Temperature-dependent photoluminescence spectra of Er–Tm-codoped Al2O3 thin film

Er–Tm-codoped Al2O3 thin films with different Tm to Er concentration ratios were synthesized by cosputtering from separated Er, Tm, Si, and Al2O3 targets. The temperature dependence of photoluminescence (PL) spectra was studied. A flat and broad emission band was achieved in the 1.4–1.7 μm and the observed 1470, 1533 and 1800 nm emission bands were attributed to the transitions of Tm3+: 3H4 → 3F4, Er3+: 4I13/2 → 4I15/2 and Tm3+: 3F4 → 3H6, respectively. The temperature dependence is rather complicated. With increasing measuring temperature, the peak intensity related to Er3+ ions increases by a factor of five, while the Tm3+ PL intensity at 1800 nm decreases by one order of magnitude. This phenomenon is attributed to a complicated energy transfer (ET) processes involving both Er3+ and Tm3+ and increase of phonon-assisted ET rate with temperature as well. It should be helpful to fully understand ET processes between Er and Tm and achieve flat and broad emission band at different operating temperatures.