Structure and Photoluminescence of p-(n-heptyloxy)benzoic Acid Liquid Crystals Dispersed With ZnO Nanoparticles

The paper investigates optical and spectral properties of ZnO nanoparticles dispersed p-(n-heptyloxy)benzoic acid (7-OBA) liquid crystalline (LC) compounds with the concentration of 1 to 2.5 wt.%. The prepared samples are characterized by various experimental techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet–visible spectroscopy, differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and photoluminescence (PL) spectroscopy. The presence of ZnO nanoparticles is confirmed by the XRD. The crystallite size is found to be 68 nm. Phase transition temperatures and enthalpy values of pure and nanodispersed LC materials are measured by DSC. The texture of pure and nanodispersed LC phases like nematic and smectic, is observed through POM. Photoluminescence spectroscopy shows the dispersion of 2.5 wt.% ZnO nanoparticles in 7-OBA compound; the blue emission maximum shifts from 368 to 375 nm. The peak observed at 655 nm, is determined by point defects in the bandgap, namely vacancies and interstitial known as deep level emission.