Sunset yellow dye doped ammonium dihydrogen phosphate single crystals with enhanced optical, mechanical and piezoelectric properties

Abstract

Pure and 0.1 mol% sunset yellow dye (SSY) doped ammonium dihydrogen phosphate (ADP) single crystals were grown by solvent evaporation technique with an aim of improving the properties of pure ADP crystals. The crystal structure and unit cell dimensions of both the crystals were analysed by using powder X-ray diffraction (XRD). Fourier transform infrared (FTIR) spectroscopy was carried out to identify the functional groups present in grown crystals. In UV-Vis-NIR absorption spectra, four characteristic absorption bands were observed at ~ 234, 314, 412 and 481 nm for the dyed crystals, due to the inclusion of SSY dye in ADP matrix. Various optical constants i.e. optical band gap (Eg), extinction coefficient (K), refractive index (n) and optical conductivity (σ) were calculated for both the samples using transmittance data. In photoluminescence spectrum, a broad emission peak centred at 582 nm in addition to blue emission band (406–462 nm) indicates yellow emission. The mechanical strength of the crystals was analysed using Vickers microhardness test in the load range 5–100 g and was found to be higher for dyed ADP crystal. Raman analysis revealed that no structural changes were induced due to indentation thereby confirming the robustness of crystals. The piezoelectric charge coefficient of the ADP crystal got enhanced from 1.8 to 2.4 pC N−1 as a result of dye doping.