Wan Nurulhuda Wan Shamsuri

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.

Structural and Luminescence Study of Rare Earth and Transition Metal Ions Doped Lead Zinc Borophosphate Glasses

A series of glasses with composition of xPbO-(50-x)ZnO-yB2O3-(50-y)P2O5 with 0 x 50 mol% and 10 y 20 mol% were prepared by melt quenching technique, with 30 minutes pre-heating and 10 minutes for melting. The structural properties of prepared samples were studied using Fourier Transform-Infrared spectroscopy. The glasses were mainly based on PO2, BOP and BO3 unit. In order to obtain luminescence properties, another series of sample at composition 20PbO-30ZnO-10B2O3-40P2O5 doped with Fe2+, Ti2+, Y2+ and Nd2+ were prepared. These samples were investigated using Photoluminescence Spectroscopy with different excitation wavelength to compare results. Results showed that with the presence of rare earth and transition metal ions as activator in lead zinc borophosphate glass system give rise to luminescence of visible light.

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.

Structural and luminescence study of antimony-zinc borophosphate glass doped with iron

Antimony zinc borophosphate glass were prepared with the composition of 20ZnO-30B2O3-xP2O5-(50-x)Sb2O3-2Fe2O3 (0≤x≤50 mol%) using the melt quenching method. The starting materials were mixed and preheat for 30 minutes and transfer into high temperature furnace for melting. The structure of samples were measured using Fourier-Transform Infrared (FT-IR) Spectroscopy. The spectra showed that network structure in the samples are mainly based on P=O, PO2, P-O, B-O-B and B-O units. With increasing P2O5 content, the vibration of P-O tends to shift towards lower wavenumber. Meanwhile, the luminescence was studied using Photoluminescence (PL) Spectroscopy. The samples were excited at specific wavelengths (265 - 300 nm). The emission profiles were obtained to study the energy transfer process. Luminescence of violet colour from samples were also recorded to correlate with PL results.

ZnO Thin Film Ga s Sensor for CO

ZnO thin films were deposited onto corning glass substrates by rf magnetron sputtering system using ZnO targets. Films were deposited under rf power of 80 W at various deposition time. The distance between the target and substrate was held at 45 cm. A mixed Ar and O2 gas was introduced into the chamber at 4×10−2 Torr. The structure of the deposited ZnO films was investigated by Scanning electron miscroscopy. The gas sensing properties were evaluated at various operation temperatures by measuring the changes of resistance of the sensor in air and in CO gas respectively using the gas sensing characterization system. The grain size was increased as the film thickness was increased during deposition. The sensor with 233 nm film thickness exhibited the highest sensitivity for CO gas.