Defect mediated mechanism in greenly synthesized undoped, Al3+, Cu+2 and Zn+2 doped TiO2 nanoparticles for tailoring bandgap, luminescence, magnetic and electrical properties

This work focuses on the green synthesis, structural, microstructural, optical, electrical and magnetic properties of undoped, Al3+, Cu+2 and Zn+2 (8 atm.% each) doped TiO2 nanoparticles (NPs). PXRD along with Rietveld refinement, SAED, TEM and Raman studies revealed crystallization of doped TiO2 NPs in single phase tetragonal symmetry (anatase phase with space group: I4(1)/amd). TEM micrographs indicated high crystallinity and a narrow size distribution of nanocrystallites (3-8 nm) in the undoped and doped TiO2 NPs. EDS analysis confirmed well incorporation of metallic cations in stoichiometry in the doped TiO2 NPs. UV-Vis-NIR absorption spectra showed strong absorption of light below similar to 400 nm and red shift in the band gap with Al3+, Cu+2 and Zn+2 doping in TiO2 NPs. Incorporation of Al3+, Cu+2 and Zn+2 ions in the TiO2 matrix leads to distortion in crystal symmetry by creating moderate perturbation to phonon modes and formation of defects. Photoluminescence and ESR analysis inferred presence of F+ defect centers and oxygen vacancies owing to charge imbalance and charge transitions from Ti(+3 )to TiO62- octahedra in these undoped and doped TiO2 NPs. Undoped and doped TiO2 NPs exhibits defect mediated semiconducting and weak ferromagnetic (FM) character at mom temperature. Conventional super exchange cannot elucidate the long range FM ordering rather bound magnetic polaron model (BMP) evidently gives a satisfactory explanation to the d(0) type ferromagnetism in undoped and doped TiO2 NPs. These nanomaterials might be suitable for magneto-optical applications.