Fluorescence properties of alloyed ZnSeS quantum dots overcoated with ZnTe and ZnTe/ZnS shells
- Authors: Adegoke, Oluwasesan , Mashazi, Philani N , Nyokong, Tebello , Forbes, Patricia B C
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/240754 , vital:50868 , xlink:href="https://doi.org/10.1016/j.optmat.2016.02.024"
- Description: Fluorescent alloyed ternary ZnSeS quantum dots (QDs) have been synthesized via the pyrolysis of organometallic precursors. The effects of passivation of ZnTe and ZnTe/ZnS shells on the optical properties of the ternary alloyed ZnSeS core have been studied. A ligand exchange reaction using L-cysteine as a capping ligand was used to obtain water-soluble nanocrystals. The nanocrystals were each characterized by UV/vis absorption and fluorescence spectroscopy, transmission electron microscopy, X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS). The photoluminescence (PL) quantum yield (QY) of alloyed ZnSeS QDs was 14% and this value increased to 27% when ZnTe was overcoated around the surface but further coating with a ZnS shell decreased the PL QY slightly to 24%. This implies that ZnTe shell suppressed non-radiative recombination exciton states in the alloyed core while further layering with a ZnS shell offered no further improvement in suppressing the defect states. XPS analysis confirmed the presence of the first shell layering but showed a weakened intensity signal of S (2p) and Se (3d) for the ZnSeS/ZnTe/ZnS QDs. Our work demonstrates for the first time that shell passivation of alloyed Zn-based QDs can offer improved optical properties. We hope the optical information presented in this work will be useful in the selection of alloyed Zn-based QDs appropriate for the intended application.
- Full Text:
- Date Issued: 2016
Graphene quantum dots functionalized with 4-amino-2, 2, 6, 6-tetramethylpiperidine-N-oxide as fluorescence “turn-on” nanosensors
- Authors: Achadu, Ojodomo J , Britton, Jonathan , Nyokong, Tebello
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/239854 , vital:50773 , xlink:href="https://doi.org/10.1007/s10895-016-1916-y"
- Description: In this study, we report on the fabrication of simple and rapid graphene quantum dots (GQDs)-based fluorescence “turn-ON” nanoprobes for sensitive and selective detection of ascorbic acid (AA). Pristine GQDs and S and N co-doped-GQDs (SN-GQDs) were functionalized with 4-amino-2,2,6,6-tetramethylpiperidine-N-oxide (4-amino-TEMPO, a nitroxide free radical). The nitroxide free radicals efficiently quenched the fluorescence of the GQDs and upon interaction of the nanoconjugates with ascorbic acid, the quenched fluorescence was restored. The linear ranges recorded were 0.5–5.7 μM and 0.1–5.5 μM for GQDs-4-amino-TEMPO and SN-GQDs-4amino-TEMPO nanoprobes, respectively. Limits of detection were found to be 60 nM and 84 nM for SN-GQDS-4-amino-TEMPO and GQDs-4-amino-TEMPO for AA detection, respectively. This novel fluorescence “turn-ON” technique showed to be highly rapid and selective towards AA detection.
- Full Text:
- Date Issued: 2016
HealthMessenger: an e-Health service to support ICT deployments in poor areas
- Authors: Gremu, Chikumbutso , Terzoli, Alfredo , Tsietsi, Mosiuoa
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/430609 , vital:72703 , 10.1109/ISTAFRICA.2016.7530632
- Description: Development and implementation of appropriate e-services as well as revenue generation are key to deploying and sustaining ICT installa-tions in poor areas in developing countries. The area of e-Health is a promising area for e-Services that are important to populations in poor areas and health service organisations that are already spending mon-ey on different health initiatives in these areas. This paper discusses an e-Health service that facilitates dissemination of health information to people living in poor areas and that is subsequently used to generate revenue to support deployment and development of ICT in the areas. The tool was developed within the context of the Siyakhula Living Lab (SLL), a multi-stakeholder operation that promotes ICT for Development in the Eastern Cape Province of South Africa. Creation of health con-tent for the e-health service and its subsequent consumption happen in two different environments from a technological and social point of view. To enable this to happen, the e-service comprises two component applications that run in a peer-to-peer fashion. The component that is used to disseminate content for end-user consumption is called the HealthMessenger. The HealthMessenger is hosted on an environment called TeleWeaver, an application integration platform developed within the SLL to host software applications targeting people living in poor ar-eas. The platform is customised to support services with a revenue generation component.
- Full Text:
- Date Issued: 2016
Heterogeneity in virulence relationships between Cryptophlebia leucotreta granulovirus isolates and geographically distinct host populations: Lessons from codling moth resistance to CpGV-M
- Authors: Opoku-Debrah, John K , Hill, Martin P , Knox, Caroline M , Moore, Sean D
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/417998 , vital:71500 , xlink:href="https://doi.org/10.1007/s10526-016-9728-1"
- Description: In South Africa, the baculovirus Cryptophlebia leucotreta granulovirus (CrleGV) is used to control the citrus pest Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae). However, the risk associated with continuous application of a single active ingredient is resistance. In order to manage resistance should it occur in field populations of T. leucotreta in South Africa, five new CrleGV genotypes from geographically distinct insect populations which were shown to exhibit some degree of phenotypic variation were recovered and genetically characterized. In droplet bioassays using seven CrleGV isolates against five T. leucotreta populations, some isolates were found to show higher virulence to some host populations than others. There were marked differences in the LD50 values of isolates and the number of occlusion bodies required per larva ranged between 0.79 and 3.12. The significance of these findings with respect to the application of CrleGV biopesticides and the management of resistance is discussed.
- Full Text:
- Date Issued: 2016
Impacts of HIV/AIDS on food consumption and wild food use in rural South Africa
- Authors: Ncube, Keitometsi , Shackleton, Charlie M , Swallow, Brent M , Dassanayake, Wijaya
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/180412 , vital:43385 , xlink:href="https://doi.org/10.1007/s12571-016-0624-4"
- Description: HIV/AIDS can affect household food consumption in many ways, including through reductions in availability and quality of labour, reductions in earned income, and increased expenditure on medications. In rural South Africa, these negative effects can be buffered by social safety net programs provided by government and collection of wild foods. Despite some acknowledgement of the potential safety net role of wild foods, however, their contribution relative to other food sources in the context of HIV/AIDS remains underexplored. Here we report empirical findings from two rural communities in the Eastern Cape province of South Africa. Qualitative and quantitative methods were used to characterise food sources, intake and calories from 68 HIV/AIDS afflicted households and 87 non-afflicted households every quarter over 12 months. Results show that diets were moderately well-balanced though limited in variety, with cereal items contributing 52 % to total calorie intake. The bulk of food consumed by households was purchased, with supplementation from own production, collected wild vegetables and collected wild fruits. Up to 20 % of respondents from both HIV/ AIDS afflicted and non-afflicted households had insufficient daily caloric intake. Multivariate analyses show that, all else equal, individuals living in households afflicted by HIV/AIDS consumed fewer calories, had less diverse diets, and were more dependent on wild foods than those living in non-afflicted households. Given the detrimental effects of HIV/AIDS on income and home production, wild foods represent a free and readily available food source for vulnerable households.
- Full Text:
- Date Issued: 2016
Improvement of nonlinear optical properties of phthalocyanine bearing diethyleneglycole chains
- Authors: Britton, Jonathan , Martynov, Alexander G , Oluwole, David O , Gorbunova, Yulia G , Tsivadze, Yulia G , Nyokong, Tebello
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/239812 , vital:50769 , xlink:href="https://doi.org/10.1142/S1088424616501042"
- Description: This paper reports the successful synthesis of the low symmetry phthalocyanines: metal-free 2,3-bis[2′-(2′′-hydroxyethoxy)ethoxy]-9,10,16,17,23,24-hexa-nn-butoxyphthalocyanine 1H22 and its zinc complex 1Zn along with their nonlinear optical (NLO) behavior in solution and in thin films. 1H NMR investigations evidenced of higher dissymmetry of electronic density in 1H22 in comparison with 1Zn. This dissymmetry is responsible for unusually higher values of Im[χ(3)χ(3)]/αα, βeffβeff, and γγ for 1H22in contrast to 1Zn, where the notable effect of heavy-metal enhancement of ISC was expected. Both compounds showed Im[χ(3)χ(3)]/αα values of the order of 10−11−11 in chloroform which are higher in comparison to the symmetrical octabutoxyphthalocyanine H2[(BuO)8Pc]. NLO properties of 1H22 were improved via its incorporation into polycarbonate polymeric matrix together with CdSe@CdS-TOPO quantum dots. In such composite the value of Im[χ(3)χ(3)]/αα was almost three times higher in comparison with 1H22 solution in chloroform. The obtained composites are expected to be perspective components of optical materials, capable of protection against strong light irradiation
- Full Text:
- Date Issued: 2016
Incorporation of environmental issues in South Africa’s municipal Integrated Development Plans
- Authors: Ruwanza, Sheunesu , Shackleton, Charlie M
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/180481 , vital:43393 , xlink:href="https://doi.org/10.1080/13504509.2015.1062161"
- Description: The transition to full democracy in South Africa in 1994 saw local government becoming the focal point for dealing with socio-economic development needs of communities. The Integrated Development Plan (IDP) has been used as the tool for guiding local development objectives, balanced against environmental demands within a sustainable development paradigm. Here we examine the extent to which this is being achieved through an analysis of IDPs from 35 different municipalities at three scales. We test the hypothesis that the metropolitan municipalities are better at mainstreaming environmental issues into their IDPs than local and district municipalities. Results indicate that mainstreaming environmental issues in IDPs is still low. The hypothesis that metropoles are better at mainstreaming environmental issues than district and local municipalities was not accepted since there were no significant differences between municipalities. There was low relative budget allocations and inclusion of vision and mission statements that mainstream environmental issues in all municipalities. For mainstreaming of environmental issues to be effective in IDPs, both proactive approaches and multi-faceted bottom-up and top-down approaches are suggested.
- Full Text:
- Date Issued: 2016
Interaction of graphene quantum dots with 4-acetamido-2, 2, 6, 6-tetramethylpiperidine-oxyl free radicals
- Authors: Achadu, Ojodomo John , Nyokong, Tebello
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/189031 , vital:44810 , xlink:href="https://doi.org/10.1007/s10895-015-1712-0"
- Description: We report on the interaction of graphene quantum dots (GQDs) with 4-acetamido-2,2,6,6-tetramethylpiperidineoxyl (4-acetamido-TEMPO) free radicals. The GQDs were N and S, N doped. The fluorescence quantum yields were higher for the doped GQDs compared to the undoped. The interaction is assessed by spectrofluorimetric, steady state/time resolved fluorescence and electron paramagnetic resonance (EPR) techniques. Fluorescence quenching was observed upon the addition of 4-acetamido-TEMPO to the GQDs. Photoinduced electron transfer (PET) mechanism was suggested as the plausible mechanism involved in the fluorescence quenching in which 4-acetamido-TEMPO acted as the electron acceptor.
- Full Text:
- Date Issued: 2016
Investigating multi-thread utilization as a software defence mechanism against side channel attacks
- Authors: Frieslaar, Ibraheem , Irwin, Barry V W
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/430190 , vital:72672 , https://doi.org/10.1145/3015166.3015176
- Description: A state-of-the-art software countermeasure to defend against side channel attacks is investigated in this work. The implementation of this novel approach consists of using multi-threads and a task scheduler on a microcontroller to purposefully leak out information at critical points in the cryptographic algorithm and confuse the attacker. This research demonstrates it is capable of outperforming the known countermeasure of hiding and shuffling in terms of preventing the secret information from being leaked out. Furthermore, the proposed countermeasure mitigates the side channel attacks, such as correlation power analysis and template attacks.
- Full Text:
- Date Issued: 2016
Knowledge structures and their relevance for teaching and learning in Introductory Financial Accounting
- Authors: Myers, Peta L
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text
- Identifier: vital:21107 , http://hdl.handle.net/10962/6413 , http://dx.doi.org/10.1080/10291954.2015.1099215
- Description: The structure of knowledge within a discipline has implications for the teaching and learning within the discipline. This research examines how the hierarchical knowledge structure of Accounting impacts on the teaching and learning which takes place in a first semester Introductory Financial Accounting course. Students used on-line questionnaires and interviews to explain how they engaged with the discipline and difficulties which they experienced during the semester. Bernstein's pedagogic Device and Maton's Legitimation Code Theory were used to analyse the structure of knowledge within the discipline and as theoretical lenses through which to view these students' perceptions. The research provides a theoretical explanation for the impact that a hierarchical knowledge structure has on teaching and learning within the discipline; how students need to develop a 'trained gaze' and thereby gain mastery over the 'procedures of investigation' to be able to produce the 'legitimate text' required for success in the course. The research also explains why some students experience a 'code clash' and the implications this has for their success in the discipline. Other pedagogical difficulties which were experienced by these students, as a result of the hierarchical knowledge structure within the discipline, are also discussed. In addition to providing a better understanding of the phenomena that drive or hinder student learning, which could contribute towards improving pedagogy and hence student learning, theorising these concepts provides a common language to enable more informed debate on these issues.
- Full Text:
- Date Issued: 2016
Knowledge, perceptions and willingness to control designated invasive tree species in urban household gardens in South Africa
- Authors: Shackleton, Charlie M , Shackleton, Ross T
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/180445 , vital:43389 , xlink:href="https://doi.org/10.1007/s10530-016-1104-7"
- Description: Many biological invasions result in negative impacts on the environment and human livelihoods, but simultaneously some also provide benefits that are valued differently by various stakeholders. To inform policy and management of invasive species it is important to assess landowners’ and broader society’s knowledge and perceptions of invasive species, something which is lacking in many contexts, especially in urban settings. In this study we interviewed 153 householders living in a medium-sized South African town who had declared invasive alien trees in their gardens. Less than half of the respondents could identify the invasive tree on their property and only one-third knew that it was an invasive alien species. There was a positive association between income and education levels with exposure to media about invasive alien species and respondents’ ability to identify the species and name any other invasive alien tree species. Knowledge levels were unequal across species. Amongst those who knew the tree was an invasive alien species, reasons why they retained it in their gardens included that it would be costly or too much effort to remove, they liked the tree, that it was not causing any harm and that the property was rented and so its removal was not their responsibility. However, the majority of people (83 %) were willing to have it removed from their garden if done for free by appropriate agencies, which is promising for compliance with new regulations on invasive species implemented at the end of 2014 in South Africa. The results also highlight the need for targeted and appropriate education and awareness programs amongst urban householders on invasive alien species, relevant legislation and their obligations.
- Full Text:
- Date Issued: 2016
MCD spectroscopy and TD-DFT calculations of magnesium tetra-(15-crown-5-oxanthreno)-phthalocyanine
- Authors: Mack, John , Mkhize, Scebi , Safonoya, Evgeniya A , Gorbunova, Yulia G , Tsivadze, Aslan Yu , Nyokong, Tebello
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/240743 , vital:50867 , xlink:href="https://doi.org/10.1142/S1088424616500322"
- Description: An analysis of the MCD spectroscopy and TD-DFT calculations of magnesium tetra-(15-crown-5-oxanthreno)-phthalocyanine is reported. This study provides a reassessment of an earlier study on the nature of the bands in UV-visible absorption spectra of magnesium and zinc tetra-(15-crown-5-oxanthreno)-phthalocyanine that was based on an analysis of TD-DFT calculations for a series of model complexes with the B3LYP functional. A detailed analysis of MCD spectral data and TD-DFT calculations with the CAM-B3LYP functional for the complete Mg(II) complex provides an additional insight into the optical properties and electronic structures of tetra-(15-crown-5-oxanthreno)-phthalocyanines. Thus, the bands in the Q-band region are reassigned as being due exclusively to the Q transition of Gouterman’s 4-orbital model, since intense pseudo-A1𝒜1 terms are observed in the MCD spectrum in a spectral region that had previously been assigned as charge transfer bands.
- Full Text:
- Date Issued: 2016
Miscellaneous provisions
- Authors: Arendse, Jacqueline A , Clegg, David , Williams, Robert C
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , book chapter
- Identifier: http://hdl.handle.net/10962/131276 , vital:36548 , https://store.lexisnexis.co.za/products/silke-on-tax-administration-skuZASKUPG1440
- Description: Miscellaneous provisions pertaining to tax administration are explained in this chapter.
- Full Text: false
- Date Issued: 2016
Molecular identification of Azolla invasions in Africa: The Azolla specialist, Stenopelmus rufinasus proves to be an excellent taxonomist
- Authors: Madeira, P T , Dray, F Allen , Coetzee, Julie A , Paterson, Iain D , Tipping, Philip W
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/424765 , vital:72182 , xlink:href="https://doi.org/10.1016/j.sajb.2016.03.007"
- Description: Biological control of Azolla filiculoides in South Africa with the Azolla specialist Stenopelmus rufinasus has been highly successful. However, field surveys showed that the agent utilized another Azolla species, thought to be the native Azolla pinnata subsp. africana, which contradicted host specificity trials. It is notoriously difficult to determine Azolla species based on morphology so genetic analyses were required to confirm the identity of the Azolla used by the agent. Extensive sampling was conducted and samples were sequenced at the trnL-trnF and trnG-trnR chloroplastic regions and the nuclear ITS1 region. Current literature reported A. filiculoides as the only Section Azolla species in southern Africa but 24 samples were identified as Azolla cristata, an introduced species within Section Azolla that was not used during host specificity trials. A. pinnata subsp. africana was only located at one site in southern Africa, while the alien A. pinnata subsp. asiatica was located at three. What was thought to be A. pinnata subsp. africana was in fact A. cristata, a closer relative of A. filiculoides and a suitable host according to specificity trials. This study confirms that S. rufinasus is a proficient Azolla taxonomist but also supports the use of molecular techniques for resolving taxonomic conundrums.
- Full Text:
- Date Issued: 2016
Morphological variations in southern African populations of Myriophyllum spicatum: Phenotypic plasticity or local adaptation?
- Authors: Weyl, Philip S , Coetzee, Julie A
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/424789 , vital:72184 , xlink:href="https://doi.org/10.1016/j.sajb.2015.07.01"
- Description: Variability in aquatic plant morphology is usually driven by phenotypic plasticity and local adaptations to environmental conditions experienced. This study aimed to elucidate which of these drivers is responsible for the morphological variation exhibited by three populations of Myriophyllum spicatum L. (Haloragaceae), a submerged aquatic plant whose status as native or exotic within southern Africa is uncertain. Individuals from three populations on the Vaal River (Northern Cape), Klipplaat River (Eastern Cape) and Lake Sibaya (KwaZulu-Natal) were grown under two nutrient treatments (high: 30 mg N/kg sediment and low: sediment only), while all other variables were kept the same. Morphological characteristics were measured at the start of the experiment to obtain a baseline morphology, and again eight weeks later. By the end of the experiment, the individuals from each population had responded to the different growing conditions. In most cases, the individuals from each population were significantly larger under the high nutrient treatment (Stem diameter: F(5,86) = 18.435, P is less than 0.001, Internode length: F(5,86) = 5.0747, P is less than 0.001, Leaf length: F(5,86) = 19.692, P is less than 0.001). Despite these differences in nutrient treatments, the growth pattern of each population remained true to the original starting point indicated by the lack of overlap between populations in the PCA groupings. This suggests that local adaptations are responsible for the differences in morphology between populations of M. spicatum, but shows that phenotypic plasticity does play a role as evidenced by individual responses to the different nutrient conditions. The development of these local adaptations within southern Africa suggests that the populations have had a long evolutionary history in the region and are relatively isolated with little reproductive mixing.
- Full Text:
- Date Issued: 2016
Natural resource use, incomes, and poverty along the rural–urban continuum of two medium-sized, South African towns
- Authors: Ward, Catherine D , Shackleton, Charlie M
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/180790 , vital:43646 , xlink:href="https://doi.org/10.1016/j.worlddev.2015.10.025"
- Description: Urbanization is a significant driver of global change, reshaping livelihoods, productive activities, and incomes. Yet, many elements of what are typically regarded as rural activities can be found in urban places and vice versa. We report on the incomes from land- and cash-based activities along the rural–urban gradient of two South African towns. Although the dominant income strategies varied, all households had more than one income source. Use of wild resources and agriculture were common in urban settings, although variable between and within towns. Poverty levels would be 5–10% higher in the absence of natural resource-based incomes.
- Full Text:
- Date Issued: 2016
Nitrogen fertilisation improves growth of Chromolaena odorata (Asteraceae) and the performance of the biological control agent, Pareuchaetes insulata (Erebidae)
- Authors: Uyi, Osariyekemwen O , Zacharariades, Costas , Hill, Martin P
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/416880 , vital:71393 , xlink:href="https://doi.org/10.1080/09583157.2015.1118615"
- Description: Recent studies have demonstrated, through their contrasting results, that relationships between nitrogen levels in host plants and phytophagous insect performance are not simple. This study examined the effect of varying fertilisation regimes on the invasive alien plant, Chromolaena odorata (L.) (Asteraceae) and the response of a specialist folivore (a biological control agent), Pareuchaetes insulata (Walker) (Lepidoptera: Erebidae). C. odorata plants were treated with 3 different levels of fertilisation and plant characteristics were measured within 2–3 months of fertiliser application. Leaves from each of the three treatments were fed to newly hatched larvae until pupation in order to determine the effect of nitrogen fertilisation on herbivore performance metrics such as survival, development time, fecundity and longevity. High and medium fertilisation significantly increased foliar nitrogen concentrations, basal stem diameter, leaf length, shoot height and above-ground biomass of C. odorata plants relative to low fertilisation. When individuals of P. insulata were fed on leaves from medium- or high-fertilisation treatments, they developed faster, grew to a larger size (by 8%) and achieved higher fecundity (19–22%) than leaves from the low-fertilisation treatment. The results suggest that in mass-rearing, increased production of this biological control agent will occur in high- or medium-fertilised plants.
- Full Text:
- Date Issued: 2016
Nonlinear optical behavior of alkyne terminated phthalocyanines in solution and when embedded in polysulfone as thin films: effects of aggregation
- Authors: Bankole, Owolabi M , Yilmaz, Yusuf , Nyokong, Tebello
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/189110 , vital:44817 , xlink:href="https://doi.org/10.1016/j.optmat.2015.11.041"
- Description: We report here for the first time, on the comparative studies of the photophysical and optical limiting behavior of our two novel phthalocyanines namely 2(3), 9(10), 16(17), 23(24)-tetrakis-(4-(5-methylhex-1-yn-3-yloxy)) phthalocyanines 2, and 2(3), 9(10), 16(17), 23(24)-tetrakis-(4-(5-methylhex-1-yn-3-yloxy)) phthalocyaninato zinc (II) (3) in solution and thin films. Nonlinear optical (NLO) properties of the samples in solution and contained in polysulfone (PSU) thin films were evaluated using Z-scan technique at 532 nm and 10 ns pulsed duration. Effects of aggregation and disaggregation on the NLO performance of metal-free phthalocyanine are reported in detail. Our findings showed that the prepared Pcs show larger nonlinear absorption coefficient and lower limiting thresholds when embedded in polysulfone films compared to in solutions. The values of nonlinear susceptibility and hyperpolarizability recorded for 3-PSU in this work are respectively, ∼2.09 × 10−8 esu and ∼1.02 × 10−26 esu. These values are among the largest values reported for phthalocyanines and other macrocycles doped on polymer matrices.
- Full Text:
- Date Issued: 2016
Nonlinear optical behavior of neodymium mono-and bi-nuclear phthalocyanines linked to zinc oxide nanoparticles and incorporated into poly acrylic acid
- Authors: Sekhosana, Kutloana E , Amuhaya, Edith , Nyokong, Tebello
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/188766 , vital:44783 , xlink:href="https://doi.org/10.1016/j.poly.2015.12.045"
- Description: Syntheses of bis{23-(3,4-di-yloxybenzoic acid)-(2(3), 9(10), 16(17), 23(24))-(hexakis-pyridin-3-yloxy phthalocyaninato)} dineodymium (III) acetate (3) and 2(3), 9(10), 16(17), 23(24)-(tetrapyridin-3-yloxy phthalocyaninato) neodymium (III) acetate (4) as well as their conjugates with ZnO nanoparticles (conjugates 6, 7 and 8) are presented. Thin films of conjugate 6 (where complex 3 is linked to ZnO nanoparticles via an amide bond) gave the best third-order susceptibility (5.89 × 10−8 esu), second-order hyperpolarizability (2.53 × 10−25 esu) and the lowest limiting threshold values (0.12 J cm−2). The nonlinear behavior is enhanced in solid state when compared to solution.
- Full Text:
- Date Issued: 2016
Nonlinear optical response of a low symmetry phthalocyanine in the presence of gold nanoparticles when in solution or embedded in poly acrylic acid polymer thin films
- Authors: Bankole, Owolabi M , Nyokong, Tebello
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/188719 , vital:44779 , xlink:href="https://doi.org/10.1016/j.jphotochem.2015.12.014"
- Description: In this article, we explored the photophysical and nonlinear optical (NLO) characterizations of low symmetry phthalocyanine (ZnPc-NH2) covalently linked to MPA-capped AuNPs (ZnPc-NH2-AuNPs) and poly acrylic acid (ZnPc-NH2-PAA). Nonlinear optical (NLO) properties of the samples were evaluated using Z-scan technique at 532 nm and 10 ns pulsed duration. We observed enhanced photophysical and nonlinear optical behaviour for the ZnPc-NH2 in presence of AuNPs. By virtue of the magnitude of absorption coefficients and other NLO optical parameters estimated in this work, ZnPc-NH2-AuNPs was found to exhibit improved nonlinear optical response compared to the ZnPc-NH2 and ZnPc-NH2-PAA. Both ZnPc-NH2-AuNPs and ZnPc-NH2 doped in PAA possess strong nonlinear absorption coefficients and very low limiting thresholds than when measured in solution.
- Full Text:
- Date Issued: 2016