Self-purification construction of interstitial O in the neighbor of Eu ³⁺ ions to act as energy transfer bridge

We develop a strategy to investigate bridge role of O-related defects in the neighbor of Eu³⁺ in energy transfer (ET). By solvothermal reactions and following annealing process, Eu³⁺ doped ZnO nanocrystal is synthesized. After low-temperature annealing, Eu³⁺ ions occupy substituted sites of ZnO. High temperature annealing results in self-purification process - the separation of Eu³⁺ ions from ZnO lattice and generation of Eu₂O₃ precipitate phases. However, in this case, the proportion of individual Eu₂O₃ particles is extremely low if they are separated. The precipitate phases have paralleled edges and parallel to (011̄1̄) plane of ZnO. By self-purification separation, these O-terminated planes are easy to couple with Eu³⁺ ions, and form Eu³⁺ trap state. In order to maintain hexa-coordinate of Eu³⁺ ions, many O-related vacancies and interstitial defects are generated in the interface of ZnO/Eu₂O ₃, among which interstitial O (O_i) in the neighbor of Eu³⁺ ions plays an important role in balance charge and ET. Thus, it is not strange to observe enhanced luminescence peak in self-purified samples.