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

• Published in: Soft matter Vol. 11; no. 2; pp. 255 - 26
• Main Authors: Amaral, Jose Jussi, Wan, Jacky, Rodarte, Andrea L, Ferri, Christopher, Quint, Makiko T, Pandolfi, Ronald J, Scheibner, Michael, Hirst, Linda S, Ghosh, Sayantani
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 14.01.2015
• Subjects: Brightening; Clusters; Fluid dynamics; Fluid flow; Liquid crystals; Magnetic fields; NANOSCIENCE AND NANOTECHNOLOGY; Nanostructure; Quantum dots
• ISSN: 1744-683X; 1744-6848
• DOI: 10.1039/c4sm02015d

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. Magnetic and semiconducting nanoparticles are co-assembled in a liquid crystalline matrix to form composite aggregates that display continuous brightening with the application of small external magnetic fields at room temperature.