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Metal halide perovskites have become more popular for applications in solar cells and optoelectronic devices. In this study, the structural, electronic, mechanical, and optical properties of lead and lead-free metal halide cubic perovskites CsPbBr3 and CsGeBr3 and their Ni-doped structures have been studied using the first-principle density functional theory. Ni-doped CsGeBr3 shows enhanced absorbance both in the visible and the ultraviolet region. The absorption edge of Ni-doped CsBBr3 (B = Pb, Ge) shifts toward the lower energy region compared to their undoped structures. Undoped and Ni-doped lead and lead-free halides are found to have a direct bandgap, mechanical stability, and ductility. A combined analysis of the electronic, mechanical, and optical properties of these compounds suggests that lead-free perovskite CsGe0.875Ni0.125Br3 is a more suitable candidate for solar cells and optoelectronic applications.

Calcium carbonates such as calcite are the dominant hosts of inorganic iodine in nature and are potentially important for the retention and removal of radioactive iodine isotopes (129 I and 131 I) in contaminated water. However, little is known about the structural environment of iodine in carbonates. In this study, iodate (IO 3 −) doped calcite and vaterite have been synthesized using the gel-diffusion method at three NaIO 3 concentrations (0.002; 0.004; 0.008 M) and a pH value of 9.0, under ambient temperature and pressure. Inductively coupled plasma mass spectrometry (ICP-MS) analyses show that iodine is preferentially incorporated into calcite over vaterite. Synchrotron iodine K-edge X-ray absorption near-edge structure (XANES) spectra confirm that IO 3 − is the dominant iodine species in synthetic calcite and vaterite. Analyses of iodine K-edge extended X-ray absorption fine structure (EXAFS) data, complemented by periodic first-principles calculations at the density functional theory (DFT) levels, demonstrate that the I 5+ ion of

The tuning of semiconductor band gaps can often provide significant performance increases and new applications for electronic, optoelectronic, and photocatalytic devices. Here, we study the band gaps of pure and nickeldoped zinc oxide thin films synthesized using the low-cost spray pyrolysis deposition method. Nickel concentration is varied from 0 to 15%, and the effects that this doping has on the electronic structure are analyzed. Using optical and synchrotron X-ray techniques, two regimes of band gap reduction via Ni doping are uncovered. For doping up to 4% Ni, there is a strong reduction in the gap, while continued doping up to 15% further reduces the gap, but to a lesser extent. The results are explained using X-ray spectroscopy and an Anderson impurity model. These tools show that the low doping case is driven by the interaction of the Ni 3d and O 2p states in both the valence and conduction bands. At high doping, the removal of Zn 3d states from the valence band and the change in Ni coordination from T d to O h both contribute to counteract the gap reduction. These results show how Ni can be used to tune the ZnO band gap over a large range useful for many applications.

Good homogeneous and stoichiometric ZnO nanofiber thin films have been deposited onto cleaned glass substrate by a simple spray pyrolysis technique under atmospheric pressure using zinc acetate precursor at temperature 200 °C. Films of various thicknesses have been obtained by varying the deposition time, while all other deposition parameters such as spray rate, carrier gas pressure and distance between spray nozzle to substrate were kept constant. Surface morphology and optical properties of the as deposited thin films have been studied by Scanning Electron Microscopy (SEM) attached with an EDX and UV visible spectroscopy. From EDX data, atomic weight % of Zinc and Oxygen were found to be 49.22 % and 49.62 % respectively. The SEM micrograph of the film shows uniform deposition and scattered nano fiber around the nucleation centers. The optical band gap of the ZnO thin films was found to be in the range 3.3 to 3.4 eV and the band gap decreases with thickness of the film. Optical constants such as refractive index, extinction coefficient, real and imaginary parts of dielelectric constants were evaluated from reflectance and absorbance spectra.