About self-activated orange emission in ZnO
Nominally undoped ZnO ceramics were sintered in air and N₂ flow at 1000 °C. Room temperature photoluminescence (PL) spectra of the samples were measured and analyzed using Gaussian fitting. The self-activated orange PL band peaking at 610 nm was separated by Gaussian deconvolution. Based on the obta...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2015
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irk-123456789-1207232017-06-13T03:03:10Z About self-activated orange emission in ZnO Markevich, I.V. Stara, T.R. Bondarenko, V.O. Nominally undoped ZnO ceramics were sintered in air and N₂ flow at 1000 °C. Room temperature photoluminescence (PL) spectra of the samples were measured and analyzed using Gaussian fitting. The self-activated orange PL band peaking at 610 nm was separated by Gaussian deconvolution. Based on the obtained results compared with some literature data, it has been concluded that the defects responsible for self-activated orange emission in ZnO are zinc vacancies. 2015 Article About self-activated orange emission in ZnO / I.V. Markevich, T.R. Stara, V.O. Bondarenko // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2015. — Т. 18, № 1. — С. 134-137. — Бібліогр.: 17 назв. — англ. 1560-8034 DOI: 10.15407/spqeo18.02.134 PACS 81.05.Dz, 81.05.Je http://dspace.nbuv.gov.ua/handle/123456789/120723 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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Nominally undoped ZnO ceramics were sintered in air and N₂ flow at 1000 °C. Room temperature photoluminescence (PL) spectra of the samples were measured and analyzed using Gaussian fitting. The self-activated orange PL band peaking at 610 nm was separated by Gaussian deconvolution. Based on the obtained results compared with some literature data, it has been concluded that the defects responsible for self-activated orange emission in ZnO are zinc vacancies. |
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Markevich, I.V. Stara, T.R. Bondarenko, V.O. |
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Markevich, I.V. Stara, T.R. Bondarenko, V.O. About self-activated orange emission in ZnO Semiconductor Physics Quantum Electronics & Optoelectronics |
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Markevich, I.V. Stara, T.R. Bondarenko, V.O. |
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Markevich, I.V. |
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About self-activated orange emission in ZnO |
| title_short |
About self-activated orange emission in ZnO |
| title_full |
About self-activated orange emission in ZnO |
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About self-activated orange emission in ZnO |
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About self-activated orange emission in ZnO |
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about self-activated orange emission in zno |
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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2015 |
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About self-activated orange emission in ZnO / I.V. Markevich, T.R. Stara, V.O. Bondarenko // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2015. — Т. 18, № 1. — С. 134-137. — Бібліогр.: 17 назв. — англ. |
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Semiconductor Physics Quantum Electronics & Optoelectronics |
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2025-07-08T18:28:09Z |
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2025-07-08T18:28:09Z |
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1837104407559274496 |
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Semiconductor Physics, Quantum Electronics & Optoelectronics, 2015. V. 18, N 2. P. 134-137.
doi: 10.15407/spqeo18.02.134
© 2015, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
134
PACS 81.05.Dz, 81.05.Je
About self-activated orange emission in ZnO
I.V. Markevich, T.R. Stara, V.O. Bondarenko
V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine,
41, prospect Nauky, 03028 Kyiv, Ukraine;
Phone: +38(044)525-7234; e-mail: stara_t@ukr.net
Abstract. Nominally undoped ZnO ceramics were sintered in air and N2 flow at
1000 °C. Room temperature photoluminescence (PL) spectra of the samples were
measured and analyzed using Gaussian fitting. The self-activated orange PL band
peaking at 610 nm was separated by Gaussian deconvolution. Based on the obtained
results compared with some literature data, it has been concluded that the defects
responsible for self-activated orange emission in ZnO are zinc vacancies.
Keywords: ZnO ceramics, photoluminescence.
Manuscript received 08.12.14; revised version received 17.02.15; accepted for
publication 27.05.15; published online 08.06.15.
1. Introduction
Among numerous applications of zinc oxide in
optoelectronics, development of light emitters is one of
the most important. In fact, it was shown that ZnO single
crystals, ceramics, films and nanostructures with both
intense excitonic UV and bright defect-related visible
emissions could be prepared [1, 2]. Based on careful
study for several decades, origin of the most of UV
bands in ZnO has been established quite unambiguously.
At the same time, the electron-hole transitions
responsible for defect-related emission and the origin of
emitting centers are thus far the matter of discussion.
In undoped ZnO, defect-related emission is known
to exhibit itself as a broad structureless green-orange band
which is stated to consist of several overlapping ones
[1, 2]. However, the number of the components and their
peak positions are still debated through the literature. The
majority of investigators believe that, in undoped ZnO,
two bands are observed in green spectral range, one of
which is related to native defects, while the other is
caused by residual copper impurity [1, 2]. Emission in the
red spectral range which exhibited itself as a shoulder at
the longwave side of orange emission [3, 4] or as a
separate band peaked at about 700 nm [4-6] was also
reported. In yellow-orange spectral region, intense
impurity-related PL bands peaked at 600 and 570 nm
were found to appear due to doping with Li and Na
accordingly [1, 2, 7]. As for self-activated orange
emission, various bands peaked at 570…590 nm [9-12],
610 nm [8, 9, 12], 614 nm [3], 620…630 nm [14, 15] and
640 nm [9, 13, 15] have been reported. This variety is
usually related to the creation of different defects
depending on the preparation method and ambient gas
used. However, one of the reasons of such a discrepancy
can be the fact that peak positions of emission bands are
often determined using Gaussian fitting procedure. At the
same time, Gaussian deconvolution of a broad
structureless band will be rather ambiguous, if the number
and peak positions of components are completely
indeterminate. More reliable results can be obtained when
the positions of some of components are established. In
the present work, photoluminescence (PL) spectra of
undoped ZnO ceramics were analyzed by Gaussian fitting.
Deconvolution was made taking into account the positions
of self-activated and Cu-related green bands determined
experimentally, as well as the position of self-activated
red band taken from the literature.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2015. V. 18, N 2. P. 134-137.
doi: 10.15407/spqeo18.02.134
© 2015, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
135
2. Experimental procedure
The samples were formed of the mixture of ZnO
(99.99% purity) powder with distilled water, dried at
room temperature, sintered for 3 hours at 1000 °C in air,
N2 flow or Zn vapor and cooled with the furnace. In the
latter case, the samples were located in a closed crucible
with metallic zinc scraps and annealed in N2 flow.
Several samples sintered in air were doped with Cu by
adding CuCl2 aqueous solution to the initial mixture.
Obtained ceramics were cut transversally and defect-
related PL spectra in 400…800 nm spectral range were
measured at room temperature from both the surface and
bulk of the samples. Xe-lamp light passing through
grating monochromator was used as the exciting source,
the wavelength 360 nm being chosen for PL excitation.
3. Results and discussion
In undoped samples sintered in air or N2 flow, a broad
green-orange PL band with a noticeable “tail” in the red
spectral region was observed. This emission was well
seen by naked eye, but its intensity was not too high
(Fig. 1, curve 1). The samples sintered in Zn vapor
exhibited very intense and comparatively narrow green
PL band peaked at 515 nm (Fig. 1, curve 3). The green
band with almost the same width, weaker intensity and
peak position at 540 nm was demonstrated by the
samples doped with Cu (Fig. 1, curve 2).
Surface and bulk PL spectra of ceramics sintered in
air and N2 flow are plotted in Figs 2 and 3. One can see
that the curves have different shape and peak positions.
Deconvolution of these curves by Gaussian fitting
testifies, however, that, after separation of two green
bands peaked at 515 and 540 nm as well as the red band
peaked at 700 nm, the residual orange band with peak
position 610 nm manifests itself in all cases. The
contribution of this band to PL spectrum is more
considerable in the samples sintered in N2 flow with
respect to that sintered in air and its intensity is higher at
the surface of the samples with respect to that in the bulk.
400 500 600 700 800 900
0
20
40
60
80
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Fig. 1. PL spectra of ZnO ceramics sintered in air (1) undoped,
(2) doped with Cu and (3) sintered in Zn vapor.
400 500 600 700 800 900
0.0
0.2
0.4
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Fig. 2. PL spectra of undoped ZnO ceramics sintered in air:
bulk (a) and surface (b) of the sample.
400 500 600 700 800 900
0.0
0.2
0.4
0.6
0.8
1.0 a
P
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nm
400 500 600 700 800 900
0.0
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1.0 b
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Fig. 3. PL spectra of undoped ZnO ceramics sintered in N2
flow: bulk (a) and surface (b) of the sample.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2015. V. 18, N 2. P. 134-137.
doi: 10.15407/spqeo18.02.134
© 2015, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
136
The results of Gaussian deconvolution also show
that self-activated green emission is the brightest one
only in the samples sintered in Zn vapor, whereas in
the samples sintered in air or N2 flow its intensity is
rather low and Cu-related band dominates in the green
spectral region.
As literature survey has shown, orange emission in
ZnO crystals, films, powders and nanostructures can be
obtained by the annealing in air or oxygen ambient, and
it is associated with stoichiometric oxygen excess in the
form of oxygen interstitials [1-3, 9, 11-14, 16]. In [8],
however, bright orange PL was obtained by annealing in
vacuum of high-purity ZnO powder that demonstrated
initially intense green PL band. With increasing the
annealing temperature Tann from 500 up to 800 °C,
gradual conversion of green band peaked at 515 nm into
the orange one peaked at 610 nm was observed, a layer
of metallic Zn being formed on the cold end of the silica
tube in which the annealing was performed [8]. Based on
these facts, it was stated that emitting centers responsible
for orange PL were related to zinc vacancies VZn created
due to zinc evaporation [8]. The annealing of the same
powder in air resulted in the appearance of both orange
and red PL bands, which relative intensities were
dependent on Tann [4]. The red band arose at
Tann = 450 °C and enhanced up to Tann = 600 °C as a
separate band, then exhibited itself as a shoulder of
growing orange band and at last hid in the tail of the
latter at Tann 800 °C [4]. When the initial powder was
annealed with Cu or Fe oxide, orange emission
disappeared, and only the intense red PL band was
observed [4]. This effect can be accounted for by the
incorporation of impurity atoms into zinc vacancies,
which is consistent with made in [8] conclusion about
the origin of emitting centers responsible for self-
activated orange PL band in ZnO.
Results obtained in the present work confirmed the
role of zinc vacancies in formation of orange emission in
intentionally undoped zinc oxide. In fact, one can expect
that more intense Zn evaporation will occur, and the
higher density of zinc vacancies will be created: i) on the
surface of the sample than that in its bulk; ii) under
annealing in N2 flow with respect to that in immobile air
due to removal of evaporated Zn from annealing zone by
gas stream. As Figs 2 and 3 show, contribution of the
orange band to PL spectrum is greater on the surface of
the samples than in their bulk and after annealing in N2
flow than in air, indeed. The other evidence of Zn
removal from undoped ceramics under annealing is a
low intensity of self-activated green emission that is
associated with stoihiometric excess of zinc [1, 2, 17].
4. Conclusion
In order to ascertain the position of self-activated
orange emission in zinc oxide, surface and bulk PL
spectra of nominally undoped ZnO ceramics sintered in
air or N2 flow were measured and analyzed using
Gaussian fitting. Gaussian deconvolution was made
using experimentally obtained positions of the self-
activated and Cu-related green PL bands as well as the
self-activated red PL band position taken from the
literature. After such a procedure, the same orange PL
band peaked at 610 nm was separated in all the PL
spectra. The contribution of this band to PL spectra was
found to be greater in the samples sintered in N2 flow
than that in those sintered in air and for the surface of
the samples with respect to their bulk. This effect was
accounted for as caused by evaporation of zinc from
the samples under annealing, which is confirmed by the
weak self-activated green PL band related to stoi-
chiometric Zn excess. The obtained results compared
with some literature data led to the conclusion that
native defects responsible for the self-activated orange
band were zinc vacancies.
Acknowledgement
This research has been financially supported by National
Academy of Sciences of Ukraine (project III-4-11).
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