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

Er–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 1640nm, 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 1640nm (I1640) to that at 1540nm (I1540) decreases and that at 1640nm (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 230nm 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 150nm. 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.