Optical properties of lanthanide doped semiconductor thin films

In this thesis it is aimed to investigate the structural and optical properties of pure ZnO and La, Dy doped (2, 5, 10, 20, 50, 80, 100%) ZnO thin films on quartz substrates at different molarities (0,2M, 0,5M, 1M) by using spin coating technique. After the introduction chapter the fundamental principles related to the work is given in Chapter 2. In Chapter 3 the experimental results for the pure ZnO samples annealed at 500 ve 1000 oC for 30min and 6 hours at 0,5 M level are given. From the experimental results the 1000 oC annealing is chosen for the following experiment as it gives the best literature agreement. In Chapter 4 dysprosium is chosen as heavy lanthanide element to be the dopant whereas lanthanum is chosen as the lighter one (Chapter 5). For both elements various dopant levels are used and the thin films are produced. XRD, SEM, EDS and UV-vis spectra are given in related chapters. In Chapter 6 experimental results for the powder form of the lanthanum doped ZnO samples are given. In Chapter 7 the experimental results are summarized and a future work is proposed. From the experimental results it has been found that the all pure and doped ZnO thin films display the willemite phase if they were annealed at 1000 oC for 6 hours. As the annealing temperature is increased then the main absorption peak at 370 nm seems to shift to 195 nm which is a sign that the willemite phase is present (which is apparent in XRD and EDS result). In the ZnO samples doped with dysprosium, it has been found that the absorption band for pure dysprosium is situated at 195 nm and the energy gap is about 1,5 eV whereas the energy bands for the ZnO doped ones stay about 5,9 eV. For the lanthanum doping 0,5M level is chosen. From the XRD and SEM results, various crystal phases are produced (La(OH)3, La2O3, LaOOH, La2Si2O7). It has been found that the increase in doping level shifts the absorption band towards 225 nm. The increase in doping level lowers the engergy band about 0,3 eV. In powder lanthanum doped zinc oxide samples only La(OH)3 and ZnO crystal structures are observed. In the fluoresence spectra the emission peaks at 505, 468 and 380 nm for ZnO, La:ZnO and La(OH)3 are observed, respectively. Keywords: Sol-gel, spin coating, lanthanides, ZnO, thin film