Journal of Minerals and Materials Characterization and Engineering, 2012, 11, 813-816
Published Online August 2012 (http://www.SciRP.org/journal/jmmce)
Crystal Growth, Optical and Dielectric Properties of
L-Histidine Hydrochloride Monohydrate Nonlinear
Optical Single Crystal
P. Koteeswari1, S. Suresh2*, P. Mani1
1Department of Physics, Hindustan Institute of Technology, Padur, India
2Department of Physics, Loyola College, Chennai, India
Received April 25, 2012; revised June 10, 2012; accepted July 1, 2012
ABSTRACT
Optically transparent and bulk single crystal of l-histidine hydrochloride monohydrate (LHHM) was successfully grown
by slow evaporation technique. The cell parameters and the crystallinity of the grown crystal were estimated by the sin-
gle crystal XRD. Optical transmittance of the crystal was recorded using the UV-vis-NIR spectrophotometer. The opti-
cal band gap and optical constant of the material were determined by using transmission spectrum. The dielectric loss
and dielectric constant measurements as a function of frequency and temperature were measured for the grown crystal.
Keywords: Single Crystal; Slow Evaporation Technique; XRD; UV and Dielectric Studies
1. Introduction
The organic NLO materials are attracted by many scien-
tists due to their frequency conversion efficiency, piezo-
electric, pyro-electric properties and their wide applica-
tions in the recent technologies like lasers, optical com-
munications and data storage [1]. New materials with
high optical nonlinearities are quite important due to
their extensive application in harmonic generation, am-
plitude and phase modulation, switching and other signal
processing device [2-4]. The main goal to design the
molecules with the third order nonlinearities is to incor-
porate them into the devices used in all types of optical
signal processing [5-6]. Nonlinear optical (NLO) materi-
als have shown potential application in optical informa-
tion storage, optical logic gates, laser radiation protection
and phase locked laser mode. Hence the interest in
searching for NLO materials has increased gradually [7].
In addition to that organic molecules also have a great
attention owing to their potential application in the frontier
areas such as nonlinear optics (NLO), optical switching
and light emitting diodes. Thus, the potential use of or-
ganic device materials in optoelectronics has now be-
come a serious matter [8]. The present investigation is
aimed at the growth of bulk LHHM single crystal by
slow evaporation technique. The grown crystal has been
subjected to single X-ray diffraction analysis, UV-vis
transmission spectral analysis, optical band gap meas-
urements, and dielectric studies.
2. Experimental Procedure
The l-histidine and hydrochloric acid were taken in equi
molar ratio in double distilled water to prepare the satu-
rated solution of l-histidine hydrochloride monohydrate
(LHHM). The solution obtained is stirred well at room
temperature using a temperature controlled magnetic stir-
rer to yield a homogenous mixture of solution. Then the
solution is filtered using a Whatmann filter paper and
was allowed to evaporate at room temperature. The solu-
tion is recrystallized several times in order to increase the
purity of the crystal. Optically clear and good quality
seed crystal is kept inside the purified saturated solution
and the solution is allowed to evaporate at room tem-
perature, which produces an improved optically high
quality within a period of 30 days. The photograph of the
as grown single crystal is shown in Figure 1.
3. Results and Discussion
3.1. Single Crystal X-Ray Diffraction
Single crystal X-ray diffraction analysis was carried out
to determine the lattice parameters. The grown crystals
have orthorhombic structure with P212121 space group.
The lattice parameter values of the grown crystals are a =
6.82 Å, b = 8.91 Å, c = 15.286 Å. The single crystal data
are in good agreement with reported values [9].
*Corresponding author.

P. KOTEESWARI ET AL.
814
3.2. Optical Transmittance Spectrum Study


12
g
Ahv E
hv





The optical transmission spectrum of LHHM single crys-
tal was recorded in the wavelength region 300 - 900 nm
and is shown in Figure 2. For optical fabrications, the
crystal should be highly transparent in the considered
region of wavelength [10] and [11]. Favorable transmit-
tance of the crystal in the entire visible region suggests
its suitability for second harmonic generation [12]. The
UV absorption edge for the grown crystal was observed
to be around 260 nm. The dependence of optical absorp-
tion coefficient on photon energy helps to study the band
structure and type of transition of electrons [13].
Optical absorption coefficient (α) was calculated from
transmittance using the following relation:
11
log
dT




(1)
where T is the transmittance and t the thickness of the
crystal. As a direct band gap material, the crystal under
study has an absorption coefficient (α) obeying the fol-
lowing relation for high photon energies (hν).
Figure 1. Photograph of as grown crystal.
Figure 2. Transmission spectrum of the grown crystal
(LHHM).
(2)
where Eg is the optical band gap of the crystal and A is a
constant. A plot of variation of (αhν)2 versus hν is shown
in Figure 3. Eg is evaluated using extrapolation of the
linear part [14]. The energy absorption gap is of direct
type and the band gap energy is found to be 3.90 eV.
3.3. Determination of Optical Constant
The dependence of optical absorption co-efficient with
photon energy helps to study the band structure and the
type of transition of the electron. The absorption coefficient
(α) and the optical constant (n, k) are determined from
the transmission (T) and reflection (R) spectrum based on
the following relations, [15,16].
2
2
1exp
1exp2
Rt
TRt




 
(3)
Reflectance can also be written in terms of absorption
coefficient and from the ab

11exp exp
1exp
tt
Rt



 


(4)
and from the above equation, refractive index (n) can also
be derived as

2
13103
21
RRR
nR


  (5)
Figure 4 show the variation of refractive index (n) as a
function of wavelength (λ), respectively. From the graphs,
it is clear that refractive index (n) depend on wavelength (λ).
3.4. Dielectric Studies
The dielectric characteristics of the material are important
Figure 3. Plot of (αhν)2 vs photon energy of the title crystal.

P. KOTEESWARI ET AL. 815
to study the lattice dynamics in the crystal. Hence, the
grown crystal was subjected to dielectric studies using a
HIOKI HITESTER model 3532-50 LCR meter in the
frequency range from 50 Hz to 5 MHz for different tem-
peratures. The surface of the sample was electrode with
silver paste for electrical contact. Figure 5 shows the
plot of dielectric constant (εr) versus log frequency. The
dielectric constant has high values in the lower frequency
region and then it decreases with the increase in fre-
quency. The very high value of εr at low frequencies may
be due to the presence of all the four polarizations,
namely, space charge, orientational, electronic and ionic
polarization and its low value at higher frequencies may
be due to the loss of significance of these polarizations
gradually. From the plot, it is also observed that dielec-
tric constant increases with an increase in temperature,
and this is attributed due to the presence of space charge
polarization near the grain boundary interfaces, which
depends on the purity and perfection of the sample [17].
Figure 6. Variation of dielectr ic loss with log frequency.
he variation of dielectric loss with frequency is shown
4. Conclusion
l of semi-organic LHHM was grown
[1] N. B. Singh, Tetz, R. Hamacher,
Figure 4. Variation of refractive index with wavele ngth.
T
in Figure 6. The characteristics of low dielectric loss
with high frequency for the sample suggest that it pos-
sesses enhanced optical quality with lesser defects and
this parameter is of vital importance for nonlinear optical
applications [18].
Bulk single crysta
from aqueous solution by a slow evaporation technique.
Single crystal X-ray diffraction studies confirm that the
grown crystal belongs to orthorhombic crystal system
with space group P212121. The optical transmission
analysis indicates that LHHM has a wide transparency
window in the entire visible and near IR regions with a
lower cutoff wavelength at 260 nm. The band gap was
estimated to be 3.90 eV. The variation of dielectric con-
stant (ε′), dielectric loss and imaginary dielectric constant
(ε″) were studied as a function of frequency at different
temperatures.
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