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Tailoring the NIR range optical absorption, band-gap narrowing and ferromagnetic response in defect modulated TiO2 nanocrystals by varying the annealing conditions

In this investigation, we report the influence of oxygen vacancy and Ti3+ related defects in the visible and IR range absorption as well as on the bandgap and magnetism of TiO2 nanocrystals annealed in different atmospheres. The X-ray diffraction patterns and Raman spectra indicate anatase phase formation and TEM analysis confirm the highly crystalline nature of TiO2 nanocrystals with a particle size of around similar to 9-12 nm. Significant absorption in the visible and IR region along with much-reduced bandgap is observed in argon, hydrogen and vacuum annealed samples. These samples exhibit strong visible photoluminescence associated mostly with oxygen vacancies. The room temperature ferromagnetism observed in argon annealed TiO2 nanocrystals is explained by taking into consideration the concept of bound magnetic polamns. Hence, this study reports the formation of TiO2 nanocrystals with extended absorption in visible as well as in IR region and ferromagnetism at room temperature which could have potential applications for future technologies.