Broadband emission in Er-Tm codoped Al2 O3 films: The role of energy transfer from Er to Tm

Abstract

Er-Tm codoped a- Al2 O3 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. © 2007 American Institute of Physics.