Photon energy up-conversion in colloidal TiO2 nanorods

Nonaqueous reaction between titanium(IV) chloride and benzyl alcohol was used for the synthesis of highly crystalline TiO2 nanorods. The X-ray diffraction measurements proved the exclusive presence of the anatase phase. The photoluminescence of anatase TiO2 nanorods with several well-resolved emission bands was observed, and quantum yield at room temperature was found to be 2.5 × 10−3. Photon energy up-conversion from colloidal TiO2 nanorods was observed at low excitation intensities. The energy of the up-converted photoluminescence spans the range of energies displayed by the normal photoluminescence emission of the TiO2 nanorods. The explanation for the photon energy up-conversion involves mid-gap energy levels.