INFLUENCE OF AMINO ACID DOPANTS ON THE GROWTH AND PROPERTIES OF POTASSIUM HYDROGEN PHTHALATE SINGLE CRYSTALS FOR NONLINEAR OPTICAL APPLICATIONS

S. Shek Dhavud 1 and * J. Thomas Joseph Prakash 2 . 1. PG and Research Department of Physics, Jamal Mohamed College (Autonomous), Affiliated to Bharathidasan University, Trichy-20, Tamilnadu, India. 2. PG and Research Department of Physics, Government Arts College, Affiliated to Bharathidasan University, Trichy-22, Tamilnadu, India. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History

Undoped and the impact of amino acid dopants such as L-Glutamic acid (LGA), L-Asparagine (LAS) and L-Serine (LS) on the growth process and properties of potassium hydrogen phthalate (KHP) single crystal by slow evaporation solution growth technique have been examined. The unit cell parameters of the grown crystals have been affirmed by means of single crystal X-ray diffraction analysis. The crystallinity of the title materials was examined by powder X-ray diffraction. The FT-IR spectral studies identify the presence of expected functional groups of the grown crystals. The optical transmission of the grown crystals has been recorded using UV-Vis spectral analysis. The thermal stability of the grown crystals has been analyzed by TG-DTA studies. Microhardness mechanical studies show that hardness number increases with the load for the grown crystals by Vickers microhardness method. The nonlinear optical (NLO) properties were analyzed utilizing Kurtz and Perry powder technique.
Currently, for a deposition of thin films of organic nonlinear materials, alkali metal hydrogen phthalate crystals have been hired as substrates. Specifically, a single orientation of thin poly (diacetylene) films is prepared by epitaxial growth on organic crystals consisting of alkali metal salts of phthalate and having a lower degree of symmetry than alkali halides [2] and those crystals are crystallized as noncentrosymmetric rhombic structures. Crystals of alkali metal hydrogen phthalates have covalent (intramolecular), ionic (cation-anion), Van-der Waals (among neighboring molecules) and intermolecular hydrogen bonds O-H···O (H-bonds among anions in chains) and for this reason they may be ascribed to strong H-bonds for which might be feasible the fermi-resonance interactions of stretching vibrations ν(O-H) with combinations of bending in-plane (β(O-H)) and out-of-plane (γ(O-H)) vibrations due to intraanionic anharmonicities. Amino acids doped KHP crystals were obtained by the calculated amount of 0.5 mole % of LGA, LAS and LS were slowly dissolved separately using different beakers in the pure KHP solution. The reactants have been stirred continuously for 4 hours to yield a homogenous mixture of the solution. The prepared solutions were filtered through Whatman filter paper. To grow the crystal of high quality, the prepared solutions were kept in the temperature controlled water bath. In the course of the slow evaporation, well-defined, colourless single crystals of LGA doped KHP, LAS doped KHP and LS doped KHP with good transparency were obtained in the duration of 32 days, 34 days and 37 days respectively. The photograph of the as-grown crystals is shown in Fig. 1b, Fig. 1c and Fig. 1d.

Results and Discussion:-
Single crystal X-ray diffraction:-The single crystal XRD data of the grown crystals have acquired using an ENRAF NONIUS CAD 4 diffractometer with MoKα radiation (λ=0.71073 Å) to identify the unit cell parameters. The grown crystals crystallize in an orthorhombic symmetry with a space group of Pca2 1 . The obtained unit cell parameters for undoped and amino acids doped KHP crystals are presented in Table 1. From Table 1, the grown crystals have been confirmed by examining the presently calculated lattice parameters values with already reported values [16] which give the close agreement.   Table 2. 891  [17].

Optical analysis:-
The optoelectronic efficiency of the NLO material is typically decided by way of the transparency window in the UV-Visible region. The optical transmission spectra of the grown crystals have been showed within the wavelength region from 190-1100 nm using a Perkin-Elmer Lambda 35 UV-Visible spectrophotometer. The lower cut-off 892 wavelength is observed at 300 nm for the grown crystals. The transmission percentage of undoped, LGA doped KHP, LAS doped KHP and LS doped KHP crystals are 70%, 94%, 82% and 60% respectively (Fig. 4a, Fig. 4b, Fig. 4c & Fig. 4d).    895 800 °C in the N 2 environment, the prevailing work is of the same opinion properly with these said consequences [18,19]. DTA showed sharp endothermic peak observed at 290°C, 300°C, 302°C and 304°C for undoped, LGA doped KHP, LAS doped KHP and LS doped KHP can be attributed to the decomposition of the grown crystals respectively. Hence, the endothermic peaks above 304.9°C can be due to the formation of volatile fragments. Further, the grown crystals are observed to decompose without melting or phase transformation. As a result, the maximum temperature up to which KHP can be exploited for nonlinear optical applications is limited to 304.9°C.   Fig. 6a, it is seen that hardness value of LGA doped KHP crystal is higher than the hardness value of other three crystals. This is due to the fact the predominant contribution to hardness is ascribed to the high stress required for homogeneous nucleation of dislocation in the small vicinity indented [20]. The presence of cracks shows the decrease in microhardness and it was observed that amino acid doped KHP crystals are highly stable towards the application of mechanical stresses. The noticed changes in the microhardness values of the amino acids doped KHP crystals may be due to the strong interaction of O-H groups of KHP with the COO groups of amino acid [21]. Greater stress is required to form dislocations in an ideal crystal. Hence, the higher hardness value of LGA doped KHP crystal indicates greater stress required to form dislocation which confirms greater crystalline perfection. The work hardening coefficient (n) was estimated by the plot of log p vs log d. The plot of log d vs log p for the grown crystals shows a straight line and its slope provides the work hardening coefficient (n) P=K 1 d n -------------(2)

896
Where K 1 (Standard hardness value which is found from the plot of P vs d n . The plot of log p vs log d of undoped KHP (Fig. 7a), LGA doped KHP (Fig. 7b), LAS doped KHP (Fig. 7c) and LS doped KHP (Fig. 7d) depicts that the grown crystals belong to the soft material category.

Second harmonic generation (SHG) analysis:-
The grown crystals have been subjected to a Q-switched Nd:YAG laser beam of wavelength 1064 nm was hired within an input beam energy of 3.2mJ/pulse and pulse width of 8 ns, the repetition rate being 10 Hz. KHP and NaAP crystals are being the phenyl ring and π-electron system that are liable for its NLO efficiency [22]. The estimated SHG efficiencies of undoped, LGA doped KHP, LAS doped KHP and LS doped KHP crystals are found to be 1.5, 1.9, 1.6 and 1.7 times that of the reference material KDP crystal respectively. It genuinely found out that LGA doped KHP crystal which is having SHG efficiency value higher than that of undoped, LAS doped KHP and LS doped KHP crystals.

Conclusion:-
Semiorganic single crystals of undoped, LGA doped KHP, LAS doped KHP and LS doped KHP were effectively grown by slow evaporation technique. Single crystal XRD confirmed that the grown crystals have an orthorhombic lattice with Pca2 1 space group for the grown crystals. The powder XRD study confirms that the crystalline perfection of the grown crystals. The presence of functional groups becomes confirmed by means of FTIR spectral analysis. The UV-Visible study implies the optical quality of LGA doped KHP crystal is better than that of undoped, LAS doped KHP and LS doped KHP crystals. The melting and decomposition temperature range of the grown single crystals has been studied by TGA/DTA analysis. In the microhardness analysis, LGA doped KHP crystal has much higher hardness value than undoped, LAS doped KHP and LS doped KHP crystals and it confirms that the grown crystals belong to the soft material. LGA doped KHP crystal is an excellent candidate for SHG applications than LGA doped KHP crystal due to its SHG efficiency value much higher than that of LGA doped KHP. All these properties suggest that LGA doped NaAP crystal may be a promising material for optical applications.