Synthesis growth and physico chemical investigations on pyridinium based single crystals for nonlinear optical applications

Abstract

The modern science and technology realizes the inevitable role of single crystals for the development of new generation devices. Researchers are showing much attention to design and growth of effective Nonlinear Optical (NLO) single crystals for the wide range of applications in various fields such as photonics, optoelectronics, high-speed information processing, laser devices, optical data storage, optical switching, THz generation and detection etc. Large size single crystals with good physico-chemical properties are the prerequisite for the above mentioned applications. In the last few decades, researchers are showing much interest on pyridinium based single crystals for the broad optoelectronic and photonic applications due to their interesting physico-chemical properties and large NLO response. In this view, the present thesis deals with synthesis, growth and physico-chemical investigations on pyridinium based single crystals such as 2-Amino-5 -Nitropyridinium Nitrate (2A5NPN), 2-Amino-5-Nitropyridinium Bromide (2A5NPBr), 2-Amino-5-Nitropyridinium Dihydrogen Phosphate (2A5NPDP), 2-Amino-5-Nitropyridinium Phenolsulfonate (2A5NPP) and Pyridinium 2-Carboxylate: 4-Nitrophenol (P2C4N) for NLO applications. Chapter 1 explains the brief introduction about the fundamental aspects of crystal growth and existing low-temperature solution growth techniques such as Slow Evaporation Solution Technique (SEST), slow cooling and unidirectional Sankaranarayanan-Ramasamy (SR) method. The criteria for the low temperature solution growth technique, solubility and the phenomenon of nucleation are explained. The theory of NLO which includes the Second Harmonic Generation (SHG), Third Harmonic Generation (THG) and the applications of NLO single crystals have been discussed. Moreover, the overview of pyridinium based materials and the scope for the present thesis have been described. Chapter 2 deals with the growth and characterization of 2A5NPN single crystals. The promising third-order nonlinear optical single crystals of 2A5NPN have been grown from the aqueous solution by SEST. The crystalline structure and morphology of the grown crystals were ascertained by the process of Single Crystal X-Ray Diffraction (SXRD) analysis. The degree of crystallinity and various planes of diffraction were tested by the Powder X-ray Diffraction (PXRD) analysis. The Fourier Transform Infrared (FTIR) spectroscopy analysis reveals the existence of various vibrational modes of functional groups in the 2A5NPN crystal. The optical quality was evaluated by UV-Vis NIR spectroscopic analysis and it is observed that the grown crystal possesses good optical transparency (more than 60%) in the range of 404-1100 nm. Thermal stability of the grown crystals was ascertained using Thermogravimetric (TG) and Differential Scanning Calorimetric (DSC) analysis. The chemical etching study was employed using DMSO as an etchant to reveal the quality of the grown crystal. The dielectric properties of the grown crystals were analyzed using dielectrics spectroscopy analysis. The fundamental solid state parameters and various type of electronic polarizability (and#945;) of the grown crystal were determined using the dielectric parameters. The 2A5NPN single crystal exhibits negative photoconductive nature and it was studied using photoconductivity analysis. The mechanical strength of 2A5NPN crystal was analyzed by Vickers microhardness tester. The Laser Damage Threshold (LDT) analysis shows that the grown crystal has large LDT value (4 GW/cm2 ) newline