Exploring Optical Properties of Nematic Liquid Crystals dispersed with Perovskite Quantum Dots

This study demonstrates the enhancement in photoluminescence (PL) of nematic liquid crystals (NLCs) doped with CsPbBr3 (perovskite) quantum dots (QDs). These perovskite QDs significantly boost the PL intensity by improving the anisotropic nature of NLC molecules, thereby reducing light leakage centers and intrinsic defects. Two different sizes of QDs were synthesized using a wet chemical method. X-ray Diffraction (XRD) confirmed the orthorhombic crystallite structure of the QDs, while Transmission Electron Microscopy (TEM) determined their size as 5.5 (±0.98) nm and 10 (±1.8) nm. The optical features of QDs were investigated by recording absorption and emission spectra at room temperature, which revealed unique excitonic peaks at 479 and 513 nm, whereas emission was seen at 503 and 518 nm for two different sizes, respectively. These highly luminescent QDs were further used to enhance the emission of NLC. Initially, liquid crystal (LC) sample cells were fabricated using the conventional polyimide technique, followed by the incorporation of NLC-QD composites via capillary action. The prepared sample cells were then characterized using polarizing optical microscope (POM) images and PL spectra measurements. The intensified dark state and brightened bright state POM images demonstrate improved unidirectional alignment along with a homogeneous texture of the NLC-QD composite. This improvement in molecular alignment, coupled with the reduction in light leakage centres and defects, is reflected in the PL spectra, showing an increased emission intensity of 18 % for the 10 nm sized sample. The enhanced emission of NLCs is attributed to the modified dielectric anisotropy in the presence of QDs. Conversely, 5.5 nm NLC–QD composites led to increased light leakage centres in the POM dark state and a subsequent reduction in PL intensity. The results indicate that these QDs are ideal for fabricating QD-based display devices with enhanced optical contrast, making them a promising choice for next-generation display technologies.