Synthesis and characterization analysis of unique organic crystal – Urea Glutaric acid, an optimistic candidate for optical device applications

Article abstract of DOI:10.1016/j.physb.2019.411804

Urea Glutaric acid (UGA), an organic compound was grown and its diverse characterizations were studied. XRD results confirmed the structure as monoclinic with the space group of C2/c. FTIR results confirmed the basic functional groups present in crystal was noticed. The optical properties have been studied by absorbance measurements in the wave length region from 200 nm to 800 nm. NLO (third order) properties were studied by Z- Scan method declares UGA, a successful material in nonlinear optics. The fluorescence spectrum indicates an electronic excitation at 481 nm and its thermal studies was done to determine the stability of the grown material under decomposition. Laser damage threshold was calculated to predict its resistance for high power laser radiation. The hardness and dielectric properties of UGA was explained from Vicker's micro hardness and dielectric analysis. Hence, the results from various characterizations confirmed that UGA is an enticing aspirant over device fabrication in nonlinear optics.

Full text of DOI:10.1016/j.physb.2019.411804

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Synthesis and characterization analysis of unique organic crystal – Urea Glutaric
Acid, an optimistic candidate for optical device applications
C. Rathika Thaya Kumari, S. Sudha, G. Vinitha, M. Nageshwari, M. Lydia
Caroline, G. Mathubala, A. Manikandan
PII:
S0921-4526(19)30700-8
DOI:
https://doi.org/10.1016/j.physb.2019.411804
PHYSB 411804
Reference:
To appear in:
Physica B: Physics of Condensed Matter
Received Date:
Accepted Date:
30 September 2019
19 October 2019
Please cite this article as: C. Rathika Thaya Kumari, S. Sudha, G. Vinitha, M. Nageshwari, M. Lydia
Caroline, G. Mathubala, A. Manikandan, Synthesis and characterization analysis of unique organic
crystal – Urea Glutaric Acid, an optimistic candidate for optical device applications, Physica B:
Physics of Condensed Matter (2019), https://doi.org/10.1016/j.physb.2019.411804
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Synthesis and characterization analysis of unique organic crystal – Urea Glutaric Acid, an
optimistic candidate for optical device applications
C. Rathika Thaya Kumari a, S. Sudha b, G. Vinitha c, M. Nageshwari d,
M. Lydia Caroline e,*, G. Mathubala f, A. Manikandan f
a Department of Physics, Bharath Institute of Higher Education and Research, Chennai, Tamil
Nadu, India
b Department of Physics, Arignar Anna Govt. Arts College, Cheyyar, Tamil Nadu, India
c Department of Physics, School of Advanced Sciences, VIT, Chennai, Tamil Nadu, India
d Department of Physics, Peri Institute of Technology, Chennai, Tamil Nadu, India
e Department of Physics, Dr. Ambedkar Govt. Arts College, Vyasarpadi, Tamil Nadu, India
f Department of Chemistry, Bharath Institute of Higher Education and Research, Chennai, Tamil
Nadu, India
Corresponding author Email ID and contact no:
lydiacaroline2006@yahoo.co.in (M.Lydia Caroline);
Tel: 044-25520151: Fax: 044 - 2552 1852:+91 9841720216
Co-authors Email id: rathikak06@gmail.com (C. Rathika Thaya Kumari);
sudhavaidhy@gmail.com (S. Sudha); vinitha.g@vit.ac.in (G. Vinitha);
nageshwari.sb@gmail.com (M. Nageshwari); lydiacaroline2006@gmail.com (M.Lydia
Caroline); madhu2705@gmail.com (G. Mathubala); mkavath15@gmail.com (A. Manikandan)
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Abstract
Urea Glutaric acid (UGA), an organic compound was grown and its diverse
characterizations were studied. XRD results confirmed the structure as monoclinic with the space
group of C2/c. FTIR results confirmed the basic functional groups present in crystal was noticed.
The optical properties have been studied by absorbance measurements in the wave length region
from 200nm to 800nm. NLO (third order) properties were studied by Z- Scan method declares
UGA, a successful material in nonlinear optics. The fluorescence spectrum indicates an
electronic excitation at 481nm and its thermal studies was done to determine the stability of the
grown material under decomposition. Laser damage threshold was calculated to predict its
resistance for high power laser radiation. The hardness and dielectric properties of UGA was
explained from Vicker’s micro hardness and dielectric analysis. Hence, the results from various
characterizations confirmed that UGA is an enticing aspirant over device fabrication in
nonlinear optics.
Key words: Organic compound; Urea Glutaric acid; Crystal growth; Hardness studies;
Dielectric studies; Nonlinear Optics.
1. Introduction
Recent implementation of many new materials with good optical parameter creates
noteworthy interest on young researchers nowadays. The major task for the present researchers is
to produce superior crystals with better mechanical strength to enhance its nonlinear optical
properties [1, 2]. Single crystals are the strength to support various engineering and
technological revolutions [3]. In general, most of the opto electronic instruments are in need of
good nonlinear crystals to enhance its applications. In search of above needs an organic material
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was chosen because of its higher efficiency and larger nonlinear susceptibilities than inorganic
materials [4]. The focus on the growth of organic NLO material is due to its application of fast
data transfer over long distances, optical frequency conversion, dynamic holography and optical
guiding of laser beams [5].
Urea, a well-known organic material used significantly on crystal engineering, reveals high
nonlinear optical coefficients with strong laser damage threshold and elevated degree of
birefrigerence. The study of urea crystal is fascinated, due to their nonlinear optical piezo
electric properties [6]. In past literature, Urea p nitrophenol crystals [6], Urea L-valine [7], Urea
succinic acid [8], Glycine glutaric acid [9] were synthesized and their NLO properties were
discussed. The description of different combinations of the present compound in the ratio 1: 1,
1:2 and 2:1 was studied already and the structure with connectivity patterns of the 1:1 complex
was discussed [10]. Further the trend on organic compound highlights that urea is an efficient
material which often holds extreme degree of delocalization [6] and signifies its importance over
nonlinear optical applications [11]. Moreover, urea (N2H4CO) is a bi-functional material with
N-H, H2 bond donors and H2 bond acceptors. The carboxylic acids are the ideal elements for co-
molecular formations [12]. In the current work, slow evaporation solution growth technique was
implemented to take Urea Glutaric acid (UGA) crystal in the ratio of 2:1 whose crystal structure
has been reported by Veneta Videnova Adrabinska [12]. The growth and extensive
characterizations were analyzed for the first time and is reported.
2. Synthesis of UGA
A material UGA was taken from urea and glutaric acid of 2/1 ratio. The weighed amount of
the material was stirred separately with double distilled water to attain homogeneous solution
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using magnetic stirrer. It continues for 6 hours. Further, the mixture is transferred into clean
beaker. Cover the beaker with transparent paper having small holes and kept for evaporation to
take place slowly. Under clear observation, an optically impressive crystal was seen after 30
days. After successive recrystallization to attain purity it was well photographed and is shown in
Fig. 2. The synthesis method of UGA is given below [Fig. 1]:
2
+
Glutaric acid
Urea
Urea Glutaric acid (2/1)
Fig. 1. Reaction Outline for UGA
.
Fig. 2. Image of UGA single crystal
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3. Results & Discussion
3.1. Single XRD analysis
The XRD was accomplished from NONIUS - CAD4-F diffractometer with MoKα (Å)
ray to verify the UGA crystal. XRD study declares that this crystal discloses in monoclinic
structure with C2/c space group. The measured values of a, b and c values are 12.07ꢀÅ, 11.05ꢀÅ
and 9.17ꢀÅ respectively, having volume 1210 Å3, which was in accordance with the already
published by Veneta Videnova Adrabinska et al. [12].
3.2 Investigation of FT- IR & Raman Spectrum
The FT-IR and RAMAN spectrum for UGA was investigated with PERKIN ELMER
spectrometer and BRUKER RFS 2.7 spectrometer from 4000 cm-1 by KBr pellet technique. The
documented spectrum is delineated in Fig. 3 and various vibrations observed were discussed.
The OH stretching wave number was pointed around 3550 cm-1 – 3200 cm-1 [13]. The vibrations
observed near 3579 cm-1, 3319 cm-1 in IR as well as Raman were attributed to OH symmetric
stretching vibration [8]. The plane deformation vibration of OH and bending out of plane
vibrations of OH were allotted at 752 cm-1, 933 cm-1 and 903 cm-1. The bands at 3198 cm-1 and
770 cm-1 arises because of symmetric stretching and rocking of NH2 respectively [9]. The peak
1414 cm-1, 1421 cm-1 clearly represents N-C-N vibrations corresponding to asymmetric
stretching of urea [8]. The C=O vibrations corresponding to stretching is present in both at 1697
cm-1, 1701 cm-1 respectively. C-H band's wagging vibrations are positioned at 1163 cm-1 in IR
and 1169 cm-1 in Raman counterpart. The CH stretching vibrations overlap upon O-H band near
2905 cm-1, 2907 cm-1 in both spectra respectively [9]. The stretching of C-O is visible at
1188 cm-1 and the pointed band at 1697 cm-1 is ascribed to C=O stretching. The peaks at 1291
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cm-1 in IR as well as Raman show the existence of carboxylic acid in glutaric acid. The presence
+
of NH3 was identified at 2573 cm-1 and is mainly ascribed to the protonation of NH2 by COOH
group of glutaric acid [14]. The asymmetric stretching of COO- is seen at 1594 cm-1 and 1564
cm-1 and COO- bending mode is seen in 612 cm-1, 613 cm-1 in both spectra respectively [6]. The
vibrational band allotments were summarized in Table 1.
Table 1. Different Vibrations of IR and RAMAN spectra - UGA (2/1)
IR Wave number in cm-1
RAMAN Wave number in cm-1
3319
Assignments
3579
3198
2905
2573
1697
1594
1414
1291
1188
1163
933
OH sym.stretching
sym. stretching NH2
CH stretching
2907
+
NH3 stretching
1701
1564
1421
1291
C=O stretching
COO- asym stretching
N-C-N asym stretching
COO- rocking
C-O stretching
1169
903
CH Wagging
O-H out of plane
NH2 rocking
770
612
613
COO- bending
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Fig. 3. FT-IR and FT – RAMAN spectrum of UGA
3.3 Optical studies
The UV-Vis spectrum was actualized from 200 - 800ꢀnm employing PERKIN - ELMER
LAMADA 35 spectrophotometer. The important enticing characteristics of the material to
analyze its usage for device applications are transmission width and cutoff wavelength [15].
Desired lower cutoff wavelength must lie within the range 200 nm – 400 nm for an efficacious
NLO material [16]. Fig. 4 portrayed the absorption spectra for UGA crystal. The prominent
lower cut off wavelength for UGA is observed as 240 nm. From 240 nm to 800 nm no further
absorption occurs which extremely supports clear transmittance in the whole visible band
suggests its excellency over application of opto electronics.
The extension of the linear part [17] that is depicted in Fig. 5, the energy gap was
assessed. The optical bandgap value for UGA was computed as 5.46 eV. The more transmittance
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and broad energy gap confirms low defect concentration in the UGA crystal which shows
outstanding possibilities for nonlinear device applications [18].
Fig 4. UV- Visible Spectra of UGA
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Fig 5. Band gap (Tauc’s plot ) of UGA crystal
3.3.1 Urbach Energy
The absorption coefficient (α) was estimated from Urbach formula [19],
α (hυ) = α0 exp (hυ/Eu)
-------- (1)
The graph hν with ln (α) is predicted in Fig. 6. The crystalline feature of the as grown material is
identified from the increase in value of α along photon energy (hυ).The observed slope of
straight line got by plotting logarithm and photon energy (hυ), interprets excellent crystallinity
in the grown crystal. The inverse of the slope was detected to be 0.3933 eV, which is Urbach
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energy for UGA. Moreover, low (0.3933 eV) estimated Urbach energy signifies minimum defect
in the grown crystal [20].
Fig 6. Variation of photon energy hν verses ln (α)
3.4 THG – Z-Scan Studies
The Z-scan method for UGA has been employed using Nd-YAG laser (Coherent compass
TM215M-50) with 532 nm to show third order nonlinearities. This was a regular method to
identify the nonlinear property of the material in centrosymmetric media. It is a delicate
technique to predict the nonlinear parameters for centrosymmetric materials. Generally for
optical switching, optical limiting sensors and sensor protection applications, the materials
should have vast nonlinearities [18]. Z Scan technique measures absorption and refraction of
NLO based on the scanning of spatial beam modifications based on the laser beam focused and
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defocussed in time through a nonlinear material and yields the nonlinear parameters from the
open and closed aperture pattern.
The closed aperture configuration is gentler to yield nonlinear absorption and refraction.
From the observed peak followed by valley configuration in Fig. 7, illustrates the negative
nonlinearity which is attributed to self-defocussing nature [18]. In the open aperture
configuration the transmittance curve shown in Fig. 8, is symmetric with respect to focus and
shows two photon absorption processes [21]. This open aperture curve is used to calculate the
nonlinear absorption coefficient and was found to be 0.02 x 10-4 cm/W.
The assessable quantity (ΔTP-V), shows the variation from the maximum and minimum
values of transmittance is represented using the formula,
훥푇 = 0.406 (1 ― 푆)0.25|휙|
------- (2)
푟2
2
)
-------- (3)
푆 = 1 ― exp ( ― 2 푎 휔푎
The on-axis phase shift ǀϕǀ [22] is specified by,
|휙| = 푘 푛2 퐿푒푓푓 퐼0
------- (4)
L denotes the length, α and k signifies linear absorption coefficient and wave number.
From the configuration of open aperture Z-scan,
2
2
. ∆푇
-------- (5)
훽 =
퐼0 . 퐿푒푓푓
The above computed data was utilized to study the real and imaginary components of nonlinear
optical susceptibility χ3.
휀0 퐶2푛20
휋
푐푚2
푊
푅푒 휒(3)(푒푠푢) = 10 ―4
푛2 (
)
-------- (6)
휀0퐶2푛20 휆
4휋2
2
퐼푚 휒(3)( 푒푠푢) = 10 ―2
훽 ( 푐푚
)
-------- (7)
푊
Also,
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1
2
(3)
(3)
2
(3)
2
|
|
( ) ( )
= [ 푅푒 휒 ) + (퐼푚 휒 ) ]
-------- (8)
휒
Table 2 elucidates the experimental particulars namely Nonlinear refractive index (n2), Nonlinear
absorption coefficient (β), Real susceptibility (χR(3)) , Imaginary susceptibility (χI(3)) and
Absolute susceptibility ǀ χ(3) ǀ are the outcome for UGA crystal. The third-order nonlinear optical
susceptibility χ3 of UGA shows a larger value compared to the other crystals and is presented in
Table 3.
Fig 7. Z-Scan Transmittance curve for closed aperture
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Fig 8. Z-Scan Transmittance curve for Open aperture.
Table 2. Nonlinear optical (Third order) parameter of UGA
(3)
n2 cm2/W
7.80 x 10-8
β cm2/W
χR esu
χI(3) esu
ǀ χ(3) ǀ esu
UGA
0.02 x 10-4
8.54 x 10-6
0.14 x 10-6
8.54 x 10-6
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Table 3. The χ(3) values of some Organic nonlinear optical crystals
Crystal
UGA
Third order susceptibility
8.54 x 10-6 esu
References
Present work
[23]
UAA
6.44 x 10-8 esu
LMSA
DLMA
6.346 x 10-6 esu
4.18 x 10-6 esu
[24]
[25]
3.5 Photoluminescence Spectrum
The fluorescence and lifetime of UGA were recorded with the help of FLUOROCUBE
Spectrofluorophotometer between 200–800nm. The fluorescence spectral investigation was
predicted to gain information about higher order energy levels during radiative recombination
[26]. The emitted spectra from the excited state and its decay components are studied clearly for
UGA crystal. This was pictured for the excitation wavelength of 240 nm [Fig. 9 (a)]. A pointed
peak at 481 nm (2.58 eV) discloses the blue light of electromagnetic spectrum near the visible
region. Time Resolved Fluorescence Spectroscopy is used to extract the life time. The
measurements of decay time with thrice of its exponential decay function are evaluated and
were illustrated in Fig. 9 (b). The decay time measurement was analyzed with a three
exponential decay function [26] of the form,
F(t)  A et /  A2et /  A3et /
-------(9)
1
2
3
1
where different orders of A, τ indicates the amplitudes and lifetimes of prompt and
delayed emissions respectively. The actual decay curve was accessed in Fig. 9 (c). Thus based on
the residuals, worthy curve fit was measured and the value χ2 ratio was estimated. The shortest
decay component of the present work was depicted in Table 4.
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Table 4. Fluorescent life time data for UGA single crystal.
Three Exponential Analysis of UGA Crystal
Life Time
τ2
Amplitude
A2
χ2
τ1
τ3
A1
A3
3
9
1
53.34
16.72
29.94
1.098
Fig. 9(a) Emission spectrum (b) Life time measurement (c) Residual fit of UGA
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3.6 LDT Studies
The LDT of an optical crystal is the noticeable parameter to strengthen its ability and
capability towards linear and nonlinear characteristics and must be endure with greater power
intensities [27]. The multi shot surface laser damage threshold experiment was also done for
UGA using Nd-YAG laser system (1064 nm). The LDT of UGA was determined utilizing the
relation,
Power density (Pd) = E / τ A (GW/cm2)
------- (10)
The computed LDT value of UGA is 3.617 GW/cm2and it possesses higher value in
comparison with KDP and urea (0.20 GW/cm2 and 1.50GW/cm2) [28]. This larger LDT value of
UGA authenticates its aptness in the field of laser applications [29]. Table 5 shows some LDT
values of other organic crystals.
Table 5. Comparison chart of UGA with Urea and related crystals
Material
Laser Damage Threshold values References
(GW/cm2 )
Urea
1.5
[28]
L -Valinium L -Valine chloride
Benzimidazole
2.59
2.9
[30]
[31]
Urea Glutaric acid
3.617
Present Work
3.7 TG/DTA Analysis
Thermal analysis is one of the substantial criteria for examining thermal stability,
decomposition, mass change and melting point of the material. The thermal behavior of the
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grown crystal was studied using TG/DTA analyses at the temperature ranges from 30-500˚C
using NANO TECHNOLOGY-MODEL 6200 thermal analyzer in N2 atmosphere at a thermal
rate of 20˚C/min to study its thermal stability. The noted TG and DSC graph is shown in Fig. 10.
From the TG profile, the major weight loss (98.82 %) was observed at 137.69 0C. The sharp peak
0
observed at 137.69 C in DSC curve shows the decomposition of the material. The weight loss
starts at 137.69 0C (5.969 mW/mg) and second stage at 181.2 0C (2.009 mW/mg) further it down
to zero weight. The loss in weight is mainly due to the ejection of water present in the material
0
[32]. This shows the stability of UGA is up to 137.69 C and beyond this limit it undergoes
decomposition.
Fig 10. TG/DSC curve for UGA crystal
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3.8 Micro hardness Analysis
The strength and hardness of the organic compounds are most decisive to regulate the
potentiality of the material in the electronic and optical device fabrication. The mechanical
strength was determined by the Vickers microhardness test for cutting and polishing the crystal.
In support to study the mechanical stability of the present material Vickers microhardness
analysis was done. Highly transparent pure crystals were subjected to indentations with different
loads with the duration of 10 s. The microhardness value (Hv) was evaluated using,
P
Hv 1.8544

kg / mm2

--------(11)
d 2
Fig 11. Variation of load P verses Hv for UGA crystal
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It is noticed from the Fig.11, that Hv value raises on applying the load substantiates high
mechanical strength of UGA crystal. Fig. 12 declares the work hardening coefficient (n = 4.12)
highlights that UGA material is soft [33].
Fig 12. Variation of log d verses log P for UGA crystal
3.9 Dielectric studies
The various parameters from dielectric analysis correlates the electro and optic properties
of the materials [25]. The dielectric constant and loss based on frequency and temperature was
studied to gain more evidence about the structural variations, flaw behavior and the phenomena
of transport.
The dielectric permittivity of the material has been formulated using the relation,
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ε = Cd/Aε0
(12)
-------
where C indicates capacitance, d denotes thickness and A be the area of the sample and ε0
indicates the permittivity of free space. Fig 13(a,b) shows the variation of dielectric constant and
loss verses frequency at several temperatures. From the graph it is pointed that the dielectric
permittivity lowers as the frequency raises and almost remains same over a wide range of
frequencies. The overlapping of the curve for different range of temperatures indicates the
occurrence of similar mechanism throughout. The low dielectric loss at greater frequency shows
good optical property with few defects present in UGA crystal and is more suited for nonlinear
optics.
Fig 13. Variation of log F verses (a) Dielectric constant (b) Dielectric loss
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4. Conclusion
In this present analysis, an optically transparent third order organic crystal Urea- Glutaric
acid (UGA), was harvested successfully. The grown material undergoes various characterizations
and the results were reported. The single crystal XRD elucidates the monoclinic structural
symmetry with the space group of C2/c and the corresponding lattice parameters were also
determined. The various vibrational modes were predicted from IR and RAMAN spectrum. The
absorbance spectrum shows good transparency with the broad gap of 5.46 eV with the
wavelength down to 240 nm. The NLO behavior has been confirmed from the Z-scan analysis
which notifies the strong defocussing nature and negative nonlinearity. The crystal has maximum
absorption peak at 481 nm in the electronic absorption spectrum and its life time was appraised.
The TG/DSC curve confirms that the crystal is stable upto 137.69 0C favors in the fabrication of
photonic device. The various characteristics estimated from hardness analysis supports the good
mechanical stability. The dielectric constant and loss for different range of frequencies suggests
that UGA is more favorable in the field nonlinear applications. From the results discussed, it is
settled that UGA is a suitable applicant for future photonics and opto electronic device
fabrications.
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