Optical properties of ZnO aggregates in KBr matrix
Zinc oxide nanocrystals were prepared, using Czochralski method of growth, in KBr matrix during pulling. Good evidences can prove that the quantum confinement effect is the special quality for this nanosystem. As an indication of quantum confinement effect, excellent emissions from band edge have be...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2003
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| Zitieren: | Optical properties of ZnO aggregates in KBr matrix / M. Samah, M. Bouguerra, H. Khelfane // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2003. — Т. 6, № 4. — С. 496-498. — Бібліогр.: 20 назв. — англ. |
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irk-123456789-1180892017-05-29T03:04:51Z Optical properties of ZnO aggregates in KBr matrix Samah, M. Bouguerra, M. Khelfane, H. Zinc oxide nanocrystals were prepared, using Czochralski method of growth, in KBr matrix during pulling. Good evidences can prove that the quantum confinement effect is the special quality for this nanosystem. As an indication of quantum confinement effect, excellent emissions from band edge have been observed in optical absorption spectra and on selective PL ones. CL spectrum exhibits several levels in band gap allotted to different types of impurities in matrix and within ZnO aggregates. 2003 Article Optical properties of ZnO aggregates in KBr matrix / M. Samah, M. Bouguerra, H. Khelfane // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2003. — Т. 6, № 4. — С. 496-498. — Бібліогр.: 20 назв. — англ. 1560-8034 PACS: 81.07.Bc http://dspace.nbuv.gov.ua/handle/123456789/118089 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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Zinc oxide nanocrystals were prepared, using Czochralski method of growth, in KBr matrix during pulling. Good evidences can prove that the quantum confinement effect is the special quality for this nanosystem. As an indication of quantum confinement effect, excellent emissions from band edge have been observed in optical absorption spectra and on selective PL ones. CL spectrum exhibits several levels in band gap allotted to different types of impurities in matrix and within ZnO aggregates. |
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Samah, M. Bouguerra, M. Khelfane, H. |
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Samah, M. Bouguerra, M. Khelfane, H. Optical properties of ZnO aggregates in KBr matrix Semiconductor Physics Quantum Electronics & Optoelectronics |
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Samah, M. Bouguerra, M. Khelfane, H. |
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Samah, M. |
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Optical properties of ZnO aggregates in KBr matrix |
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Optical properties of ZnO aggregates in KBr matrix |
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Optical properties of ZnO aggregates in KBr matrix |
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Optical properties of ZnO aggregates in KBr matrix |
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Optical properties of ZnO aggregates in KBr matrix |
| title_sort |
optical properties of zno aggregates in kbr matrix |
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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2003 |
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Optical properties of ZnO aggregates in KBr matrix / M. Samah, M. Bouguerra, H. Khelfane // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2003. — Т. 6, № 4. — С. 496-498. — Бібліогр.: 20 назв. — англ. |
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Semiconductor Physics Quantum Electronics & Optoelectronics |
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AT samahm opticalpropertiesofznoaggregatesinkbrmatrix AT bouguerram opticalpropertiesofznoaggregatesinkbrmatrix AT khelfaneh opticalpropertiesofznoaggregatesinkbrmatrix |
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2025-07-08T13:20:50Z |
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2025-07-08T13:20:50Z |
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1837085074218024960 |
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Semiconductor Physics, Quantum Electronics & Optoelectronics. 2003. V. 6, N 4. P. 496-498.
© 2003, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine496
PACS: 81.07.Bc
Optical properties of ZnO aggregates in KBr matrix
M. Samah*, M. Bouguerra, H. Khelfane
Département de Physique, Groupe de Physique du solide (GPS), Laboratoire de Physique Théorique (LPT), Université de Bejaia.
*Corresponding author, Département de Physique, Université A/Mira de Bejaia, 06000, Algérie, e-mail: madanisamah@yahoo.fr
Abstract. Zinc oxide nanocrystals were prepared, using Czochralski method of growth, in
KBr matrix during pulling. Good evidences can prove that the quantum confinement effect is
the special quality for this nanosystem. As an indication of quantum confinement effect,
excellent emissions from band edge have been observed in optical absorption spectra and on
selective PL ones. CL spectrum exhibits several levels in band gap allotted to different types of
impurities in matrix and within ZnO aggregates.
Keywords: quantum confinement effect, zinc oxide, nanocrystals, exciton.
Paper received 26.04.03; revised manuscript received 11.10.03; accepted for publication 11.12.03.
1. Introduction
Semiconductor nanocrystallites are of great interest be-
cause of their unique optical properties and potential
applications for optoelectronics [1,2]. In recent years, a
great deal of work has been carried out focusing a spe-
cial emphasis on the nanocomposites of quantum dots
embedded in some wide-band-gap dielectric matrices, for
the advantage of stabilizing dots and being adapted to
device manufacturing process [3,4]. One can list manu-
facturing nanoparticles encapsulated in carbon nano-
cage structures used as cluster protection, nano-ball bear-
ings, nano-optical�magnetic devices, catalyst and bio-
technology [5�7]. Insulating sheets such as alkali halide
matrixes are required for optical devices since these hosts
are optically isotropic and transparent in a large visible
field. Over the past decade, the optical properties of ZnO
QDs have been extensively investigated [8,9]. It can be
used in field-emission displays with development of the
fat panel display industry and various optical devices,
and the luminescence efficiency of ZnO is required to be
substantially improved.
In this paper we report optical studies of ZnO QDs
embedded in KBr matrix. Samples are obtained using
Czochralski method. During pulling process, with trans-
lating and rotating rates equal to 1cm/houre and one lap
by minute, respectively, we dope the melted solution of
KBr, in a temperature around 900°C, with a commercial
ZnO fine powder. It is important to note that the property
of this powder seems to be sufficiently good. A PL spec-
trum done on this ZnO powder proves this assertion. Then,
samples in the form of plate discs with thickness averag-
ing 1mm are subjects for optical absorption measurements
at ambient temperature, photoluminescence at the tem-
perature of liquid helium and finally cathodoluminescnece
studies. CL experiments have been done at an ambient
temperature, where a fine electronic beam are used hav-
ing an energy equal to 5eV. The ambient temperature is
only done because this device is, unfortunately, not
adapted to low temperatures ones.
2. Optical absorption measurements
Absorption measurements were carried out using a
Shimadzu spectrophotometer at ambient temperature.
Fig. 1 exhibits a series of picks corresponding to a vari-
ous size distributions. The first transition corresponding
to the absorption edge is located at 4.3816 eV, with a
displacement of 1.07eV compared to the absorption edge
of bulk ZnO crystal which is about 3.307eV.
Such displacements were observed in crystallites of
ZnO produced by oxidation of zinc metal where authors
measured displacement of 0.1 eV for a diameter varia-
tion of 610 Å to 200 Å [10]. In addition, C.L.Yang and
al.[11] measured the absorption of ZnO crystallites about
31 Å average size and they find a threshold absorption
around 3.974 eV. A blue shift averaging 0.667 eV com-
pared to the bulk crystal.
We evaluate the mean size of crystallites by applying
the Kayanuma formula [12] defined in the case of a strong
confinement by:
M. Samah et al.: Optical properties of ZnO aggregates in KBr matrix
497SQO, 6(4), 2003
22
4
2
22
2
248.0
786.1
2 ε
µ
εµ
π
h
h e
RR
EE gex −−+=
Where Eg is the band gap of bulk semiconductor; R is
the mean radius of QDs; ε is the dielectric constant;
he
he
mm
mm
+
= *µ reduced mass of the electron (me) and the
hole (mh); e is the electronic charge and h is the Planck
constant, devided by 2π.
With mh = 0.59me, e = 7.8 [13] and the band gap
value is estimated to be equal to 3.307 eV in ambient
temperature [14], we find a mean size of ZnO particles
equal to 26Å.
3. Cathodoluminescence spectra
In the UV part, the spectra presents a very solved band,
whose center is located at 4.312 eV bellow 69 meV from
edge of absorption of the sample which is positioned at
4.381 eV. This shift value corresponds to the energy of
phonon replica in crystallites which equal, in bulk ZnO,
to 72 meV. This prevalence of the transitions coupled to
optical phonons is observed in the spectrum of photolu-
minescence of ZnO crystallites in KBr matrix [15]. Based
on arguments mentioned above, this band corresponds to
the recombination of excitons, free or/and bound slightly
on impurities with phonon replica. The broadening of
this band is due to several factors; coupling with phonons
and the size distribution. In addition, the interaction of
the acoustic phonons with exciton increase with the re-
duction of the crystallites size whereas the interaction
with optical phonons remains almost insensitive with the
reduction of the size [16,17] due to the relaxation of
rules selection in crystallites caused by the deterioration
of the translation symmetry required in bulk crystal.
The appearance of emission band of free excitons is a
very rare experimental fact particularly in crystallites
within strong confinement due to the fact that for small
crystallite dimensions, the surface-volume ratio being
large and induce strong densities of levels in the band
gap. Consequently, it induces radiative and non-radiative
recombinations via these levels with densities depending
on crystallite-matrix interface quality and the chemical
nature of elements which can diffuse in crystallite through
its surface.
On the weak side of energies, appears a second band
relatively strongly intense, located at 3.53 eV. It is allot-
ted to recombinations via levels in the gap introduced by
surface defects or by impurities which would have dif-
fused from matrix within ZnO crystallites. One also ob-
serves a third less intense band located at 3.1147 eV as a
tail. This contribution is identified in KBr as emission
levels of Cu+ ions in KBr matrix [18].
Fig. 2 exhibits also a fourth band, strong intense, with
the position of 2,769 eV. This peak is due to the
recombinations via the levels introduced by the impuri-
ties Cu into ZnO. Into the green area of the spectrum, one
observes a broad and very intense band whose center lo-
cates at 2.420 eV. This green band is observed around
3.4 eV in bulk ZnO crystals worked out by vapor phase
deposition [19].
4. Photoluminescence spectra
To consolidate cathodoluminescence results, we carried
out a photoluminescence characterization at tempera-
ture of 1.6 K with a power of 10 mW, using the excitation
2.0 2.5 3.0 3.5 4.0 4.5 5.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.38 eV
Energy, eV
A
b
so
r
b
a
n
c
e
,
u
.a
.
Fig. 1. Absorption spectra of ZnO crystallites embedded in KBr
matrix in ambient temperature.
Fig. 2. Cathodoluminescence spectra of ZnO particles embed-
ded in KBr matrix at ambient temperature.
2.0 2.5 3.0 3.5 4.0 4.5 5.0
0
2
4
6
8
2 .4 5 eV
2 .7 1 eV
3 .5 3 eV
4 .3 1 eV
E n erg y, eV
C
L
, a
rb
.u
n.
498
SQO, 6(4), 2003
M. Samah et al.: Optical properties of ZnO aggregates in KBr matrix
of laser based Argon plasma emitting a wavelength of
351nm. This measurement is likely used to confirm the
presence of various size distributions of crystallites by a
selective excitation.
The spectrum obtained is represented on fig. 3. It ex-
hibits a peak of intensity of width at half height equal to
5 meV roughly. This effect demonstrates the low dispar-
ity of the size distribution of crystallites. The band is
located at 3.367 eV. Y. Harada and al.[15] obtained an
emission band of ZnO crystallites averaging 200 Å size
in a matrix similar to the position 3.363 eV. Referring to
this paper, we allot this band to bound excitons emission
related to defects located on the surface of crystallites.
Compared with the value of the energy position of the
emission band of bulk crystal (3.360), we find a shift to-
wards great energies of 7 meV, due probably to quantum
confinement effect. This weak shift involves the situation
of weak confinement defined within the framework of the
approximation of the effective mass. The mean size of
crystallites corresponds to 157 Å, with the effective masses
of electron and hole equal to 0.28m0 and 0.59m 0 respec-
tively [20].
The difference between QDs sizes measured by opti-
cal and PL measurements can be explained by the fact
that PL one is a selective experiments where a photonic
beam, at a precise energy was used contrary to optical
ones. Then in PL measurements only a part of size distri-
bution will response to excitation and all particles or
aggregates having a size less then this mean size of dis-
tribution will not appears leading, consequently to an
apparent mean radius greatest.
5. Conclusions
In conclusion, with Czochralskï growth device, we can
manufacture ZnO nanocrystals embedded in alkali-halide
matrix with different size distributions. Optical results
confirm the presence of theses particles within host ma-
trix with several size distributions. Our results can be
described in terms of the quantum confinement effect. In
both PL and optical absorption spectrum, we observe tran-
sitions involving excitonic and impurities levels inside
bandgap. Therefore, this surface defaults can improve
the emission property of ZnO, which is very important
for the developing high quality nano-devices.
References
1. A.P. Alivisatos // Science 271 (1996) 933.
2. L.E. Brus // Appl. Phys. A 53 (1991) 465.
3. S. Jursenas, G. Kurilcik, M. Strumskis, A. Zukauskas // Appl.
Phys. Lett. 71 (1997) 2502.
4. J. Zhou, L. Li, Z. Gui, S. Buddhudu, Y. Zhou // Appl. Phys.
Lett. 76 (2000) 1540.
5. C.N.R. Rao, R. Sechadri, A. Govindaraj, R. Sen // Mater.Sci.
Eng. R15 (1995) 209.
6. J. Sloan, J. Cook, M.L.H. Green, J.L. Hutchinson, R.Tenne
// J. Mater. Chem. 7 (1997) 1089.
7. T. Oku, K. Niihara, K. Suganuma // J. Mater. Chem. 8 (1998)
1323.
8. M. Liu, A.H. Kitai, P. Mascher // J. Lumin. 54 (1992) 35.
9. M. Haps, H. Weller, A. Henglein // J. Phys. Chem. 92 (1988)
482.
10. S.Cho, J.Ma, Y.Kim, Y.Sun, G.K.L.Wong, J.B.Ketterson //
Appl. Phys. Lett. 75, No.18, (1999)
11. C.L.Yang, J.N. Wang, W.K. Ge, L.Guo, S.H.Yang,
D.Z. Shen // J.App.Phys 90, No09, (2001).
12. Y. Kayanuma, H. Momiji // Phys. Rev. B 1990, 41, 10261.
13. Landolt et Bronstein: Intrinsic Properties of group IV ele-
ments, III-V,II-VI and I-VII compounds, Madelung and
M. Shulz, Springer Verlag, Berlin (1982).
14. Y.Chen, N.T. Tuan, Y. Segawa, H.Ko, S.Honh, T.Yao. // J.
App. Phys; 78, No 11,(2001).
15. Fu.Z W, Dow J.D, Bull. Amer.Phys.Soc. 34,33 -557 (1986).
16. CRC: Handbook of Chemistry and Physics , CRC Press,
Cleavland, 67th Edition, F-160 (1986-87).
17. P. Wright, Quantum confinement effects in semiconductor clus-
ters, Churchill College, Cambridge (2000).
18. G. Fishman, I. Mihalcescu, R. Romestain // Phys.Rev. B.48,
(1993).
19. A. Davidov, Théorie du solide. Edition Mir. Moskow.(1976).
20. M. Nirmal, L. Brus // Acc. Chem. Res., 32,407-414. (1999).
Fig. 3. Photoluminescence spectra of both bulk and nanosized
ZnO at the temperature of liquid helium.
3.30 3.32 3.34 3.36 3.38 3.40
0
5000
10000
15000
20000
25000
30000
35000
40000
3 .3 6 eV
7 m eV
K B r (Z nO )
B u lk C ry sta l
E n erg y, eV
P
L
, a
rb
.u
n.
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