Synthesis and photoluminescent properties of rare earth doped ZnO hierarchical microspheres

Hierarchical ZnO microspheres constructed by mesoporous quasi-single-crystalline ZnO nanosheets were fabricated by pyrolysis of the microspheres of layered hydroxide zinc carbonate, Zn-5(CO3)(2)(OH)(6), which was the hydrothermal precipitate of zinc nitrate and urea. A growth mechanism of Zn-5(CO3)(2)(OH)(6) microspheres was proposed. During the pyrolysis process, single-crystalline Zn-5(CO3)(2)(OH)(6) nanosheets were transformed into mesoporous quasi-single-crystalline ZnO nanosheets. When the samples were doped with trivalent rare earth ion, RE3+ (RE = Pr, Sm, Tb, Ho, Tm), no ZnO --> RE3+ energy transfer was observed. However, the ZnO:Eu3+ sample showed efficient Eu3+ emissions under UV photon excitation (lambda < 365 nm), which is attributed to energy transfer from photon-generated electron-hole pairs to Eu3+ ions in the surface layer of the ZnO nanosheet.