CRYSTAL GROWTH & DESIGN
Effect of Sodium Fluoroborate (NaBF4) Doping on the NLO Properties of L-Histidine Single Crystals D.
Syamala,†
V.
Rajendran,*,†
R. K.
Natarajan,†
and S. Moorthy
2007 VOL. 7, NO. 9 1695-1698
Babu‡
Department of Physics, Presidency College, Chennai 600 005, India, and Crystal Growth Centre, Anna UniVersity, Chennai 600 025, India ReceiVed October 12, 2006; ReVised Manuscript ReceiVed May 23, 2007
ABSTRACT: Single crystals of nonlinear optical material of sodium fluoroborate doped L-histidine have been grown by the solution growth technique. The grown crystals were subjected to single crystal and powder X-ray diffraction studies to identify the morphology and structure. FTIR and UV spectra reveal the functional group identification and optical property of the grown crystals. The presence of sodium in the crystal has been confirmed. The thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) traces reveal the thermal stability of the sample. Microhardness studies have been carried out to assess the mechanical properties. The nonlinear optical (NLO) property of the crystal has been confirmed by Kurtz Perry test. 1. Introduction In recent years, efforts have been made to develop UV lasers for photonics, optoelectronics, and infrared and medical applications.1-3 Based on the nonlinear optical (NLO) property in borate crystals, considerable progress has been made in the development of coherent UV sources. L-HFB is a semiorganic material with molecular formula C6H10O2N3BF4. L-HFB belongs to the monoclinic system with space group P21. This material has second harmonic generation (SHG) efficiency much larger than that of KDP crystal.4 In the present investigation, efforts have been made to find the effect of sodium fluoroborate in L-histidine crystals. Some of the metals used as dopant enhance the material properties like optical, mechanical, and chemical stability. A series of metal-organic compounds such as lanthanum-doped KDP, zinc cadmium thiocyanate, and mercury cadmium thiocyanate have been reported with moderately high mechanical and chemical stability. In this series, a potential semiorganic nonlinear optical single crystal of NaBF4-doped L-histidine has been grown by a slow evaporation growth technique at room temperature. NaBF4-doped L-histidine crystallizes in a monoclinic crystal system with P21 space group. The grown crystal was confirmed by single-crystal X-ray diffraction (XRD), powder XRD, inductively coupled plasma (ICP), FT-Raman, and FTIR analysis. The optical, thermal, and mechanical properties are investigated.
Figure 1. Solubility curve of NaBF4-doped L-histidine crystals.
2. Experimental Methods 2.1. Material Synthesis and Crystal Growth. The NaBF4-doped L-histidine compound was synthesized by dissolving equimolar quantities of L-histidine and sodium tetrafluoroborate in 100 mL of deionized
Millipore water. The pH of the solution was adjusted to 3. It is known that the solubility of L-histidine is more in water.5 The solubility curve for NaBF4-doped L-histidine is shown in Figure 1. The solubility is found to increase with an increase in temperature. After a few days, transparent, spontaneously nucleated seed crystals were formed. Figure 2 shows the as grown crystals of NaBF4-doped L-histidine. 2.2. Elemental Analysis. The percentage composition of sodium in the grown crystal was established using a Perkin-Elmer inductively coupled plasma (ICP) analyzer at Indian Institute of Technology (IIT), Chennai. The percentage of sodium in the crystal as obtained by ICP is given in Table 1. * Corresponding author. E-mail:
[email protected]. † Presidency College. ‡ Anna University.
Figure 2. Photograph of as grown NaBF4-doped L-histidine crystals. Table 1. Percentage of Sodium in NaBF4-Doped L-Histidine from ICP Analysis sample ID
analyte
mean
sample weight 0.1978 g
Na 330.237 (λ in nm)
0.268 mg/L (wt % 0.01355%)
2.3. Structural, Morphological, and Optical Property Studies. In order to confirm the structure of grown crystals, the powder X-ray diffraction pattern was recorded using Rich Seifert (model 2002) diffractometer with Cu KR (1.54598 Å) radiation. Finely crushed powder of the grown crystal was used for the analysis at a scan speed of 0.2°/s. The morphology of NaBF4-doped l-histidine has been identified using an ENRAF NONIUS CAD4 X-diffractometer, and the cell parameter values have been determined by single-crystal XRD
10.1021/cg0607001 CCC: $37.00 © 2007 American Chemical Society Published on Web 08/01/2007
1696 Crystal Growth & Design, Vol. 7, No. 9, 2007
Syamala et al.
Figure 3. FTIR spectrum of NaBF4-doped L-histidine.
Figure 4. FT-Raman spectrum of NaBF4-doped L-histidine. analysis using a Bruker axs Kappa Apex2 XRD diffractometer. The optical transmission spectrum of the NaBF4-doped L-histidine crystal was recorded with a UV-vis spectrophotometer. FTIR spectrum of the crystal was recorded on a Bruker IFS 66V spectrophotometer by the KBr pellet method in the wave number range of 4000-500 cm-1. The FT-Raman spectrum was recorded in the wavelength range 1003300 cm-1 using a Bruker RFS 100/S spectrometer having an excitation laser Nd:YAG source (neodymium-doped yttrium aluminum garnet). 2.4. NLO Property Studies. The Kurtz SHG test6 was performed for the comprehensive analysis of second-order nonlinearity of NaBF4doped L-histidine crystals. The crystal was illuminated using a Spectra Physics quanta Ray GCR-2(10) Nd:YAG laser using the first harmonics output of 1064 nm with a pulse energy of up to 300 mJ. The second harmonic signal generated in the crystal was confirmed from the emission of green radiation by the crystal. The output power of the crystal was measured using an OPHIR power meter model DG with power head model OPHIR 30A. The output power of NaBF4-doped L-histidine was measured and compared with the output power of L-histidine tetrafluoroborate (HFB) and potassium dihydrogen phosphate (KDP) crystals. The results are tabulated. 2.5. Thermal Studies. The chemical decomposition, the phase transition temperature, the melting point, and the weight loss of the grown crystals were determined by means of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) studies. The instruments used are the Perkin-Elmer DSC 7 differential scanning calorimeter and the Perkin-Elmer TGA 7. The DSC experiments were carried out within the temperature range 50-550 °C, and the sample was heated at the rate 20 °C/min under nitrogen atmosphere. For TGA
studies, the crystals were taken in an alumina crucible and were heated from 50 to 800 °C at a scanning rate 20 °C/min (in nitrogen atmosphere).
3. Results and Discussion Infrared spectroscopy was effectively used to identify the functional groups in the grown crystal. The FTIR spectrum of NaBF4-doped L-histidine is shown in Figure 3. The NH3+ stretching region shows broad bands in the range 3500-2500 cm-1 characteristic of hydrogen bonding. The N-H stretching vibration of the amino group in L-histidine gives rise to an amide band between 3310 and 3270 cm-1. The amide band is usually part of a Fermi resonance doublet with the second component absorbing weakly between 3100 and 3030 cm-1.7 In the FTIR spectrum for NaBF4-doped L-histidine, a sharp peak at 3110 cm-1 is assigned to N-H asymmetric stretching and a peak at 2937 cm-1 is assigned to N-H symmetric stretching. The amide I vibration, absorbing near 1650 cm-1, arises mainly from the CdO stretching vibration with minor contributions from the out-of-phase C-N stretching vibration, the C-C-N deformation, and the N-H in-plane bending.8 The peak at 1637 cm-1 is assigned CdO stretching in NaBF4-doped L-histidine.9 The CdO stretching frequency occurs at a higher value because the Na+ site makes direct interaction with the O- site of the
NaBF4 Doping and NLO Properties of Histidine
Crystal Growth & Design, Vol. 7, No. 9, 2007 1697
Figure 5. Morphology of NaBF4-doped L-histidine. Table 2. FTIR Frequencies of the Vibrational Mode of the Crystal NaBF4-Doped L-Histidine and Their Assignments wavenumber (cm-1)
band assignment
3445 3146 3110 2937 2602 1637 1574 1471 1336 1060 1060 959 914 864 521 490
O-H stretching of the COOH group C-H asymm. Stretching N-H asymm. Stretching N-H symm. Stretching C-H symm. Stretching CdO asymm. Stretching Skeletal vibrations of Histidine ring CdO symm. Stretching CsCsH in plane deformation C-C-N asymm. Stretching BF4 asymm. Stretching BF4 symm. Stretching C-C-N symm. Stretching C-H out of plane bending Bending deformation of BF4 COOsrocking
carboxylate. This interaction largely suppresses the resonance delocalization of negative charge on oxygen over the CdO grouping. Hence the latter acquires more double bond character thus giving stretching at a higher value of 1637 cm-1. The CH2 group of histidine produces peaks at 2602 and 3146 cm-1 due to its symmetric and asymmetric stretching modes. The peak at 1574 cm-1 is attributed to the skeletal vibrations of the histidine ring in NaBF4-doped L-histidine. The rocking of CO2mode of band vibrations is assigned the wave number 533 cm-1 in the FTIR spectrum of NaBF4-doped L-histidine. The FT-Raman spectrum of NaBF4-doped L-histidine is shown in Figure 4. The frequencies of the vibrational mode of the crystal NaBF4-doped L-histidine and their assignments are given in Table 2. The lattice parameters determined for NaBF4-doped Lhistidine from single-crystal XRD studies were a ) 5.0540(2) Å, b ) 9.0192(2) Å, c ) 10.2158(3) Å, β ) 93.419°. The cell volume of NaBF4-doped L-HFB is 465.833 Å.3 The structure is confirmed to be monoclinic with space group P21. The morphology NaBF4-doped L-histidine is indexed, and it is seen to have only four well-defined planes with clear-cut edges. The morphology of NaBF4-doped L-histidine is shown in Figure 5. The morphology of NaBF4-doped L-histidine also shows that the growth along the b- and a-axes are more dominant than that along the c-axis. The powder X-ray diffraction pattern of NaBF4-doped L-histidine is shown in Figure 6. The peaks are sharp, confirming the crystalline nature of the grown crystal. The transmission spectra of the NaBF4-doped L-histidine crystal recorded using a UV-visible spectrometer in the wavelength range 200-2500 nm is shown in Figure 7. The cutoff wavelength of NaBF4-doped L-histidine is 210 nm, and its higher cut off wavelength is 1600 nm. The transmittance percentage of NaBF4-doped L-histidine is found to be marginally higher than that of L-HFB.
Figure 6. Powder X-ray diffraction pattern of NaBF4-doped L-histidine.
Figure 7. Transmission spectrum of NaBF4-doped L-histidine.
Figure 8. Hardness behavior of NaBF4-doped L-histidine.
A NaBF4-doped L-histidine crystal of size 1 cm × 1 cm × 0.3 cm after lapping and polishing was used for the microhardness study. The indentations were made using a Vickers pyramidal indenter for various loads from 5 to 60 g. Several trials of indentations were calculated using the relation HV ) 1.8544P/d2, where HV is theVickers hardness number, P is the indentor load in kilograms and d is the diagonal length of the impression in millimeters. For loads above 55 g, cracks started developing around the indentation mark. The hardness behavior of NaBF4-doped L-histidine as measured on the prominent plane 100 is shown in Figure 8. It is seen that the hardness decreases with increasing load.
1698 Crystal Growth & Design, Vol. 7, No. 9, 2007
Syamala et al. Table 3. Output Power Developed from the Crystals of NaBF4-Doped L-Histidine, L-HFB, and KDP output power (mW) L-HFB
NaBF4-doped L-histidine
KDP
relative efficiency of NaBF4-doped L-histidine
135 325 500 600
175 580 680 750
80 230 320 370
2.18 2.52 2.125 2.02
4. Conclusion
Figure 9. TGA of NaBF4-doped L-histidine.
Figure 10. DSC of NaBF4-doped L-histidine.
The TGA and DSC thermograms of the grown crystals are shown in Figures 9 and 10. There is a major weight loss of 81% at 325 °C, which is assigned to the decomposition of L-histidine. There is one more weight loss between 350 and 400 °C due to the decomposition of the residue that is left over after the major weight loss corresponding to 18.709%. The DSC peak at 275.6 °C coincides well with the decomposition observed in TGA trace. It can be concluded that the crystal is thermally stable up to 275 °C. The NLO property of the crystal was confirmed by the Kurtz Perry powder technique. The determination of SHG intensity of the crystals using the powder technique was developed by Kurtz and Perry.6 The crystals are ground to powder and packed between two transparent glass slides. The first harmonic output of 1064 nm from a Nd:YAG laser was made to fall normally on the prepared sample with a pulse width of 8 ns. The second harmonic signal generated in the crystal was confirmed from the emission of green radiation by the sample. The output power developed from the crystals of NaBF4-doped L-histidine and KDP are tabulated in Table 3. From the table, it can be concluded that the efficiency of NaBF4-doped L-histidine is two times higher than that of KDP.
The NaBF4-doped L-histidine crystals were successfully grown by a slow evaporation technique. The solubility of NaBF4-doped L-histidine in deionized water was found to be comparable to that of L-HFB. The incorporation of sodium in single crystals has been quantified by ICP analysis. Singlecrystal X-ray diffraction analysis confirms the structure of grown crystals to be monoclinic. The morphology reveals that the growth rates along the a- and b-axes are faster than the growth rate along the c direction. The optical transmission range of NaBF4-doped L-histidine is found to be from 210 to 1600 nm and the percentage transmittance is higher than that of L-HFB. The FTIR and FT-Raman studies confirm the vibrational frequencies of NaBF4-doped L-histidine. From the thermogram, it is concluded that these crystals are thermally stable up to 275 °C. The microhardness test confirms the mechanical stability of the grown crystals. The crystal is found to be a potential NLO material having SHG efficiency higher than that of L-HFB and twice that of KDP. The presence of sodium in the crystal has caused a change in the morphology, UV transmission spectrum, and relative SHG efficiency. References (1) Marcy, H. O.; Warren, L. F.; Webb, M. S.; Ebbers, C. A.; Velsko, S. P.; Kennedy, G. C.; Catella, C. C. Appl. Opt. 1992, 31, 5051. (2) Warren, L. F. In Electronic MaterialssOur Future; Allred, R. E., Martinez, R. J., Wischmann, K. B., Eds.; Society for the Advancement of Material and Process Engineering: Covina, CA, 1990; pp 388-396. (3) Meredith, G. R. In Nonlinear Optical Properties of Organic and Polymeric Materials; Williams, D. J., Ed.; ACS Symposium Series 233; American Chemical Society: Washington, DC; 1982; pp 2756. (4) Aggarwal, M. D.; Choi, J.; Wang, W. S.; Bhat, K.; Lal, R. B.; Shiels, A. D.; Penn, B. G.; Frazier, D. O. J. Cryst. Growth 1999, 204, 179. (5) Rajendran, K. V.; Jayaraman, D.; Jayavel, R.; Mohan Kumar, R.; Ramasamy, P. J. Cryst. Growth 2001, 224, 122-127. (6) Kurtz, S. K.; Perry, T. T. J. Appl. Phys. 1968, 39, 3798. (7) Silverstein, R.; Bassler, G. C.; Morrill, T. C. Spectrometric Identification of Organic Compounds; John Wiley & Sons: Singapore, 1981. (8) Socrates, G. Infrared Characteristic Group Frequencies; John Wiley & Sons: Singapore, 1980. (9) Dobrzynska, D.; Lis, T. J. Mol. Struct. 1997, 406, 89-98.
CG0607001
