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 I-4(11/2) to I-4(15/2) 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 degrees 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. (C) 2013 Elsevier B. V. All rights reserved.