CdSe quantum dots enhancing blue emission of nematic liquid crystals

Abstract

Herein, we report the enhancement in blue emission of nematic liquid crystals (NLCs) doped with CdSe quantum dots (QDs) at room temperature. CdSe QDs were synthesized by a high temperature wet chemical method. X-ray diffraction pattern suggest zinc blend crystal structure of CdSe QDs without impurity phase formation. The absorption peak and PL emission of QDs is observed at 503 nm and 526 nm respectively. The QDs size is found to be 2.3 nm calculated by excitonic peak. The polarization states of the QD-based NLCs were studied by using polarising optical microscopic (POM) images under crossed geometry of polarizer and analyser. The uniform colour distribution throughout the cell indicates uniform cell thickness with a planar alignment of liquid crystal molecules. Moreover, dark, and bright states of POM images are used to analyse the defects in alignment of NLC molecules. It is worthwhile to note here that the incorporation of QDs in NLCs helps in reducing defects and light leakage centres which further increases the absorption and hence emission of NLCs. The significant enhancement in the PL intensity of the NLC of about 60% upon CdSe QDs doping is observed at room temperature which attributed to the increase in molecular alignment of NLCs composite.