9 research outputs found
Structural, elastic and optical properties of zinc tellurite glass system doped with samarium, samarium nanoparticles and silver oxide
Four series of zinc tellurite glasses doped with samarium, samarium nanoparticles and silver oxide were successfully fabricated using the conventional melt-quenching technique. The glasses were prepared based on the empirical formulas of [(TeO2)0.7 (ZnO)0.3[1-x [Sm2O3/ Sm2O3Nps]X, where x = 0.01 to 0.05 molar fraction and [{(TeO2)0.7 (ZnO)0.3}0.99 (Sm2O3/ Sm2O3Nps)0.01]1-y (Ag2O) y, with y = 0.005 to 0.025 molar fraction. The XRD tests confirmed that the glasses are amorphous. The Fourier Transform Infrared Spectrometer (FTIR) showed that all the glasses have a structural unit of TeO4 and TeO3. The TEM-images confirmed the existence of samarium nanoparticles with particle size of about 72.43 nm. The density of Sm2O3 and Sm2O3 NPs increased from 5.0419 to 5.3005 g/cm3 and from 5.1095 to 5.3286 g/cm3. Meanwhile, the molar volume increased from 27.4238 to 27.6901 cm3/mol, and from 27.0610 to 27.5441 cm3/mol. For Ag2O(Sm) glasses the density increased from 5.1999 to 5.3747 g/cm3 and decreased for Ag2O (Sm NPs) from 5.3162 to 4.9163 g/cm3.The molar volume decreased from 26.6788 to 26.1590 cm3/mol for Ag2O(Sm) and increased from 26.0952 to 28.5981 cm3/mol for Ag2O (Sm NPs) glasses. The elastic moduli and other elastic parameters increase with increase in dopant while the values of Poisson’s ratio lie in the range of 0.2734 to 0.2902. The direct and indirect optical band gap increased from 2.7855 eV to 2.9867 eV and from 2.6714 eV to 3.0676 eV for Sm2O3 and Sm2O3 NPs doped series. Similarly, Eopt increased from 2.9691 eV to 3.1054 eV and from 2.7417 eV to 2.6278 eV for Ag2O (Sm) and Ag2O (Sm NPs). Photoluminescence investigation reveals that the glass samples can be used as a laser active medium for emission at 605 and 607 nm wavelength corresponding to the 4G 5/2 to 6H 7/2 transitions. The Judd-Offelt analysis reveals that the large values of gain bandwidth (4.427x 10-21), optical gain (5.199 x10-25) and the radiative transition probabilities [(16195 S-1)/ (15894 S-1)] can be used for laser application. Furthermore, Ag2O (Sm NPs) doped series having the largest value of gain bandwidth (9.975x 10-21), optical gain (9.061 x10-25) and the radiative transition probabilities [(119021 S-1)/ (16832 S-1)] made it the best candidate for laser materials. Therefore, this research contributes to addressing the pressing challenge of developing new materials for laser
Ecological determinants of blindness in Nigeria: the Nigeria National Blindness and Visual Impairment Survey.
OBJECTIVE: To determine the prevalence and causes of visual loss in different ecological zones across Nigeria. METHODS: A population-based survey using multi-stage, stratified, cluster random sampling with probability proportional to size comprising a nationally representative sample of adults aged > or = 40 years from six ecological zones. OUTCOME MEASURES: Distance vision was measured using reduced logMAR charts. Clinical examination included basic eye examination for all respondents and a detailed examination including visual fields, gonioscopy and fundus photography for those who were visually impaired or blind (i.e. presenting vision or = 40 years were enumerated, 13 599 (89.9%) of whom were examined. The prevalence of blindness varied according to ecological zone, being highest in the Sahel region (6.6%; 95% confidence interval (CI) 4.2 - 10.4) and lowest in the rain forest region (3.23%; 95% CI 2.6 - 3.9). Age/ gender-adjusted analyses showed that risk of blindness was highest in Sahel (odds ratio (OR) 3.4; 95% CI 2.1 - 5.8). More than 80% of blindness in all ecological regions was avoidable. Trachoma was a significant cause only in the Sudan savannah belt. The prevalence of all major blinding conditions was highest in the Sahel. CONCLUSIONS: The findings of this national survey may be applicable to other countries in West and Central Africa that share similar ecological zones. Onchocerciasis and trachoma are not major causes of blindness in Nigeria, possibly reflecting successful control efforts for both these neglected tropical diseases
Causes of blindness and visual impairment in Nigeria: the Nigeria national blindness and visual impairment survey.
PURPOSE: Determine causes of blindness and visual impairment among adults aged >or=40 years. METHODS: Multistage, stratified, cluster random sampling with probability proportional to size procedures were used to identify a nationally representative sample of 15,027 persons >or=40 years of age. Distance vision was measured with a reduced logMAR tumbling E-chart. Clinical examination included a basic eye examination of all subjects and a more detailed examination of those who had presenting vision or=40 years who were enumerated, 13,599 (89.9%) were examined. In 84%, blindness was avoidable. Uncorrected refractive errors were responsible for 57.1% of moderate (40% over the next decade
Review of the publications of the Nigeria national blindness survey: methodology, prevalence, causes of blindness and visual impairment and outcome of cataract surgery.
This is a review of the major publications from the Nigeria national blindness survey in order to highlight major findings and challenges of eye care in Nigeria. The review summarizes methodology and key findings. Survey publications on methodology, prevalence and causes of visual impairment and outcome of cataract surgery were retrieved, reviewed and relevant data extracted, reported and discussed. The study was the largest and more detailed eye survey in Nigeria (15,375 people 40 years and older recruited). Participants had detailed eye examination including visual acuity, autorefractokeratometry, A- scan biometry, visual field and basic eye examination. Cause(s) of visual impairment in each eye using WHO algorithm was determined among participants with vision < 6/12. Some of the participants also had qualitative questions on barriers to uptake of services, quality of life and visual function. Major highlights of the results as contained in the publications include a high prevalence of blindness with 4.2% (95% CI: 3.8-4.6%;),of the study population having blindness (using presenting vision (PVA)) even with best correction the prevalence was 3.4% (95% CI: 3.0-3.8%. The prevalence of SVI using PVA was 1.5% (95% CI: 1.3-1.7%).and with best correction 0.8% (95% CI: 0.7-1.0%). Blindness varied by age groups, sex, literacy level and geopolitical zone. Furthermore, 84% of blindness was due to avoidable causes with cataract responsible for 43% of blindness, glaucoma 16.7%, uncorrected aphakia 8.4% and corneal opacity 7.9%. Of the total 538 eyes that had cataract surgery procedures, 42.7% had couching and the remaining had cataract surgery, but only 41.4% of cataract operated eyes had IOL surgery. Outcome of cataract surgery was good at presentation for only 30.8% of eyes (84 eyes) which improved to 56.8% with correction. The possible remedy for the high burden of needless blindness and harmful eye health practices in Nigeria are discussed
Characteristics of hydrothermally synthesized SnS2 for thin film use
Tin disulfide (SnS2) nanoparticles were synthesized via hydrothermal process and were deposited as ultrathin layer (27.5 nm) onto SLG via vacuum thermal evaporation. The SnS2 nanoparticles were characterized for their structural, purity, chemical, morphological, optical and electrical properties. The XRD patterns and the Raman spectra confirmed the successful synthesis of SnS2 nanoparticles. The stoichiometry and leaf like structure obtained from EDS and FESEM analysis of the SnS2 nanoparticles further proved its formation. The ultrathin layer deposited and annealed at 300 °C for 1 h showed XRD patterns of hexagonal structured SnS2 with crystallinity of 57.7 nm, bandgap energy of 2.7 eV and resistivity of 0.65 Ω cm
Effects of irradiation time on the structural, elastic, and optical properties of hexagonal (wurtzite) zinc oxide nanoparticle synthesised via microwave-assisted hydrothermal route
Zinc oxide (ZnO) is a vital nanomaterial highly valued in electronics and optoelectronics due to its remarkable multifunctional properties. This study prepared ZnO nanoparticles using a simple hydrothermal microwave process. The influence of irradiation time on the structural, elastic and optical properties of the ZnO nanoparticles was investigated. X-ray diffraction (XRD) analysis confirmed the hexagonal (wurtzite) structure of the ZnO nanoparticles. In addition, various XRD profile analysis techniques were used in this study, including Scherer method, strain size plot method, Halder–Wagner method, Monshi–Scherer method, and Williamson–Hall method consisting of a uniform deformation model, a uniform stress density model and a uniform deformation energy density model. The estimated mean crystallite size was found to be at 43.53–56.08 nm. Furthermore, atomic force microscopy and transmission electron microscopy were used to investigate the average particle size of the ZnO nanoparticles at different irradiation times. The results were consistent with the mean crystallite size calculated using the X-ray diffraction peak profile analysis techniques. Furthermore, a decrease in the energy band gap estimated by diffuse reflectance spectroscopy was observed, transitioning from 3.32s to 3.29 eV with increasing irradiation time. This observation was confirmed by the distinct and unique ultraviolet photoluminescence emission peaks of the synthesized ZnO nanoparticles, supporting the results of the diffuse reflectance analysis. Based on the presented results, it can be concluded that the X-ray diffraction peak profiling technique is a practical approach for determining the average crystallite size of ZnO nanoparticles prepared using the microwave hydrothermal technique and that it can be used for size-dependent applications
The Nigerian national blindness and visual impairment survey: Rationale, objectives and detailed methodology.
BACKGROUND: Despite having the largest population in Africa, Nigeria has no accurate population based data to plan and evaluate eye care services. A national survey was undertaken to estimate the prevalence and determine the major causes of blindness and low vision. This paper presents the detailed methodology used during the survey. METHODS: A nationally representative sample of persons aged 40 years and above was selected. Children aged 10-15 years and individuals aged <10 or 16-39 years with visual impairment were also included if they lived in households with an eligible adult. All participants had their height, weight, and blood pressure measured followed by assessment of presenting visual acuity, refractokeratomery, A-scan ultrasonography, visual fields and best corrected visual acuity. Anterior and posterior segments of each eye were examined with a torch and direct ophthalmoscope. Participants with visual acuity of < = 6/12 in one or both eyes underwent detailed examination including applanation tonometry, dilated slit lamp biomicroscopy, lens grading and fundus photography. All those who had undergone cataract surgery were refracted and best corrected vision recorded. Causes of visual impairment by eye and for the individual were determined using a clinical algorithm recommended by the World Health Organization. In addition, 1 in 7 adults also underwent a complete work up as described for those with vision < = 6/12 for constructing a normative data base for Nigerians. DISCUSSION: The field work for the study was completed in 30 months over the period 2005-2007 and covered 305 clusters across the entire country. Concurrently persons 40+ years were examined to form a normative data base. Analysis of the data is currently underway. CONCLUSION: The methodology used was robust and adequate to provide estimates on the prevalence and causes of blindness in Nigeria. The survey would also provide information on barriers to accessing services, quality of life of visually impaired individuals and also provide normative data for Nigerian eyes