Topological Defects in CdSe and CdSe/CdS Quantum Dot–Liquid-Crystal Composites for Spatial Light Modulation and Filtering

Long-range topological order in optically functional materials has recently been of intense study, as it opens smart ways for electrical manipulation of optical response within these materials. Liquid crystals (LCs) doped with photonically active nanoparticles like quantum dots (QDs) provide a highly suitable platform to create such topological order due to the ease of long-range orientational ordering via external stimuli provided by the LC medium. However, such ordering with more photostable core–shell QDs has not yet been fully explored along with effects of QD size. In this work, we present our investigations of topological order in 5CB LC doped with core and core–shell CdS/CdSe QDs. Electro-optical examination suggests robust formation of topological defects (TDs) for both core and core/shell QDs albeit with higher-order parameters for core CdSe QDs. Interestingly, we show that while surfactants/ionic dopants like cetyltrimethylammonium bromide (CTAB) improve the long-range order, it is not necessary to create robust TDs in this hybrid photonic medium. We demonstrate robust electrically controlled diffraction filtering with these devices, stable over a long period of time. These results imply greater flexibility in designing LC–QD-based devices for applications like optical spatial filters, optical filters, and micro-LEDs.