Defect-mediated energy transfer in ZnO thin films doped with rare-earth ions

The rare-earth (RE) (Eu, Er, Nd) doped ZnO thin films were fabricated by a cost-effective chemical solution deposition method. The emission properties of ZnO:RE films were investigated under different excitation conditions, where the RE ions were excited either through direct pumping into the 4f energy levels of RE ions or through indirect excitation by energy transfer from the host material. It is demonstrated that under both excitation methods, the films showed strong emission from the RE ions at room temperature, which confirms the hypothesis that the RE ions can be effectively excited by the host material. Moreover, the influence of RE doping on the development of the crystalline structure of the ZnO thin film was studied. Only a small amount of REs was incorporated into the ZnO grains; most of the REs remained segregated at the grain boundaries, forming a thin oxide shell that strongly suppresses the sintering of the grains and reduces their size. •The possibility of indirect excitation of RE ions was demonstrated•The emission properties of the thin films were tailored in a wide range from UV to IR•The influence of RE doping on the formation of ZnO sol-gel thin films was discussed