Trypan blue stained KAP crystal: A comparative study on morphological, structural, optical, di-/piezo-electric and mechanical properties

Abstract

Single crystals of pure and trypan blue (TB; C34H28N6O14S4) stained (0.01 mol%) potassium hydrogen phthalate (KAP; C8H5KO4) were grown by slow evaporation solution method. Experimentally obtained crystal habit of KAP matched well with the theoretical morphology predicted using BFDH laws. Eight planes ({111} & {111¯}) out of total fourteen planes got selectively coloured by TB dye molecules. Affinity of TB dye towards specific growth sectors can help various scientists to understand the selective nature of dye molecules and thereby will help in proposing novel tailor-made stained photonic crystals. UV–Vis-NIR spectra for TB stained KAP crystals displayed a strong absorption peak at 563 nm, which was blue shifted for TB dye in KAP matrix relative to neutral aqueous solution of TB dye. This shift in the absorption maxima towards lower wavelength confirms the successful colour insertion into selective growth sectors of stained KAP crystals. The effect of TB staining on various optical parameters namely optical conductivity, optical band gap, refractive index and extinction coefficient of host KAP matrix was studied. The structural conformation and the recognition of different functional groups present in as grown KAP crystals were approved by powder XRD and FTIR studies, respectively. Dielectric constant increased and dielectric loss decreased as a result of TB dye staining in KAP material. The piezoelectric conversion efficiency got increased from 1.22 pC/N for un-dyed KAP single crystal to 1.53 pC/N for TB stained KAP single crystals. In Vickers micro-hardness studies, TB stained KAP crystals displayed better mechanical strength.