Enhanced electrochemical and electro-optical properties of nematic liquid crystal doped with Ni:ZnCdS/ZnS core/shell quantum dots

Abstract

The doping effects of Ni-doped ZnCdS/ZnS (Ni:ZnCdS/ZnS) core/shell quantum dots (QDs) on the electrochemical and electro-optical properties of a nematic liquid crystal (LC) system were demonstrated. The impedance response of pure and QD-dispersed nematic LCs was investigated in the frequency range of 0.1 Hz–100 kHz. By fitting a suitable equivalent electric circuit model to the experimental data, it was concluded that the QDs doping noticeably increases the electrical conductivity and charge-capacitance of nematic LC. The ionic mobility and diffusion coefficient are strictly dependent on the QD concentration and the amount of these parameters decreases when 0.25 wt% of the QDs is introduced to the nematic LC, and then increases on further addition of the QDs. This phenomenon is due to the competition between the generated ionic impurities during assembling and the ion-capturing effect of the QDs. The viscosity of nematic LC increased at first and then decreased with increasing concentration of the QDs. Dielectric permittivity of nematic LC samples was also measured at different temperatures. The QD-doped samples exhibited higher permittivity compared to pure nematic LC. The dielectric anisotropy exhibited an increasing trend upon the addition of the QDs up to 0.75 wt% and decreased with further adding QDs. The dielectric results indicated that the nematic phase LC induced self-assembly on QDs to form one-dimensional arrays along the nematic director. Moreover, QDs dispersed in the LC mixture trapped ionic impurities, suppressed the ionic screen effect, and strengthened the electric field in the nematic LC bulk. Therefore, the QDs doping decreased the threshold voltage of the nematic LC cell. The estimated field-off response time initially increased and then decreased with an increase in the concentration of QDs. These results suggest that Ni:ZnCdS/ZnS QDs doped into an LC system can be beneficial for both the display industry as well as circuits working at the highly sensitive system.