Zuhairi Ibrahim

Luminescence characteristics of Li2CO3–K2CO3–H3BO3 glasses co-doped with TiO2/MgO

Understanding the influence of co-dopants in the luminescence enhancement of carbonate glasses is the key issue in dosimetry. A series of borate glasses modified by lithium and potassium carbonate were synthesized by the melt-quenching method. The glass mixture activated with various concentrations of TiO2 and MgO was subjected to various doses of gamma-rays ((60)Co). The amorphous nature of the samples was confirmed by x-ray diffraction (XRD) spectra. The simple glowing curve of the glass doped with TiO2 features a peak at 230°C, whose intensity is maximal at 0.5 mol% of the dopant. The intensity of the glowing curve increases with the concentration of MgO added as a co-dopant up to 0.25 mol%, where it is two times higher than for the material without MgO thermoluminescence properties, including dose response, reproducibility, and fading were studied. The effective atomic number of the material was also determined. Kinetic parameters, such as kinetics order, activation energy, and frequency factor are estimated. The photoluminescence spectra of the titanium-doped glass consist of a prominent peaks at 480 nm when laser excitation at 650 nm is used. A three-fold photoluminescence enhancement and a blue shift of the peak were observed when 0.1% MgO was introduced. In addition, various physical parameters, such as ion concentration, polaron radius and internuclear distances were calculated. The mechanism for the thermoluminescence and photoluminescence enhancements are discussed.

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 Study of Antimony Borate Glass System Doped with Transition Metal Ions Using Infrared and Raman Spectroscopy

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.

Structural and luminescence properties of borate glass with lithium and strontium modifier doped with transition metal ions

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.

The Effect of V/III Ratio on the Crystal Structure of Gallium Arsenide Nanowires

Gallium arsenide (GaAs) nanowires were grown vertically on GaAs (111)B substrate by gold particle-assisted using metal-organic chemical vapour deposition. Transmission electron microscopy and X-Ray diffraction analysis were carried out to investigate the effects of V/III ratio and nanowire diameter on structural properties and crystallinity changes. Results show that GaAs nanowires grow preferably in the wurtzite crystal structure than zinc blende structure with increasing V/III ratio. Additionally, XRD studies have revealed that wurtzite nanowires show prominent peaks especially at (222) orientation. The optimum V/III ratio was found to be 166 with less defect structure, uniform diameter and peak prominence. The nanowires with high quality are needed in solar cells technology for energy trapping with maximum capacity.Keywords : Nanowire; crystal structure; Gallium arsenide; Vapor Liquid Solid

Optical Properties of Undoped and Dy3+-Doped Boro-Tellurite Glass

A series of undoped and Dy3+-doped boro-tellurite glasses were prepared, and their optical properties have been studied through XRD, absorption, optical band gap energy and photoluminescence. The XRD pattern has been used to confirm the amorphous nature of the prepared glass. The optical absorption spectra showed eight absorption bands which corresponded to 4I15/2, 4F9/2, 6F3/2, 6F5/2, 6F7/2, 6F9/2, 6F11/2 and 6H11/2 transitions from the ground state, 6H15/2. The optical band gap energy, Eopt for undoped glass was 3.08 eV and the Dy3+-doped glasses Eopt values varied from 3.16 3.24 eV. The emission spectra from photoluminescence spectroscopy showed two dominant emission peaks at 483 nm and 574 nm with an excitation wavelength of 325 nm (3.82 eV). Keywords: X-ray diffraction, boro-tellurite glass, photoluminescence, absorption spectrum, UV-Vis spectroscopy, energy band gap.

Structure and electrical characterization of gallium arsenide nanowires with different V/III ratio growth parameters

Gallium arsenide (GaAs) nanowires were grown vertically on GaAs(111)B substrate by gold-assisted using metal-organic chemical vapour deposition. Field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and conductivity atomic force microscopy (CAFM) analysis were carried out to investigate the effects of V/III ratio on structural properties and current-voltage changes in the wires. Results show that GaAs NWs grow preferably in the wurtzite crystal structure than zinc blende crystal structure with increasing V/III ratio. Additionally, CAFM studies have revealed that zincblende nanowires indicate ohmic characteristic compared to oscillation current occurred for wurtzite structures. The GaAs NWs with high quality structures are needed in solar cells technology for trapping energy that directly converts of sunlight into electricity with maximum capacity.

Structural study of cadmium lead borophosphate glass

Two series of cadmium and lead oxide modified borophosphate glass were fabricated using the melt quenching technique. The glass samples composition were xPbO:(50-x)CdO:10B2O3:40P2O5 and xPbO:(50-x)CdO:20B2O3:30P2O5. As different combinations of modifier oxides were added to the host system, changes in structural properties were expected to be observed and compared. For the study of structural properties, Fourier-Transform Infrared (FT-IR) spectroscopy and Raman spectroscopy were used. FT-IR and Raman spectroscopy were expected to produce structural information regarding the network forming borate and phosphate. Within the wavelength range of 400-2000 cm−1, multiple types of borate and phosphate stretching and bending groups were detected confirming the presence of borate and phosphate as glass forming host. Compositions and physical characteristics of all prepared samples were recorded to correlate with the both FT-IR and Raman spectroscopy spectra.

Luminescence properties of rare earth and transition metal ions doped potassium lead borophosphate glass

A series of potassium lead borophosphate glass doped with rare earth and transition metal ions were fabricated using melt-quenching method without annealing process. With the composition of glass 0.15K2O–0.15PbO–0.35B2O3–0.5P2O5 as host doped with 0.01 mole % of neodymium oxide, iron oxide, yttrium oxide, and titanium oxide as activator and different composition were used to investigate the luminescence effect by using Photoluminescence Spectroscopy and UV-Vis (Ultraviolet-Visible) spectrophotometer. By exciting the samples at different wavelength (200-900 nm), the excitation and emission profile were obtained and analyzed to study the energy transfer process. By referring to the spectra obtained, selected samples were also codoped among each other to obtain desired luminescence properties. UV-Visible spectroscopy results revealed the absorption and transmission wavelength of samples for targeted application as a selected band filter. Physical properties such as chemical stability and color of the samples...

Structural study of lithium strontium borophosphate crystal using x-ray diffraction and infrared spectroscopy

In order to study the influence of deionized water and heat treatment on the structure of the crystal, a compositional series of 20Li2O:20SrO:30B2O3:30P2O5 with deionized water and without de-ionized water as a solvent were prepared at 800ᵒC for different sintering time from 7 to 24 h. The crystalline phase and structural of 20Li2O:20SrO:30B2O3:A 30P2O5 crystal was studied using X-ray powder diffraction (XRD) and Infrared (IR) Spectroscopy. From the XRD result, samples prepared with deionized water as solvent displayed better crystalline respond. The samples showed a better crystalline structure when it was sintered for 24 h as compared to 7 h. The infrared spectra of the samples showed three distinctive regions around 1200 – 650 cm-1, 650 – 360 cm-1 and 360 cm-1 showing clear signs of boron units as the major host structure.