RESEARCH ACTIVITIES   Oxide Semiconductor Nanostructures 182.　Soumen Dhara, Kenji Imakita, P. K. Giri1, Minoru Mizuhata, and Minoru Fujii, "Aluminum Doped Core-Shell ZnO/ZnS Nanowires: Doping and Shell Layer Induced Modification on Structural and Photoluminescence Properties", Journal of Applied Physics, Vol. 114, Issue 13, 134307 (2013), pp. 1–8 (2013). (Copyright (2013) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. ) In this work, we investigated the combined effects of Al doping and surface modification on the fabrication of a core–shell type ZnO/ZnS nanowires (NWs) and its structural, electrical, and photoluminescence (PL) properties. A systematic investigation for different concentrations of Al doping followed by surface modification with different thicknesses of ZnS layer was performed. Significant changes in the nature of PL spectra and electronic conductivity are observed and insight discussions are present. Structural characterization on the core-shell NWs reveals the successful fabrication of Al doped highly single crystalline ZnO core and polycrystalline ZnS shell with both ZnO and ZnS are of hexagonal wurtzite structure. Compared with the bare undoped ZnO NWs, Al doped core-shell ZnO/ZnS NWs exhibit two orders of magnitude improvement in the electronic conductivity and fivefold enhancement in the UV PL intensity. The Al doped core-shell ZnO/ZnS NWs shows an efficient improvement in the UV PL intensity than the undoped core-shell ZnO NWs. The obtained improvement in the PL result is explained on the basis of interfacial transfer of photogenerated charge carriers and modification of defects. 176.　Batakrushna Santara, Pravat K. Giri, Kenji Imakita, and Minoru Fujii, "Evidence of Oxygen Vacancy Induced Strong Room Temperature Ferromagnetism in Solvothermally Synthesized Undoped TiO2 Nanoribbons", Nanoscale, Vol. 5, pp. 5476-5488 (2013). We report on the oxygen vacancy induced ferromagnetism (FM) at and above room temperature in undoped TiO2 nanoporous nanoribbons synthesized by a solvothermal route. The origin of FM in as-synthesized and vacuum annealed undoped nanoribbons grown for different reaction durations followed by calcinations was investigated by several experimental tools. X-Ray diffraction pattern and micro-Raman studies reveal the TiO2(B), TiO2(B)-anatase, and anatase–rutile mixed phases of TiO2 structure. Field emission scanning electron microscopy and transmission electron microscopy observations reveal nanoribbons with uniform pore distribution and nanopits/nanobricks formed on the surface. These samples exhibit strong visible photoluminescence associated with oxygen vacancies and a clear ferromagnetic hysteresis loop, both of which dramatically enhanced after vacuum annealing. Direct evidence of oxygen vacancies and related Ti3+ in the as-prepared and vacuum annealed TiO2 samples are provided through X-ray photoelectron spectroscopy analysis. Micro-Raman, infrared absorption and optical absorption spectroscopic analyses further support our conclusion. The observed room temperature FM in undoped TiO2 nanoribbons is quantitatively analyzed and explained through a model involving bound magnetic polarons (BMP), which include an electron locally trapped by an oxygen vacancy with the trapped electron occupying an orbital overlapping with the unpaired electron (3d1) of Ti3+ ion. Our analysis interestingly shows that the calculated BMP concentration scales linearly with concentration of oxygen vacancies and provides a stronger footing for exploiting defect engineered ferromagnetism in undoped TiO2 nanostructures. The development of such highly porous TiO2 nanoribbons constitutes an important step towards realizing improved visible light photocatalytic and photovoltaic applications of this novel material.