Crystal growth, spectral, optical, thermal, photoconductivity, laser damage threshold and fluorescence studies of β-P-amino benzoic acid
SenthilKumar Chandran, Rajesh Paulraj*, P.Ramasamy
Centre for crystal growth, Department of Physics, SSN College of Engineering, Kalavakkam Tamilnadu, India-603 110
P-amino benzoic acid (PABA) chemical formula C7H7NO2, an organic single crystal was grown by slow evaporation technique. Single crystal X-ray diffraction studies shows that the grown crystal has β- polymorph-P-amino benzoic acid form and lattice determined parameters a=6.30 Å, b= 8.61 Å, c= 12.436 Å α=90°, β=100.20°, γ =90° and V=664(Å3). FTIR analysis confirms that bands at 1588 cm-1, 1415 cm-1 are assigned to ring skeletal vibrations…show more content… The commercially available P-aminobenzoic acid (MERK AR, 99.5% purity) were purified by repeated recrystallization using deionised water as solvent which has resistivity 18.2 MΩ cm. The solution was stirred well for 12 hours until homogeneous mixture of clear solution is obtained. Then the solution was filtered using filter paper and transferred to a glass vessel and evaporation was allowed to take place at room temperature. After two weeks 1mm3 seed crystals were obtained from super saturated solution. Defect free single crystals are selected as seed for growing large size single crystals. Seed crystals were located at the bottom of the beaker containing the super saturated solution. The beaker was kept in a constant temperature bath to maintain the growth solution at constant temperature 28 ˚ C with accuracy 0.01° C. Prismatic single crystals have been harvested in a growth period of 45 days. When amino group materials are kept for a long growth period its solution predominately effects by fungus. In order to avoid fungus some drops of hydrofluoric acid was added to mother solution. The chemical structure and grown crystals of PABA are shown in Fig. (1) and Fig.…show more content… It is also depends on: (i) applied field (ii) temperature (iii) intensity of light (iv) energy of radiation. . The photoconductivity studies were carried out using KEITHLEY 485 picoammeter in the presence of DC electric field at room temperature (303 K). Silver paint was coated on the both surface of the crystal in order to make contact between the electrode and the crystal. The sample was kept in vacuum to measure the dark current and photo current. The varation of both dark current (Id) and photo current (IP) are shown in plot.9, which is increase with the applied electric field. It is observed that the dark current is always less than the photo current and this material exhibits positive photoconductivity. When the crystal is illuminated with photons of energy E > Eg, electron-hole pairs are created and the conductivity of the material increases. This may be attributed to generation of mobile charge carriers by the absorption of photons [12,19].
3.8 Evaluation of solid state parameters.
From the crystallographic  data some of the following parameters can be evaluated. β-PABA valence electron plasma energy and Fermi energy have been calculated by taking into account of its molecular weight (M=137.14 g/mol ), density ( =1.389 Mg m-3 ) and its total number of valence electrons (Z).