Efficient green and red up-conversion emissions in Er/Yb co-doped TiO2 nanopowders prepared by hydrothermal-assisted sol-gel process

In this work, erbium and ytterbium co-doped titanium dioxide (Er-Yb:TiO2) nanopowders have been successfully prepared by hydrothermal-assisted sol-gel method using supercritical drying of ethyl alcohol and annealing at 500 degrees C for 1 h. Nanopowders were prepared with fixed 5 mol% Erbium concentration and various Ytterbium concentrations of 5 and 10 mol%. The powders were characterized by studying their structural, morphology and photo-luminescent properties. The annealing treatment at 500 degrees C was found to enhance the crystallinity of the TiO2 anatase structure and the upconversion (UC) emission of the nanopowders. UC emissions were investigated under 980 nm excitation, and the Er-Yb: TiO2 nanopowders exhibited the intense green (520-570 nm) and red (640-690 nm) upconverted emissions of Er ions originating from an efficient Yb-Er energy transfer process. The absolute upconversion quantum yield (UC-QY) of each nanopowders was measured for the UC emissions centered at 525, 550 and 655 nm at varying excitation power densities. UC-QY analysis has revealed that 5 mol% Er 5 mol% Yb:TiO2 nanopowders possess the highest total quantum yield of 2.8 +/- 0.1% with a power density of 16.7 W/cm(2). These results make these nanopowders promising materials for efficient upconversion in photonic applications. (C) 2016 Elsevier B.V. All rights reserved.