ZnSe NANOCRYSTALS EMBBEDED IN KDP CRYSTALS
A. Bensouici, O. Halimi & M. Sebais
Laboratory of Crystallography (LC), Department of Physics, Mentouri-Constantine
University, Constantine, Algeria
Tel.: +21331818675, Fax.: +21331818872
bensouicia@yahoo.fr
Abstract
ZnSe nanocrystals were elaborated in KDP dielectric crystalline matrix by addition of ZnSe
powder to the mother solution during crystal growth. Optical absorption spectra show a band
situated at 270nm indicating impurity of KDP. X-ray diffraction confirm ZnSe inclusions
incorporation, the average size was estimated to 13 nm. Micro-Raman measurement showing
widening and blue-shifting of LO and TO ZnSe phonon due to size effect.
Keywords: ZnSe nanocrystals ; KDP ; Micro-Raman
PACS 78.67.Bf
1- Introduction
Fabrication and isolation of nanocrystals in
different type of matrix (glass, polymer,…)
has been the subject of several fundamental
research. There exist few work to fabricate
nanocrystals embedded in crystalline matrix,
because of low concentration embedding in
crystalline matrices. Almost solid particles
can be embedded in crystalline matrices such
inclusions. The most important aim of
dopping crystalline matrix is to search
adequate materials which can be oriented in
host matrix and verify the influence of these
inclusions on dielectric properties of host
matrix to provide possible application in
photonic.
II-VI
semiconductors
have
interesting
optical
properties,
ZnSe
semiconductor is known by his complet
integration in technologies based on III-V
compounds (heterostructures). Nevertheless,
the study of electronic properties of these
materials is necessary to achieve high
efficiency of electro-optical devices [1,2]. The
ZnSe has a direct gap, which allows vertical
transitions between the valence band and the
conduction band and therefore have radiative
transitions. This property is the main cause of
the integration of ZnSe in the field of
optoelectronics. His energy gap is equal to
2.72 eV to 100 K [3] and 2.80 to 300 K [4,5].
In this work, we fabricate ZnSe nanocrystals
in KDP crystalline matrix, KDP is dielectric
crystal, optically transparent in the spectral
range covering the visible and near-ultraviolet
(Eg=8.8 eV), so it can be used for studying the
optical properties of ZnSe nanocrystals in the
visible region of the electromagnetic
spectrum. [6, 7], it’s commonly used
nonlinear optical materials for harmonic
generation of laser radiation [8].
Optical characterisation
was by optical
absorption, then micro-Raman spectroscopy,
X-ray diffraction measurement are also
studied.
2- Experimental
KDP crystals are obtained from aqueous
solution by lowering technique (from 50 to 20
°C, 60 mm/day), ZnSe powder obtained by
mechanical grinding was added to KDP
mother solution during crystal growth. We
obtain crystals with prismatic bipyramidal
morphology, terminated by the most stable
faces (100) and (101) (Fig. 1).
higher. The 270 nm known as peak indicator
of impurities [9,12].
2,0
Fig. 1 KDP crystal
Intensity (a.u.)
1,5
1,0
0,5
200
300
400
500
600
Wavelength (nm)
Fig. 3 optical absorption spectra : 1- pure
KDP(dashed line), 2- KDP doped ZnSe (solid
line)
The measurements of optical absorption were
carried out by a spectrophotometer type
Shimadzu UV-3101 PC, X-ray diffraction
data were collected using BRUKER - AXS
D8 diffractometer (λKα= 1.54 Å) and
graphite.The micro-Raman spectra are
recorded using a spectrometer Jobin-Yvon
equipped with an Olympus microscope DX40
using laser wavelength 632 nm and power of
10 mW.
500
KD
P
Fig. 1 Crystal growth apparatus (LC)
X-ray diffraction pattern (Fig. 4) of KDP
pellet (X-ray incidents on the face parallel to
the plane (100)) , show the appearance of
KDP peaks situated at 24.16 and 49.27°
relative, respectively, to the (100) and (200)
planes. Furthermore, we note the appearance
of a peak with low intensity situated at 28.57
°, which corresponds to (101) plane of
diffraction of ZnSe nanocrystals (hexagonal
structure)
There has been a shift of the position of the
peak because of the contraction of the
parameters of ZnSe unit cell which due to size
effect. Using Sherrer formula, the average
size was estimated to be 13 nm.
400
300
(101)
100
(200)
Zn
Se
KD
P
200
(100)
The absorption spectrum of a KDP pellet
doped by ZnSe is given in figure 3 (solid
line), showing of peak indicator of the
impurity of the KDP in the 270 nm and
according to its intensity can be deduced that
there was an incorporation of impurities
added to the solution for growth, and this
peak is even more intense when the
concentration of impurities incorporated is
Intensité (u.a)
3- Results and discussion
0
21
28
35
42
49
2 (°)
Fig. 4 X-ray diffraction of KDP doped ZnSe
(wafer // (100) face)
Acknowledgment
The results of micro-Raman diffusion
measurement on the KDP sample doped by
ZnSe are presented in figure 5, Can be seen
on the spectrum peaks with wave numbers
184, 365, and 474 cm-1. They are identical to
some peaks of Raman spectrum of KDP.
According to Subramony et al. [13] the
prominent bands between 300and 1200 cm-1
are due to internal vibrations of the PO4
group, the bands below 200 cm-1 are lattice
mode, we note the appearance of two bands
with low intensity situated at 202 and 241cm-1
representing, respectively LO and TO ZnSe
phonon frequencies [14], red shifting to
lower wave-numbers is due to size effect
(optical phonon energies of 1TO at 210 cm-1
and 1LO at 254 cm-1 for ZnSe crystal at room
temperature) [14].
-1
-1
474 cm
365 cm
cm
cm
-1
18
4
8000
24
1
cm
-1
20
2
Intensity (a.u.)
-1
8500
7500
200
400
600
-1
Wavenumber (cm )
Fig. 5 Micro-Raman Spectrum of KDP doped
ZnSe
4- Conclusion
UV-Vis absorption spectra reveal the band
indicating impurity of KDP. Structural
characterization by using X-ray diffraction
indicates the incorporation of ZnSe
nanocrystals in the host matrix of KDP. The
low intensity of peak of diffraction, LO and
TO phonon bands of ZnSe inform us about
the low concentration of crystallites
incorporated.
This work has been supported by Laboratory
of Crystallography of Mentouri-Constantine
University (Algeria).
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