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

Abstract

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°C for 1h. Nanopowders were prepared with fixed 5mol% Erbium concentration and various Ytterbium concentrations of 5 and 10mol%. The powders were characterized by studying their structural, morphology and photo-luminescent properties. The annealing treatment at 500°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 980nm excitation, and the Er–Yb:TiO2 nanopowders exhibited the intense green (520–570nm) and red (640–690nm) 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 655nm at varying excitation power densities. UC-QY analysis has revealed that 5mol% Er–5mol% Yb:TiO2 nanopowders possess the highest total quantum yield of 2.8±0.1% with a power density of 16.7W/cm2. These results make these nanopowders promising materials for efficient upconversion in photonic applications.