transition from a shallow state 50 meV below the conduction band
(CB) to a deep trap level 0.8 eV above the valence band (VB) and
electron transfer from CB to oxygen vacancy (VO) [19], respectively.
The peak at 526 nm is assigned to a non-radiative electron capture
from the CB by a singly charged oxygen vacancy ðVþO
Þ recombines
with a photoexcited hole in the VB [19,24]. The peak at 552 nm
is due to the transition from interstitial Zn (Zni) to oxygen vacancy
(VO) [25]. Furthermore, it will be noted that intensity ratio of ultraviolet
band to the emission peaks at 505, 526 and 552 nm for the
Mg-doped ZnO nanowire-on-spherical shell at 850 C is much
smaller than that of the Zn1xMgxO nanomaterials at 750, 900
and 1000 C, as shown in Fig. 6, implying that the amount of
defects related to VO in the Zn1xMgxO nanowire-on-spherical shell
at 850 C is larger than that of the Zn1xMgxO nanomaterials at
750, 900 and 1000 C, which is due to the large amount of
Zn1xMgxO nanowires with the smallest diameter of 15 nm on
the spherical shell at 850 C, as shown in Fig. 2(c)–(e), resulting
transition from a shallow state 50 meV below the conduction band
(CB) to a deep trap level 0.8 eV above the valence band (VB) and
electron transfer from CB to oxygen vacancy (VO) [19], respectively.
The peak at 526 nm is assigned to a non-radiative electron capture
from the CB by a singly charged oxygen vacancy ðVþO
Þ recombines
with a photoexcited hole in the VB [19,24]. The peak at 552 nm
is due to the transition from interstitial Zn (Zni) to oxygen vacancy
(VO) [25]. Furthermore, it will be noted that intensity ratio of ultraviolet
band to the emission peaks at 505, 526 and 552 nm for the
Mg-doped ZnO nanowire-on-spherical shell at 850 C is much
smaller than that of the Zn1xMgxO nanomaterials at 750, 900
and 1000 C, as shown in Fig. 6, implying that the amount of
defects related to VO in the Zn1xMgxO nanowire-on-spherical shell
at 850 C is larger than that of the Zn1xMgxO nanomaterials at
750, 900 and 1000 C, which is due to the large amount of
Zn1xMgxO nanowires with the smallest diameter of 15 nm on
the spherical shell at 850 C, as shown in Fig. 2(c)–(e), resulting
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