The room temperature infrared to visible upconversion properties of Nd3+ doped Ta2O5 rib waveguides deposited on a silica substrate have been investigated in the 720-900 nm excitation range. Two possible upconversion mechanisms exist at different excitation wavelengths. The main one is due to energy transfer upconversion and results in the population of the (4)G(7/2) level. Radiative relaxations from this level to the I-4(9/2), I-4(11/2) and I-4(13/2) multiplets produce visible emission bands in the green, orange and red regions. Excited state absorption from the F-4(3/2) to the P-2(1/2) state can also occur, giving rise to a blue emission band (P-2(1/2) -> I-4(9/2)). A rate equation analyses supports the proposed mechanisms. (c) 2006 Elsevier B.V. All rights reserved.