Journal of Minera ls & Materials Ch ar ac teri zatio n & Engineeri ng, Vol. 11, No.6, pp.631-639, 2012
jmmce.org Printed in the USA. All rights reserved
631
Growth, Structural, Spectral and Optical Studies on Pure and
L-Alanine Mixed Bisthiourea Cadmium Bromide (LABTCB) Crystals
M.Senthilkumar and C.Ramachandraraja*
Department of Physics, Govt. Arts College (Autonomous), Kumbakonam 612 001, India.
*Corresponding author: [e-mail]
ABSTRACT
Pure bisthiourea cadmium bromide (BTCB) and 1 mole % L-alanine mixed bisthiourea
cadmium bromide (LABTCB) single crystals have been grown by slow evaporation method.
The grown crystals have been characterized by single crystal XRD analysis, powder XRD
analysis, FTIR analysis, UV-Vis-NIR analysis and SHG studies. XRD analysis confirms the
crystalline nature of the materials. The addition of L-alanine changes the crystal structure
from orthorhombic to tetragonal. The presence of various functional groups present in the
pure BTCB and LABTCB crystals have been confirmed by FTIR analysis. The UV-Vis-NIR
spectrum shows the transmission characteristics of the crystals. The SHG study depicts the
nonlinear optical efficiency of the crystals.
Keywords: Crystal growth; Slow evaporation method; X-ray diffraction; FT-IR, UV-Vis-NIR;
Second harmonic generation.
1. INTRODUCTION
Nonlinear optical (NLO) materials play a vital role in optical modulation, fiber optic
communication and optoelectronics since they are capable of producing higher values of
original frequency. A continuous effort is on in growing organic, inorganic and semiorganic
materials with high damage threshold, wide transparency range and high nonlinear coefficient
which make them suitable for device fabrication. Bisthiourea cadmium bromide is one semi
organic material which exhibits both. Semiorganic materials possess better thermal stability
property of inorganic materials and higher nonlinear coefficient property of organic materials
[1-5]. As we do doping in semiconductor to improve its conductivity, we dope the semi
organic material with an organic material which may yield better nonlinear optical
properties.They are identified as useful crystals for nonlinear optical applications in optical
communication, optical switching, optical data storage, optical information processing,

632 M. Senthilkumar and C. Ramachandraraja Vol.11, No.6
frequency conversion and electro-optical modulation[6-11]. The authors in the present work
have tried to dope bisthiourea cadmium bromide with 1 mole % of L- alanine.
2. EXPERIMENTAL DETAILS
BTCB crystal is synthesized by dissolving AR grade thiourea and AR grade cadmium
bromide in the molar ratio 2:1 in distilled water. The saturated solution of cadmium bromide
was slowly added to the saturated solution of thiourea. This was stirred well to get a clear
solution. Pure BTCB crystal was synthesized according to the reaction:
2[CS (NH2)2] + CdBr2 → Cd [CS (NH2)2]2 Br2
The solution was purified by repeated filtration. The saturated solution was kept in a beaker
covered with polythene paper. For slow evaporation 6 or 7 holes were made in the polythene
paper. Then the solution was left undisturbed in a constant temperature bath (CTB) kept at a
temperature of 35 °C with an accuracy of ± 0.1° C. As a result of slow evaporation, after 75
days colorless and transparent pure BTCB crystals were obtained. The same procedure was
followed to grow 1 mole % L-alanine mixed BTCB crystals.
3. RESULT AND DISCUSSION
3.1. Single Crystal XRD Analysis
The single crystal XRD analysis of pure BTCB and 1 mole % L-alanine mixed BTCB
crystals were carried out using ENRAF NONIUS CAD 4 single crystal X-ray diffractometer
with MoKα (λ=0.071073 Å) radiation. From the XRD data, it was observed that the crystal
system of pure BTCB crystal is orthorhombic. The observed unit cell parameters are in
agreement with the reported literature values. BTCB mixed with 1 mole % L-alanine belongs
to tetragonal crystal system. The determined unit cell parameters and the observed crystal
system are presented in Table 1. The increase in cell volume is due to the incorporation
L-alanine in the grown crystals.
Table 1: Unit cell parameters of BTCB and LABTCB crystals
S. No. Crystal name
Axial lengths
of unit cell
(a, b and c)
Inter axial
angles
(α, β and γ)
Volume
Crystal
system
1 Pure BTCB
a = 5.6949 Å
b = 6.6051 Å
c = 7.5937 Å
α=β= γ=90° 285.6399(4) Å3 Orthorhombic
2 LABTCB
a = 9.234 Å
b = 13.747 Å
c = 13.75 Å
α=β= γ=90° 1746.7(9) Å3 Tetragonal

Vol.11, No.6 Growth, Structural, Spectral and Optical Studies 633
3.2. Powder XRD Analysis
The grown crystals of pure and L-alanine mixed BTCB crystals were crushed into fine
powder and powder X-ray diffraction analysis have been carried out using Rich Seifert X-ray
diffractometer. The sample was subjected to intense X-ray of wavelength 1.5406 Å (CuKα) at
a scan speed of 1°/minute to obtain lattice parameters. The recorded patterns are shown in
Fig. 1(a) &1(b). The observed diffraction pattern has been indexed by Reitveld index
software package. The lattice parameters have been calculated by Reitveld unit cell software
package. It is found that there is a close agreement with values obtained by single crystal
X-ray diffraction Table 2.
Table 2: Comparative XRD data of BTCB and LABTCB crystals
Fig. 1(a): Powder XRD pattern of BTCB
Sl.
No.
Crystal
name
Observed a ,b, c
values by single
crystal XRD
analysis
Calculated a, b, c
values by powder
XRD analysis
Observed
volume by
single crystal
XRD analysis
Calculated
volume by
powder XRD
analysis
1 Pure
BTCB
a = 5.6949 Å
b = 6.6051 Å
c = 7.5937 Å
a = 5.794 Å
b = 6.461 Å
c = 13.139 Å
285.63(4) Å3 291.961 Å3
2 LABTCB
a = 9.234 Å
b = 13.747 Å
c = 13.755 Å
a = 9.2413 Å
b = 13.7394 Å
c = 13.7533 Å
1746(9) Å3 1746.2572 Å3

634 M. Senthilkumar and C. Ramachandraraja Vol.11, No.6
Fig. 1(b): Powder XRD pattern of LABTCB crystal
3.3. FT-IR Spectral Analysis
The FTIR spectroscopy studies were used to analyze the presence of functional groups in
synthesized compound. The FTIR spectra of pure BTCB and LABTCB were recorded using
Perkin Elmer spectrometer model spectrum RX1 using KBr pellet technique in the range
4000 - 400 cm-1 and are shown in Fig. 2(a) & 2(b). The characteristic vibrational frequencies
of the functional groups of pure and L-alanine mixed BTCB have been compared with
thiourea. The comparison of characteristic vibrational frequencies has been tabulated in
Table 3.
NH stretching vibration of thiourea was observed at 3376 cm-1. The same vibrations were
observed in pure BTCB at 3386 cm-1 and 3395 cm-1 in LABTCB. NCN symmetric bending
vibrations were observed in pure thiourea at 494 cm-1 .The same vibrations are observed in
BTCB at 473 cm-1and at 471 cm-1 in LABTCB. C=S asymmetric stretching vibrations are
observed in pure thiourea near 1417 cm-1. The same vibrations are observed in pure BTCB at
1388 cm-1 and in LABTCB, it was observed at 1392 cm-1.
In the FTIR spectra, the NH stretching vibrational bands of NH2 asymmetric stretching were
observed around 3280 cm-1, 3281 cm-1 and 3285 cm-1. The NH2 symmetric stretching
vibrations are observed around 3167 cm-1, 3194 cm-1 and 3197 cm-1. These bands were
shifted to higher wave number region when compared to that of the free ligand. This shift
may be due to the increase in the polar character of thiourea molecule because of the
formation of S→M bonds in pure and L-alanine mixed BTCB complex.
The band observed around 1627 cm-1 corresponds to NH bending vibration of thiourea. The
same vibration was observed in BTCB at 1616 cm-1 and in LABTCB, it was observed at

Vol.11, No.6 Growth, Structural, Spectral and Optical Studies 635
1619 cm-1. The bands observed around 1490 cm-1 were identified as the C-N asymmetric
stretching vibration.
The bands observed around 709 cm-1 corresponds to C=S stretching vibration. The bands for
CN symmetric stretching vibration in the grown crystal were observed around 1089 cm-1. The
standard IR bands of thiourea and that obtained for BTCB and LABTCB are compared along
with their assignments and are presented in Table 3. It is found that the CN stretching (1089
and 1472 cm-1) bands of thiourea are shifted to higher frequencies for BTCB and LABTC.
Table 3: Vibrational assignments of thiourea, BTCB and LABTCB crystals
THIOUREA
( cm-1 )
BTCB
( cm-1 )
LABTCB
( cm-1 ) ASSIGNMENT
3376 3386 3395 NH stretching
3280 3281 3285 NH2 asymmetric stretching
3167 3194 3197 NH2 symmetric stretching
1627 1616 1619 NH bending
1472 1491 1490 CN asymmetric stretching
1417 1388 1392 CS asymmetric stretching
1089 1090 1089 CN symmetric stretching
740 708 709 CS symmetric stretching
494 473 471 N-C=N symmetric bending
Fig. 2 (a): FT-IR spectrum of BTCB crystal

636 M. Senthilkumar and C. Ramachandraraja Vol.11, No.6
Fig. 2 (b): FT-IR spectrum of LABTCB crystal
Also the CS stretching bands of thiourea (1417 and 740 cm-1) are shifted to lower frequencies
in BTCB and LABTCB. These results reveal that the metals coordinate with thiourea through
sulphur [12]. The slight variation in the observed frequencies of BTCB and LABTCB are due
to the presence of L-alanine.
3.4. UV-Vis-NIR Analysis
The absorption and transmission spectrum of pure BTCB and LABTCB was recorded
using UV-Vis-NIR spectrophotometer in the range from 190nm to 1100nm using Cary 500
scan UV-Vis-NIR spectrometer and it is shown in Fig. 3(a) & 3(b). The crystal shows a good
transmittance in the visible region which enables it to be a good material for optoelectronic
applications. As observed in the spectrum, the pure BTCB crystal was transparent in the
region from 269 nm to 1100nm and LABTCB was transparent in the region from 259 nm to
1100 nm. The lower cut off wavelength for pure BTCB is found at 269 nm and the lower cut
off wavelength for LABTCB is found at 259 nm. The wide range of transparency suggests
that the crystals are good candidates for nonlinear optical applications. The shift of lower cut-
off wavelength in UV region is due to mixing of L-alanine and is desirable for optoelectronic
application.

Vol.11, No.6 Growth, Structural, Spectral and Optical Studies 637
Fig. 3(a): UV-Vis-NIR spectrum of BTCB crystal
Fig. 3(b): UV-Vis-NIR spectrum of LABTCB crystal
3.5 Second Harmonic Generation Studies
The second harmonic generation test was carried out by classical powder method developed
by Kurtz and Perry [13]. It is an important and popular tool to evaluate the conversion
efficiency of NLO materials. The fundamental beam of 1064 nm from Q switched Nd: YAG
laser was used to test the second harmonic generation (SHG) property of pure BTCB and
LABTCB crystals. Pulse energy 2.9 mJ/pulse and pulse width 8 ns with a repetition rate of
10 Hz were used. The photo multiplier tube (Hamamatsu R2059) was used as a detector and

638 M. Senthilkumar and C. Ramachandraraja Vol.11, No.6
90 degree geometry was employed. The input laser beam was passed through an IR detector
and then directed on the microcrystalline powdered sample packed in a capillary tube. The
SHG signal generated in the sample was confirmed from emission of green radiation from the
sample. The nonlinear optical (NLO) efficiency of pure BTCB crystal was 95 mV and that of
LABTCB was 87 mV. The green light output was detected by a photomultiplier tube. KDP
and urea crystals were powdered to the identical size and were used as reference materials in
the SHG measurement. The SHG relative efficiency of LABTCB crystal was found to be 7.9
times higher than that of KDP and 0.836 times that of urea Table 4.
Table 4: Comparative study of SHG Efficiency
Crystal NLO efficiency
(in mV)
Pure BTCB 95
LABTCB 87
KDP 11
Urea 104
4. CONCLUSION
The potential semiorganic NLO crystals of pure BTCB and LABTCB were grown by slow
evaporation method. The grown crystals were characterized by single crystal XRD analysis,
powder XRD analysis, FTIR analysis, UV-Vis-NIR analysis and SHG studies. The XRD
analysis confirms the crystalline nature of the materials. The presence of various functional
groups present in the pure BTCB and LABTCB crystals have been confirmed by FTIR
analysis. The UV-Vis-NIR spectrum of grown crystals shows that the crystals are transparent
in the wavelength region from 269nm to 1100nm. The SHG efficiency of the grown
LABTCB crystal was 7.9 times greater than the KDP crystals. Owing to all these properties
LABTCB could be a promising material for NLO applications.
ACKNOWLEDGEMENTS
The authors are thankful to SAIF, IIT Chennai, Dr.P.K.Das, IPC, IISc, Bangalore, and ACIC,
St. Joseph’s College, Trichy for the spectral facilities. The corresponding author wishes to
thank University Grants Commission, New Delhi, Government of India for granting a minor
research project to do this research work.
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