Karim Deraman

Effects of Eu3+ and Dy3+ doping or co-doping on optical and structural properties of BaB2Si2O8 phosphor for white LED applications

Abstract A series of Eu3+ and Dy3+ doped/co-doped as well as un-doped BaB2Si2O8 phosphors were synthesized via solid state reaction method. The PL result showed typical blue and green emission from Dy3+ and red emission from Eu3+. The f-f transitions involving the lanthanide ions along with dopant site occupancy were discussed thoroughly. Phonon assisted energy transfer process was observed from Eu3+ to Dy3+, which enhanced the emissions of Dy3+. Combinations of the emissions from Eu3+ and Dy3+ showed a possible white to red tuneable emission on the CIE diagram. The white warmth emissions of the phosphor were revealed to be adjustable through designing the dopant concentration and excitation wavelengths. An unusual energy transfer that originated from Eu3+ to Dy3+ was also discovered and the energy transfer mechanism was discussed. Proposed energy transfer mechanism was investigated using luminescence decay lifetime. All the phosphor exhibited efficient excitation in the UV range which matched well with the emissions from GaN-based LED chips. This presented the BaB2Si2O8 phosphor as a promising candidate for white LED applications. The effects of doping on the structural properties and the optical band gap of BaB2Si2O8 phosphor were also discussed in this study.

Electrical conductivity measurements in evaporated tin sulphide thin films

Tin sulphide (SnS) has been evaporated on to substrates maintained at fixed temperatures in the range 50-300°C. X-ray diffraction measurements have shown that the films deposited at the lower substrate temperatures are non-stoichiometric, containing higher sulphides of tin, but that those deposited at 300°C consist essentially only of SnS. Film conductivity increased in the range 0·5-20 Sm-1 as the substrate temperature during deposition increased from 50°C to 250°C, this effect being attributed to the changing film composition. Films deposited at 50°C and 150°C showed thermally activated conductivity at temperatures above 220-250 K, with activation energies EB; of 0·12 eV and 014eV, respectively. At lower temperatures both conductivity and activation energy were considerably lower, consistent with hopping via localized states. The conductivity is modified after prolonged cooling to 160K, although the mechanism of this process is not understood

Nanostructure of Al-ZnO thin films on ITO/glass substrate prepared via sol-gel spin coating process

Solar energy is probably the most important source of renewable energy available today. ZnO is a potential material for the fabrication solar cell. Zinc oxide (ZnO) nano-structure semiconductors have been recently gained much attention in the electronic and optical device applications. ZnO is a compound semiconductor, which has a high extention band gap (E= 3.37 eV) at room temperature (RT) with a Wurtzite crystal structure. In particular ZnO can be employed as the transparent conducting oxide (TCO) in solar cell applications due to its high productivity, non-toxic, low cost, and excellent electrical conductivity. In this study, aluminum doped ZnO (AZO) polycrystalline films have been fabricated on ITO/substrates via a sol-gel spin-coating method. The quantity of aluminum doping in the solution was 4.0 %. After synthesis, the films were pre-heated at 300°C for 25 min and after that the films were inserted in a Tub-furnace and post-annealing at 450°C to 750°C for 1 h. The microstructural and structural properties of AZO films were studied through X-ray diffraction (XRD), UV-Vis NIR and scanning electron microscope (SEM) analysis. The TCO applications of the transmittance of samples were also examined. The results showed that the annealing temperature does not seriously affect on the transmittance of AZO films over the visible range.

The Structural and Surface Morphology of Annealed ZnO Films

ZnO thin films were deposited on the glass substrates via the sol-gel dip coating method. The films were annealed at various temperatures ranging from 350 °C to 550 °C. X-ray diffraction (XRD), and atomic force microscopy (AFM) were used to investigate the effect of annealing temperature on the structural and morphology properties of the films. The as grown films exhibited amorphous pattern while annealed films were polycrystalline structure with (002) preferential growth along c-axis orientation. The AFM micrographs revealed that the RMS roughness of the films increased as the annealing temperature increased. The grain size was ranging from 32.1 nm to 176.0 nm as the annealing temperature increased from 350 °C to 450 °C and decreased to 56.1 nm for 550 °C.

Photoluminescene and Fourier Transform Infrared Measurement of Undoped Diamond-Like Carbon Thin Films by Direct Current – Plasma Enhanced Chemical Vapour Deposition

Undoped diamond like thin films have been prepared by using Direct Current - Plasma Enhanced Chemical Vapour Deposition system. A potentially diamond thin films was fabricated in the presence of gas mixture which accordance to the ratio CH4 (1%) + H2 (39%) + Ar (60%). The substrate temperature was controlled and adjusted from 300 °C to 500 °C in a vacuum chamber with the optimum pressure of 4 X 10-1 Torr. The films were characterized by X ray diffraction microscopy (XRD), Photoluminescene spectroscopy (PL) and Fourier Transform Infrared (FTIR) spectroscopy. It shows that, XRD pattern shown that the film was formed in the amorphous phase with a high fraction of sp3 hybridization. Luminescene band shows the peak position at (3.16 eV and 2.94 eV), (3.16 eV and 2.95 eV), (3.17 eV and 2.93 eV) and (3.26 eV) for the films deposited at 300, 350, 400 and 500 °C, respectively. The structural configuration of film obtained which corresponding to the sp3 hybridization of C H bonding gives a most significant result at approximately 760 cm-1 region was presented.

Effect of Substrate Temperature on Structural and Optical Properties of Un-Doped Diamond Thin Film

Un-doped diamond thin films were deposited at various substrate temperatures (from 300 °C to 500 °C) onto glass substrates by using direct current plasma enhanced chemical vapour deposition (DC-PECVD) system. The fabricated films were having amorphous phase which shown by X-ray diffraction (XRD). Atomic force microscopy (AFM) has discovered that the RMS surface roughness and the thickness which were obtained in the range of 0.69 nm to 1.67 nm and 4.8 nm to 0.83 nm, respectively as increasing substrate temperatures. From UV visible spectroscopy (UV-VIS), it was found that the optical transition had changed from forbidden indirect transition to allowed indirect transition as the substrate temperature increased. The optical band gaps were increased (3.14 eV, 3.93 eV and 4.09 eV) when the substrate temperatures increased. Hence, the higher the substrate temperatures, the larger the cluster size and RMS surface roughness and result in decreasing of films thickness and increasing the optical band gap.

Effect of Pressing Force on the Physical Properties of CaMgTiO3 Ceramic Prepared by HEBM

CaMgTiO3 ceramics were synthesized by using the high energy ball-milling method (HEBM) at different pressing forces. The raw materials were ball milled for 20 hours and sintered at 1000°C. Ceramics surfaces morphologies and particle sizes were measured using SEM analysis. Archimedes’ method was adapted to obtain their densities and porosities. It was found that pressing forces influenced both morphologies and particle sizes. As pressing forces increased, the particle sizes decreased as shown in SEM observation. However, the particle sizes increased at 200 kN due to agglomerated grain growth. The densities were almost constant with increasing of pressing forces while porosities were reduced.

Evaporated SnS semiconducting thin films

Evaporated tin sulphide thin films (SnS) have been prepared onto glass substrates maintained at fixed temperatures in the range 50-300 degree(s)C and controlled film thicknesses. The films are nonstoichiometric, containing both SnS and its higher derivative compounds with different compositions. X-ray results showed that SnS was initially formed at 100 degree(s)C, accumulating and eventually became a stable compound at a substrate temperature, Ts of 300 degree(s)C. Observation on SEM micrographs revealed the existence of nonoriented film structures at low Ts and compacted crystalline structures at Ts equals 300 degree(s)C with the associated change in grain sizes from 0.1 to 1.2 micrometers . Film conductivity increased from 0.62 to 2.54 Sm-1 with increasing substrate temperature. The low temperature measurements showed that the films underwent hopping and free band conduction at temperatures lower and higher than 220 K, respectively. A further investigation on the films transmittance spectrum shows the dependent of optical bandgaps (1.26-1.07 eV) with substrate temperatures; these were attributed to the changes in the films compositions.