Structural, thermal and optical characterization of an organic NLO material - Benzaldehyde thiosemicarbazone monohydrate single crystals

Article abstract of DOI:10.1016/j.saa.2010.11.043

Single crystals of the organic NLO material, benzaldehyde thiosemicarbazone (BTSC) monohydrate, were grown by slow evaporation method. Solubility of BTSC monohydrate was determined in ethanol at different temperatures. The grown crystals were characterized by single crystal X-ray diffraction analysis to determine the cell parameters and by FT-IR technique to study the presence of the functional groups. Thermogravimetric and differential thermal analyses reveal the thermal stability of the crystal. UV-vis-NIR spectrum shows excellent transmission in the region of 200-1100 nm. Theoretical calculations were carried out to determine the linear optical constants such as extinction coefficient and refractive index. Further the optical nonlinearities of BTSC have been investigated by Z-scan technique with He-Ne laser radiation of wavelength 632.8 nm. Mechanical properties of the grown crystal were studied using Vickers microhardness tester. Second harmonic generation efficiency of the powdered BTSC monohydrate was tested using Nd:YAG laser and it is found to be ～5.3 times that of potassium dihydrogen orthophosphate.

Full text of DOI:10.1016/j.saa.2010.11.043

Spectrochimica Acta Part A 78 (2011) 653–659
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Structural, thermal and optical characterization of an organic NLO
material—Benzaldehyde thiosemicarbazone monohydrate single crystals
a
b,∗
R. Santhakumari , K. Ramamurthi
a
Department of Physics, Govt. Arts College for Women, Pudukkottai 622 001, Tamil Nadu, India
Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620 024, Tamil Nadu, India
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 June 2010
Received in revised form
Single crystals of the organic NLO material, benzaldehyde thiosemicarbazone (BTSC) monohydrate, were
grown by slow evaporation method. Solubility of BTSC monohydrate was determined in ethanol at dif-
ferent temperatures. The grown crystals were characterized by single crystal X-ray diffraction analysis to
determine the cell parameters and by FT-IR technique to study the presence of the functional groups. Ther-
mogravimetric and differential thermal analyses reveal the thermal stability of the crystal. UV–vis–NIR
spectrum shows excellent transmission in the region of 200–1100 nm. Theoretical calculations were car-
ried out to determine the linear optical constants such as extinction coefficient and refractive index.
Further the optical nonlinearities of BTSC have been investigated by Z-scan technique with He–Ne laser
radiation of wavelength 632.8 nm. Mechanical properties of the grown crystal were studied using Vickers
microhardness tester. Second harmonic generation efficiency of the powdered BTSC monohydrate was
tested using Nd:YAG laser and it is found to be ∼5.3 times that of potassium dihydrogen orthophosphate.
1
3 November 2010
Accepted 30 November 2010
PACS:
8
6
6
4
1.10.Dn
1.66.Hq
5.60.+a
2.65.Ky
Keywords:
Characterization
©
2010 Elsevier B.V. All rights reserved.
Growth from solution
Organic compound
Nonlinear optical material
1
. Introduction
cyclic rings [7]. Further extensive electron delocalization reported
in these types of structures helps the thiosemicarbazone complexes
to acquire second harmonic generation (SHG) efficiency [8–11].
Gu and Zhu [12] have reported on the three dimensional crys-
tal and molecular structure of benzaldehyde thiosemicarbazone
(BTSC) monohydrate. The crystal belongs to the well known non-
centrosymmetric orthorhombic system with space group P2 2 2 ,
thus satisfying the requirements for second order NLO activities.
To our knowledge no systematic studies on the growth and char-
acterization of the benzaldehyde thiosemicarbazone monohydrate
have been made. Hence, in this investigation we report for the first
time on the bulk growth and characterization of BTSC monohydrate
single crystals.
The overwhelming success of molecular engineering on control-
ling nonlinear optical (NLO) properties has attracted the attention
of the researchers to search for a variety of new types of non-
linear optical materials [1] and to improve the NLO efficiency
of the known materials. Organic molecules containing ␲ elec-
tron conjugation systems asymmetrized by the electron donor and
acceptor groups are highly polarizable entities for NLO applica-
tions [2]. The donor/acceptor of benzene derivatives can produce
high molecular nonlinearity. Nonlinear optical materials, which
can generate highly efficient second harmonic blue–violet, are of
great interest for various applications including high speed optical
communication, wireless optical computing, optical parallel infor-
mation processing, optical disk data storage, laser fusion reactions,
laser remote sensing, color display and medical diagnostics [3–5].
Recently there has been considerable interest in the co-ordination
chemistry of aryl hydrazones such as semicarbazones, thiosemi-
carbazones and guanyl hydrazones due to their importance for
drug design [6], organocatalysis and for the preparation of hetero
1
1 1
2. Experimental
2.1. Synthesis and solubility
The BTSC monohydrate was synthesized following the proce-
dure given by Gu and Zhu [12] by reacting benzaldehyde and
thiosemicarbazide in 100 ml flask in the presence of aqueous
◦
medium. After refluxing it for 2 h at 100 C the mixture was
∗ Corresponding author. Tel.: +91 431 2407057.
E-mail address: krmurthin@yahoo.co.in (K. Ramamurthi).
allowed to cool slowly to room temperature which yielded col-
orless crystalline powder solid of the compound. The reaction is
1
386-1425/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2010.11.043

6
54
R. Santhakumari, K. Ramamurthi / Spectrochimica Acta Part A 78 (2011) 653–659
Scheme 1.
depicted in Scheme 1. Repeated recrystallization of BTSC monohy-
drate from ethanol was carried out to improve the purity of the
compound. As a first step towards crystallization, the selection
of suitable solvent is essential for the growth of good qual-
ity single crystals [13,14]. The solubility of BTSC monohydrate
was determined at five different temperatures, viz., 25, 30, 35,
◦
◦
4
0 and 45 C. The solubility at 25 C was determined by dis-
3
solving the BTSC salt in 100 cm ethanol taken in an air-tight
container with continuous stirring. After attaining the saturation
the concentration of the solute was estimated gravimetrically.
The same procedure was repeated to estimate the solubility
at different temperatures [15] and the results are presented in
Fig. 1.
Fig. 2. The as-grown single crystal of BTSC monohydrate.
2.2. Crystal growth
3
. Results and discussion
The purified colorless crystalline sample of BTSC monohydrate
◦
was dissolved thoroughly in ethanol at 30 C to form the saturated
solution. The pH of the solution was about 4. The solution of 50 ml
was taken in a beaker and was properly sealed and placed in a
constant temperature bath. The solvent was allowed to evaporate
slowly at room temperature. Well defined crystals with good trans-
parency were appeared in the beaker in a growth period of 10 days.
One of the best crystals was selected as the seed crystal and inserted
into a 100 ml beaker containing the solution of pH ∼ 4 and placed
3.1. Single crystal X-ray diffraction
The X-ray diffraction (XRD) data were collected using a
computer-controlled Enraf Nonius-CAD 4 single crystal X-ray
diffractometer. Single crystal of suitable size was selected for
the X-ray diffraction analysis and the unit cell parameters were
determined using 25 reflections. XRD results show that BTSC mono-
hydrate crystal belongs to the orthorhombic system and the unit
cell parameters obtained are in good agreement with the reported
values of Gu and Zhu [12] (Table 1). It has been observed that
BTSC crystal belongs to the most popular space group of P2 2 2 ,
◦
in a constant temperature bath maintained at 30 C. Single crystal
of size 10 mm × 10 mm × 3 mm was harvested by slow evapora-
tion method in a growth period of 25 days. The as-grown crystal
is shown in Fig. 2.
1
1 1
with molecules containing a chiral centre which allow maximal
contribution from the microscopic molecular nonlinearity to the
macroscopic crystal nonlinearity [16].
3.2. FT-IR spectral analysis
Fourier transform infrared (FTIR) spectrum of BTSC mono-
hydrate was recorded using Perkin Paragon-500 by KBr pellet
−
1
−1
technique between 400 cm and 4000 cm and is shown in Fig. 3.
As expected, the peak corresponding to imine group (C N) was
−
1
observed at 1595 cm , which confirms the formation of the imine
bond between aldehyde and hydrazide. The peaks lying below
500 cm could be due to C N and N–N stretching vibration. As
−
1
1
it is very broad, nearly all NH2 groups in the crystal are expected
Table 1
Unit cell parameters of BTSC monohydrate.
Cell parameters
Single crystal XRD
present work)
Single crystal
XRD [12]
(
a (Å)
b (Å)
c (Å)
6.240(2)
6.1685(10)
7.6733(12)
21.131(2)
1000.2(2)
7.5820(10)
21.129(36)
998.3(9)
3
Volume (Å )
Orthorhombic system
Fig. 1. Solubility curve of BTSC monohydrate.

R. Santhakumari, K. Ramamurthi / Spectrochimica Acta Part A 78 (2011) 653–659
655
The extinction coefficient (K) is obtained in terms of the absorp-
tion coefficient,
ꢀ
˛
K = 4
(2)
ꢁ
where ꢀ is the wavelength.
The reflectance (R) in terms of absorption coefficient is derived
from the relation,
ꢀ
1
± (1 − exp(−˛d) + exp(˛d))
+ exp(−˛d)
R =
(3)
(4)
1
and the linear refractive index (n) is given by
ꢀ
−(R + 1) ±
(−3R + 10R − 3)
(R − 1)
n =
.
2
Also the complex dielectric constant is given by the relation,
Fig. 3. FT-IR spectrum of BTSC monohydrate.
εc = εr + εi
(5)
εr and ε are the real and imaginary part of the dielectric constant
respectively. The real and imaginary dielectric constants are related
to the refractive index and extinction coefficient as given below,
to be in hydrogen bonding interaction with neighbouring groups
i
[
17]. The C–H stretching absorption, a weak absorption, is observed
−1
at 3026 cm [18]. The C S stretch of thiosemicarbazide moiety
is observed at 1100 cm [19]. Absence of characteristic aldehyde
−1
2
2
εr = n − K
(6)
(7)
−1
band at 2720 cm indicates that there is no aldehyde group in the
final product.
εi = 2nK
The optical conductivity (ꢂop) is a measure of the frequency
3.3. Linear and nonlinear optical properties
response of the material when irradiated with light
˛
nc
ꢂop =
(8)
The grown crystals were subjected to spectral analysis for study-
4
ꢁ
ing the linear optical properties. The optical absorption spectrum
of BTSC monohydrate crystal of 2 mm thickness was recorded in
the range of 200–1100 nm using Varian Cary 5E UV–vis–NIR spec-
trophotometer (Fig. 4). The lower cut off of BTSC monohydrate is
observed ∼370 nm and the crystal is found to be transparent in the
region of ∼400–1100 nm, an essential parameter required for fre-
quency doubling process [20]. The hump at 220 nm is due to the
electronic excitation of the aromatic compound containing sulfur
and nitrogen [21].
where c is the velocity of light. The electrical conductivity (ꢂe) can
also be estimated by optical method using the relation
2
ꢀꢂop
ꢂe =
(9)
˛
The Z-scan is a simple and popular experimental technique to
measure the intensity dependent third order nonlinear suscepti-
bility of the materials. It allows the simultaneous measurement
of both the nonlinear refractive index and the nonlinear absorp-
tion coefficient. In this method, the sample is translated in the
Z-direction along the axis of a focused Gaussian beam from the
He–Ne laser at 632.8 nm and the far field intensity is measured as
a function of the sample position. The schematic diagram of Z-scan
technique is as shown in Fig. 5. By properly monitoring the trans-
mittance change through a small aperture at the far field position
(closed aperture), one is able to determine the amplitude of the
phase shift. By moving the sample through the focus and without
placing an aperture at the detector (open aperture) one can mea-
sure the intensity dependent absorption of the sample. When both
the methods (open and closed) are used for the measurements,
the ratio of the signals determines the nonlinear refraction of the
sample.
The optical absorption coefficient (˛) was calculated using the
following relation
.303 log (1/T)
˛
= 2
(1)
d
where T is the transmittance and d is the thickness of the crystal. The
various other optical constants were calculated using the following
theoretical formulae [22,23].
The recorded transmission spectrum of BTSC shows the lower
cutoff wavelength at 370 nm and a wide transparency in the
entire visible region which makes the material suitable for sec-
ond harmonicgeneration. Theenergydependenceofthe absorption
coefficient suggests the occurrence of direct band gap and hence it
obeys the relation for high photon energy,
(
˛hꢃ)2 = A(hꢃ − Eg)
(10)
where Eg is the optical band gap and A is a constant. The variation
2
of (˛hꢃ) vs hꢃ in the fundamental absorption region is plotted in
Fig. 6 and Eg is evaluated by the extrapolation of the linear part. The
band gap is found to be 3.6 eV.
From the recorded absorption spectra, the linear optical con-
stants of BTSC were calculated and the variation of optical constants
as a function of photon energy is plotted (Figs. 7–10). The refractive
Fig. 4. UV–vis–NIR spectrum of BTSC monohydrate.

6
56
R. Santhakumari, K. Ramamurthi / Spectrochimica Acta Part A 78 (2011) 653–659
Fig. 5. Experimental set up for Z-scan.
2
2
1
1
5
0
5
0
5
0
1
2
3
4
5
6
7
Photon Energy (eV)
Fig. 6. (˛hꢃ)2 vs hꢃ.
Fig. 9. Dielectric constant as a function of photon energy.
index of the material at 211 nm is 1.332. Also the extinction coef-
ficient shows exponential decay as the photon energy increases.
Refractive index being the measure of percentage of intensity of
light reflected, the reflectance shows an increasing value along the
photon energy. From Figs. 7 and 8, it is clear that the extinction
coefficient and the reflectance depend upon the absorption coeffi-
cient. The internal energy of the device depends on this absorption
coefficient. The high transmission, low absorbance, low reflectance
and low refractive index of BTSC in the UV–vis region makes the
material a prominent one for antireflection coating in solar thermal
devices and nonlinear optical applications. The low extinction value
−
3
2
−1
(
10 ) and electrical conductivity (10 (ꢄ cm) ) of the present
work show the semiconducting nature of the material. The high
magnitude of optical conductivity (1010
s
−1
) confirms the presence
of very high photo response nature of the material [22]. This makes
the material more prominent for device applications in information
processing and computing. From Figs. 9 and 10, the lower dielectric
constant and the higher optical response suggest the better con-
version efficiency of the material. Thus linear optical properties of
Fig. 7. Extinction coefficient as a function of photon energy.
Fig. 8. Reflectance as a function of photon energy.
Fig. 10. Optical conductivity as a function of photon energy.

R. Santhakumari, K. Ramamurthi / Spectrochimica Acta Part A 78 (2011) 653–659
657
Table 2
Open Curve
Measurement details and the results of the Z-scan technique.
3
2
1
0
.5
a
Laser beam wavelength
Focal length of the lens
Optical path length
Beam radius of the aperture (ωa)
Aperture radius (ra)
632.8
3
24 cm
175 cm
4 mm
.5
2
4 mm
Sample thickness (l)
Beam radius (ωL)
1.7 mm
3 mm
.5
1
Effective thickness (Leff)
Linear absorption coefficient
Nonlinear refractive index (n2)
Nonlinear absorption coefficient (ˇ)
1.69 mm
0.625
−
8
2
−3.126 × 10 cm /W
.5
0
4.076 × 10−3 cm/W
3
−6
−6
Real part of the third-order susceptibility [Re(ꢆ )]
3.27 × 10 esu
Imaginary part of the third-order susceptibility
2.15 × 10 esu
-
15
-10
-5
0
5
10
15
3
[
Im(ꢆ )]
3
3.915 × 10−6 esu
Third-order susceptibility (ꢆ )
Z-Position (mm)
nonlinear absorption coefficient is estimated from the equation
Closed curve
√2ꢅT
6
ˇ = 2
(14)
I L
0
eff
b
5
4
3
2
1
where ꢅT is the one valley value at the open aperture Z-scan curve.
The value of ˇ will be negative for saturable absorption and positive
for two photon absorption. The real and imaginary parts of the third
order nonlinear optical susceptibility ꢆ( are defined by
3)
−
4
2 2
Re(ꢆ(3)) (esu) = 10
Im(ꢆ(3)) (esu) = 10
(ε c n n )
ꢁ
(cm /W)
(15)
(16)
0
o
2
2
−2
2 2
(ε c n n )
0
o
2
(cm/W)
4
ꢁ2
where ε is the vacuum permittivity, no is the linear refractive index
0
of the sample and c is the velocity of light in vacuum. Table 2
portrays the experimental details and the results of the Z-scan
technique for BTSC. The calculated value of the nonlinear refrac-
0
0
-
10
-5
5
10
−
8
2
tive index n2 is −3.126 × 10 cm /W. From the open aperture
Z-scan curve, it can be concluded that as the minimum lies near
the focus (Z = 0), the nonlinear absorption is regarded as two pho-
ton absorption. The nonlinear absorption coefficient is found to
Z-Position in mm
Fig. 11. (a) Z-scan open curve. (b) Z-scan closed curve.
−
3
be 4.076 × 10 cm/W. The third order susceptibility of BTSC is
BTSC confirm the material suitability for NLO and semiconducting
applications.
−
6
3
.915 × 10 esu.
The third order nonlinear refractive index and the nonlinear
absorption coefficient were evaluated by the Z-scan measurements
3.4. Microhardness
(
Fig. 11a and b). A spatial distribution of the temperature in the crys-
Measurement of hardness is a useful nondestructive testing
tal surface is produced due to the localized absorption of a tightly
focused beam propagating through the absorbing sample. Hence
a spatial variation of the refractive index is produced which acts
as a thermal lens resulting in the phase distortion of the propagat-
ing beam. The difference between the peak and valley transmission
method to determine the hardness of the materials. The micro-
hardness value correlates with other mechanical properties such
as elastic constants and yield strength. The hardness of a mate-
rial depends on different parameters such as lattice energy, Debye
temperature, heat of formation and interatomic spacing [24,25].
According to Gong [26], during an indentation process, the exter-
nal work applied by the indentor is converted into a strain energy
component which is proportional to the volume of the resul-
tant impression and a surface energy component found to be
proportional to the area of the resultant impression. Vickers micro-
hardness test was carried out on BTSC monohydrate single crystal
using Vickers hardness tester fitted with pyramidal indenter. Sev-
eral trials of indentation were carried out on the prominent (0 1 1)
face of the crystal and the average diagonal length was calculated
for an indentation time of 15 s. The Vickers hardness number is
calculated using the relation
(
ꢅTp–v) is written in terms of the on axis phase (|ϕ |) shift at the
0
focus as,
0
.25
ꢅTp–v = 0.406(1 − S)
|ϕ |
0
(11)
where S is the aperture linear transmittance and is calculated using
the relation
ꢁ
ꢂ
2
a
−
2r
S = 1 − exp
(12)
2
ω
a
where ra is the radius of aperture and ωa is the beam radius at the
aperture. The nonlinear refractive index is given by
ꢅϕ
P
d2
kg/mm2
(17)
n2
=
(13)
Hv = 1.8544
KI0Leff
where K = 2ꢁ/ꢀ (ꢀ is the laser wavelength), I is the intensity of the
where P is the applied load in kg and d is the average diagonal length
of impression in mm. The variation of Hv with applied load for BTSC
monohydrate crystal is shown in Fig. 12. Cracks were observed for
loads more than 100 g. Work hardening coefficient n, a measure of
0
laser beam at the focus (Z = 0), Leff = [1 − exp(−˛L)]/˛, is the effec-
tive thickness of the sample, ˛ is the linear absorption and L is the
thickness of the sample. From the open aperture Z-scan data, the

6
58
R. Santhakumari, K. Ramamurthi / Spectrochimica Acta Part A 78 (2011) 653–659
Table 3
Microhardness value obtained on the BTSC crystal.
Parameters
Values
n
2.08
K1 (kg/mm)
K2 (kg/mm)
27.7
30.16
0.0535
1.58 × 10
3
/2
Kc (g/␮m
)
−
1/2
8
Bi (m
)
3.5. Thermal analysis
Thermogram provides information about the thermal proper-
ties of materials [32]. The thermal stability of BTSC monohydrate
crystal was studied by thermogravimetric analysis (TGA) and dif-
ferential thermal analysis (DTA) using SDT Q600 V8.3 Build 101
◦
◦
instrument between the temperatures 50 C and 1100 C at a heat-
◦
ing rate of 10 C/min in nitrogen atmosphere (Fig. 13). The BTSC
monohydrate sample weighing 1.745 mg was taken for the mea-
surement. There are three weight losses noted in the thermogram.
The earlier one is due to expulsion of water present in the crys-
tal. The second and third major weight loss is observed just above
Fig. 12. The variation of hardness number vs load P.
the strength of the crystal, is computed from the plot of log P vs
log d. The plot of log P vs log d of BTSC monohydrate crystal yields a
straight line and its slope, the work hardening index n, is found to
be 2.08.
◦ ◦
2
20 C and 400 C. It is due to decomposition of BTSC monohy-
drate crystal. The formation of minute quantities of decomposition
residues is also noted in the thermogram. From the DTA curve it
According to Meyer’s law [27],
◦
is observed that, the material is stable up to 153 C, the melting
point of the substance. The melting point, also measured directly
using a GUNA melting point apparatus, confirmed this value. Above
this point, the material begins to attain an endothermic transition
and begins to decompose. The sharpness of this endothermic peak
shows the good degree of crystallinity of the sample [33].
n
P = K1d
(18)
n
where K is the standard hardness found out from the P vs d graph.
1
It is known that the material takes some time to revert to elastic
mode after the applied load is removed, so a correction x is applied
to the observed d value [28]. Kick’s law [29] may be modified as,
3.6. Nonlinear optical studies
2
P = K (d + x)
(19)
2
Kurtz and Perry [34] second harmonic generation (SHG) test was
Simplifying Eqs. (18) and (19) become
performed to estimate the NLO efficiency of powdered BTSC mono-
hydrate crystal. The grown single crystal of BTSC was powdered
with a uniform particle size and then packed in a micro capillary of
uniform boreandwas illuminated usingSpectra PhysicsQuanta Ray
DHS2. Nd:YAG laser using the first harmonics output of 1064 nm
with pulse width of 8 ns and repetition rate 10 Hz. The second har-
monics signal, generated in the crystal was confirmed from the
emission of green radiation by the crystal. A sample of potassium
dihydrogen orthophosphate, also powdered to the same particle
size as the experimental sample, used as a reference material in
the present measurement. The SHG radiation of 532 nm green light
was collected by a photomultiplier tube (PMT-Philips Photonics-
ꢃ
ꢄ
1/2
ꢃ
ꢄ
1/2
K2
K1
K2
K1
dn/2
=
d +
x
(20)
n/2
1/2
The slope of d verses d yields (K /K ) and the intercept is a
2
1
measure of x. The fracture toughness (Kc) is given by
P
Kc =
(21)
ˇ × C3/2
where C is the crack length measured from the centre of the inden-
tation mark to the crack tip, P is the applied load and geometrical
constant ˇ = 7 for Vicker’s indenter. The brittleness index (B) is
given by
Hv
B =
(22)
Kc
The yield strength (ꢂv) of the material can be found out using
the relation
ꢅ
ꢈ
ꢆ
ꢇ
n−2
Hv
12.5(n − 2)
1 − (n − 2)
ꢂv =
[1 − (n − 2)] ×
(23)
2
.9
From the Vicker’s microhardness studies, it is observed that the
hardness value increases up to a load of 100 g. Cracks developed
around the indentation mark for loads above 100 g. The forma-
tion of cracks confirms the decrease in microhardness [30]. Onitsch
[
31] inferred that for hard materials the value of n lies between 1
and 1.6 and for soft materials it is above 1.6. Thus the BTSC mono-
hydrate crystal comes under the soft materials category. The load
dependent hardness parameters n, K , K , fracture toughness (Kc),
1
2
brittleness index (B) and yield strength (ꢂv) were calculated for the
BTSC monohydrate crystal and are given in Table 3.
Fig. 13. TGA/DTA curves of BTSC monohydrate.

R. Santhakumari, K. Ramamurthi / Spectrochimica Acta Part A 78 (2011) 653–659
659
model 8563) after being monochromated (monochromator-model
Triax-550) to collect only the 532 nm radiation. The optical sig-
nal incident on the PMT was converted into voltage output at the
CRO (Tektronix-TDS 3052B). The input laser energy incident on the
powdered sample was chosen to be 3.4 mJ. Powder SHG efficiency
obtained for BTSC monohydrate is about 5.3 times that of potas-
sium dihydrogen orthophosphate crystal. This may be due to the
existence of intermolecular N–H· · ·N and N–H· · ·S hydrogen bonds
and N–H· · ·O and O–H· · ·S hydrogen bonds due to water molecules
in BTSC, which link the molecules into ribbons extended along the
a-axis [12].
Chemistry, Indian Institute of Science, Bangalore for extending the
laser facilities for the SHG measurement.
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4
. Conclusion
Well developed transparent benzaldehyde thiosemicarbazone
[
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◦
was grown by the slow evaporation technique at 30 C. Determi-
[
nation of unit cell constants by the single crystal X-ray diffraction
technique confirmed the identity of the synthesized material. FTIR
spectral studies confirmed the presence of functional groups of
BTSC monohydrate crystal. Optical transmittance window and the
lower cut off wavelength identified through UV–vis–NIR spectrum
reveal that BTSC monohydrate is a potential candidate for second
harmonic generation. The high transmission, low absorbance, low
reflectance and low refractive index of BTSC in the UV–vis–NIR
make the material a prominent one for antireflection coating in
solar thermal devices. Thus BTSC with many attracting linear
and nonlinear optical properties is a suitable candidate for opto-
electronic applications. Vickers microhardness study reveals the
mechanical strength of the BTSC monohydrate crystal. TGA and
[
[
[
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2
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DTA reveal that this compound is stable up to its melting point
◦
1
53 C. Second harmonic generation efficiency of the powdered
[
23] J.I. Pankove, Optical Processes in Semiconductors, Prentice hall, New York,
971, p. 412.
BTSC monohydrate crystal is ∼5.3 times that of potassium dihy-
1
drogen orthophosphate crystal.
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Acknowledgments
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The authors (RS and KR) thank to Dr. K. Panchanatheeswaran,
Professor in Chemistry (Rtd), Bharathidasan University, Tiruchi-
rappalli for fruitful discussion. Further one of the authors [RS]
thank University Grants Commission, Government of India for
financial assistance [File No. MRP 2976/2009 (RS)]. Authors thank
Prof. D. Sastikumar, Department of Physics, NIT, Tiruchirappalli, for
the support in recording the Z-scan measurements. The authors
acknowledge Prof. P.K. Das, Department of Inorganic and Physical
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8
[