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Featured researches published by L.F. Koao.


Journal of Electronic Materials | 2016

The Effects of Cd2+ Concentration on the Structure, Optical and Luminescence Properties of MgAl2O4:x% Cd2+ (0 < x ≤ 1.75) Nanophosphor Prepared by Sol–Gel Method

S.V. Motloung; F.B. Dejene; M. E. Sithole; L.F. Koao; O.M. Ntwaeaborwa; H.C. Swart; T.E. Motaung

Cadmium-doped magnesium aluminate (MgAl2O4:x% Cd2+) powders with different cadmium concentrations (0 < x ≤ 1.75) were prepared by the sol–gel method. Energy dispersive x-ray spectroscopy (EDS) analysis confirmed the presence of the expected elements (Mg, Al, O, and Cd). The x-ray diffraction (XRD) analysis revealed that the powders crystallized into the cubic spinel structure. Cd2+ doping influenced crystallinity of the powder samples. The crystallite size and particle morphology were not affected by variation in the Cd2+ concentration. Ultraviolet–visible spectroscopy (UV–vis) measurements revealed that the band gap of the MgAl2O4 was influenced by Cd2+ doping. Un-doped and Cd2+-doped MgAl2O4 nanophosphors exhibited violet emission at 392 nm. There was no evidence of the emission peak shift, which suggested that all emissions originated from the defects within the host material. Increasing the Cd2+ concentration up-to 0.88 mol.% lead to luminescence intensity enhancement, while further increase of Cd2+ concentration lead to concentration quenching. The critical energy transfer distance (Rc) between the neighbouring donors and acceptors was found to be 5.21 Å, suggesting that the multipole–multipole interaction (M-MI) is the major cause of concentration quenching. Commission Internationale de l’Elcairage (CIE) colour coordinates confirmed non-tuneable violet emission with intensity dependent on the Cd2+ concentration.


Journal of Reinforced Plastics and Composites | 2016

The effect of boehmite alumina nanoparticles on the properties of polylactide/polypropylene blend composites

Mpitloane J. Hato; T.E. Motaung; S.V. Motloung; L.F. Koao

The effect of boehmite alumina nanofiller on properties of polylactide/polypropylene blend compatibilized with 3% maleic anhydride grafted polypropylene was investigated. Boehmite alumina nanoparticles were finely dispersed in polylactide/polypropylene/boehmite alumina blend up to 7 wt.% to form blend nanocomposites which were prepared by twin-screw melt compounding. The morphology, thermal, mechanical, heat distortion temperature, thermomechanical and degradation characteristics were investigated. Scanning electron microscopy indicated a tubular morphology with increasing boehmite alumina in the blend matrix particularly at 5 and 7 wt.% of boehmite alumina loadings with few agglomerates. Transmission electron microscopy indicated a highly dispersed boehmite alumina in the blend nanocomposites. Boehmite alumina nanoparticles significantly influenced the thermal properties and a nucleation of the blend matrix. A significant improvement in the tensile modulus and tensile strength upon addition of boehmite alumina in the blend nanocomposites was obtained. However, beyond 3 wt.% of boehmite alumina addition, there was a clear deterioration in mechanical properties.


International Scholarly Research Notices | 2012

Luminescence Properties of Eu- and Mg-Codoped Sol-Gel SiO2 Glasses

Martin O. Onani; Paul Mushonga; L.F. Koao; F.B. Dejene

A series of SiO2 nanostructures codoped with Eu3+; Mg2+ ions were obtained by a sol-gel method. The gels synthesized by the hydrolysis of Si(OC2H5)4, Eu(NO3)3·6H2O, and Mg(NO3)2 were heated in air at 600°C for 2 hours. Firstly, the total amount of Eu3+ ions was varied from 0 to 2.0 mol% to investigate the effect of self-damping, while in the second case, the Eu3+ ions were kept constant in the experiment at 0.5 mol% total doping and Mg2+ ions varied. The samples were characterized by X-ray diffraction, TEM, EDS, and UV lamp-excited luminescence spectroscopy. The Eu3+ ions were homogeneously dispersed in the silica and interacting with the small (1–5 nm) amorphous silica matrix. Strong red emissions located at 614 nm and 590 nm for doped and codoped SiO2 were observed from the UV light excitation at room temperature. The composition of around 1.25 mol% Eu3+ gave highest emission intensity. SiO2; Mg2+ ions portray strongly enhanced emissions due to energy transfer from Mg2+ to Eu3+, which is due to radiative recombination. An increase in luminescence intensity was observed as the Mg2+-to-Eu3+ ratio increased for the range investigated. The results show Eu3+ ion is located inside or at the surface of disordered SiO2 nanoparticles.


Plastics Rubber and Composites | 2017

Effect of sodium dodecylbenzene sulphonate modifier and PP-g-MA on the morphology and thermal conductivity of PP/EG composites

Lesley Tsitsi Mukwada; Mokgaotsa Jonas Mochane; T.E. Motaung; S.V. Motloung; L.F. Koao

ABSTRACT This study investigates the influence of expanded graphite (EG) and sodium dodecylbenzene sulfonate (SDBS) treated EG (SDBS/EG) on the structure, thermal stability and thermal conductivity of polypropylene (PP) and polypropylene/maleic anhydride-grafted polypropylene (PP/MAPP) blend. The dispersion of EG and SDBS/EG was characterized by scanning electron microscopy (SEM). The SDBS-EG showed a crushed and randomly deformed structure. There was an improved interfacial adhesion between the polymer and the SBDS-EG particles. The graphite dispersed much better with less restacking for PP/MAPP/SDBS/EG system. The better dispersion also contributed towards the improved compatibility between the PP or PP/MAPP and SBDS/EG. The SDBS functionalised EG composites showed better thermal stability than the non-functionalized SDBS composites. It was further shown that the functionalized graphite significantly improved the thermal conductivity of the PP and PP/MAPP. This is because the functionalized SDBS/EG seemed to improve the interfacial heat transfer between the conductive filler (EG) and PP matrix.


Journal of Luminescence | 2014

Effect of Eu3+ on the structure, morphology and optical properties of flower-like ZnO synthesized using chemical bath deposition

L.F. Koao; F.B. Dejene; R.E. Kroon; H.C. Swart


Journal of Luminescence | 2011

Synthesis and characterization of Ce3+ doped silica (SiO2) nanoparticles

L.F. Koao; H.C. Swart; R.I. Obed; F.B. Dejene


Journal of Luminescence | 2013

The effect of Ce3+ on structure, morphology and optical properties of flower-like ZnO synthesized using the chemical bath method

L.F. Koao; F.B. Dejene; H.C. Swart; J.R. Botha


Physica B-condensed Matter | 2009

The effect of Mg2+ ions on the photoluminescence of Ce3+-doped silica

L.F. Koao; H.C. Swart; E. Coetsee; M.M. Biggs; F.B. Dejene


Physica B-condensed Matter | 2014

Effect of reaction time on structural, morphology and optical properties of ZnO nanoflakes prepared by chemical bath deposition method

F.V. Molefe; L.F. Koao; J. J. Dolo; B.F. Dejene


Journal of Alloys and Compounds | 2016

Effect of annealing temperature on structural and optical properties of ZnAl2O4:1.5% Pb2+ nanocrystals synthesized via sol-gel reaction

S.V. Motloung; Moges Tsega; F.B. Dejene; H.C. Swart; O.M. Ntwaeaborwa; L.F. Koao; T.E. Motaung; M.J. Hato

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F.B. Dejene

University of the Free State

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H.C. Swart

University of the Free State

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S.V. Motloung

Health Science University

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B.F. Dejene

University of the Free State

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O.M. Ntwaeaborwa

University of the Free State

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Hendrik C. Swart

University of the Free State

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Martin O. Onani

University of the Western Cape

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Moges Tsega

University of the Free State

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J.R. Botha

Nelson Mandela Metropolitan University

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