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6 pages, 5 figures, 1 table.-- PACS: 78.55.Hx;\ud78.66.Nk; 81.15.Fg; 42.70.HjEr–Tm codoped a-Al2O3 thin films prepared by alternate pulsed laser deposition show a broad photoluminescence band with two characteristic peaks at 1540 and at 1640  nm, respectively, related to Er3+ and Tm3+ emissions. Two series of films have been prepared. For the first series, the Tm concentration [Tm] has been increased while keeping constant the Er concentration [Er]. The results show that the photoluminescence intensity at 1640  nm (I1640) to that at 1540  nm (I1540) decreases and that at 1640  nm (I1640) increases, i.e., the (I1640/I1540) ratio increases as [Tm] is increased. For [Tm]/[Er]=3, a fairly flat emission spectrum (I1640/I1540~1) with a full width at half maximum of 230  nm is achieved. For the second series both [Tm] and [Er] are increased while keeping the [Tm]/[Er] ratio constant. The I1640/I1540 ratio tends to be constant with a full width at half maximum of 150  nm. The lifetime values decrease in all cases as [Tm] increases. The evolution of the I1640/I1540 and lifetimes as a function of [Tm] as well as the analysis of the latter considering Er as a donor and Tm as an acceptor evidence that there is an efficient energy transfer from Er3+ to Tm3+. These results suggest that enhanced performance with a flat broadband emission useful for planar integrated devices is achievable by further dopant engineering in the nanoscale.This work was supported by CICYT (Spain) under\udMAT2003-01490, MAT2005-06508-C02-01, and TEC2006-\ud04538-MIC projects. One of the authors (Z.X.) acknowledges\uda fellowship from MEC (SB2002-0013, Spain).Peer reviewe

Broadband emission in Er–Tm codoped Al2O3 films: The role of energy transfer from Er to Tm