of IR and Raman Spectroscopy revealed that the network structure of the studied glasses is mainly based on BO3 and BO4 units placed in different structural groups, the BO3 units being dominant. IR spectra obtained shows conversion of BO3 to BO4 units upon the introduction of Sb2O3 commonly known as boron anomaly effect. The glass network can be modified with the presence of Sb2O3 and activator ions. The significant behavior in Raman Spectra indicates the presence of boroxol groups consisting of pure BO3 groups and mixed BO3-BO4 structural units. This study shows that the vibrational spectroscopy (Infrared and Raman) provide useful method, and inter-complementary information about the structural properties of antimony modified borate glasses.

Abstract: We report a model for the explanation of the single molecule magnet behavior of the [CuIILTbIII(hfac)2]2 cluster. The model takes into account the crystal field acting on the TbIII –ion and the exchange interaction between the TbIII and CuII ions. The energies of the low-lying levels are shown to increase with the decrease of the mean value of the z-projection of the total angular momentum of the cluster, thus forming a barrier for magnetization reversal that is in accordance with the experimental evidence.

Abstract: Nanoparticles of wide band gap II-VI compounds doped with transition metal (TM) or rare earth (RE) ions are perspective phosphor materials and fluorescence labels for optoelectronic, biology and medical applications. The efficiency of 3d-3d and 4f-4f intra-shell transitions is shown to be enhanced in TM, RE doped nanoparticles. Two mechanisms of emission enhancement related to spin dependent interactions of free carriers with impurities are discussed. These interactions enhance the TM, RE intra-shell transitions by increasing the rate of host to impurity energy transfer. It is shown also that Al doping increases the intensity of light emission from ZnO nanoparticles.