Synthesis growth and studies on optical, thermal and terahertz analyses of bulk size sodium acid phthalate single crystal: a metal–organic material for nonlinear optical applications

Optical grade semi-organic single crystal of sodium acid phthalate (NaAP) was synthesized, and the crystals were harvested by slow evaporation solution growth technique (SEST) in an ambient condition. The titled compound is a promising material for nonlinear optical (NLO) applications and crystallized in non-centrosymmetric system. The structural information of the above-mentioned crystal was investigated by powder X-ray diffraction (PXRD), which reveals that it belongs to orthorhombic structure and B2ab space group. The presence of defects in the harvested crystal was assessed by high-resolution X-ray diffraction (HRXRD) and found that grown single crystal is moderately good. The optical behaviour of NaAP crystal was examined by UV–Vis, photoluminescence (PL) and time-resolved PL (TRPL), respectively. Thermal response and stability of the title compound were tested using thermogravimetry (TG), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC) analyses. The coefficient of thermal expansion (CTE) was evaluated using thermomechanical analyzer (TMA). The third-order NLO properties of NaAP single crystal had been evaluated by Z-scan method. The two-photon absorption coefficient (β) was calculated from open-aperture curve of Z-scan. The nonlinear study reveals that NaAP crystal is an appropriate choice in optical limiting usage. Terahertz (THz) time domain spectroscopy was used to study optical characteristics like refractive index and absorption coefficient of NaAP single crystal.