Enhanced upconversion red light emission of TiO2:Yb,Er thin film via Mn doping.

TiO2:Yb,Er films with different concentrations of Mn2+ are grown on SiO2 glass substrates by pulsed laser deposition. It is found that the introduction of Mn2+ enhanced the intensity of upconversion emission. In particular, TiO2:Yb,Er thin film with 5% Mn2+ ions exhibits the brightest upconversion emission. The upconversion red emission intensity is increased by 2.5-fold than that of a TiO2:Yb,Er thin film without Mn2+ ions, which is ascribed to the multi-photon absorption and efficient exchange-energy transfer process between Er3+ and Mn2+. The high transmittance and good conductivity of the films made them possible to act as electron transport layer in solar cells.