Green and red up-conversion emissions of Er3+–Yb3+ Co-doped TiO2 nanocrystals prepared by sol–gel method

In this paper, green and red up-conversion emissions of Er3+–Yb3+ co-doped TiO2 nanocrystals were reported. The phase structure, particle size and optical properties of Er3+–Yb3+ co-doped TiO2 nanocrystals samples were characterized by using X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–vis–NIR absorption spectra and photoluminescence (PL) spectra. Green and red up-conversion emissions in the range of 520–570 nm (2H11/2, 4S3/2→4I15/2) and 640–690 nm (4F9/2→4I15/2) were observed for the Er3+–Yb3+ co-doped TiO2 nanocrystals. The visible up-conversion mechanism and temperature dependence of up-conversion emission for Er3+ in TiO2 nanocrystals were discussed in detail.