Sol–gel method has been used to prepare pure anatase and anatase–rutile mixed phase TiO2 nanoparticles by calcination at different temperatures. The influences of calcination temperature on structure, band gap, luminescence properties and Raman spectra have been investigated. A clear evidence of structural transformation from pure anatase to anatase–rutile mixed phase structures has been confirmed by X-ray diffraction (XRD). Photoluminescence spectroscopy (PL) shows that the change in structure is also responsible for exhibiting the change in PL intensity. The Raman spectroscopy exhibits the anomalous behavior for band broadening and shifting of Raman bands with increasing crystallite size.