Optical and photoluminescent properties of Ag/Al₂O₃ nanocomposite films obtained by pulsed laser deposition
The method of pulsed laser deposition in vacuum from forward and backward particle flows from an erosion torch was used to prepare silver films and Ag/Al₂O₃ nanocomposite films. Measured were transmission and time-resolved photoluminescence spectra. The authors studied the influence of conditions...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2009
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irk-123456789-1188802017-06-01T03:06:12Z Optical and photoluminescent properties of Ag/Al₂O₃ nanocomposite films obtained by pulsed laser deposition Manoilov, E.G. The method of pulsed laser deposition in vacuum from forward and backward particle flows from an erosion torch was used to prepare silver films and Ag/Al₂O₃ nanocomposite films. Measured were transmission and time-resolved photoluminescence spectra. The authors studied the influence of conditions for film formation on their optical and photoluminescent properties. For the first time, there observed was luminescence with quantum energy 1.6 eV and relaxation times up to several microseconds. 2009 Article Optical and photoluminescent properties of Ag/Al₂O₃ nanocomposite films obtained by pulsed laser deposition / E.G. Manoilov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2009. — Т. 12, № 3. — С. 298-301. — Бібліогр.: 14 назв. — англ. 1560-8034 PACS 78.67.-n, 78.55.-m http://dspace.nbuv.gov.ua/handle/123456789/118880 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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The method of pulsed laser deposition in vacuum from forward and backward
particle flows from an erosion torch was used to prepare silver films and Ag/Al₂O₃
nanocomposite films. Measured were transmission and time-resolved photoluminescence
spectra. The authors studied the influence of conditions for film formation on their
optical and photoluminescent properties. For the first time, there observed was
luminescence with quantum energy 1.6 eV and relaxation times up to several
microseconds. |
| format |
Article |
| author |
Manoilov, E.G. |
| spellingShingle |
Manoilov, E.G. Optical and photoluminescent properties of Ag/Al₂O₃ nanocomposite films obtained by pulsed laser deposition Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Manoilov, E.G. |
| author_sort |
Manoilov, E.G. |
| title |
Optical and photoluminescent properties of Ag/Al₂O₃ nanocomposite films obtained by pulsed laser deposition |
| title_short |
Optical and photoluminescent properties of Ag/Al₂O₃ nanocomposite films obtained by pulsed laser deposition |
| title_full |
Optical and photoluminescent properties of Ag/Al₂O₃ nanocomposite films obtained by pulsed laser deposition |
| title_fullStr |
Optical and photoluminescent properties of Ag/Al₂O₃ nanocomposite films obtained by pulsed laser deposition |
| title_full_unstemmed |
Optical and photoluminescent properties of Ag/Al₂O₃ nanocomposite films obtained by pulsed laser deposition |
| title_sort |
optical and photoluminescent properties of ag/al₂o₃ nanocomposite films obtained by pulsed laser deposition |
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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2009 |
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http://dspace.nbuv.gov.ua/handle/123456789/118880 |
| citation_txt |
Optical and photoluminescent properties of Ag/Al₂O₃ nanocomposite films obtained by pulsed laser deposition / E.G. Manoilov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2009. — Т. 12, № 3. — С. 298-301. — Бібліогр.: 14 назв. — англ. |
| series |
Semiconductor Physics Quantum Electronics & Optoelectronics |
| work_keys_str_mv |
AT manoiloveg opticalandphotoluminescentpropertiesofagal2o3nanocompositefilmsobtainedbypulsedlaserdeposition |
| first_indexed |
2025-07-08T14:49:43Z |
| last_indexed |
2025-07-08T14:49:43Z |
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1837090665431826432 |
| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2009. V. 12, N 3. P. 298-301.
© 2009, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
298
PACS 78.67.-n, 78.55.-m
Optical and photoluminescent properties of Ag/Al2O3 nanocomposite
films obtained by pulsed laser deposition
E.G. Manoilov
V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine
41, prospect Nauky, 03028 Kyiv, Ukraine
E -mail: dept_5@isp.kiev.ua
Abstract. The method of pulsed laser deposition in vacuum from forward and backward
particle flows from an erosion torch was used to prepare silver films and Ag/Al2O3
nanocomposite films. Measured were transmission and time-resolved photoluminescence
spectra. The authors studied the influence of conditions for film formation on their
optical and photoluminescent properties. For the first time, there observed was
luminescence with quantum energy 1.6 eV and relaxation times up to several
microseconds.
Keywords: nanocomposite film, metal in oxide matrix, time-resolved photolumines-
cence, local surface plasmon resonance, pulsed laser deposition.
Manuscript received 25.05.09; accepted for publication 14.05.09; published online 30.06.09.
1. Introduction
Silver nanoparticles (NP), clusters and composite
nanostructures based on them demonstrate local surface
plasmon resonance (LSPR) [1-3], luminescence in the
visible spectral range [2-8], photochromism [2], which
opens wide possibilities to study distinctive optical
properties of nanoparticles as compared to those in bulk
objects as well as to use them in various applications
from biosensors to informatics and storage devices.
Excitation of LSPR results in creation of strong local
fields around the nanoparticles, which causes
enhancement of Raman scattering, luminescence, optical
non-linearity, etc. To observe luminescence enhanced by
plasmons, Ag NP are more preferable than Au NP due to
lower contribution of interband transitions to the
imaginary part of dielectric function [9-11].
Up to date, obtained were silver nanoparticles and
clusters, bands of local (interface) surface plasmon
absorption of which cover a wide spectral range from
visible up to near infra-red regions. Using the methods
of electron lithography, arrays of silver nanostructures
with dimensions of hundreds nanometers were formed
on SiO2 substrate [9]. Ag NP and clusters were reduced
from silver oxides by using ultra-violet irradiation or
thermal processing [4-6]. 2D Ag NP arrays with
dimensions about 10 nm in amorphous silicon were
deposited using electron-beam evaporation [9].
Developed also were the ways to prepare metal-
dielectric composites, the so-called nanocermets, by ion
implantation, sol-gel technologies, magnetron sputtering
of targets, etc. Prepared were glasses with Ag NP [3, 9],
also formed were Ag NP in TiO2 matrix [2, 7, 8]. There
are only single works where the method of pulsed laser
deposition (PLD) was used to prepare thin
nanocomposite films containing Ag nanocrystals
embedded into Al2O3 matrix [12, 13]. In [12], the authors
used the method of spectroscopic ellipsometry to
determine the effective complex refraction index versus
the silver concentration in Al2O3 film. Considered in [13]
was desorption of xenon enhanced by plasmons of Ag
NP. As to our knowledge, optical and photoluminescent
properties of Ag/Al2O3 nanocomposite films remain
unstudied.
The nature of luminescence in Ag NP, clusters and
composite nanostructures based on them is the matter of
intensive discussions. A prevalent part of works is
devoted to fluorescence of Ag nanoclusters, the minor
one – to photoluminescence (PL) of Ag NP and
nanostructures. In [4], the fluorescence spectrum of
photoactivated AgO films contains five separate features
(at 548, 594, 641, 673 and 725 nm) that are related with
emission of Agn clusters (n = 2 – 8 atoms). In composite
films Ag/TiO2, emission with the wavelength close to
552 nm was explained by interband transitions in Ag2O
[2]. In alkaline glasses, containing Ag NP formed by
thermal processing, present in PL spectra are both the
band at 2.23 eV (ascribed to the interband transition in
Ag2O) and red bands with the energies lying below 2 eV
and related with presence of small Ag NP [3]. But up to
date, there is no information upon the luminescence
relaxation times longer than several nanoseconds.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2009. V. 12, N 3. P. 298-301.
© 2009, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
299
There exist wide opportunities to control
photoluminescent and optical properties of silver NP as
compared to those of gold, since their sizes, shape and
surrounding can be controlled by formation of Ag2O,
AgO oxides with a set ratio between silver atoms and
ions [2, 3, 6, 14]. The aim of this work is to prepare
Ag/Al2O3 nanocomposite films by using the LPD
method in vacuum, to study the influence of the silver
concentration in target on extinction and time-resolved
photoluminescence spectra as well as to ascertain
interrelation between optical and photoluminescent
properties of these films.
2. Experimental
Silver films and Ag/Al2O3 nanocomposite ones were
prepared by the PLD method in vacuum chamber under
the argon pressure 10 – 20 Pa. Deposition was carried
out onto silicon and glass substrates. The silver films
were prepared using forward and backward (high energy
and low energy, respectively) particle flows from the
erosion torch. Ag/Al2O3 nanocomposite films were
deposited using the backward flow. The target consisted
of small pieces of Al and Ag. The Ag concentration in
the film was set by the ratio of areas of these pieces. The
target was scanned by the YAG:Nd3+ laser beam
(wavelength 1.06 μm, pulse energy 0.2 J, pulse duration
10 ns, and repetition frequency 25 Hz). When depositing
the films from the forward flow, the substrates were
located normally to the torch axis at the distance 20 –
25 mm from the target. When using the backward flow,
the substrates were located in the target plane. In the
vicinity of the torch axis, the deposited nanoparticles
were larger, far of the axis these were smaller. The
thickness profile of the films was wedge-like within the
range 500 down to 50 nm. The films prepared using the
forward flow had no pores, rough, with grain dimensions
up to hundreds nanometers, while those prepared using
the backward flow were porous, smooth, with particle
dimensions not exceeding tens nanometers.
Time-resolved PL spectra were measured within
the energy range 1.4 – 3.2 eV with excitation by
emission of a nitrogen laser (wavelength 337 nm, pulse
duration 8 ns) and stroboscopic registration of signals in
the photon-counting mode. The minimum strobe
duration was 250 ns. Transmission spectra of the films
were recorded using the spectrophotometer СФ-26
within the wavelength range 340 – 1000 nm.
3. Results and discussion
Shown in Fig. 1 are the transmission spectra of silver
films (a) and those of Ag/Al2O3 nanocomposite
films (b). It can be seen from Fig. 1a that all the silver
films demonstrate clearly pronounced local surface
plasmon absorption within the range 500 – 600 nm. At
the same time, LSPR is extremely weak and practically
is not observed in the nanocomposite films (Fig. 1b,
curves 1 – 3) and can be seen only for the high (> 90 %)
silver concentration in the target (Fig. 1b, curve 4).
Plasmon absorption in the nanocomposite films is
slightly increased when exposing them to ambient air
(compare curves 3 and 3´ in Fig. 1b). The transmission
minimum of the nanocomposite films is shifted to the
blue range (415 – 430 nm) as compared to its position in
the silver films. All the extinction spectra are broad,
which is mainly related with dispersion of Ag NP sizes,
shape and their surrounding.
Manifestation of LSPR in the silver films prepared
using the forward particle flow from the erosion torch
(Fig. 1a, curves 1 and 2) is caused by their rough
surface. This fact was confirmed by an additional
experiment checking the influence of the YAG:Nd3+
laser beam ( = 1.06 μm, free generation mode) on the
target. Laser modification of its surface resulted in
nanostructuring, which had an effect on the plasmon
absorption spectrum (Fig. 1a, curves 1 and 2). In smooth
films deposited from the backward flow, plasmon
absorption is related with their porosity, with formation
of a granulated structure (Fig. 1a, curves 3 and 4). In
these films, with lowering the Ag NP sizes, in the film
located at a great distance from the torch axis (Fig. 1a,
30
40
50
60
70
80
T, %
1
2
3
4
400 500 600 700 800 900 1000
20
30
40
50
60
70
80
90
4
, nm
1
2
3
3'
Fig. 1. Transmission spectra of the silver films (a) and
Ag/Al2O3 nanocomposite films (b) prepared from forward (a,
curves 1 and 2) and backward (a, curves 3, 4 and b) particle
flows of the erosion torch under the following conditions of
formation and measurements: - a, curve 2 – for the laser
modified film (curve 1); - a, curves 3 and 4 – respectively for
far and near points of the film from the torch axis; - b – for
the films prepared with various silver concentrations in the
target CAg, %: 1 – 20, 2 – 50, 3,3΄ – 75, 4 – 90. The curve 3´ –
for the film (curve 3) after 3-day exposure to air.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2009. V. 12, N 3. P. 298-301.
© 2009, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
300
curve 3) the transmission minimum is shifted to the
short-wave side as compared with that in the film
located near the torch (Fig. 1a, curve 4).
The observed optical properties of films,
dependences of the intensity and energy positions for the
plasmon resonance bands are inherent to NP of noble
metals, since their extinction spectra depend on sizes,
shape and surrounding of NP. The low LSPR efficiency is
a distinctive feature of the optical properties of the films
under investigation. We shall try to ascertain whether this
fact is related with Landau decay, with losses of free
electrons taking part in recombination processes.
Shown in Fig. 2 are time-resolved PL spectra of
Ag/Al2O3 nanocomposite films that differ in their silver
concentration CAg in the target during preparation. In the
case of amorphous Al2O3 films (CAg = 0), we observed
PL with a low intensity (IPL) and relaxation times
< 250 ns (Fig. 2a, insert). Its spectra are broad, the
band is located within the range 1.5 – 3.2 eV with the
peak position close to 2.7 eV. Following the tradition,
PL in Al2O3 films is related with emission of electron
centers based on defect aggregates containing oxygen
vacancies. PL is not observed in every silver film. It is
explained by Coulomb electron-electron energy
scattering, which is a faster process than radiative
recombination.
On the contrary, all the nanocomposite films, even
prepared with the lowest silver concentration in the
target (CAg = 1 %) demonstrated PL (Fig. 2). As seen
from this figure, photoluminescent properties of films
strongly depend on preparation conditions. With
increasing the CAg value, the PL spectrum is
transformed, and the non-monotonic dependence of PL
relaxation times is observed. Already at CAg = 1 % the
PL spectrum of films differs from that of Al2O3 films
that do not contain Ag NP (Fig. 2a). There clearly
pronounced are two peaks: narrower low-energy one at
1.6 eV and broader high-energy one within the range
2.2 – 3.0 eV. If the PL relaxation times in Al2O3 films
were shorter than 250 ns, then in nanocomposite films
with CAg = 1 % they grow up to 500 ns.
With increasing the CAg value, the intensity of low-
energy peak in PL spectra grows, and the shortwave
shoulder of high-energy peak sharply constricts. When
CAg = 50 %, the high-energy peak is approximately
located at 2.2 eV (Fig. 2d, curve 1). When CAg = 90 %,
the only shortwave shoulder remains (Fig. 2d, curve 2).
The dependence of the relaxation time on CAg reaches its
maximum at CAg = 10 %, and the relaxation time equals
several microseconds (Fig. 2b). With further increase of
CAg, the value is reduced: for CAg = 20 % – = 500 ns
(Fig. 2c), and for CAg > 50 % – < 250 ns (Fig. 2d).
Our analysis of the PL kinetics for the film
prepared with CAg = 10 % shows that if within the time
range 0 < < 250 ns one can observe a broad high-
energy peak, then with increasing the relaxation time the
latter sharply decreases, and for 750 ns < < 1 μs the
only low-energy peak remains (Fig. 2b).
1,5 2,0 2,5 3,0
0
5
10
15
20
0
5
10
I
PL
, arb. units
I
PL
, arb. units
h, eV
0
5
10
15
20
0
5
10
15
1,4 1,6 1,8 2,0 2,2 2,4 2,6 2,8 3,0 3,2
0
5
10
h, eV
1
2
Fig. 2. Time-resolved photoluminescence spectra of Ag/Al2O3
nanocomposite films prepared with various Ag concentrations
in the target CAg, %: a – 1, b – 10, c – 20; d, curve 1 – 50,
d, curve 2 – 90. PL relaxation times for the top curves
= 250 ns, for the bottom ones: a, c – 250 ns < < 500 ns, b –
750 ns < < 1000 ns; d, curves 1, 2 – < 250 ns. Insert in
Fig. 2a – PL spectrum of the Al2O3 film, < 250 ns.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2009. V. 12, N 3. P. 298-301.
© 2009, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
301
We observed correlated changes in the PL intensity
and relaxation time. The quantum efficiency of PL is
lower than several percents. It is indicative of the fact that
the PL efficiency is mainly determined by the degree of
damping in the radiationless recombination channel. To
ascertain the PL nature and recombination mechanisms
needs further investigations. These can be related in the
red range at short relaxation times with silver
nanoclusters, the electron energy structure of which
consists of discrete energy levels with respective
interlevel transitions [3, 4]. PL in the spectral range close
to 2.2 eV can be consistently explained by interband
transitions in Ag2O shell of Ag NP [2, 3]. Revealed for the
first time in the prepared films the long PL relaxation
times (up to several microseconds) cannot be explained by
NP sizes within the simple free-electron model. Made in
[10] are the attempts to relate them with the oxidized
states of metal atoms, with interaction between metal ions
and organic ligands, with complexes possessing
hybridizied states, with bands of charge transfer.
Juxtaposition of optical and photoluminescent
properties of films is indicative of the fact that films
possessing efficient PL do not display plasmon
absorption. This confirms the assumption that damping
the LSPR is related with leakage of free electrons from
Ag NP that might display plasmon absorption. Instead,
these electrons take part in recombination processes
determining PL. Moreover, red PL does not excite
plasmons in Ag NP, the absorption range of which lies
in more shortwave range (< 600 nm).
4. Conclusion
The silver films and nanocomposite ones containing Ag
NP in Al2O3 matrix were prepared using the method of
pulsed laser deposition with forward and backward
particle flows from the erosion torch. Local surface
plasmon resonance was observed in the silver films and
weakly pronounced in nanocomposite films prepared
even at the high (close to 90 %) silver concentration in
the target. Plasmon absorption in rough non-porous
silver films is related with developed surface microrelief,
while in the smooth porous ones – with the structure
close to that in granulated films. PL is only inherent to
nanocomposite films. PL spectra cover the broad
spectral range 1.4 – 3.2 eV with the low-energy peak at
approximately 1.6 eV and the high-energy one located
within the range 2.2 – 2.7 eV. When the Ag
concentration in the target grows, the intensity of the
low-energy PL band grows, too. The measured
relaxation times comprise the range 250 ns – 1 μs. In this
work, we observed for the first time PL in the red
spectral range with long relaxation times up to several
microseconds. The dependence of the relaxation time on
the Ag concentration in the target is non-monotonous
and has its maximum at CAg ~ 10 %. The films that
possess plasmon absorption do not display PL, and vice
versa efficient PL is not inherent to the films where local
surface plasmon resonance is clearly pronounced.
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