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(a) Typical PL spectra at 5 K from bulk ZnO (the dashed line) and an ensamble of tetrapods (the solid line). TES denotes two-electron-satellite transitions of the BX. The peaks denoted as SD are from BX transition occurring at structural defects. (b) Temperature dependent PL spectra measured from the same samples as in (a). The spectra are normalized to the same FX intensity at each temperature and are offset vertically, for clarity. Open squares (circles) denote the maximum positions of the FX (FX-1LO) transitions.
(a) PL spectra from an ensamble of tetrapods measured at 130 K with light excitation powers of 1 mW (the solid line) and 130 mW (the dashed line). (b) RT CL spectra recorded at a facet of a hexagonal leg (denoted as T) with acceleration voltages of 5 keV (the solid line) and 20 keV (the dashed line). The spectra are normalized to the same peak intensity. The indicated positions of the FX, FX-1LO and FX-2LO transitions are based on the reported data in Ref. 1.
(a) An SEM image of a single tetrapod. (b) RT CL spectra measured at the P1, P2, and P3 positions of the tetrapod shown in (a), together with a typical CL spectrum from the reference bulk ZnO. SEM and CL measurements were performed with an electron beam acceleration voltage of 5 keV, to ensure a high spatial resolution .
Calculated refractive index and critical angle of ZnO within the spectral range of the FX transition and its phonon replica. The inset schematically shows light propagation in the tetrapods with round and faceted surfaces.
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