Structure and Up-conversion Luminescence Properties of Er3+-Yb3+Co-doped TiO2 Nanocrystals Prepared by Sol-gel Method

Er(3+)/Yb(3+) co-doped TiO(2) nanocrystals were prepared by Sol-gel method in which titanium tetrachloride was adopted as the precursor The structure, particle size, and optical properties of samples were characterized by X-ray diffraction(XRD), Field emission-Scanning Electron Microscopy(FE-SEM) and photoluminescence(PL) spectra Er(3+) concentration was fixed at 1.0mol%, and Yb(3+) concentration was changed from 3 to 10mol% Intense upconversion luminescence was observed when the samples were excited by 980nm laser. The dependence of upconversion luminescence on Yb(3+) concentration was presented The results show that the upconversion luminescence increases with the Yb(3+) concentration and gets its peak at 5% The ratio of red emission to green emission(R/G) was strikingly enhanced with the increase of Yb(3+) concentration Under the excitation of 980nm, the green emission in the ranee of 520-570nm ((2)H(11/2), (4)s(3/2)->(4)I(15/2)) and the red emission in the range of 640 similar to 690nm ((4)F(9/2)->(4)I(15/2)) are both due to two photons process. The possible upconversion mechanism was discussed