Modified CZ technique for the growth of organic crystals having low melting point and high vapour pressure

Abstract

Abstract Most of the industrially important semiconductor, oxide and optical crystals are grown by Czochralski (CZ) technique. However, CZ technique is seldom used for the growth of low melting point organic/semi organic crystals for which solution grown method is popularly used. Further, due to requirement of sophisticated infrastructure and high cost, CZ set up is normally out of reach of universities in developing country. This article is about designing a low-cost crystal growth system, based on the concepts of CZ technique, which can be used to grow single crystals of low melting point (about 100 °C) and high vapour pressure organic materials. The main changes are in the design of heating system and growth chamber. The difficulties in the crystal growth of low melting and high vapour pressure organic materials by conventional CZ set up and various modifications in the set up for the growth of these crystals are discussed. In the present article, single crystal growth of organic 2-hydroxy biphenyl (2-HBP) single crystal (with diameter ~1 cm and 7 cm length) by low cost modified CZ setup is reported. The crystal structure and composition of 2-HBP crystal were studied by powder X-ray diffraction and CHNS analysis. The orthorhombic system with non-centrosymmetric space group Fdd2 were confirmed by powder XRD study. The thermal stability and melting point of grown crystal was obtained with the help of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) technique. The observed optical properties viz. lower cut-off wavelength at 312 nm and optical bandgap of 3.91 eV in UV spectroscopy along with intense photoluminescence (PL) emission in UV region at 332 nm make 2-HBP crystal a suitable material for photo-electronic applications and tuneable laser system.