Properties of ZnO:Mn Nanoparticles Immobilized in Polyethylene Matrix
ZnO:Mn nanoparticles (of 3—5 nm) immobilized in polyethylene matrix are synthesized. The samples with different content of the manganese (5%, 10%, and 20% of initial solution of Mn and Zn precursors) are investigated by means of ESR, PL, and XRD. Thus, the behaviour of the Mn impurities in ZnO is st...
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Інститут металофізики ім. Г.В. Курдюмова НАН України
2010
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| Cite this: | Properties of ZnO:Mn Nanoparticles Immobilized in Polyethylene Matrix / G.V. Lashkarev, P.V. Demydiuk, G.Yu. Yurkov, O.I. Dmitriev, O.I. Bykov, L.I. Klochkov, Yu.P. Pyratinskiy, E.I. Slynko, A.G. Khandozhko, O.V. Popkov, N.A. Taratanov // Наносистеми, наноматеріали, нанотехнології: Зб. наук. пр. — К.: РВВ ІМФ, 2010. — Т. 8, № 3. — С. 663-673. — Бібліогр.: 13 назв. — англ. |
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Lashkarev, G.V. Demydiuk, P.V. Yurkov, G.Yu. Dmitriev, O.I. Bykov, O.I. Klochkov, L.I. Pyratinskiy, Yu.P. Slynko, E.I. Khandozhko, A.G. Popkov, O.V. Taratanov, N.A. 2015-01-05T15:03:09Z 2015-01-05T15:03:09Z 2010 Properties of ZnO:Mn Nanoparticles Immobilized in Polyethylene Matrix / G.V. Lashkarev, P.V. Demydiuk, G.Yu. Yurkov, O.I. Dmitriev, O.I. Bykov, L.I. Klochkov, Yu.P. Pyratinskiy, E.I. Slynko, A.G. Khandozhko, O.V. Popkov, N.A. Taratanov // Наносистеми, наноматеріали, нанотехнології: Зб. наук. пр. — К.: РВВ ІМФ, 2010. — Т. 8, № 3. — С. 663-673. — Бібліогр.: 13 назв. — англ. 1816-5230 PACS numbers: 61.72.Hh, 76.30.-v, 78.55.Et, 78.67.Bf, 78.67.Tf, 82.35.Np, 82.80.Ej https://nasplib.isofts.kiev.ua/handle/123456789/73137 ZnO:Mn nanoparticles (of 3—5 nm) immobilized in polyethylene matrix are synthesized. The samples with different content of the manganese (5%, 10%, and 20% of initial solution of Mn and Zn precursors) are investigated by means of ESR, PL, and XRD. Thus, the behaviour of the Mn impurities in ZnO is studied. As revealed, the most of the manganese in ZnO forms the second undetermined phase MnOx or substitute zinc in cation sublattice at the surface layer of the nanoparticles. The value of constant of hyperfine structure of Mn is higher than an expected one (|A| = 89.5⋅10−4 cm−1 that is significantly differ from the constant of hyperfine structure of Mn incorporated into ZnO single crystal (76⋅10−4 cm−1)). Photoluminescence measurements reveal wide band of emission in green—red region (500—600 nm), with different position of the maximum depending on the manganese content. Одержано наночастинки ZnO:Mn розмірами 3—5 нм. За допомогою метод ЕПР, рентґеноструктурної аналізи та фотолюмінесценції досліджувалася структура цих наночастинок з різним вмістом мангану: 5%, 10% та 20% масової частки по відношенню до вихідного розчину прекурсорів. Було показано, що переважна кількість мангану формує другу фазу та заміщує цинок у катіонній підґратниці в поверхневому прошарку цих наночастинок. Значення надтонкої структури в ЕПР-дослідженнях виявилися більшими за очікуване (|A| = 89,5⋅10−4 см−1, що значно відрізняється від довідникових даних константи надтонкої структури для мангану в кристалічній ґратниці ZnO – 76⋅10−4 см−1). Фотолюмінісцентні міряння виявили широку лінію випромінення в зелено-червоній області спектру 500—600 нм з різним положенням максимуму (залежно від типу зразка). Получены наночастицы Zno:Mn размерами 3—5 нм. С помощью методов ЭПР, рентгеноструктурного анализа и фотолюминесценции исследовалась структура этих наночастиц с разным содержимым марганца: 5%, 10% и 20% массовой части по отношению к исходному раствору прекурсоров. Было показано, что преобладающее количество марганца формирует вторую фазу и замещает цинк в катионной подрешетке в поверхностной прослойке этих наночастиц. Значение сверхтонкой структуры в ЭПР-исследованиях оказались больше ожидаемых (|A| = 89,5⋅10−4 см−1, что значительно отличается от справочных данных константы сверхтонкой структуры для марганца в кристаллической решетке ZnO – 76⋅10−4 см−1). Фотолюминесцентные измерения выявили широкую линию излучения в зелено-красной области спектра 500—600 нм с разным положением максимума (в зависимости от типа образца). This work was financed by the Russian Foundation for Basic Research (grant nos. 10-08-90421-Укр and 10-03-00466-a) and the grant of the President of the Russian Federation MD-5551.2010.3. en Інститут металофізики ім. Г.В. Курдюмова НАН України Наносистеми, наноматеріали, нанотехнології Properties of ZnO:Mn Nanoparticles Immobilized in Polyethylene Matrix Article published earlier |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| title |
Properties of ZnO:Mn Nanoparticles Immobilized in Polyethylene Matrix |
| spellingShingle |
Properties of ZnO:Mn Nanoparticles Immobilized in Polyethylene Matrix Lashkarev, G.V. Demydiuk, P.V. Yurkov, G.Yu. Dmitriev, O.I. Bykov, O.I. Klochkov, L.I. Pyratinskiy, Yu.P. Slynko, E.I. Khandozhko, A.G. Popkov, O.V. Taratanov, N.A. |
| title_short |
Properties of ZnO:Mn Nanoparticles Immobilized in Polyethylene Matrix |
| title_full |
Properties of ZnO:Mn Nanoparticles Immobilized in Polyethylene Matrix |
| title_fullStr |
Properties of ZnO:Mn Nanoparticles Immobilized in Polyethylene Matrix |
| title_full_unstemmed |
Properties of ZnO:Mn Nanoparticles Immobilized in Polyethylene Matrix |
| title_sort |
properties of zno:mn nanoparticles immobilized in polyethylene matrix |
| author |
Lashkarev, G.V. Demydiuk, P.V. Yurkov, G.Yu. Dmitriev, O.I. Bykov, O.I. Klochkov, L.I. Pyratinskiy, Yu.P. Slynko, E.I. Khandozhko, A.G. Popkov, O.V. Taratanov, N.A. |
| author_facet |
Lashkarev, G.V. Demydiuk, P.V. Yurkov, G.Yu. Dmitriev, O.I. Bykov, O.I. Klochkov, L.I. Pyratinskiy, Yu.P. Slynko, E.I. Khandozhko, A.G. Popkov, O.V. Taratanov, N.A. |
| publishDate |
2010 |
| language |
English |
| container_title |
Наносистеми, наноматеріали, нанотехнології |
| publisher |
Інститут металофізики ім. Г.В. Курдюмова НАН України |
| format |
Article |
| description |
ZnO:Mn nanoparticles (of 3—5 nm) immobilized in polyethylene matrix are synthesized. The samples with different content of the manganese (5%, 10%, and 20% of initial solution of Mn and Zn precursors) are investigated by means of ESR, PL, and XRD. Thus, the behaviour of the Mn impurities in ZnO is studied. As revealed, the most of the manganese in ZnO forms the second undetermined phase MnOx or substitute zinc in cation sublattice at the surface layer of the nanoparticles. The value of constant of hyperfine structure of Mn is higher than an expected one (|A| = 89.5⋅10−4 cm−1
that is significantly differ from the constant of hyperfine structure of Mn incorporated
into ZnO single crystal (76⋅10−4 cm−1)). Photoluminescence measurements reveal wide band of emission in green—red region (500—600 nm), with different position of the maximum depending on the manganese content.
Одержано наночастинки ZnO:Mn розмірами 3—5 нм. За допомогою метод ЕПР, рентґеноструктурної аналізи та фотолюмінесценції досліджувалася структура цих наночастинок з різним вмістом мангану: 5%, 10% та 20% масової частки по відношенню до вихідного розчину прекурсорів. Було показано, що переважна кількість мангану формує другу фазу та заміщує цинок у катіонній підґратниці в поверхневому прошарку цих наночастинок. Значення надтонкої структури в ЕПР-дослідженнях виявилися більшими за очікуване (|A| = 89,5⋅10−4 см−1, що значно відрізняється від довідникових даних константи надтонкої структури для мангану в кристалічній ґратниці ZnO – 76⋅10−4 см−1). Фотолюмінісцентні міряння виявили широку лінію випромінення в зелено-червоній області спектру 500—600 нм з різним положенням максимуму (залежно від типу зразка).
Получены наночастицы Zno:Mn размерами 3—5 нм. С помощью методов ЭПР, рентгеноструктурного анализа и фотолюминесценции исследовалась структура этих наночастиц с разным содержимым марганца: 5%, 10% и 20% массовой части по отношению к исходному раствору прекурсоров. Было показано, что преобладающее количество марганца формирует вторую фазу и замещает цинк в катионной подрешетке в поверхностной прослойке этих наночастиц. Значение сверхтонкой структуры в ЭПР-исследованиях оказались больше ожидаемых (|A| = 89,5⋅10−4 см−1, что значительно отличается от справочных данных константы сверхтонкой структуры для марганца в кристаллической решетке ZnO – 76⋅10−4
см−1). Фотолюминесцентные измерения выявили широкую линию излучения в зелено-красной области спектра 500—600 нм с разным положением максимума (в
зависимости от типа образца).
|
| issn |
1816-5230 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/73137 |
| citation_txt |
Properties of ZnO:Mn Nanoparticles Immobilized in Polyethylene Matrix / G.V. Lashkarev, P.V. Demydiuk, G.Yu. Yurkov, O.I. Dmitriev, O.I. Bykov, L.I. Klochkov, Yu.P. Pyratinskiy, E.I. Slynko, A.G. Khandozhko, O.V. Popkov, N.A. Taratanov // Наносистеми, наноматеріали, нанотехнології: Зб. наук. пр. — К.: РВВ ІМФ, 2010. — Т. 8, № 3. — С. 663-673. — Бібліогр.: 13 назв. — англ. |
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663
PACS numbers: 61.72.Hh, 76.30.-v,78.55.Et,78.67.Bf,78.67.Tf,82.35.Np, 82.80.Ej
Properties of ZnO:Mn Nanoparticles Immobilized
in Polyethylene Matrix
G. V. Lashkarev, P. V. Demydiuk, G. Yu. Yurkov*, O. I. Dmitriev,
O. I. Bykov, L. I. Klochkov, Yu. P. Pyratinskiy**, E. I. Slynko,
A. G. Khandozhko***, O. V. Popkov*, N. A. Taratanov*
I. M. Frantsevych Institute for Problems of Materials Science, N.A.S. of Ukraine,
3, Krzhyzhanovsky Str.,
03142 Kyyiv, Ukraine
*A. A. Baikov Institute of Metallurgy and Materials Science of RAS,
49, Leninsky Prospekt,
119991 Moscow, Russia
**Institute of Physics, N.A.S. of Ukraine,
46, Prospekt Nauky,
03650 Kyyiv, Ukraine
***Yuriy Fedkovych Chernivtsi National University,
2, Kotsyubynsky Str.,
58012 Chernivtsi, Ukraine
ZnO:Mn nanoparticles (of 3—5 nm) immobilized in polyethylene matrix are
synthesized. The samples with different content of the manganese (5%,
10%, and 20% of initial solution of Mn and Zn precursors) are investigated
by means of ESR, PL, and XRD. Thus, the behaviour of the Mn impurities in
ZnO is studied. As revealed, the most of the manganese in ZnO forms the se-
cond undetermined phase MnOx or substitute zinc in cation sublattice at the
surface layer of the nanoparticles. The value of constant of hyperfine struc-
ture of Mn is higher than an expected one (|A| = 89.5⋅10
−4
cm
−1
that is signifi-
cantly differ from the constant of hyperfine structure of Mn incorporated
into ZnO single crystal (76⋅10
−4
cm
−1)). Photoluminescence measurements re-
veal wide band of emission in green—red region (500—600 nm), with different
position of the maximum depending on the manganese content.
Одержано наночастинки ZnO:Mn розмірами 3—5 нм. За допомогою метод
ЕПР, рентґеноструктурної аналізи та фотолюмінесценції досліджувалася
структура цих наночастинок з різним вмістом мангану: 5%, 10% та 20%
масової частки по відношенню до вихідного розчину прекурсорів. Було по-
казано, що переважна кількість мангану формує другу фазу та заміщує ци-
нок у катіонній підґратниці в поверхневому прошарку цих наночастинок.
Значення надтонкої структури в ЕПР-дослідженнях виявилися більшими
Наносистеми, наноматеріали, нанотехнології
Nanosystems, Nanomaterials, Nanotechnologies
2010, т. 8, № 3, сс. 663—673
© 2010 ІМФ (Інститут металофізики
ім. Г. В. Курдюмова НАН України)
Надруковано в Україні.
Фотокопіювання дозволено
тільки відповідно до ліцензії
664 G. V. LASHKAREV, P. V. DEMYDIUK, G. Yu. YURKOV et al.
за очікуване (|A| = 89,5⋅10
−4
см
−1, що значно відрізняється від довідникових
даних константи надтонкої структури для мангану в кристалічній ґратниці
ZnO – 76⋅10
−4
см
−1). Фотолюмінісцентні міряння виявили широку лінію
випромінення в зелено-червоній області спектру 500—600 нм з різним по-
ложенням максимуму (залежно від типу зразка).
Получены наночастицы Zno:Mn размерами 3—5 нм. С помощью методов
ЭПР, рентгеноструктурного анализа и фотолюминесценции исследовалась
структура этих наночастиц с разным содержимым марганца: 5%, 10% и
20% массовой части по отношению к исходному раствору прекурсоров.
Было показано, что преобладающее количество марганца формирует вто-
рую фазу и замещает цинк в катионной подрешетке в поверхностной про-
слойке этих наночастиц. Значение сверхтонкой структуры в ЭПР-
исследованиях оказались больше ожидаемых (|A| = 89,5⋅10
−4
см
−1, что зна-
чительно отличается от справочных данных константы сверхтонкой струк-
туры для марганца в кристаллической решетке ZnO – 76⋅10
−4
см
−1). Фото-
люминесцентные измерения выявили широкую линию излучения в зелено-
красной области спектра 500—600 нм с разным положением максимума (в
зависимости от типа образца).
Key words: nanoparticles, ZnO, Mn, photoluminescence, luminescence, ESR.
(Received 10 June, 2010)
1. INTRODUCTION
Onrush of nanotechnology give rise to reconsideration of functional capaci-
ty of well-known materials. In particular, many papers have been dedicated
to the research on nanosized systems that are based on zinc oxide.
ZnO is a direct wide-gap (3.37 eV) semiconductor with extremely
high exciton binding energy (60 meV). In addition, it is nonexpensive,
nontoxic and resistive to the high-energy radiation [1]. These features
should create prerequisites for ZnO to be applied in crystalline phos-
phors as work medium for luminescent centres. Quantitative charac-
teristics of such optical system are altered with transition to nanoscale
as a result of profound influence of confinement effects and surface
states. The former is based on effect of surface restriction that in turn
acts as a potential barrier with endless walls.
As a result, confinement effect leads to increasing of band gap, bind-
ing energy of exciton and overlapping of electron—hole wave functions.
Each mentioned effect makes its positive contribution to quantum ef-
ficiency of the crystalline phosphors what consists in increasing of os-
cillator strength of band-to-band transition, lifetime of excitons and
probability of their interaction with luminescent centres [2].
In order to study such a system, ZnO:Mn2+
nanoparticles (NP) im-
mobilized in polyethylene matrix (hereafter samples) were synthe-
sized. Manganese is expected to be centre of yellow—green lumines-
PROPERTIES OF NANOPARTICLES ZnO:Mn IMMOBILIZED IN POLYETHYLENE 665
cence (∼ 580 nm) due to
4T1(G)—6A1 transition in crystal field of hexag-
onal symmetry [3] (e.g., ZnS). Moreover, orbital and spin quantum
numbers of Mn2+
in ground state are LQ0 and S = 5/2. Therefore it is
also proper element for probing of local surroundings in the host by
means of ESR (Mn2+
has six lines of hyperfine structure). That is very
important upon studying of doped nanoparticles.
As for the synthesis process, the mixture of precursors containing
Zn2+
and Mn2+
ions was introduced into the solution of polyethylene in
hydrocarbon oil. Thus, separated particles were protected from agglom-
eration and atmospheric impact. It was also observed that behaviour of
the NP had been correlated by option of zinc and manganese precursors.
Therefore, influence of mixtures of precursors Zn(NO3)2 with Mn(NO3)2
and Zn(CH3COO)2 with Mn(CH3COO)2 on the NP properties was studied.
2. EXPERIMENT
2.1. Synthesis
Investigated NPs were synthesized in compliance with the methodolo-
gy that was described elsewhere [4, 5]. A water solution of Zn and Mn
precursors with the concentration varying from 0.05 to 0.06 mol/l was
prepared. LDPE (low-density polyethylene) was dissolved in mineral
oil in argon atmosphere using intensive stirring and heating. A solu-
tion of precursors was being introduced dropwise into the reaction
mass for 24 hours at 250°C. Throughout a synthesis, gaseous products
of the reaction and residual water were removed from the reaction ves-
sel by an argon stream. Afterwards, a reaction mass (polymer-
nanoparticles—oil) was stirred at a proper temperature for 40 minutes
with the purpose to complete thermal decomposition of the initial pre-
cursors, then cooled down to room temperature and placed into a
Soxhlet extractor where residual oil was completely removed.
Two groups of samples were prepared. Zn(NO3)2 with Mn(NO3)2 and
Zn(CH3COO)2 with Mn(CH3COO)2 were used as the zinc and manganese
precursors for preparation of the first and second groups of samples,
respectively. Three types of samples containing 5%, 10%, and 20% wt.
of Mn in the initial solution of precursors were studied in both groups
(see Table 1).
TABLE 1. List of synthesized samples.
Precursor
I group II group
Zn(NO3)2 + Mn(NO3)2 Zn(CH3COO)2 + Mn(CH3COO)2
Samples #291 #292 #293 #294 #295 #296
Content of manganese
(% Mn)
5% 10% 20% 5% 10% 20%
666 G. V. LASHKAREV, P. V. DEMYDIUK, G. Yu. YURKOV et al.
2.2. Measurement Equipment
X-ray diffraction measurements (XRD) were performed with modified
computer-controlled diffractometer DRON-3M equipped with X-ray
tube BSV-28, cupper anode (λ = 1.54 μkm) and nickel filter. Data pro-
cessing was performed according to the database of standard XRD
spectrum value ASTM (American Society of Testing Materials).
The ESR experiments were performed at X band ∼ 10 GHz at
room temperature and T = 77 K.
Photoluminescence (PL) spectra were excited by nitrogen laser
(337 nm) and measured at room temperature.
3. RESULTS AND DISCUSSION
Six samples were synthesized (see Table 1). The average size of NP was
estimated using TEM instrument (Fig. 1) and assigned to be ∼ 3—5 nm.
Basing on minimum energy principle for surface strain and TEM image
(Fig. 1), the NPs are suggested to have sphere-like shape.
The XRD pattern exhibited a wurtzite structure of ZnO (Fig. 2), for
both groups of samples. Two samples with the highest content of man-
ganese (20%) from every of the groups (#3 and #6) and one sample #1
(5% Mn) were chosen to compare with one another. As it can be seen
from Fig. 2, they have particularly identical XRD spectra that are
characterized by six lines of ZnO hexagonal structure and weak uni-
dentified lines with 2Θ = 38—49°. According to the ASTM, these un-
known lines can be assigned to be compounds of manganese with oxy-
gen. Thus, we could hardly give unambiguous answer what these phas-
es are, so hereinafter they are referred as MnOx (Manganese—Oxygen).
A comparative analysis of XRD spectra for #1, #3, and #6 was per-
formed. To reveal difference between these samples, two parameters for
Fig. 1. TEM image of ZnO:Mn nanoparticles. The average size of the NP is
3—5 nm.
PROPERTIES OF NANOPARTICLES ZnO:Mn IMMOBILIZED IN POLYETHYLENE 667
each spectrum were estimated. The first parameter is an interplanar
spacing of crystalline structures calculated by Bragg’s equation (Fig. 3):
2sin
d
λ=
θ
. (1)
Second parameter is a relative size of coherent scattering region
(CSR), calculated on the basis of Debye—Scherrer equation (Table 2):
λΛ ≅
⋅ θFWHM cos
. (2)
This parameter in contrast to the first one depends on FWHM of the
XRD spectra lines and is used to estimate comparative characteristic
(not absolute) of coherent scattering region of the nanoparticles.
Fig. 2. XRD spectrum for samples #1, #3, #6.
Fig. 3. Comparative values of interplanar spacing of samples #1,#3, #6
and corresponding ASTM value for three different directions.
668 G. V. LASHKAREV, P. V. DEMYDIUK, G. Yu. YURKOV et al.
FWHM have been calculated as full width at half maximum on Gauss
curve that approximate the XRD spectrum lines.
In both equations (1) and (2), the notations θ and λ stand for the
scattering angle and wavelength of 1.54 μm, respectively.
One can see (Fig. 3) that interplanar spacing of crystalline lattice of
ZnO nanoparticles in sample #1 (5% Mn) are slightly shifted to the
lower values in comparison with the ones for #3, #6, and ASTM. Such
behaviour can be explained if we take into account an effect of surface
tension on periods of the crystalline structure. For nanoparticles
where surface-to-volume ratio is high, crystalline structure is strongly
affected by surface tension that results in decreasing of the periods of
the crystalline lattice. In addition, the dimension of the coherent scat-
tering region (Table 2) for these three samples has similar dependence,
except for the (002) case. Thus, basing on these facts, we can assume
that average size of NPs ZnO:Mn #1 is smaller than NP #3 and #6.
3.1. ESR Measurements
Due to half-filled d shell (3d5) with spin S = 5/2, angular momentum
L = 0 and nucleus spin I = 5/2, the resonance of an isolated Mn2+
ion
located substitutionally on a Zn site in hexagonal ZnO is described by
the spin Hamiltonian:
Б ij i j ij i j
H g HS A S I D S S= μ + + . (3)
At low concentration (< 0.1%) of Mn in doped ZnO single crystals,
an isotropic Zeeman (the first term in Eq. (3)) and hyperfine interac-
tion (the second term in Eq. (3)) were observed (g = 2.0016, |A| = 76⋅10
−4
cm
−1) together with an axial fine structure splitting (D = 216.9⋅10
−4
cm
−1) [6].
In the case of randomly oriented nanocrystals, anisotropic contribu-
tions are washed out and one can expect a six line spectrum with a hy-
perfine splitting (hereafter, HFS) of about 76⋅10
−4
cm
−1
from isolated
Mn2+
incorporated in the ZnO single crystal.
ESR measurements were used to investigate behaviour of Mn2+
in
the host material ZnO. ESR spectrums for all six samples are given in
TABLE 2. Relative value of coherent scattering region of three samples
#1, #3, and #6 calculated by Eq. (2).
Coherent Scattering Region (Å) ZnO (100) ZnO (002) ZnO (101)
#1 2.07 2.46 2.02
#3 2.25 2.25 2.16
#6 2.49 3.30 2.49
PROPERTIES OF NANOPARTICLES ZnO:Mn IMMOBILIZED IN POLYETHYLENE 669
Fig. 5 and Fig. 6. According to these measurements, three spectrum
patterns can be highlighted.
S1–broad background line (g = 1.999) that inhere for all ESR spec-
trums (dash-dotted lines in Fig. 5) is related to the exchange and di-
a b
Fig. 4. PL spectra for samples (a) #1—#3 and (b) #4—#6.
Fig. 5. ESR spectrum for samples ##292—296 at T = 300 K.
670 G. V. LASHKAREV, P. V. DEMYDIUK, G. Yu. YURKOV et al.
pole—dipole interaction of Mn between nearby magnetic centres. Thus,
this line can be attributed to the unknown phase MnOx (Fig. 2).
S2–six lined hyperfine structure with constant of HFS (CHFS)
A = 94⋅10
−4
cm
−1
and g = 2.001 are related to the isolated Mn in ZnO lattice.
In hexagonal ZnO lattice, manganese ions, which substitute Zn2+
in
the single crystal, undergo the effect of tetrahedral electrostatic field
of the surroundings. In such a case, the CHFS of Mn2+
is 76⋅10
−4
cm
−1,
in contrast to observed HFS of Mn in ZnO nanoparticles with consider-
ably higher CHFS (A = 94⋅10
−4
cm
−1).
Similar increasing of CHFS for manganese in hexagonal lattice has
been observed earlier in nanopowders CdS, ZnS [7—9], and ZnO [10] syn-
thesized in colloidal solution. Such increasing in these works related to
formation of cubic Zn(OH)2 crystalline phase on the surface of the nano-
particles. In this structure, Mn2+
can substitute zinc ions in octahedral
surrounding of hydroxide groups. However, in our work the synthesis
was held under such conditions that exclude formation of any com-
pounds except ZnO and manganese oxides. Thus, explanation of such
Fig. 6. ESR spectrum for #291 at T = 77 K.
TABLE 3. Comparative table of constants of hyperfine structure for Mn in
local octahedral and tetrahedral surroundings.
Octahedral surrounding Tetrahedral surrounding
А(10
−3 cm
−1) А(10
−3 cm
−1)
ZnF2 9.6 ZnО 7.4
NaCl 8.2 CdS 6.48
KCl 8.86 CdTe 5.51
NaF 9.1 Al2O3 7.5
AgCl 8.1 ZnS 6.4
SrCl2 9.7
PROPERTIES OF NANOPARTICLES ZnO:Mn IMMOBILIZED IN POLYETHYLENE 671
value of CHFS can be related to the disturbances of tetrahedral Zn sub-
lattice at the surface layer of ZnO and formation of octahedral sur-
rounding around manganese ions.
This conclusion is based on the fact that CHFS of Mn in tetrahedral
surrounding has lower value than in the case of octahedral one (Table
3). As it can be seen from this table, CHFS A = 94⋅10
−4
cm
−1
lay in the
range of the values for octahedral local environment.
S3–narrow intensive line with g = 2.001. The one is absent on
(Fig.5) but emerge on the ESR spectrum for #1 at T = 77 K (Fig. 6).
This line is obviously attributed to electrons localized on the surface
defect centres [11].
These three spectra S1, S2 and S3 are more or less detected for inves-
tigated samples ##1—6. In particular, S1 ESR signal is well observed
for whole number of Samples that indicate the second phase formation
(compound with Mn component) for all of them. In addition, detailed
investigations have shown that S3 signal is present in all ESR spectra
too, but strongly overlapped with wide S1 signals. Sextet structure S2
is weakly resolved for members of second group (##4—6), but nearly
absent for samples #1 and #2. The difference between these two
groups lays in type of Zn and Mn precursors that are used in chemical
synthesis reaction. From this point of view manganese, which is easily
oxidized metal, differently acts in nitride and acetate solutions [3]. In
the second group of precursors, the Mn oxidation is more inhibited
than in nitrides solution. That leads to increasing of second phase for-
mation in the last medium in comparison with the first one. Therefore,
one can observe more intensive six lined structure for #4 and #5 than
for #1 and #2.
3.2. PL Spectrum
The PL spectrum of bulk ZnO is characterized by two lines. The first
one lies in UV region of 350—370 nm and is attributed to the near band-
gap exciton recombination PL. The second one, wide band line, lies in
green-red region of the visible spectrum (500—600 nm) and caused by
intrinsic point defects within zinc oxide that lead to appearing of deep
and shallow defects levels in the band gap [12, 13].
At the transition to nanosized objects, the PL spectrum becomes
more ambiguous than in the bulk case. Since influence of surface, layer
states in such entities are significantly enhanced with decreasing of
their size. Thus, it is expected to observe additional lines in the spec-
trum of nano-ZnO attributed to the surface layer. The lines can be var-
ied depending on the shape of the nanoparticles.
In Figure 4, spectra of nanoparticles ZnO doped with Mn are shown.
All samples are characterized by UV component (∼ 370 nm) that is poor
resolved on the UV band of nitrogen laser background (this line is not
672 G. V. LASHKAREV, P. V. DEMYDIUK, G. Yu. YURKOV et al.
shown on the pictures). In addition, wide band in visible region of the
spectrum (500—600 nm) is observed too. The significant widening of
this line is clearly attributed to wide distribution of the emission spec-
trum of the individual nanoparticle within any of the samples. Charac-
teristic dimensions of these nanoparticles are decreased enough that
their shape and dimensions have significant influence on the optical
transitions.
For the samples #1—2, the intensity of the lines in visible region lies
at the noise level. In these nanoparticles, the radiationless transition is
dominated. However, as for the samples with higher manganese con-
tent, there is intensive line of emission centred at the 590 nm (Fig. 4,
a). Similar picture is observed for Samples #4—6, the samples with the
highest manganese content show the most intensive line in the visible
region (Fig. 4, b).
There is not enough information to conclude definitely about origin
of these lines, but some assumption can be made. Whereas the band
line strongly overlaps region of defect emission that attributed to the
native point defects in ZnO [12], we can assume that one of the sources
of the green emission is these point defects.
It is also shown by ESR measurement that revealed point defects in
the samples. Even in the samples #1—2 there are low resolved picks in
530 nm. Other sources of the emission are assumed the surface states,
which depend on manganese content at the surface layer of the nano-
particles. Absence of the isolate manganese in the samples #1—2 is also
confirmed by ESR measurements. For other samples where isolate
manganese was found by ESR, the PL spectra have been observed.
Therefore, we can assume that manganese acts as surface agent that in
some way activate emission in visible region of the spectrum.
The role of the manganese as surfactant agent, but not luminescence
centre is proved by different position of the PL lines for the Samples
with different manganese contents. However, luminescence of the
manganese (580 nm) could not be eliminated.
4. SUMMARY
In this work, nanoparticles ZnO doped with Mn immobilized in polyeth-
ylene matrix with average size 3—5 nm were synthesized.
Two different localizations of Mn have been revealed. The first one is
localization at the surface layer substituting zinc in cation sublattice
(|A| = 89.5⋅10
−4
cm
−1
that differs from constant of hyperfine structure for
ZnO (76⋅10
−4
cm
−1)). The second one is thought to form undefined phase
MnOx with unresolved hyperfine structure and with factor g = 2.001.
Under nitrogen laser excitation (337 nm), visible emission in the range
500—600 nm has been observed that is attributed to defect surface states
that are predominant in the nanoparticles.
PROPERTIES OF NANOPARTICLES ZnO:Mn IMMOBILIZED IN POLYETHYLENE 673
ACKNOWLEDGEMENT
This work was financed by the Russian Foundation for Basic Research
(grant nos. 10-08-90421-Укр and 10-03-00466-a) and the grant of the
President of the Russian Federation MD-5551.2010.3.
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