Efficient blue upconversion emission due to confined radiative energy transfer in Tm3+-Nd3+ co-doped Ta2O5 waveguides under infrared-laser excitation

Intense blue upconversion emission at 480 nm has been obtained at room temperature in Tm3+-Nd3+ co-doped Ta2O5 channel waveguides fabricated on a Si substrate, when the sample is excited with an infrared laser at 793 nm. The upconversion mechanism is based on the radiative relaxation of the Nd3+ ions (F-4(3/2) -> I-4(11/2)) at about 1064 nm followed by the absorption of the emitted photons by Tm3+ ions in the H-3(4) excited state. A coefficient of energy transfer rate as high as 3 x 10(-16) cm(3)/s has been deduced using a rate equation analysis, which is the highest reported for Tm-Nd co-doped systems. The confinement of the 1064 nm emitted radiation in the waveguide structure is the main reason of the high energy transfer probability between Nd3+ and Tm3+ ions. (C) 2008 Elsevier B.V. All rights reserved.