Re-doped Oxide Photoluminescence Study

Information is increasingly indispensible for people in the 21th century since the development and advances in science and technology. The communication and interconnect with photon as the carrier of information will become the next generation of communication scheme. The 1.54μm emission from the intra-4f transition of Er3+ ions is an important telecommunication wavelength which has attracted wide attention in the application of optic-electric integration technology. The future studies will be dedicated on improving the luminescence efficiency of Er3+ doped materials and devices, and understanding the energy transfer (ET) mechanism. Si nanocrystal (Si-NC) which has a very wide broadband absorption in the visible region and an absorption cross section ten thousand times more than Er3+ is considered as efficient broadband sensitizers for Er3+. The photoluminescence (PL) efficiency of Er Si codoped films is markedly improved compared to the that of Er doped films. Due to their emission bands at 1.47 and 1.6-2.1μm of Tm and 1.54μm of Er, Er-Tm-codoped materials are of great interests because of the continuous increasing of optical information traffic demand for full utilization of the 1.4- 1.7μm low-loss band of silica-based optical fibers. According to the above background, this thesis mainly focus on the optical properties of Er-Si codoped Al2O3 thin films, Er-Tm-Si codoped Al2O3 thin films, Er-Si codoped ZnO thin films and Er-Tm-Si codoped ZnO thin films.The main contents in my thesis are as follows:1. Er and Si codoped Al2O3 filmsAlternately Er and Si codoped Al2O3 multilayer films, consisting of alternate Er-Si-codoped Al2O3 (Er:Si:Al2O3) and Si-doped Al2O3 (Si:Al2O3) layers, have been synthesized by co-sputtering from separated Er, Si, and Al2O3 targets. The dependence of Er3+ related PL properties on annealing temperatures over 700 to 1100℃was studied. The maximum PL intensity of Er3+, about 10 times higher than that of the bilayer films, was obtained from the multilayer films annealed at 950℃. The enhancement of Er3+ PL intensity is attributed to the ET from the Si-NCs in the Si:Al2O3 layers to the neighboring Er3+ ions in the Er:Si:Al2O3 layers. The PL intensity exhibits a nonmonotonic temperature dependence:with increasing temperature, the integrated intensity almost remains constant from 14 to 50 K, then reaches maximum at 225K, and slightly increases again at higher temperatures. Meanwhile, the PL integrated intensity at room temperature is about 30% higher than that at 14K. 2. Er and Tm codoped Al2O3 filmsEr-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 PL spectra was studied. A flat and broad emission band was achieved in the 1.4-1.7μm 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 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.3. Er and Si codoped ZnO filmsThe near-infrared emission from Er and Si codoped ZnO films, synthesized by cosputtering from separated Er, Si, and ZnO targets, has been investigated. By designing the multilayer film structure, controlling the Er concentration, and optimizing the annealing condition, the intensity of Er3+ related 1.54μm PL, originating from the transition of Er3+ 4I13/2→>4I15/2, can be optimized. It is shown that the maximum intensity of Er3+ related 1.54μm PL is obtained when the Si:ZnO/Er:Si:ZnO/Si:ZnO sandwiched multilayer films and the alternate Er:ZnO/Si:ZnO multilayer films were annealed at 1000℃and 950℃, respectively. The Er3+ related 1.54μm PL intensity of the multilayer films, which can be attributed to the presence of the Si-NCs that could act as sensitizers of Er3+ ions, were higher than that of the Er:ZnO bilayer films. The PL of the sandwiched multilayer films and the alternate multilayer films were measured under different temperature (14-300K). The sandwiched multilayer films and the alternate multilayer films exhibit a nonmonotonic temperature dependence, different from that of Er-doped ZnO previously reported. The ET processes between Er ions and Si-NCs and temperature behavior have been discussed.4. Er Tm codoped ZnO filmsEr Tm codoped ZnO monolayer films have been synthesized by co-sputtering from separated Er, Tm, and ZnO targets. The dependence of Er3+, Tm3+related PL properties on the annealing temperatures and concentration ratio of Tm3+ to Er3+ was studied. A flat and broad emission band was achieved. The ET processes between Er ions and Tm ions have been discussed.5. Er Tm and Si codoped ZnO films Er Tm Si codoped ZnO bilayer films, consisting of one Er-Si-codoped ZnO (Er:Si:ZnO) layer and one Tm-Si-codoped ZnO (Tm:Si:ZnO) layer as well as Er Tm codoped ZnO bilayer films, consisting of one Er doped ZnO (Er:ZnO) layer and one Tm doped ZnO (Tm: ZnO) layer, have been synthesized by co-sputtering from separated Er, Tm, Si, and ZnO targets. The dependence of Er3+, Tm3+ related PL properties on annealing temperatures was studied. A flat and broad emission bands with full width at half maximum of 494 and 478 nm were achieved, both in the Er-Tm and Er-Tm-Si codoped ZnO bilayer films annealed at 900℃. And the observed 1533 and 1800 nm emission bands were attributed to the transitions of Er3+:4I13/2→4I15/2 and Tm3+:3F4→3H6, respectively. The Tm and Er related PL intensities at 1800nm and 1533nm were both enhanced when codoped with Si-NC as broadband sensitizer due to a strong coupling between quantum confined excitons in Si-NCs and Er,Tm. It was noticed that the PL intensity of Er3+ was lower and the PL intensity of Tm3+ was stronger when the annealing temperature was above 900℃. It might be due to the formation of crystallized Er2SiO5 silicate by annealing above 900℃observed from TEM, XPS and Raman experiments, which decrease the density of Si-NCs and thus the absorption of light.