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L.R. Nirmala, J. Thomas Joseph Prakash / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 110 (2013) 425–429
Phthalate crystals are used as substrates for deposition of thin
films of organic nonlinear materials [17]. Sodium Acid Phthalate
single crystal is an excellent compound for SHG applications in
the phthalic acid family. There are only a few reports available
on the effect of amino acid on the NLO efficiency of SAP crystals.
Synthesis, growth and characterization of Sodium Acid Phthalate
(SAP) single crystal was reported by Bairava Ganesh et al. [18],
and Krishnan et al. [19]. The effect of metallic dopants on KAP
single crystals was reported by Chithambaram et al. [20] and
Kejalakshmy and Srinivasan [21]. In continuation of the above
works, an attempt is made to reveal the effect of L-Valine on the
growth and characterization of Sodium Acid Phthalate single crys-
tals. The results of the characterization studies conclude that the
amino acid (L-Valine) dopant play a significant role in the view
point of device applications.
Fig. 2. Photograph of as grown L-Valine doped SAP crystal.
group of B2ab which is in good agreement with the reported values
[18,19] of undoped SAP crystal as in Table 1. The slight variations
in the cell parameters indicated the incorporation of L-Valine into
the crystal lattice of undoped SAP crystals.
Experimental procedure
Synthesis and crystal growth
Pure Sodium Acid Phthalate salt was synthesized using a slow
evaporation technique by dissolving stoichiometrical amounts of
sodium bicarbonate and phthalic acid in equimolar ratio in double
distilled water. The saturated solution of the above synthesized
salt was prepared and the undoped SAP crystals were grown by
slow evaporation solution growth technique at room temperature.
Good quality optically transparent and non-hygroscopic crystals
were collected from the mother solution in a time span of 20 days
which is shown in Fig. 1.
The mother solution was prepared as before using SAP salt in
double distilled water and the amino acid L-Valine was taken as
a dopant with 0.5% concentration by weight in the mother solution.
The saturated solution was filtered with the microfilter and it was
kept in the dust free atmosphere for evaporation. Optically trans-
parent crystal of L-Valine doped SAP crystal was obtained within
30 days which is shown in Fig. 2.
FT-IR spectral studies
The powdered samples of undoped and L-Valine doped SAP
crystals were subjected to FT-IR analysis by Perkin Elmer RXI
FT-IR Spectrometer using KBr pellet technique in the wavelength
range between 400 and 4000 cmꢁ1. The recorded FT-IR spectrum
of undoped and L-Valine doped SAP crystals were recorded as
shown in Fig. 3 and the observed bonds along with their vibra-
tional assignments were tabulated in Table 2. The observed spectra
of these crystals were similar except for a small shift in the peak
positions and hence the crystals are expected to preserve nearly
the same interactions among the groups and ions. The Carboxyl
group C@O vibrations appeared near 1710 cmꢁ1. The peak at
1613 cmꢁ1 was due to the CAC skeletal aromatic ring vibration.
The absorption band in the region 500–900 cmꢁ1 was due to
CAH out-of-plane deformations of the aromatic ring which were
in good agreement with the reported values [18].
Results and discussion
Optical transmission studies
Single crystal X-ray diffraction studies
Transmission spectra are very important for any NLO material
because an NLO material is used for practical purposes only if it
has a wide transparent window. To determine the suitability and
the transmission range of the grown crystal for optical applica-
tions, the UV–Visible spectrum was recorded in the range
200–1200 nm by using LAMBDA-35 UV–Visible spectrometer.
The grown L-Valine doped crystal was well polished and a speci-
men of 3 mm thick was subjected to transmission measurements
in the specified spectral region. The recorded spectrum of L-Valine
doped SAP single crystal was shown in the Fig. 4. This agreed well
with the spectrum of undoped SAP crystal [18,19]. The lower cutoff
wavelength around 330 nm is due the n–pꢂ transition of the
carbonyl group of the carboxyl function. This transition causes its
The grown doped crystal was subjected to single crystal X-ray
diffraction studies using an ENRAFNONIUS CAD 4 diffractometer
with Mo K
a radiation (k = 0.71073 Å) to determine the unit cell
parameters. The observed lattice parameter values of L-Valine
doped SAP crystal are found to be a = 6. 75 Å, b = 9.28 Å,
c = 26.72 Å and V = 1682 Å3 and the crystal belongs to the space
Table 1
Unit cell parameters of doped and undoped SAP crystals.
Crystal data
SAP [18]
L-Valine doped SAP
a
6.75 Å
6.75 Å
b
9.31 Å
9.28 Å
c
26.60 Å
1662 Å3
Orthorhombic
B2ab
26.72 Å
1682 Å3
Orthorhombic
B2ab
Volume
System
Space group
Fig. 1. Photograph of as grown SAP crystal.
Nirmala, L. Ruby
