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Papers by Rebecca Mhlongo

Heliyon

x% Sm 3þ (0 x 1.9) (hereafter called BCCC:x% Sm 3þ) nanophosphors were successfully prepared by c... more x% Sm 3þ (0 x 1.9) (hereafter called BCCC:x% Sm 3þ) nanophosphors were successfully prepared by citrate sol-gel method. The structure, morphology and photoluminescence properties of the prepared nanophosphors were investigated. X-ray diffraction (XRD) indicated that the nanophosphors composed of the mixed phases of the hexagonal (CaAl 2 O 4 , BaAl 2 O 4) and cubic (Ca 4 Al 6 O 13 , Ca 3 Al 2 O 6) crystal structures. Scanning electron microscopy (SEM) revealed that doping influences the morphology of the prepared nanophosphor. High resolution transmission electron microscopy (HR-TEM) confirmed that the prepared phosphor particles are in the nanoscale range. Photoluminescence (PL) results showed emission peaks originating from the intrinsic defects within the BaAl 2 O 4 , CaAl 2 O 4 and Sm 3þ transitions. The optimum luminescence intensity was found at 0.7% Sm 3þ. Commission Internationale de l' eclairage (CIE) shows that the Sm 3þ doped samples emitted the orange colour.

Condensed Matter

The present study evaluates the effect of mesoporous multiphase titanium dioxide (TiO2) nanoparti... more The present study evaluates the effect of mesoporous multiphase titanium dioxide (TiO2) nanoparticles (NPs) as an electron transporting layer and investigates the influence of phase composition on the perovskite solar cell (PSC) performances. This study also aims to evaluate PSC performance using conductive silver ink as an alternative counter electrode. The heterogeneous PSC thin-film solar cells were successfully fabricated and assembled by using a simple a doctor blade and two-step spin coating methods under ambient conditions. Scanning electron microscopy (SEM) micrograph images investigate methyl ammonium lead iodide (MAPbI3) crystal formation on the mesoporous TiO2 surface structure. Energy-dispersive x-ray spectroscopy (EDX) spectra reveal excellent qualitative and quantitative analysis corresponding to the SEM images in the TiO2/MAPbI3 heterogeneous thin films. Thermogravimetric analysis (TGA) characterization reveals that the TiO2/MAPbI3 thin films are thermally stable reco...

Journal of Molecular Structure, 2022

Electrode Materials for Energy Storage and Conversion, 2021

Optical Materials, 2020

Abstract This paper reports on the effects of varying the Cu2+ doping concentration on the struct... more Abstract This paper reports on the effects of varying the Cu2+ doping concentration on the structure, morphology and optical properties of the BaAl2O4 phosphor. BaAl2O4:x% Cu2+ (0 ≤ x ≤ 1) series were successfully synthesized via citrate sol-gel method. The X-ray diffraction (XRD) results revealed that the prepared phosphor sample consist of a single phase hexagonal structure. The presence of Ba, Al, O and Cu were confirmed by the energy dispersive X-ray spectroscopy (EDS). Scanning electron microscope (SEM) revealed that the morphology of the prepared samples highly depends on the Cu2+ concentration. Transmission electron microscopy (TEM) results revealed the hollow tubular and nano-nature of the crystallite sizes. When the un-doped sample was excited at 283 nm, the photoluminescence (PL) results revealed six emission peaks located at 420, 435, 457, 521, 612 and 722 nm, which were attributed to the intrinsic intra band gap defects within the BaAl2O4 (host). The emission at 425 nm observed for the BaAl2O4:Cu2+ samples was attributed to the 3d84s1 → 3d9 transition in Cu2+ ion. The optimum doping Cu2+ concentration was found to be 0.075% Cu2+. Critical energy transfer distance (Rc) of Cu2+ ions was found to be 12.01 A, which suggested that the multipole-multipole interaction was the main reason for the luminescence quenching. The International Commission on Illumination (CIE) colour showed that the bluish emission colour of the prepared samples depends on the excitation wavelength and Cu2+ concentration. Thermo stimulated luminescence (TSL) of the host material showed the presence of both the swallow and deep traps respectively located at 75 and 240 °C.

Applied Physics A, 2020

In this study, magnesium aluminate nanopowders doped with manganese ions (MgAl 2 O 4 :0.1% Mn 2+)... more In this study, magnesium aluminate nanopowders doped with manganese ions (MgAl 2 O 4 :0.1% Mn 2+) were prepared by citrate sol-gel technique. The consequences on the structural, morphological and optical properties when varying the annealing period (AP) at a fixed annealing temperature of 800 °C and dopant concentration (0.1% Mn 2+) were investigated. The AP was varied at the range of 1-6 h. X-ray powder diffraction (XRD) results showed that doping with 0.1% Mn 2+ and varying the AP did not influence the crystal structure of the host (un-doped) material. The scanning electron microscope (SEM) images suggested that doping does not influence the morphology of the prepared nanopowders and varying the AP slightly influence the particle size. Transition electron microscopy (TEM) image suggested that the crystallite sizes were below 15 nm. The ultraviolet-visible (UV-Vis) diffuse reflection spectroscopy showed that the band gap of the MgAl 2 O 4 :0.1% Mn 2+ can be tuned from 5.04 to 4.58 eV with varying AP. Photoluminescence (PL) results showed two emission peaks located at around 413 and 655 nm. They were attributed to the defect levels within the host material and to the (4 T 1 → 6 A 1) transitions of Mn 2+ , respectively. Increasing the AP significantly influences the luminescence of the prepared powders. The CIE coordinate results showed that the bluish emission colour can be changed to the violet region when AP was increased.

Physica B: Condensed Matter, 2019

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Results in Physics, 2019

Neodymium activated strontium zinc aluminate (Sr 3 ZnAl 2 O 7 :x%Nd 3+) nanophosphor was synthesi... more Neodymium activated strontium zinc aluminate (Sr 3 ZnAl 2 O 7 :x%Nd 3+) nanophosphor was synthesized using the sol-gel technique whereby the Nd 3+ concentration was varied in the range 0 ≤ x ≤ 2. The effect of Nd 3+ concentration on the structure, particle morphology and photoluminescence properties of Sr 3 ZnAl 2 O 7 were investigated. The X-ray diffraction (XRD) results revealed that all samples resembled the mixture of both ZnAl 2 O 4 and Sr 3 Al 2 O 6 cubic structures. Nd 3+ doping influenced the crystallite sizes of the prepared phosphor materials. The energy dispersive X-ray spectroscopy (EDS) results confirmed the presence of all expected elements in the composition. Scanning electron microscopy (SEM) revealed that as the Nd 3+ concentration increased the surface morphology changed to smooth mountain-like structures. The ultraviolet-visible (UV-Vis) diffuse reflection spectroscopy showed that the band gap of Sr 3 ZnAl 2 O 7 can be tuned from 2.74 to 2.95 eV by increasing the Nd 3+ concentration. When the host is excited above the bandgap (374 nm), broad emission attributed to defects occurs with the maximum near 585 nm. Doped samples excited in this manner do not exhibit additional luminescence due to the Nd 3+ ions, but in contrast there is a small dip in the defect emission band near 585 nm due to absorption attributed to Nd 3+ ions. Characteristic infrared emissions of Nd 3+ ions at 885, 1064 and 1340 nm were observed by directly exciting the Nd 3+ ions at 585 nm (4 I 9/2 → 5 G 5/2 + 2 G 7/2) and were attributed to 4 F 3/2 → 4 I 9/2, 4 I 11/2 and 4 I 13/2 transitions, respectively. The Commission Internationale de l'Eclairage (CIE) coordinates results showed that the orange emission colour is from the host.

Journal of Molecular Structure, 2019

Nanophosphor powders of the mixed phases of ZnAl 2 O 4 /ZnO/SrAl 2 O 4 /Sr 3 Al 2 O 6 (ZZSS) dope... more Nanophosphor powders of the mixed phases of ZnAl 2 O 4 /ZnO/SrAl 2 O 4 /Sr 3 Al 2 O 6 (ZZSS) doped with Tb 3þ (ZZSS:0.025%Tb 3þ) were successfully prepared by sol-gel technique. The effect of the annealing period at a fixed annealing temperature (1000 C) and dopant concentration (0.025% Tb 3þ) on the structure and photoluminescence properties was investigated. X-ray diffraction results revealed that the crystallite size was influenced by the annealing period. Scanning electron microscopy showed that varying the annealing period influenced the particle morphology of the prepared nanophosphor material. High resolution transmission electron microscopy confirmed that the prepared material is on the nanoscale. The photoluminescence results showed that the ZZSS emits at 585 nm when excited at 374 nm, which is attributed to the defects centres within the ZnO phase. The Tb 3þ doped samples showed emissions peaks at 545, 590 and 623 nm which were attributed to the 4f transitions of Tb 3þ , specifically 5 D 4 / 7 F J (J ¼ 5, 4, 3). Increasing the annealing period up to 5.4 h led to luminescence enhancements, while a further increase led to quenching. The Commision Internationale de l'Eclairage coordinates showed that the greenish emission colour could be tuned by varying the annealing period.

Materials Research Express, 2020

The mixed phases of the un-doped MgAl2O4/MgO/Sr3Al2O6/SrAl2O4 (MMSS), MgAl2O4/MgO (MM) Sr3Al2O6/S... more The mixed phases of the un-doped MgAl2O4/MgO/Sr3Al2O6/SrAl2O4 (MMSS), MgAl2O4/MgO (MM) Sr3Al2O6/SrAl2O4 (SS), and the doped MMSS:x% Er3+ (0 ≤ x ≤ 1.8) nanopowders were synthesized using the citrate sol-gel method. The effect of Er3+ concentration on the structure, morphology and optical properties were investigated. X-ray powder diffraction (XRD) analysis indicated the cubical MgAl2O4, MgO and Sr3Al2O6; and monoclinic SrAl2O4 phases. The scanning electron microscopic images revealed the transformation of irregular particles to rod-like structure with an increase in Er3+ concentration. Transmission electron microscope indicated the nanosized particles depends on Er3+ concentration. Severals distinct absorption bands located at 444, 546, 653 and 704 nm under UV excitation (285 nm) corresponding to the defects states of the MgAl2O4, MgO, SrAl2O4, and Sr3Al2O6 phases were observed. There were traces of emission peaks at 546 and 653 nm attributed to the 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 ...

ii Practical work is regarded as an essential part of learning; hence most tertiary institutions ... more ii Practical work is regarded as an essential part of learning; hence most tertiary institutions have included a practical component in their physics courses. There is a concern about the effectiveness of the practical work in most universities. The present study is a case study that assessed the contributions of simulations on Foundation Physics students ’ practical work. In assessing the contribution of simulations, two tests, Determining and Interpreting Resistive Electric Circuits Concepts Test (DIRECT) and the Test of Integrated Science Process Skills (TISP) were used. A class test, observations and worksheets from students ’ practical work were analyzed and interviews with a selected group were conducted. There were 20 Foundation Physics students participating from the University of Limpopo. Results indicated that the simulations contributed positively on students’ understanding of electric circuits. However the study revealed that the students who did simulations do not diffe...

Multicultural Education & Technology Journal, 2011