Luminescence properties of Sm3+-doped TiO2 thin films prepared by laser ablation

Abstract

Samarium-doped anatase TiO2 (A-TiO2 : Sm3+) and rutile TiO2 (R-TiO2 : Sm3+) single phase thin films were fabricated on silicon substrates by laser ablation, resulting from the control of O2 pressures during ablation. These thin films show the Sm3+-related emissions in the visible and in the infrared wavelength regions. Visible photoluminescence (PL) and cathodoluminescence originating from the 4G5/2 → 6HJ intra-4f transitions in Sm3+ ions were observed at room temperature. The results of the photoluminescence excitation spectroscopy measurement imply that the Sm3+ emissions are due to the indirect excitation of the Sm3+ ions through an energy transfer process from electron–hole pairs generated in the TiO2 hosts. Intense 1.2 µm PL emissions originating from 4G5/2 → 6F9/2 and 6F7/2 → 6H5/2 transitions were also observed. A clear difference in the fine structure of the PL spectra between the A-TiO2 : Sm3+ and the R-TiO2 : Sm3+ thin films was observed, resulting from the difference in the Sm3+ configuration in the host crystal matrices.