Photoelectric Properties Of Liquid Crystals Doped With CsPbBr₃ Quantum Dots

Liquid crystals（LCs）possess a distinct place in the modern electronics since it became an inevitable component of devices such as liquid crystal displays（LCD）,light modulators,optical and biological sensors.Nanoparticle doped liquid crystal can improve its photoelectric properties and accelerate the response of liquid crystal devices.The quantum dot doping not only improves the properties of liquid crystal,but also widens the application range of liquid crystal due to its size uniformity and fluorescence tunable properties.Inorganic halide perovskite quantum dots,CsPbX₃（X=Cl,Br,I）,have been used in many devices due to their excellent electrical and optical properties.For example,their relatively high quantum efficiency（90%）and narrow-band emission（half-height width of approx.20 nm）and scale-dependent luminescence properties covering the entire visible spectrum（400-700 nm）make them attractive materials for use in a wide range of optoelectronic applications,such as LEDs,solar panels,vivid colour displays and various other devices.In this paper,Cs₄PbBr₆ quantum dots were synthesized by hot injection with two distinct absorption peaks and no fluorescence peaks.Cs₄PbBr₆ PQDs were generated by water-trigger method to CsPbBr₃ PQDs.Here,Si O₂ was chosen to modify CsPbBr₃PQDs to improve their stability.The absorption and fluorescence peak positions of the modified CsPbBr₃PQDs were unchanged,and the crystal structure was also unchanged,i.e.the modification of CsPbBr₃ PQDs by Si O₂ did not destroy its structure and optical properties,but the light stability and fluorescence lifetime were increased,and the stability of CsPbBr₃ PQDs was enhanced by Si O₂.In order to improve the optoelectronic properties of liquid crystals,the optoelectronic properties of CsPbBr₃ PQDs nematic liquid crystals（E7）were investigated,and the synthesized CsPbBr₃/Si O₂ PQDs composites were dispersed in liquid crystals by high-speed oscillation.The CsPbBr₃/Si O₂ PQDs were observed to induce vertical alignment of the liquid crystals in the unoriented liquid crystal cell,while this phenomenon was not observed in the parallel oriented liquid crystal cell.Due to the interaction of the long alkyl ligands of the PQDs with the liquid crystals,the liquid crystal molecules tend to align perpendicularly to the surface of the PQDs,disrupting the ordering of the liquid crystals and reducing the liquid crystal clear point.The doping of PQDs into liquid crystals reveals a gradual decrease in dielectric anisotropy（Δε）,elastic constant(K₁₁)and threshold voltage(V_th)with increasing PQDs concentration,which offers the possibility of reducing energy consumption in many optoelectronic devices.CsPbBr₃ PQDs can act not only as nanomaterials to modify the physical properties of liquid crystals but also as luminescent materials in cholesteric liquid crystals,reducing the response time and relaxation time of the device.The fluorescence intensity of CsPbBr₃ PQDs can be controlled by applying an electric field,and in this system CsPbBr₃ PQDs can be stably present and high fluorescence intensity contrast can be obtained.Quantum dot doped liquid crystals extend the application of liquid crystals in optoelectronic devices.