Optimization of Er3Â +-doped TiO2-thin films for infrared light up-conversion

We have studied up-conversion in TiO2 thin films doped with Er3 + deposited using radio frequency-magnetron sputtering. The TiO2 host was optimized to achieve efficient up-conversion signal from Er3 +. We controlled the TiO2 microstructure by varying the substrate temperature and radio frequency target power during deposition, and by changing the Er3 + doping concentration. Photoluminescence was used to investigate the influence of the microstructure of TiO2 on the up-conversion efficiency. This was attained by exciting the thin films with 1550 nm light from a CW laser, and studying the emission at a wavelength of 980 nm, corresponding to the transition from 4I11/2 to 4I15/2 in Er3 +. Our results demonstrate that strong up-conversion luminescence is obtained when the TiO2:Er3 + thin film is deposited at low radio frequency powers, high substrate temperature (≥ 255 °C) and with Er3 + doping above 4.5 at.%. The TiO2 host matrix was found to yield stronger up-conversion luminescence when amorphous than when polycrystalline.