STUDIES ON L -ARGININE ACETATE SINGLE CRYSTALS

FOR NLO APPLICATIONS N.Kanagathara1, G.Anbalagan 1*, N.G.Renganathan2*

1 Department of Physics, Vel Tech Multi Tech Dr.Rangarajan , Dr.Sakunthala Engg.College,

Ch-62, 1* Department of Physics, Presidency College, Chennai-5

2 Department of Chemistry, Vel Tech University, Avadi, Chennai,600 062

ngrenganathan@gmail.com

ABSTRACT NLO materials have a significant impact on laser technology, optical communication and optical storage technology.

This review paper deals with studies on the L-arginine acetate single crystal, a promising crystal for non linear

application. Growth of bulk single crystals of these materials has been a subject of perennial concern to enable to

be useful for device applications. Nonlinear optical studies reveal that the dopant has increased the efficiency of the

LAA crystal. L-arginine acetate (LAA) is one among them which is considered to be a potential nonlinear optical

(NLO) material and several reports are available on it. Recent studies reveal that LAA possess excellent optical,

thermal, mechanical properties which make it a strong candidate for photonic devices.

Keywords: L-arginine acetate, slow evaporation, dopant, NLO, powder XRD, FTIR, dielectric etc

Introduction Non liner optical materials will be the key

elements for future photonic technologies

based on the fact that photons are capable of

processing information with the speed of

light. Due to this fact the rapid development

of optical communication system has led to

a demand for non linear optical materials of

high structural and high optical quality. L-

arginine acetate (LAA) single crystal is an

interesting nonlinear optical and dielectric

material. Crystalline salts of L-arginine have

attracted considerable interest among

researchers. Therefore crystals of L arginine

acetate are selected for the present review

with regard to the growth and

characterization. Single crystals of L-

Arginine Acetate (LAA) with good degree

of transparency were grown from aqueous

solution by slow evaporation technique

LAA crystallizes in the monoclinic system

with space group P21 and the lattice

parameters are a = 9.226 Å, b = 5.243 Å, c =

13.049 Å, β = 108.92 and V = 597.14 Å

Experiments conducted by Monaca et.al

[1]and Petrosyan et.al [2] reveal the

suitability of L-arginine family crystal for

their non linear optical properties and

applications. L arginine has good

transparency of 77% . The lower value of

wavelength cut off of the crystal is found to

be 240 nm. Hence it can very well be used

for frequency conversion applications.

Attempts have been made to improve the

physicochemical properties by incorporating

metal dopants. A systematic study has been

carried out on the growth of pure and metal

(Cu2+ and Mg 2+ ) doped LAA crystals.

Praveen Kumar et.al [3] developed good

quality of single crystals of pure , and Cu2+

and Mg 2+ doped LAA by slow

evaporation technique. The content of Cu

and Mg has been determined by Atomic

Absorption Studies. Absorption of these

crystals grown thus has been analyzed using

UV-VIS-NIR studies, and it is found that

these crystals possess minimum absorption

in the entire visible region. This is which is

needed for NLO activity. The doped one

should have minimum absorption and as

expected it should have lower cut off

wavelength. Non linear optical (NLO)

studies of pure and doped crystals has been

carried out and it reveals that the dopants

have increased the efficiency of LAA

crystals. From the X-ray studies it is clear

that both pure and doped crystals crystallize

in monoclinic P21 space group. In this Cu2+

and Mg2+ doped crystals of LAA have

lower cell volume and between Cu2+ and

Mg2+ doped crystals, Mg2+ has lower cell

volume compared to Cu2+ doped crystals

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and this is understandable from the fact that

Mg radius is 0.65Ao is lower compared to

radius of copper 0.72Ao.Second Harmonic

Generation efficiency of pure, Cu2+ and Mg

2+ doped crystals is nearly 3,3.2 and 3.35

times greater than KDP. It is seen that Cu2+

and Mg 2+ metal dopants have increased the

efficiency of pure LAA. SHG signal occurs

at 820mV for pure , 885mV for Cu2+ and

920mV . For Cu2+ and Mg 2+ doped LAA

crystals show similar features as that of pure

LAA but there is a distinct shift in the

decomposition temperature and this

indicates the thermal stability of these

crystals.

Single crystals of organic nonlinear optical

material of pure, Cu2+ and Mg2+ doped L-

arginine acetate (LAA) were successfully

grown by slow evaporation method at room

temperature by Gulam Mohammed et.al

[10] The UV-Vis-NIR spectra of pure and

doped LAA indicate that these crystals

possess a wide optical transmission window

from 240-1600 nm. Non-linear optical

studies reveal that the SHG efficiency of

LAA is nearly three times that of KDP. The

dielectric response of the samples was

studied in the frequency region 100 Hz to 2

MHz and the influence of Cu2+ and Mg2+

substitution on the dielectric behavior had

been investigated. Photoconductivity study

proves that both pure and Cu2+ and Mg2+

doped LAA crystal exhibit positive

photoconductivity. It is evident from the

Vickers hardness study that the hardness of

the crystal decreases with increasing load

both for pure and doped samples. ESR

studies confirmed the incorporation of Cu2+

into LAA and the value of g-factor was

found to be 2.1654.

V.Natarajan et.al [5] developed single

crystals of pure and Lithium doped LAA by

slow evaporation method. The presence of

Li in the grown crystal was confirmed by

Atomic Absorption Spectroscopic analysis.

Electrical properties of the Li doped LAA

crystal was analyzed by AC impedance

studies. The optical transmission study

shows that the Li doped LAA crystal has

good optical transparency in the UV and

visible region.

Based on literature survey in the field of Li

based research, many of the physical

properties of a particular material were

enhanced by the addition of Li+ ions. Tri

lithium citrate was selected as the source

material for Li dopant because of high

electro negativity value. It has been found

that the number of nucleation was increased

in the Li doped LAA growth than the pure

LAA solution. From the XRD data, it is

observed that the pure and Lithium doped

LAA crystals retain the monoclinic structure

but a slight deviation is observed in the

intensity values in addition to minor shift in

the case of Lithium doped LAA crystals

when compared to the pure LAA.

FT-IR spectrum has no conspicuous

changes for pure and Lithium doped LAA

crystals but AAS analysis clearly established

in the presence of dopant in the lattice of

LAA. This may be due to low quantity of

dopant to produce any characteristic change

in the IR spectrum.

It has been found that the presence of Li ion

in LAA lattice does not affect the dielectric

properties of the material. It may result in

improving NLO properties of Li doped LAA

crystal. This conclusion has been arrived at

from the low frequency data from the

impedance results. This result is significant

with sense that it decides the mobility of

lithium ions, which is highly restricted and

hence the Lithium dopant doesnot affect the

dielectric properties of the material.

Gnanasekaran et.al [9]developed pure

LAA and rare earth dopant Lanthanum LAA

crystals. It was found that the amount of

dopant incorporated into the doped crystal is

less than the concentration of the dopant in

the corresponding solution. The studies

confirm that the grown crystals were non-

linear in nature and metal substitution has

enhanced the non-linearity of the crystals.

Meena et.al [6] obtained single crystals of

LAA by slow cooling method. LAA is a

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promising low εr value dielectric material.

In effect, Meena et.al established that LAA

is not only a potential NLO material but also

promising low εr value dielectric material,

expected to be useful in the micro electronic

industry. The dielectric constant of ζAC

values have been determined at 40oC. The

dielectric constant and dielectric loss tanδ

are found to decrease whereas the

conductivity value is found to increase with

increase in frequency and hence this

indicates the normal dielectric behavior

which goes well with the mechanism of

polarization that is happening in the

conduction process.

Conductivity value was found to increase

with increase in temperature and this

behavior was similar to tartrate crystals. The

conduction mechanism may be better

understood if one considers rotation of

acetate ions. In this work, potentiality of

NLO material synthesis with low dielectric

constant is indicated.

Meena et.al [10] developed LAA single

crystals by the slow cooling method] and

the investigation shows the effect of NaCl,

KCl, glycine and urea, added separately as

impurities, on the electrical properties of the

synthesized crystal.. The results obtained in

the present study indicate that the organic

impurities considered are able to reduce the

electrical parameters. In the case of NaCl

and KCl, NaCl is able to increase while KCl

is able to decrease the electrical parameters

even though the change is observed to be

small . In accordance with the Miller rule,

the lower value of dielectric constant is a

suitable parameter for the enhancement of

second harmonic generation (SHG)

coefficient. It is already known [7] that LAA

is a promising low- εr value material. It is

interesting to note that the organic impurity

addition leads to a reduction of dielectric

constant for a wide temperature range

significantly and consequently leads to low -

εr value dielectric material which is gaining

more importance nowadays in the

microelectronics industry. Both glycine and

urea are found to be equally good in

reducing the εr value. Oxygen content of the

impurity may be a considerable factor in

choosing the impurity for reducing the εr

value.

Muralidharan et.al [7] developed the

optical quality of bulk single crystals by low

temperature solution growth method.

Laser damage threshold studies were made

on the grown bulk crystals and it was found

to be 19.7 GWcm-2. From the FT-IR results

it has been concluded that the acetic acid

proton is not transferred to –coo- group of

L-arginine but to the one of un-protonated

amino group.

The transparency of the synthesized crystal

is reported to be 77% and the lower cut off

value of the crystal is reported to be 240 nm.

The crystal thus synthesized will find

usefulness in SHG studies and a small

absorption band that is observed at 330nm is

attributed due to n-π * transition and azo

methyne group. K.Selvaraju et.al

[8]investigated the nucleation parameters of

LAA , which are essential for the growth of

bulk crystals. Also the interfacial energy

radius of critical nucleus and the critical free

energy barrier have also been estimated. The

interfacial energy, radius of critical nucleus

and the critical free energy barrier have been

estimated. From the induction period data

obtained experimentally, the interfacial

energy has been calculated. Nucleation

kinetics and fundamental growth have been

investigated. This study was highly helpful

to get good quality crystals by controlled

nucleation rate. The radius of the critical

nucleus and the critical energy barrier were

found to decrease exponentially with the

increase of super-saturation.

Y.L. Geng, et.al [4] carried out atomic

force microscopy (AFM) study to

understand the growth mechanism and

morphology of LAA single crystal on a nano

meter scale and reported the cleavage

morphology of {100} faces of LAA crystal.

They characterized cleaved surfaces by

several step trains such as straight, V-shaped

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and irregular steps. From their studies , it

was concluded that dissolution of the surface

materials by the adsorbed moisture in air

and re-crystallization of the micro-solution

leads to the morphology transformation of

the cleaved faces.

S.Suresh et.al [11] developed good quality

single crystals of LAA were grown by slow

evaporation technique. Single-crystal XRD

analysis confirmed that the crystals belong

to monoclinic system with the space group

P21. Fundamental parameters like plasma

energy, Penn gap, Fermi energy and

electronic polarizability of the crystal have

been calculated. The band gap energy for the

grown crystal is found to be 3.75 e.V. The

optical investigations show a high value of

both extinction coefficient (K) and refractive

index (n) indicating high transparency of the

crystal which confirms its suitability for

optical switch device fabrications. The

frequency dependence of dielectric constant

decreases with increasing frequency at

different temperatures.

Conclusion

Non linear optical material, L-Arginine

acetate single crystal growth has been dealt

with in this review. Mostly the crystals were

grown from aqueous solution by slow

evaporation technique. Crystals grown has a

good transparency of 77 % and the lower

cut off value of wavelength was found to be

240 nm. Cu2+ and Mg2+ doped crystals

were also grown by the slow evaporation

technique and dopants have increased

second harmonic generation efficiency to

the extent of 3.2 to 3. 5 times greater than

KDP crystals and optical transmission

window was also wider from 240 -1600 nm.

Doped crystals exhibit positive

photoconductivity. Hardness of the crystal

decreases with increasing load for pure and

doped samples. Li doped LAA crystal has

good optical transparency in the UV and

visible region. Li dopant does not affect the

dielectric properties of the material. Rare

earth metal lanthanum doped LAA crystals

has enhanced non linearity of the crystals.

LAA crystals grown have found to have low

dielectric constant and low die electric loss

values. Organic impurities if added as

dopants , reduce the electrical parameters.

But NaCl and KCl are added as inorganic

impurities , NaCl increases the electrical

parameters while KCl decreases the

electrical parameters. This review will

provide encouraging inputs to continue the

research with various dopants in the growth

of LAA crystals which will be a highly

useful NLO material.

Acknowledgement The authors are highly thankful to Prof. Vel.

R.Rangarajan, Chairman, Vel Group of

Insititutions, Avadi, ch-62 and

Dr.K.Siddapa Naidu, Principal, Vel Tech

Multi Tech Dr.Rangarajan Dr.Sakunthala

Engg.College, Ch-62 for giving constant

encouragement and kind attention towards

their research work.

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(2002) 356

3. P Praveen Kumar etal Bull. Mater. Sci.,

Vol. 32, No. 4, August 2009, pp. 431–

435. © Indian Academy of Sciences

4. Y.L. Geng etal Journal of Crystal Growth

282 (2005) 208–213

5. V. Natarajan etal Journal of Crystal

Growth 311 (2009) 572–575

6. M. Meena etal Materials Letters 62

(2008) 3742–3744

7. R. Muralidharan etal Journal of Crystal

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8. K. Selvaraju etal , Materials Letters 61

(2007) 3041–3044

9. P. Gnanasekaran, and J. Madhavan,

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