Magnetic field induced quantum dot brightening in liquid crystal synergized magnetic and semiconducting nanoparticle composite assemblies

Abstract

The design and development of multifunctional composite materials from artificial nano-constituents is one of the most compelling current research areas. This drive to improve over nature and produce 'meta-materials' has met with some success, but results have proven limited with regards to both the demonstration of synergistic functionalities and in the ability to manipulate the material properties post-fabrication and in situ. Here, magnetic nanoparticles (MNPs) and semiconducting quantum dots (QDs) are co-assembled in a nematic liquid crystalline (LC) matrix, forming composite structures in which the emission intensity of the quantum dots is systematically and reversibly controlled with a small applied magnetic field (<100 mT). This magnetic field-driven brightening, ranging between a two- to three-fold peak intensity increase, is a truly cooperative effect: the LC phase transition creates the co-assemblies, the clustering of the MNPs produces LC re-orientation at atypical low external field, and this re-arrangement produces compaction of the clusters, resulting in the detection of increased QD emission. These results demonstrate a synergistic, reversible, and an all-optical process to detect magnetic fields and additionally, as the clusters are self-assembled in a fluid medium, they offer the possibility for these sensors to be used in broad ranging fluid-based applications.

Anisotropic Fast Electrically Switchable Emission from Composites of CsPbBr3 Perovskite Quantum Cuboids in a Nematic Liquid Crystal

“…Visual observations of the switching process through POM did not show any reorientation of the QDs. While the PL emission from quantum rods could be polarized caused by their shape anisotropy, emission from symmetric QDs is expected to be isotropic, and thus the present results appear to be puzzling. It is however noted that the absorption profiles show that the magnitude of absorption is higher in the X configuration than in the Z configuration (See Figure b).…”

“…A variety of nanoparticles have been employed to alter/tune the LC properties. In fact, QDs have received their fair share of attention in this regard . Presence of QDs has been found to diminish the threshold voltage, accelerate the electro‐optic response, photorefractivity, increase the birefringence, and control PL .…”

Directed assembly of magnetic and semiconducting nanoparticles with tunable and synergistic functionality

“…Here, we investigate the formation and modulation of co-assemblies of Fe 3 O 4 magnetic nanoparticles (MNPs) and CdSe/ZnS core/shell quantum dots (QDs), directed by the thermotropic phase transition of a liquid crystalline (LC) material. This study builds on a prior effort by our group 41 , where we observed the formation of these co-assemblies and demonstrated that a small magnetic field could be used to enhance QDs PL, up to almost three-fold. Simultaneously, the co-assemblies appeared to spatially compress, and from this we indirectly inferred that the clustering of the MNPs produced localized high fields that caused LC re-orientation at low external magnetic fields.…”

Phase Transition-Driven Nanoparticle Assembly in Liquid Crystal Droplets

“…There have been several recent attempts to use liquid crystal defects to assemble and cluster nanoparticles of several types, including semiconducting (e.g., quantum dots), metallic (e.g., gold, silver), and magnetic particles [ 15 ]. Such assemblies may exhibit collective electronic, photonic, or magnetic properties not seen in isolated nanoparticles [ 16 , 17 ].…”