ARTICLE IN PRESS

Journal of Crystal Growth 312 (2010) 443–446

Contents lists available at ScienceDirect

Journal of Crystal Growth

0022-02

doi:10.1

n Corr

E-m

journal homepage: www.elsevier.com/locate/jcrysgro

Laser heated pedestal growth and characterization of the crystalline fibers ofKDP doped L-arginine phosphate

Shivani Singh, Bansi Lal n

Centre for Laser Technology, Indian Institute of Technology Kanpur, Kanpur-208016, India

a r t i c l e i n f o

Article history:

Received 15 September 2009

Received in revised form

28 October 2009

Accepted 29 October 2009

Communicated by R.S. Feigelsonregion with cut-off frequency at 220 nm. Powder and single crystal XRD analysis led to the conclusion

Available online 6 November 2009

Keywords:

A1. Characterization

A2. Growth from melt

A2. Laser-heated pedestal growth

B1. Organic compounds

B2. Nonlinear optic materials

48/$ - see front matter & 2009 Elsevier B.V. A

016/j.jcrysgro.2009.10.063

esponding author. Tel.: +91 512 259 7930; fa

ail address: bansi@iitk.ac.in (B. Lal).

a b s t r a c t

Transparent crystalline fibers of �25 mm length and �1 mm diameter of KDP (0.3 and 0.4 mol%)doped

L-arginine phosphate (LAP) were prepared by laser heated pedestal growth technique. The crystalline

fibers were prepared with �5.4 W of CW CO2 laser power, �7.7 cm/hr sample rodpushing speed and

�19.4 cm/hr fiber pulling speed. The crystalline fibers were almost 100% transparent in 250–1200 nm

that KDP doping did not change the crystal structure of LAP. The calculations based on single crystal

XRD data produced the structure of the KDP: LAP identical to undoped LAP. This observation is further

confirmed by FTIR analysis. The presence of KDP in LAP was confirmed by energy dispersive X-ray

analysis (EDX). The shifting and broadening of the photoluminescent emission also indicated KDP

doping in LAP. Thermal behavior of crystalline fiber showed significant increase in the decomposing

temperature of LAP on doping with KDP so as to make the melt growth of KDP: LAP easy.

& 2009 Elsevier B.V. All rights reserved.

1. Introduction

The intense studies on the crystal growth and characterizationof L-arginine phosphate (LAP) recently [1–9] have led to theconclusions that compared to KDP, LAP has higher nonlinearity(41 pm/V), higher damage threshold (415 J/cm2 at 20 ns) and isless hygroscopic making it a potential material which can replacethe KDP used presently as harmonic generator at opticalfrequencies. However, almost no commercial application, to thebest of our knowledge, of LAP has been reported till date. Thiscould be due to non-availability of the proper crystal-growthtechnique to grow crystals of required size and quality forcommercial application. The inherent slow growth rate of thesolution growth technique used exclusively presently not onlymakes it difficult to grow large size crystals but also limits theoptical quality due to solvent inclusion. On the other hand, meltgrowth is very difficult because of its thermal properties. Themelting point of LAP is 1411C and its thermal behavior showsalmost no weight loss from 25–1501C after which there is rapidweight loss indicative of the decomposition of the material.Modification of the thermal properties of LAP by dopents has beenreported recently. Hameed et al [10] observed a decrease(compared to undoped LAP) in the decomposition temperatureof KF doped LAP. Similar behavior has been reported in case of

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Li+ doped LAP [11] Singh et al [12] reported an increase in thedecomposition temperature of LAP when doped with Rd6G dye.They have shown that the dye doped LAP has almost no weightloss in 25–2001C range and have been able to grow crystallinefibers from the melt. The present paper reports increase in thedecomposition temperature of LAP when doped with KDP. Thisincrease is significant enough to grow the KDP doped LAPcrystalline fibers from the melt by laser heated pedestal growthtechnique. The crystalline fibers thus prepared were characterizedby XRD, FTIR, EDX and optical techniques.

2. Experimental

Crystalline fibers of KDP: LAP were grown by laser heatedpedestal growth (LHPG) technique using a CW CO2 laser basedsetup described elsewhere [12] The sample rods (2�2�25 mm3)required for LHPG setup were prepared from the powder obtainedby crushing the crystals obtained by solution growth. Equi-molarquantities of L-arginine and orthophosphoric acid were dissolvedin de-ionized water at 601C. To this solution KDP (0.3 and0.4 mol%) and NaN3(0.4g, to prevent the growth of microbes)were added. This mixture was stirred for �5h at 601C.The fullyreacted solution after filtering was evaporated at 501C for � 24 h.The residual saturated solution was left at room temperature toobtain the crystals in � 4 days. The crystals thus obtained weredried in vacuum desiccators. The dried crystals were handgrounded in a mortar until no resistance was felt. Three to four

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S. Singh, B. Lal / Journal of Crystal Growth 312 (2010) 443–446444

grams of this finely grounded powder was thoroughly hand mixedwith �0.8 ml PVA. This mixture was pressed into a pellet byplacing it in a 25�25 mm2 die. The 25�25 mm2 pellets thusobtained had a thickness of about 2 mm. Sample rods of2�2�25 mm3 were cut from the pellets using a thin steel blade.

3. Results and discussion

(i)

Transparent crystalline fibers of �25 mm length and�1 mm diameter (Fig. 1)were grown using the followingexperimental parameters: (a) CW CO2 laser power: �5.4 W,(b) sample rod pushing speed: �7.7 cm/hr and (c) crystallinefiber pulling speed: �19.4 cm/hr.The temperature of themelt zone was monitored by a non-contact IR thermometer(Model MT-5, Metravi India). The stability of CO2 laser wasgood enough to maintain the temperature of the melt zonewithin 711C. The optical transmission spectrum recorded inthe range 250–1200nm using Shimadzu Model 1601 spectro-photometer showed (Fig. 2) almost 100% transmission in theinvestigated region with cut-off frequency �220 nmindicating the potential of the material for non-linearoptical devices.

(ii)

Fig. 2. Optical transmission spectrum of KDP:LAP crystalline fiber.

The indexed powder XRD spectra (1.5418A Cu-Ka, ModelJSO-Debyeflex 2002) of the crystalline KDP (0.3 and 0.4 molwt%) doped LAP fiber along with that of undoped LAP areshown in Fig. 3 As seen in this figure the XRD spectra of allthe two doped samples are identical and coincide very wellwith that of undoped LAP implying that the KDP doping didnot change its crystal structure. This was further confirmedby the analysis of the single-crystal X-ray data (Table 1)collected on Bruker Smart Apex CCD diffractometer using�1 mm�1 mm disc cut from the crystalline fibers. Thisdata was analyzed by the procedure outlined in reference[13]. The perspective view and the schematics of thestructure of the KDP:LAP fiber obtained from the single-crystal analysis are shown in Fig. 4 As seen in this figure thecrystalline fiber consists of arginine cation, a phosphateanion, and a molecule of water. This composition is similarto that of undoped LAP grown by solution technique [14]indicating that the structural features of KDP dope LAP areidentical to that of undoped LAP. Similar observation werereported in case of LAP doped with Li [11] and Rd6G [12] aswell as in KDP doped with LAP [15].

(iii)

Fig. 3. Powder XRD spectra of (a) undoped LAP, (b) 0.3 mol% KDP: LAP and (c) 0.4

mol% KDP:LAP.

Room temperature FTIR spectra in 400–4000 cm�1 regionwere recorded with Bruker Optics USA Model Vertex70spectrophotometer using the KBr pellet (� 1wt % sample)method. Typical spectrum of 0.4 mol% KDP doped LAP alongwith those of KDP and undoped LAP is shown in Fig. 5 while

Fig. 1. Photograph of the crystalline KDP:LAP fibers.

Table 1Crystal

Com

Empi

Form

Cryst

Space

a(A)

b(A)

C(A)

a(deg

b(deg

g(deg

V(A3)

the observed frequencies and their transition assignmentsare summarized in Table 2 The observed frequencies aremainly due to lattice and internal vibrations of LAP [14]

data of LAP and KDP: LAP.

pound LAP [16] KDP:LAP(present study)

rical formula C6H19N4O7P C6H19N4O7P

ula weight 290.22 290.22

al system Monoclinic Monoclinic

group P21 P21

7.321(8) 7.318 (5)

7.918(9) 7.924 (5)

10.763(12) 10.771 (5)

) 90 90

) 98.04(5) 98.014 (5)

) 90 90

623.90 624.58

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Fig. 4. (A) perspective view and (B) schematics of the structure of KDP:LAP crystalline fiber.

Fig. 5. Room temperature FTIR spectra of KDP : LAP, KDP and LAP.

Table 2Assignment of the IR frequencies observed in KDP (0.4 mol%) doped LAP.IR

frequencies of undoped LAP [14] are given for comparison.

Observed

frequencies

of undoped LAP

(solution

growth[14])

Observed frequencies

of KDP:LAP(0.4 mol%):

LAP(crystalline fiber

grown by LHPG

technique,

Present work)

Functional group assignment

3450 3450 n3 H2O

3330 3335 n1(H2O)

3160 3168 NH3+Asymmetric stretching

1690 1692 C=N stretching

1650 1653 NH2+ deformation

1570 1568 COO asymmetric stretching

1530 1528 NH3+Symmetric deformation

1450 1454 n2(H2O)

1410 1409 COO- symmetric stretching

1370 1371 C-C-H in plane deformation

1350 1357 P=O stretching

1330 1334 CH2 wagging

1320 1321 CH2 wagging

1290 1289 P-OH angular

1180 1178 NH3+ rocking

1160 1159 NH2+wagging

1135 1135 NH2 wagging

1050 1046 n1(PO4)

1035 1033 P-OH deformation

950 949 P-OH stretching

885 884 C-C Stretching, P-OH

stretching

790 791 NH2 rocking

750 751 COO scissoring

710 711 NH2 out of plane bending

623 621 OH out of plane deformation

555 555 Wagging COO-

525 528 n4(PO4)

S. Singh, B. Lal / Journal of Crystal Growth 312 (2010) 443–446 445

which further confirmed the conclusion arrived at from XRDinvestigations.

(iv)

Energy dispersive X-ray spectrum (EDX) recorded onZEISS Supra40 VP FESEM is shown in Fig. 6 In this figure,the energy peaks due to K confirm KDP doping in LAPcrystalline fiber.

(v)

Fig. 6. EDX spectrum of KDP:LAP crystalline fiber.

The room-temperature photoluminescence spectra (350 nmexcitation, Jobin-yvon Model Fluorolog-3) of 0.4 mol% ofKDP-doped LAP along with undoped LAP and KDP areshown in Fig. 7 As seen in this figure, broad emission isobserved in all the three materials. However, the emissionfrom LAP is centered � 420 nm with �100 nm FWHM (full

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Fig. 7. 350 nm excited (Xe lamp) room temperature photoluminescence of KDP:

LAP, LAP and KDP.

Fig. 8. TG Thermographs of KDP:LAP and LAP.

S. Singh, B. Lal / Journal of Crystal Growth 312 (2010) 443–446446

spectral width at half maximum) while for KDP FWHMis �90 nm for the emission peaked �431nm. On the otherhand in case of KDP (0.4 mol%):LAP the emission peaks� 473 nm with FWHM of � 110nm. This shifting andbroadening of emission line could be due to KDP doping inLAP. Similar behavior was observed in case of 0.3 mol% doping.

(v)

Fig. 8 shows the thermal behavior of the crystalline fiber ofKDP: LAP (thermograph of undoped LAP is shown forcomparison) investigated (Model NETZSCH STA 409 PC/PG)in the temperature range 30–500 1C at a heating rate of5 1C/min in N2 atmosphere. As seen in this figure, TGthermograph of KDP:LAP shows almost no weight loss inthe range 30–200 1C after which slow decomposition startswhile in case of undoped LAP decomposition of the materialis observed �150 1C indicating an increase in thedecomposing temperature of LAP on KDP doping. Thisincrease in the decomposition temperature makes the meltgrowth of KDP:LAP easier.

4. Conclusions

The decomposition temperature of LAP on doping with 0.3–0.4%KDP increases significantly so that KDP : LAP can be grown from

melt easily. However, the structural properties of LAP are notmodified on doping. The crystalline fibers grown by LHPG techniquewere of significant size for commercial exploitation.

Acknowledgements

Financial support provided to one of the authors, ShivaniSingh, by CSIR, New Delhi. India is gratefully acknowledged.

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