Spectroscopic study of l -arginine interaction with potassium dihydrogen phosphate crystals
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Inorganic potassium dihydrogen phosphate (KDP) is widely known for its value as a nonlinear optical material. In this study, pure and L-arginine–doped KDP single crystals were grown by the slow solvent evaporation technique and further subjected to infrared absorption and Raman studies for the confirmation of chemical group functionalization and possible bonding between the organic and inorganic materials. The appearance in the infrared absorption spectra of additional vibrational lines, which mostly originate from disturbed N–H, C–H, and C–N bonds of the L-arginine–doped salt, confirm the interaction between KDP and the organic material. This affirmation is supported by more evidence from Raman measurements, where the disappearance of NH vibrations of the amino group is observed. We are thus led to the possibility of hydrogen bonding primarily between the nucleophilic O of the phosphate unit of KDP and the amino group of the L-arginine.
I. INTRODUCTION
The inorganic transparent dielectric potassium dihydrogen phosphate (KDP, KH2PO4), is extensively used in laser systems.1–4 Its usefulness in frequency conversion and optoelectronic switching is attributable to its structural, mechanical, and optical properties such as its relatively high-laser damage threshold, wide region of optical transparency, and large nonlinear optical (NLO) coefficient. Furthermore, large defect-free KDP single crystals in the 40- to 55-cm size range can be conveniently grown at a rapid growth rate of 10–20 mm/day.4 These features make KDP an excellent candidate for electrooptical devices, where efficient operation requires that the crystal possess a high degree of perfection, and occasionally, large size, e.g., the case of large-aperture highpower lasers. In contrast, because amino acid materials crystallize in noncentrosymmetric space groups, which is an essential characteristic for NLO applications and for second harmonic generators (SHGs), one of the main foci of recent research in quantum electronics is on organic NLO materials with qualities superior to those of the inorganic materials.5,6 Both organic and inorganic materials have particular merits for application to optical technology. If inorganic materials are appropriately combined with organic molecules, the resultant hybrid materials can offer the combined merits of both classes of materials and can acquire individual properties or combinations of properties with practical suitability that exceeds that of conventional para)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0290
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J. Mater. Res., Vol. 24, No. 7, Jul 2009
ent materials. Therefore, doping KDP crystals with amino acid families has been under extensive investigation in recent times because of the favorable enhancement of the NLO properties of the standard KDP crystals.7–13 The search for effective NLO materials has shown that L-arginine–based crystals such as L-arginine phosphate monohydrate (LAP),7 which was first reported by Xu et al.,8 exhibit higher nonlinearity, c
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