Enhancement in Photoluminescence of Nematic Liquid Crystals Doped with CsPbBr3 Quantum Dots

Abstract

We report the enhancement in photoluminescence (PL) of nematic liquid crystals (NLCs) doped with CsPbBr3 (perovskite) quantum dots (QDs). QDs play a vital role to enhance the PL intensity, which has been attributed to the increase in the planar alignment of NLC molecules by reducing light leakage centres and intrinsic defects. QDs were synthesized by the hot injection chemical method. The structural properties of QDs were examined by X-ray Diffraction (XRD) and Transmission Electron Microscopic (TEM) measurements. Orthorhombic crystallite structure of CsPbBr3 QDs without secondary phase formation was confirmed from XRD pattern. The particle size of QDs was calculated by TEM and found to be 7.3 (± 1.1) nm. The optical properties of QDs were studied by recording UV-Visible absorption and PL spectra at room temperature. The absorption spectrum reveals the excitonic peak at 509 nm and PL emission is observed at 514 nm. The chemically prepared QDs were further used to enhance the emission of NLC. Firstly, liquid crystal sample cells were fabricated by conventional polyimide technique. NLC doped with CsPbBr3 QDs were inserted into the sample cell via the capillary action. The filled sample cells were characterized by polarising optical microscope (POM) images and PL spectra measurements. The dark and bright state images of POM demonstrate the uniform alignment and homogeneous texture of liquid crystal molecules in both cells. The molecular alignment is further improved while the light leakage centres and defects were reduced after doping QDs in the host NLC material. This leads to a significant enhancement in absorption and hence the emission of NLC. We found the enhancement in PL intensity by 11% compared to pure NLC. The improved emission of NLC is attributed to modified molecular alignment in presence of QDs. Results based on present work will help to fabricate QDs based display devices with improved the optical contrast and lower the operating voltage