Abstract
A specific organization of optically active nanoscale objects can greatly affect the optical response of a system. Here, we report the controlled modification of the fluorescent emission by the assembly of water-soluble quantum rods (QRs). Our study combines optical, electron microcopy, and X-ray scattering characterizations to reveal a correlation between the self-assembly behavior of QRs into ordered 3D-arrays and the optical properties (luminescence) of formed assemblies, where the observed optical response is highly dependent on the QR aspect ratio. Specifically, shorter, 18 nm long QRs (QR18), exhibiting a well-defined smectic packing, demonstrate an enhancement of the emission intensity accompanied by a red shift and a lifetime reduction. In contrast, 40 nm long QRs (QR40), forming a columnar phase, does not show these optical properties.
Highlights
Assembling colloids, thanks to bottom-up approaches offers an effective way to create a wide range of new materials with specific properties that emerge from the organization of uniform objects into structures periodic at all scales [1,2,3,4]
Electron microcopy, and X-ray scattering characterizations to reveal a correlation between the self-assembly behavior of quantum rods (QRs) into ordered 3D-arrays and the optical properties of formed assemblies, where the observed optical response is highly dependent on the QR aspect ratio
We have described a simple, yet powerful, strategy for shaping self-assemblies of water-soluble rod-like nanoparticles, either gold nanorods [36] or QRs [37]: an aqueous suspension is imprinted between a flat substrate and a topologically micropatterned mold, and, after water has evaporated, walls displaying a smectic B packing are obtained, organized on a regular lattice over several square millimeters
Summary
Assembling colloids, thanks to bottom-up approaches offers an effective way to create a wide range of new materials with specific properties that emerge from the organization of uniform objects into structures periodic at all scales [1,2,3,4]. Quantum dots (QDs) are spherical colloids made of semiconductor materials, 2 to 10 nm in size, which exhibit a robust, efficient, and spectrally well-defined fluorescence emission [4,5,6,7] Taking advantage of these remarkable fluorescence properties and of the opportunities offered by superstructures, many applications in the field of electronics and photonics have emerged, from lasing [8,9,10,11,12] to light harvesting devices [ 13, 14], and new physical effects have been evidenced, from fluorescence intensity enhancement to superradiance [15,16,17,18]. We characterized the fluorescence emission properties of the obtained assemblies and found that QR organization into 3D-ordered smectic crystal induced a red shift of the wavelength and an enhancement of the intensity of the fluorescence emission as well as a reduction of its lifetime
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