Structural, optical and magnetic resonance properties of TiO2 fibres grown by laser floating zone technique

TiO2 fibres grown by the laser floating zone technique show the rutile crystalline phase as identified by X-ray diffraction and Raman spectroscopy. Scanning electron microscopy evidences a uniform surface, free of inclusions and without low-angle grain boundaries and bubbles. At low temperatures, the fibres luminescence is dominated by a richly structured optical centre with two well-defined zero-phonon lines at 1.579 eV and 1.574 eV followed by an intense vibronic sideband with a maximum close to 1.47 eV. Electron paramagnetic resonance revealed that substitutional chromium and iron ions are present as contaminants in the grown fibres, alongside with Ti3+ interstitials and other structural defects. The chemical nature of the defect responsible for the structured near-infrared luminescence is discussed.