One-step synthesis of ZnO nanosheets: a blue-white fluorophore

Zinc oxide is synthesised at low temperature (80°C) in nanosheet geometry using a substrate-free, single-step, wet-chemical method and is found to act as a blue-white fluorophore. Investigation by atomic force microscopy, electron microscopy, and X-ray diffraction confirms zinc oxide material of nanosheet morphology where the individual nanosheets are polycrystalline in nature with the crystalline structure being of wurtzite character. Raman spectroscopy indicates the presence of various defects, while photoluminescence measurements show intense green (centre wavelength approximately 515 nm) blue (approximately 450 nm), and less dominant red (approximately 640 nm) emissions due to a variety of vacancy and interstitial defects, mostly associated with surfaces or grain boundaries. The resulting colour coordinate on the CIE-1931 standard is (0.23, 0.33), demonstrating potential for use as a blue-white fluorescent coating in conjunction with ultraviolet emitting LEDs. Although the defects are often treated as draw-backs of ZnO, here we demonstrate useful broadband visible fluorescence properties in as-prepared ZnO

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In this chapter several aspects of the electronic and phonon structure are considered for the design and engineering of advanced thermoelectric materials. For a given compound, its thermoelectric figure of merit, zT, is fully exploited only when the free carrier density is optimized. Achieving higher zT beyond this requires the improvement in the material quality factor B. Using experimental data on lead chalcogenides as well as examples of other good thermoelectric materials, we demonstrate how the fundamental material parameters: effective mass, band anisotropy, deformation potential, and band degeneracy, among others, impact the thermoelectric properties and lead to desirable thermoelectric materials. As the quality factor B is introduced under the assumption of acoustic phonon (deformation potential) scattering, a brief discussion about carrier scattering mechanisms is also included. This simple model with the use of an effective deformation potential coefficient fits the experimental properties of real materials with complex structures and multi-valley Fermi surfaces remarkably well—which is fortunate as these are features likely found in advanced thermoelectric materials