Hendrik C. Swart

Bio: Hendrik C. Swart is an academic researcher from University of the Free State. The author has contributed to research in topics: Phosphor & Photoluminescence. The author has an hindex of 40, co-authored 329 publications receiving 6645 citations. Previous affiliations of Hendrik C. Swart include University of Florida & Mintek.

Upconversion based temperature sensing ability of Er3+–Yb3+codoped SrWO4: An optical heating phosphor

Abstract: The present paper covers a detail explanation about the laser induced optical heating and temperature sensing ability of intense green upconversion emitting Er 3+ –Yb 3+ codoped SrWO 4 phosphor. The structural studies based on X-ray diffraction and Fourier transform infrared analysis confirmed the phase formation, crystallinity and the presence of vibrational bands of the corresponding host lattice. The optical investigation was performed by recording the diffuse reflectance and upconversion emission spectra upon a 980 nm excitation. Multiphoton upconversion processes were confirmed by pump power dependence study for the various emission bands throughout the visible region. Optical thermometry has been performed using the fluorescence intensity ratio technique in which two thermally coupled levels of the green emission bands were used. A relatively low temperature (518 K) sensor with very high sensor sensitivity (14.98 × 10 −3 K −1 ) is determined from the observed results. The optical heating ability of the synthesized phosphor is also determined by using the results of the optical thermometry and found the heat generation up to ∼417 K. The results obtained may possibly be used in cancer therapy.

Defect correlated fluorescent quenching and electron phonon coupling in the spectral transition of Eu3+ in CaTiO3 for red emission in display application

Abstract: This paper reports on the defect correlated self-quenching and spectroscopic investigation of calcium titanate (CaTiO3) phosphors. A series of CaTiO3 phosphors doped with trivalent europium (Eu3+) and codoped with potassium (K+) ions were prepared by the solid state reaction method. The X-ray diffraction results revealed that the obtained powder phosphors consisted out of a single-phase orthorhombic structure and it also indicated that the incorporation of the dopants/co-dopants did not affect the crystal structure. The scanning electron microscopy images revealed the irregular morphology of the prepared phosphors consisting out of μm sized diameter particles. The Eu3+ doped phosphors illuminated with ultraviolet light showed the characteristic red luminescence corresponding to the 5D0→7FJ transitions of Eu3+. As a charge compensator, K+ ions were incorporated into the CaTiO3:Eu3+ phosphors, which enhanced the photoluminescence (PL) intensities depending on the doping concentration of K+. The concentration quenching of Eu3+ in this host is discussed in the light of ion-ion interaction, electron phonon coupling, and defect to ion energy transfer. The spectral characteristics and the Eu-O ligand behaviour were determined using the Judd-Ofelt theory from the PL spectra instead of the absorption spectra. The CIE (International Commission on Illumination) parameters were calculated using spectral energy distribution functions and McCamy's empirical formula. Photometric characterization indicated the suitability of K+ compensated the CaTiO3:Eu3+ phosphor for pure red emission in light-emitting diode applications.

Rare Earth Doped Zinc Oxide Nanophosphor Powder: A Future Material for Solid State Lighting and Solar Cells

Abstract: A comprehensive review of up-conversion (UP) and down-conversion (DC) or down shifting of rare earth (RE) doped zinc oxide (ZnO) nanophosphors is presented. Research interest in the development of RE3+ doped ZnO for UP and DC nanophosphors has been encouraged by the potential application of these materials in light emitting diodes and different types of photovoltaic cells. A range of remarkable characteristics, which are organized into different sections describing the structure, optical, and luminescence properties of these materials, are discussed in detail. Undoped ZnO has two characteristic emissions in the ultraviolet and visible regions related, respectively, to excitonic recombination and intrinsic defects. X-ray photoelectron spectroscopy (XPS) data demonstrated a correlation between the visible emission and intrinsic defects. In the case of the DC or shifting process, there was simultaneous emissions related to f → f transitions of RE ions and defects in ZnO host. These emissions were dependent o...

Principles of Neural Science

Abstract: I have developed "tennis elbow" from lugging this book around the past four weeks, but it is worth the pain, the effort, and the aspirin. It is also worth the (relatively speaking) bargain price. Including appendixes, this book contains 894 pages of text. The entire panorama of the neural sciences is surveyed and examined, and it is comprehensive in its scope, from genomes to social behaviors. The editors explicitly state that the book is designed as "an introductory text for students of biology, behavior, and medicine," but it is hard to imagine any audience, interested in any fragment of neuroscience at any level of sophistication, that would not enjoy this book. The editors have done a masterful job of weaving together the biologic, the behavioral, and the clinical sciences into a single tapestry in which everyone from the molecular biologist to the practicing psychiatrist can find and appreciate his or

Enhancing solar cell efficiency: the search for luminescent materials as spectral converters

Abstract: Photovoltaic (PV) technologies for solar energy conversion represent promising routes to green and renewable energy generation. Despite relevant PV technologies being available for more than half a century, the production of solar energy remains costly, largely owing to low power conversion efficiencies of solar cells. The main difficulty in improving the efficiency of PV energy conversion lies in the spectral mismatch between the energy distribution of photons in the incident solar spectrum and the bandgap of a semiconductor material. In recent years, luminescent materials, which are capable of converting a broad spectrum of light into photons of a particular wavelength, have been synthesized and used to minimize the losses in the solar-cell-based energy conversion process. In this review, we will survey recent progress in the development of spectral converters, with a particular emphasis on lanthanide-based upconversion, quantum-cutting and down-shifting materials, for PV applications. In addition, we will also present technical challenges that arise in developing cost-effective high-performance solar cells based on these luminescent materials.

Solution Combustion Synthesis of Nanoscale Materials

Abstract: Solution combustion is an exciting phenomenon, which involves propagation of self-sustained exothermic reactions along an aqueous or sol–gel media. This process allows for the synthesis of a variety of nanoscale materials, including oxides, metals, alloys, and sulfides. This Review focuses on the analysis of new approaches and results in the field of solution combustion synthesis (SCS) obtained during recent years. Thermodynamics and kinetics of reactive solutions used in different chemical routes are considered, and the role of process parameters is discussed, emphasizing the chemical mechanisms that are responsible for rapid self-sustained combustion reactions. The basic principles for controlling the composition, structure, and nanostructure of SCS products, and routes to regulate the size and morphology of the nanoscale materials are also reviewed. Recently developed systems that lead to the formation of novel materials and unique structures (e.g., thin films and two-dimensional crystals) with unusual...