Abstract
Er3+-doped ZnO nanocrystals with hexagonal wurtzite structure were prepared by addition of LiOH to Zn−O−Er precursors in ethanol. The well-known green hot band from the 2H11/2 → 4I15/2 transition in the 520 − 540 nm region and Stokes emissions were investigated. And the blue, green, and red upconversion emissions were observed from the annealed samples under near-infrared light (808 nm) excitation. The upconversion emission intensity ratio of the hypersensitive 2H11/ 2 → 4I15/2 to 4S3/2 → 4I15/2 transition (I530nm/I550nm) in the sample annealed at 400 °C is different from that in the sample annealed at 700 °C, which is attributed to the variation of the local structure around Er3+ ions. The upconversion emission spectra and the pump power dependence of the luminescence intensities are provided to explain the upconversion mechanisms. These results confirm that visible upconversion emissions of Er3+ in the ZnO nanocrystals are mainly produced via two-photon excited-state absorption (ESA) and energy transfer...
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