Electronic Supplementary Material
Vertically aligned ZnO-ZnGa2O4 core-shell
nanowires: from synthesis to optical
properties
Miao Zhong·Yanbo Li·Takero Tokizono·Ichiro Yamada·Maojun Zheng·Jean-Jacques
Delaunay
Miao Zhong·Yanbo Li·Takero Tokizono·Ichiro Yamada·Jean-Jacques Delaunay
Department of Mechanical Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku,
Tokyo 113-8656, Japan
Maojun Zheng
Laboratory of Condensed Matter Spectroscopy and Opto-Electronic Physics, Department of
Physics, Shanghai Jiao Tong University, Shanghai 200240, People’s Republic of China
Miao Zhong() email: miaozhong@lelab.t.u-tokyo.ac.jp
Jean-Jacques Delaunay() email: jean@mech.t.u-tokyo.ac.jp
Information about ELECTRONIC SUPPLEMENTARY MATERIAL
SM-1) Graphs showing [F(R)*hv]1/2 versus hv calculated from the measured UV-VIS diffuse
reflectance spectra
SM-2) Cathodoluminescence properties of the vertically aligned ZnO nanowires and the ZnOZnGa2O4 core-shell nanowires
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SM-1) Graphs showing [F(R)*hv]1/2 versus hv calculated from the measured UV-VIS
diffuse reflectance spectra
The curves of [F(R)*hv]1/2 versus hv calculated from the measured UV-VIS diffuse reflectance
spectra of the ZnO nanowires (NWs) and the ZnO-ZnGa2O4 (ZnO-ZGO) NWs are shown in Fig.
SM-1. Two near-band-gap values of Eg = ~3.2 eV and Eg = ~4.2 eV were obtained from the ZnOZGO core-shell NW samples. The smaller value of ~3.2 eV is related to the near-band-gap
absorption of ZnO cores and the larger value of 4.2 eV is from the near-band-gap absorption of
ZGO shells (Irie et al. 2011).
Fig. SM-1 [F(R)*hv]1/2 versus hv of the fabricated samples
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SM-2) Cathodoluminescence properties of the vertically aligned ZnO nanowires and the
ZnO-ZGO core-shell nanowires
The room-temperature cathodoluminescence (CL) properties of the vertically aligned ZnO NWs
and the ZnO-ZGO core-shell NWs were investigated. In addition, CL property of a-plane sapphire
substrate was also measured for comparison. Fig. SM-2a shows the CL spectrum of the vertically
aligned ZnO NWs sample. Only one sharp emission peak centered at ~382 nm (corresponding to a
near-band-gap energy of ~3.25 eV) was observed. This is considered to be the near-band-gap
emission of ZnO. Fig. SM-2b shows the CL spectrum of the vertically aligned ZnO-ZGO coreshell NWs. A broad emission ranging from 300 nm to 800 nm was observed. Peak fitting with
Gaussian curves (Fig. SM-3c) shows that the broad emission band is composed of four bands
centered at 355 nm, 415 nm, 520 nm, 680 nm. The ~355 nm emission is considered to be from the
Ga-O transition at distorted octahedral sites due to the existence of oxygen vacancies in ZGO. Also,
the ~680 nm emission is always accompanying the ~355 nm emission as the transition from
oxygen vacancy state Vo· to O2- in ZGO (Park et al. 2003; Wu et al. 2005). In addition, the other
two emissions at ~415nm and ~520 nm are related to the octahedrally coordinated Ga3+ site in
ZGO. The ZGO material is an AB2O4 type spinel structure, which consists of an fcc sublattice of O
with trivalent cations (Ga3+) occupying one half of the octahedral interstices. In the octahedral
complexes of ZGO, the five 3d energy levels of Ga3+ split into two different energy levels of T2g
and Eg as a result of Ga3+ ligand-field splitting in the octahedral sites. The ~415 nm emission is
related to the transition from T 2g of Ga3+ to O2- site (Irie et al. 2011; Park et al. 2003). The emission
at ~520 nm (corresponding to ~2.38 eV) is related to the energy transition from Eg of Ga3+ to O2site (Hsieh et al. 1994).
Fig. SM-2 a CL spectrum of the vertically aligned ZnO nanowires. b CL spectrum of the vertically aligned
ZnO-ZnGa2O4 core-shell nanowires. c Peak fitting result of the CL emission band from 300 nm to 800 nm
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References
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