Síntese de Nanocristais YAl3(BO3)4:TM para Ótica Não Linear

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YAl3(BO3)4:TM (TM = Mn, Co, Cr) nanocrystals synthesis
for laser operated nonlinear optics
A. Majchrowski • L. R. Jaroszewicz •
I. Cieslik • A. O. Fedorchuk
Received: 16 September 2012 / Accepted: 24 October 2012 / Published online: 4 November 2012
� Springer Science+Business Media New York 2012
Abstract An attempt to synthesize YAB matrices doped
with cobalt, manganese, and chromium ions by means of
the Pechini method for photo-induced nonlinear optics was
performed. The best results were obtained for the Cr doped
samples. It may be related with the fact that YAB:Cr main
absorption peak is situated near the photo-inducing green
second harmonics of Nd:YAG laser at 532 nm. It was
established that after 600 s of samples illumination there
was observed some maximum of the SHG. With the further
treatment of the materials the SHG starts to decrease. The
maximal enhancement was achieved at 150 K. After the
switching off of the photo-inducing treatment the output
SHG was relaxed to initial state during 2–3 min. Local
increase of temperature due to heating did not exceed 6 K.
For the Mn doped YAB NC the behavior is quite non-
monotonic. The SHG changes are within the accuracy of
the YAB NC NLO measurements. One can see two slight
maxima at 200 and 800 s. At the same time Co suppress
the output SHG, which may be caused by specific features
of Co ions.
1 Introduction
Recently one can observe increasing interest in synthesis of
nanocrystals operated by laser light [1, 2]. Such interest is
caused by possibility to operate their polarizability using
external coherent laser light. This is of particular interest
when nanoparticles of such materials are used in biological,
medical and biophysical studies [3–5]. One of the inter-
esting applications of such nanocomposites is use of the
optical coherent beams with the SHG transformed fre-
quencies which allow obtaining the tuning of fundamental
wavelength and forming some degree of macroscopic non-
centrosymmetry [6]. Among such nanocrystals substantial
interest present the YAl3(BO3)4 (YAB) nanocrystallites
doped with different ions due to specific features of band
structure of this crystal [7].
The electronic structure and linear optical properties of
YAl3(BO3)4 calculated by density functional method with
the local-density approximation showed the existence of an
indirect band gap of 6.54 eV and a direct gap of 6.91 eV
[8]. The calculated total and partial densities of states
indicate that the top of the valence band is formed by O 2p,
B 2s, and B 2p states and the lowest conduction band
mostly originates from Y 4d and B 2p states. The wide
energy gap allows introducing different dopants into the
matrix and the thermal and mechanical properties allow
using YAB crystals as appropriate matrices for transition
metals and rare earth atoms.
It is well known that YAB crystals doped with transition
metals, for example with Cr, demonstrate excellent non-
linear optical properties including excited absorption, self-
frequency doubling and different photo-induced nonlinear
optical effects [9]. This crystal was also used as fluorescent
material [10, 11]. In transition metals doped YAB crystals
principal role play electron–phonon interactions [12]. In
case of Cr3? doping it was found that Cr3? ions are situated
in sites of octahedral symmetry with a slight orthorhombic
distortion. The ground state 4A2 splitting was established to
be equal about 1.05 ± 0.04 cm-1, and it was assigned to
A. Majchrowski � L. R. Jaroszewicz � I. Cieslik
Institute of Applied Physics, Military University
of Technology, Kaliskiego 2, 00-908 Warszawa, Poland
A. O. Fedorchuk (&)
Department of Inorganic and Organic Chemistry,
Lviv National University of Veterinary Medicine and
Biotechnologies, Pekarska Street, 50, 79010 Lviv, Ukraine
e-mail: ft.1958@yahoo.co.uk
123
J Mater Sci: Mater Electron (2013) 24:1485–1489
DOI 10.1007/s10854-012-0959-3
the combined effect of a low-symmetry distortion and
spin–orbit coupling. The g-values and fine-structure coef-
ficients of the ground state 4A2 were measured to be
gx & gy & gz = 1.978 ± 0.005 [13]. One can conclude
that the polarizability of the dopants may be principal for
the different local charge density distribution influencing
non-centrosymmetric response and the observed nonlinear
optical effects [14].
Following our data concerning the two-photon absorp-
tion in Cr3? doped YAB crystallites [15] one can expect
that discrete localized d-splitted levels of cationic transition
metal ions may also play principal role in the optically
induced SHG and the defect states may be crucial as well
[16].
As a consequence in the present work we study influ-
ence of doping with several transition metal ions on the
photo-induced nonlinear optical effects in YAB crystals.
For the study we chose YAB crystals doped with Cr3?,
Mn2? and Co2? ions. Photo-inducing illumination was
performed by the second harmonic (k = 532 nm) of the
Nd:YAG laser generating 10 ns pulses at 1,064 nm
wavelengths. The frequency repetition was equal to about
1 kHz.
Because the absolute values of ionic radii for transition
metals are closer to Al3? with respect to Y3? [17], and in
oxides of the above mentioned transition metals atoms of
metallic components have prevailingly octahedral (not
trigonal) coordination, the metallic impurities, i.e. Cr, Mn
or Co are likely located in octahedral voids, i.e. statistically
they replace Al ions. The pictures of polyhedra surrounding
metallic atoms and Me–O distances are presented in Fig. 1,
the coordinates of atoms from Ref. [18] were chosen as the
basis.
2 Nanocrystalline synthesis
YAB matrices doped with cobalt, manganese, and chro-
mium ions were obtained by means of the Pechini method.
The inorganic precursors were dissolved in water and nitric
acid to form the sol medium. Mannitol and citric acid
solutions used as polymerizing agents to prepare matrices
of YAB were obtained by dissolving in water (the molar
ratio of the citric acid to mannitol was 1:2). The solutions
were mixed using a magnetic stirrer and heated at 60 �C
under air atmosphere for one and a half hours. Created
polyester acted as a dispersing agent that lowered the
reaction temperature and prevented particle agglomeration
as well as excessive growth of crystallites.
High purity (99.99 %) yttrium oxide, hydrate of alumi-
num nitrate, and cobalt (CoO), manganese (MnO) or
chromium (Cr2O3) oxide powders were used as metal
precursors. Boric acid was the source of boron. Boric acid
and hydrate of aluminum nitrate were dissolved in distilled
water under stirring and heating in order to obtain clear
solution. The nitric acid solution of yttrium oxide was
added into mixture of citric acid and mannitol with
simultaneous increase of temperature up to 80 �C and kept
in furnace for 1 h. Then, it was mixed with the solution of
boron acid and aluminum precursor creating a complex. In
the next stage oxides of transitions metals were dissolved
in concentrated nitric acid. After complete homogenization
these solutions were added to the mixture of polymer
solution and yttrium aluminum borate precursors. Thus
prepared mixture was left in a quartz crucible for several
hours at 90 �C in order to concentrate the solution, and the
transition from sol to gel occurred. After receiving the gel
the temperature was increased up to 340 �C and kept for
4 h. The resulting sample was subjected to pyrolysis at
900 �C for at least 12 h till the wanted huntite phase was
the only phase detected in powder diffractograms. Then the
sample was milled in an agate mortar. Samples of yttrium
aluminum borate nanopowders containing 100 nm grains
were prepared. Preliminary fractionation was made using
cellulose membrane syringes with 1, 0.6 and 0.45 lm pores
diameter. The final fractionation was carried out with use
of centrifuge in a Ficoll PM400 solution in deionized
water. Obtained samples contained2 at.% of Mn2? or Co2?
ions. In case of chromium doping only 1 at.% of Cr3?
could be introduced into YAB matrix without inducing
formation of unwanted phases.
The samples for measurements were put between the
two ITO transparent electrodes to create some additional
alignment of the nanopowders and such prepared samples
were put in optical cryostat for performance of the SHG
measurements using the Kurtz Perry technique [19].
Because the effective layers of the inter-layer nanopowders
did not exceed 600 nm the applied dc-electric field up to
9 kV cm-1 allowed to produce additional nanopowder
alignment favoring the second harmonic generation.
2.1 Optically induced second harmonic generation
In Fig. 2 dependences of the optical second harmonic
generation versus the time of treatment by the 10 ns
532 nm illumination of doubled Nd:YAG laser radiation
with varying power density are presented. The data are
presented for maximal values of the photo-induced SHG at
temperature about 150 K and photo-inducing 532 nm
power density about 0.50 GW cm-2. Because we deal with
different contents of transition metals we present the draft
in the arbitrary units to know the relative changes of the
SHG for 1,064 nm. One can clearly see that the best results
were obtained for the Cr doped samples what may be
related with the fact that the principal absorption line of the
Cr3? ions lies near the 532 nm laser wavelength. It is clear
1486 J Mater Sci: Mater Electron (2013) 24:1485–1489
123
Itália
Realce
that after 600 s of the so performed optical treatment there
was observed some maximum of the SHG. With the further
treatment of the materials the output SHG starts to
decrease. It may be related to the occurrence of multi-
excitation of the optically induced defects which lead to the
suppression of the SHG. Generally the maximal enhanced
increase of the SHG did not exceed 1.35 times. After the
switching off of the photo-inducing beam, the output SHG
was relaxed to initial state during the 2–3 min. Local
increase of the temperature due to heating did not exceed
6 K. Maximal SHG signal was achieved for the angle of
polarization between the fundamental beams equal to about
45�. The photo-inducing beam spot diameter was equal to
about 0.9–1.2 mm and for the probing beam it was fixed at
about 0.5 mm. The output filter cut off the fundamental
1,064 nm laser wavelength and the registration was per-
formed by Tectronix 1 GHz oscilloscope. To avoid some
non-homogeneity of the nanopowder’s distribution
between the transparent electrode plates the measurements
were done in 30 points to achieve the necessary statistics.
For the Mn doped YAB NC the behavior is quite non-
monotonic. The changes of the SHG are within the accu-
racy of the corresponding SHG measurements. One can see
two slight kinetics maxima: at 200 and 800 s. It is impor-
tant that the dependence is almost independent on light
polarization as well as power densities. This fact
additionally confirms our previous assumption that the
transition metals plays here crucial role due to different
photo-induced cross-section absorption. The transfer of
Fig. 1 View of the YO6
trigonal prisms, AlO6 octahedra,
and BO3 triangles in the
structure of YAl3(BO3)4
0 200 400 600 800 1000
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1,0
S
H
G
 [
ar
b
.u
n
.]
t [s]
 Co
 Mn
 Cr
Fig. 2 Dependence of the second harmonic generation in the YAB
NC aligned under the external dc-electric field (about 9 kV cm-1)
versus the time of treatment by the photo-inducing 532 nm illumi-
nation at 150 K
J Mater Sci: Mater Electron (2013) 24:1485–1489 1487
123
photo-inducing 532 nm signal to the borate matrices is
determined by the energy positions of the particular crystal
field split energy levels. It is worth to underline that in case
of YAB:Cr the observed effect was substantially stronger
than in YAB:Co and YAB:Mn despite lower level of
doping.
The role of Co ions seems to be principally different.
Without the illumination Co ions suppress the output SHG,
which may be caused by suppression of the corresponding
polarizability due to Co ions. However, the photo-induced
dependence is quite similar to the YAB:Cr dependence
observed at the lower level of photo-inducing power den-
sity. Moreover, relative changes are even higher for the Co
ions.
To show how the observed SHG responses are depen-
dent on the regime of treatment, in Fig. 3 are presented the
corresponding power dependences at different tempera-
tures for the case of the Cr doped samples. It is clear that
the corresponding SHG dependences achieved their max-
ima at temperature equal to about 150 K. This fact may
serve as an additional confirmation of principal role played
by electron–phonon interactions. The latter determined the
kinetics of occupation of the localized d Cr levels. Com-
paring the photo-induced effect with other materials [2,
20], where the principal role play nanotrapping levels on
the borders of the nanocrystallites [21], in this case the
main role belongs to polarizabilities of the introduced
transition metals and energy positions of the corresponding
transition metal’s levels with respect to matrices [22].
3 Conclusion
YAB nanocrystalline matrices doped with cobalt, manga-
nese, and chromium ions were obtained by means of the
Pechini method The obtained nanocrystallites with sizes
about 100 nm were studied by photo-induced SHG at
fundamental frequency 1,064 nm and inducing beam
532 nm of the same 10 ns Nd:YAG laser. It was estab-
lished that the best SHG efficiencies were obtained for the
Cr doped YAB samples. It is clear that after 600 s of the
samples illumination there was observed some maximum
of the SHG. With the further treatment of YAB:Cr the SHG
starts to decrease. The maximal SHG output was obtained
at 150 K. After the switching off of the photo-inducing
beam the output SHG was relaxed to initial state during
2–3 min. Local increase of temperature due to heating did
not exceed 6 K. For the Mn doped YAB NC the behavior is
quite non-monotonic and the SHG variations are within the
accuracy of the NLO measurements. One can see two slight
maxima at 200 and 800 s. Without the illumination Co
suppresses the output SHG, what may be caused by sup-
pression of the corresponding polarizability due to the
presence of Co ions. However, the photo-inducing depen-
dence is quite similar to the YAB:Cr dependence observed
for the lower level of photo-inducing power density.
Moreover, relative changes are even higher for the Co ions.
Acknowledgments This work was partly supported by the Polish
Ministry of Sciences and Higher Education, Key Project POIG.
01.03.01-14-016/08 ‘‘New photonic materials and their advanced
applications’’.
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	YAl3(BO3)4:TM (TM = Mn, Co, Cr) nanocrystals synthesis for laser operated nonlinear optics
	Abstract
	Introduction
	Nanocrystalline synthesis
	Optically induced second harmonic generation
	Conclusion
	Acknowledgments
	References