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Journal of Crystal Growth 310 (2008) 2039–2042

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Crystalline fiber growth of dye-doped L-arginine phosphateby the laser-heated pedestal growth technique

Shivani Singh, Bansi Lal�

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

Available online 6 January 2008

Abstract

About 25-mm-long and �1-mm-diameter transparent crystalline fibers of Rd6G (0.01, 0.1 and 1.0molwt%) doped L-arginine

phosphate (LAP) have been grown by the laser-heated pedestal growth technique using �4W CO2 laser power, 36mm/h fiber pulling

speed and 14mm/h sample rod pushing speed. TG analysis shows the improvement in the thermal properties of LAP by Rd6G doping.

XRD and photoluminescence techniques have been used for the characterization of fibers. Optical transmission studies indicate that in

normal laboratory conditions there is less degradation in Rd6G:LAP compared to undoped LAP.

r 2007 Elsevier B.V. All rights reserved.

PACS: 42.70.Mp; 61.66.Hq; 81.10.Fq

Keywords: A1. Characterization; A2. Melt growth; A2. Laser-heated pedestal growth; B1. Organic compounds; B2. Nonlinear optic materials

1. Introduction

The growth and characterization of the crystalline L-arginine phosphate (LAP) family has been an activeresearch area [1–8] because of its interesting nonlinearproperties at optical frequencies. Several studies on themodification of thermal and nonlinear properties of LAP(family) by various dopents have been reported recently.Joseph Arul Pragasam et al. [9] have reported the enhancednonlinear activity in Cu-, Mg-doped L-arginine di-phos-phate. They also observed positive photoconductivity inthis metal-doped crystal. Geng et al. [10] investigated thecrystal growth morphology of Cu2+:LAP by atomic forcemicroscopy. Haja Hameed et al. [11] observed that thegrowth of the LAP crystal along the c-axis is suppressed byCu while it is enhanced by Mg doping. The EPR andoptical absorption studies of Cu2+- and VO2+- dopedLAP by Angeli Mary and Dhanuskodi [12,13] show thatthe crystal field around these doped ions has rhombicsymmetry while Dhanuskodi et al. [14] observed anenhanced second harmonic generation efficiency for thesulfhate-mixed LAP and its doped analogs. In all these

e front matter r 2007 Elsevier B.V. All rights reserved.

rysgro.2007.11.235

ing author. Tel.: +91 512 259 7930; fax: +91 512 259 7766.

ess: bansi@iitk.ac.in (B. Lal).

studies the crystals are grown by the solution growthtechnique, as it is difficult to grow these crystals from meltbecause of their thermal properties. The thermal behaviorof crystalline undoped LAP shows that there was almostno weight loss from 25 to 150 1C after which there wasrapid weight loss, indicative of the decomposition ofthe material. The melting point of LAP according toDTA measurements is �141 1C. The LAP can be grownfrom melt provided the temperature of the melt ismaintained precisely at its melting point. This paperreports the modification in the thermal behavior of LAPwhen doped with Rd6G. The dye-doped LAP has almostno weight loss in 25–200 1C, making it possible to grow thecrystalline fibers by the laser-heated pedestal growthtechnique. Also, dye-doped LAP compared to undopedLAP is less degraded in normal laboratory conditions.

2. Experimental procedure

Equi-molar quantities of L-arginine and orthophospho-ric acid are dissolved in de-ionized water at 50 1C. To thissolution Rd6G (0.01, 0.1 and1.0molwt%) and NaN3

(0.4 g) are added (NaN3 is added to prevent the growthof microbes) and the whole mixture is stirred for �3 h at

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Fig. 2. Photograph of the crystalline Rd6G:LAP fibers.

S. Singh, B. Lal / Journal of Crystal Growth 310 (2008) 2039–20422040

50 1C. The fully reacted solution after filtering is evaporatedat 40 1C and the residue is dried in vacuum desiccators.XRD, FTIR and photoluminescence techniques are em-ployed to identify the material prepared. The material thusprepared in the laboratory is hand grounded in a mortaruntil no resistance is felt. Four grams of this finely groundedpowder is thoroughly hand mixed with �0.8ml of polyvinylalcohol (PVA, 2wt% in distilled water). This mixture ispressed into a pellet by placing it in a 25� 25mm2 die that issubjected to about 24MPa pressure. The 25� 25mm2 pelletsthus obtained have a thickness of about 2mm. Sample rodsof 2� 2� 25mm3 are cut from the pellet using a thinhacksaw blade. These rods are used as feed rods for thepreparation of crystalline Rd6G: LAP fibers by CW CO2

laser-based LHPG setup. In this setup, radiation from a CO2

laser is split into two equal-intensity beams by a beamsplitter. Both the beams are steered by two independent-plane high-reflecting mirrors so as to make them incident onthe two concave mirrors (25mm diameter, 50mm ROC, goldcoated). The two concave mirrors are adjusted so as to focusthe two beams on the top of the sample rod, which ismounted on a stepper motor-driven translation stage ofabout 7.5 cm linear movement with 0.7mm pitch. A similarstepper motor-driven translation stage is used for pulling thecrystalline fibers. The sample rod-pushing speed as well asthe fiber-pulling speed can be adjusted in 0–180mm/h range.The experimental parameters used to grow the transparentcrystalline fibers are:

(i)

CW CO2 laser power: �4W, (ii) sample rod-pushing speed: 14mm/h, (iii) fiber-pulling speed: 36mm/h.

3. Results and discussion

(i)

Fig. 3. Powder XRD spectrum of crystalline fibers of Rd6G:LAP at

various doping levels of Rd6G.

Thermal analysis (Model NETZSCH STA 409PC/PG) in the temperature range 50–400 1C has beencarried out in nitrogen atmosphere with a heating rate

Fig. 1. Thermo-grams of undoped L

of 5 1C/min. TG/DTA graphs of Rd6G:LAP andundoped LAP are shown in Fig. 1. The TG graphsclearly show the dramatic change in the thermal

AP and Rd6G:LAP.

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Fig.

vario

Fig

S. Singh, B. Lal / Journal of Crystal Growth 310 (2008) 2039–2042 2041

behavior of LAP when doped with dye. The meltingpoint of LAP from DTA measurements is 141 1C whileTG graphs show that it decomposes almost completelyat 150 1C, making it very difficult to grow the LAPcrystal from melt. On the other hand, Rd6G:LAP canbe grown from melt easily as it shows (Fig. 1) noweight loss (decomposition) in 50–175 1C and decom-poses completely at about 250 1C.

(ii)

Transparent crystalline Rd6G:LAP fibers have beenobtained with about 4W of CW CO2 laser power,36mm/h fiber-pulling speed and 14mm/h sample rod-pushing rate. The temperature of the melt zone ismonitored by a non-contact IR thermometer (ModelMT-5, Metravi India). The stability of CO2 laser isgood enough to maintain the melt zone temperature at

4. Room-temperature photoluminescence spectra of Rd6G:LAP at

us doping levels of Rd6G. The excitation wavelength is 350 nm.

. 5. Transmission intensity at 532 nm as a function of storage (without oil) tim

14071 1C with 4W CW power. Typical fibers areshown in Fig. 2.

(iii)

The indexed powder XRD spectra (1.5418 A Cu-Ka,Model JSO-Debyeflex 2002) of the crystalline Rd6G(0.01, 0.1 and 1.0molwt%)-doped LAP grown by theLHPG technique are shown in Fig. 3. The XRDspectra of all the three samples are identical andcoincide very well with that of pure LAP reported inthe literature [1], indicating that the dye molecules donot enter the lattice sites to change the crystal structure.

(iv)

The room-temperature photoluminescence spectra(350nm excitation, Jobin-yvon Model Fluorolog-3) ofdifferent molwt% of Rh6G-doped LAP are shown inFig. 4. The peak at 420nm is characteristic of theundoped LAP while the observed peak at 565 nm is dueto Rd6G, which confirms the doping of Rd6G in LAP.

(v)

Undoped LAP crystals need to be stored in oil as itdegrades fast even in normal laboratory conditions. Toassess the effect of dye doping on the environmentaldegradation of LAP transmission properties at 532 nmhas been investigated. The results are shown in Fig. 5where the decrease in the transmission of 532 nmradiation is monitored as a function of storage time innormal laboratory conditions. In case of undopedLAP the transmitted intensity decreases by a factor�2.5 after it is stored for 4 weeks in normal laboratoryconditions without any oil while in case of Rd6G:LAPthe transmitted intensity is almost unchanged when ithas been stored in conditions similar to undoped LAP.

4. Conclusions

Rd6G:LAP has been successfully grown from melt bythe laser-heated pedestal growth technique as it decom-poses at much higher temperatures compared to undoped

e. Time ‘‘0’’ corresponds to the freshly prepared crystalline fiber.

ARTICLE IN PRESSS. Singh, B. Lal / Journal of Crystal Growth 310 (2008) 2039–20422042

LAP. Also, Rd6G:LAP, compared to undoped LAP, isquite stable when stored in normal laboratory conditionswithout any oil.

Acknowledgment

Financial support provided to one of the authors,Shivani Singh, by CSIR, New Delhi. India is gratefullyacknowledged.

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