Original research articleStructural, spectral, thermal and nonlinear optical analysis of anhydrous citric acid crystal
Introduction
A number of organic nonlinear optical crystals were grown owing to their great interest in the field of laser technology, optical data storage and high speed information processing. When compared with inorganic crystals, organic crystals have good nonlinear optical efficiency. Due to its high nonlinearity organic materials have a wide range of design possibilities [1]. Third order NLO material with strong refraction and weak absorption are important due to its potential use in all optical signal processing devices [2]. These materials play an important role in several laser devices [3]. Citric acid is an organic acid. It is used in food, beverages, pharmaceuticals and other industries. The salts of citric acid with other compounds produces hydrogen bonded crystals that are extensively studied from X-ray and spectroscopic methods [[4], [5], [6], [7]]. Citric acid exists in two forms namely anhydrous and monohydrous differing in solubility and crystal packing [8]. Citric acid monohydrate crystal have been grown by several researchers and studied extensively, but only a few reports on citric acid anhydrous were made. In the present study, the growth of ACA from slow evaporation technique and its characterisation is reported.
Section snippets
Experimental procedure
Citric acid was dissolved in water kept at 75 °C. Then the solution was allowed to cool to room temperature. This was kept undisturbed for slow evaporation. Slow solvent evaporation leads to supersaturation and nucleation. Transparent crystals of ACA were grown after a period of 10 days.
Structural analysis
Powder XRD analysis was done by using NONIUS CAD4 diffractometer which reveals that the lattice parameters. The observed powder XRD pattern is shown in Fig. 1. Indx software was employed to index the obtained plane. From it, the unit cell values were determined using unitcell software and the values matches with single crystal XRD and literature [9]. These are presented in Table 1. The sharp diffraction peaks shown in Fig. 1 establishes the purity and good crystalline nature of ACA crystal.
Optical transmission studies
The
Conclusion
Single crystals of Anhydrous citric acid have been grown. It crystallizes in monoclinic system and possess a wide transmission window from 200 to 1100 nm. Vibrations of the functional groups are identified and assigned. The molecular structure of ACA is ascertained through NMR spectroscopy. ACA is thermally stable till 162 °C. n2, β and χ3 are determined. Good thermal stability coupled with wide transmission may be exploited in optical applications.
Acknowledgements
The authors thank the sophisticated analytical instruments facility (SAIF), Indian Institute of Technology (IITM), Chennai for providing single crystal XRD and FT Raman spectrum and gratefully acknowledge the Instrumentation centre of St. Joseph’s College, Trichy for recording FTIR and UV–vis-NIR spectra. The authors wish to thank Alagappa University, Karaikudi, for powder XRD studies and SASTRA university, Thanjavur for NMR and TG/DTA studies.
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