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Materials Science

Research of Nanoparticles and 2D Materials

Quantum Dots, Carbon Dots, TMDs

Nanomaterials, including nanoparticles and 2D materials, are unique due to their remarkable physical, chemical, and electronic properties that emerge at the nanoscale because of quantum confinement. For example, they can scatter, absorb, or emit light differently from bulk materials. 2D materials like graphene have excellent electron transport properties, making them attractive for next-generation electronic devices and transparent conductive films.

The properties of nanomaterials can be finely tuned by adjusting their size, shape, or composition. This tunability is essential for tailoring them to specific applications, from electronics to catalysis. Working with nanomaterials also presents challenges, and TRPL is one of the characterization techniques that can address these challenges.

Image Research of Nanoparticles and 2D Materials

Carbon dots

Carbon dots, which are small carbon nanoparticles, have gained significant attention in recent years due to their versatile properties. One of their most notable features is a strong and tunable photoluminescence across the visible and NIR spectrum. They also exhibit good electrical conductivity, making them attractive for optoelectronic devices and light-emitting diodes.

Complexes of carbon dots and plasmonic metal nanoparticles with enhanced emission

When carbon dots and plasmonic metal nanoparticles form complexes, the carbon dot's absorption and emission overlaps with the plasmon resonance of the metals. For the most optimized complex architecture, this increases emission up to 5-fold.

Metal nanoparticles may on the one hand enhance PL emission of nearby emitters due to local enhancement of excitation or the acceleration of spontaneous recombination, on the other hand they may quench emission due to non-radiative decay via plasmon-induced energy transfer. The overall effect on the PL depends on many parameters, among them the nanoscale architecture. To determine the nanoscale architecture, the weight ratio of carbon dots to gold nanoparticles can be varied systematically during sample preparation. This ratio influences the number of carbon dots conjugated to nanoparticles in the resulting complexes.

PL decays were acquired on a MicroTime 100 time-resolved confocal microscope equipped with a 405 nm excitation laser. When the carbon dot/gold nanoparticle weight ratio was increased, the PL quantum yield also increased, while the PL lifetime decreased. This is probably due to PL quenching via energy transfer, enabled by the overlap between the gold nanoparticle plasmon resonance spectra and the carbon dot PL band. These observations support the determination of optimal complex architecture and composition.

To learn more, read the paper in Nanomaterials (2023): Carbon Dot Emission Enhancement in Covalent Complexes with Plasmonic Metal Nanoparticles

Carbon dots with NIR absorption and emission

PL decay curves of carbon dots in different solventsCarbon dots with NIR absorption and emission in the NIR region in aqueous solution are desirable for bioimaging applications, among others. In this work, researchers modified the surface of carbon dots with polyethyleneimine (PEI) to achieve just that. They characterized the optical properties of their new PEI-CDs, recording PL intensity and decay curves under various conditions with a MicroTime 100 time-resolved confocal microscope. PEI-modification increases the PL lifetime, probably by inhibiting energy dissipation by water molecules.

To learn more, read the paper in Advanced Science (2022): Toward Strong Near-Infrared Absorption/Emission from Carbon Dots in Aqueous Media through Solvothermal Fusion of Large Conjugated Perylene Derivatives with Post-Surface Engineering

Carbon dot/graphene hybrid white laser characterization

Left: TRPL decays of the deformed (red, shorter) and undeformed (blue, longer) CQDs/graphene devices at a single pumping power density, right: carrier lifetimes of the deformed and undeformed CQDs/graphene devices decrease with increasing pumping power densityFor future wearable technologies such as e-skins and personal health monitors, flexible, stretchable, and lightweight optoelectronic devices are required. To this end, researchers developed a cavity-free white laser integrating fluorescent carbon dots and crumpled graphene.

To characterize the optical properties of the new device, TRPL spectra and PL decay curves of deformed and undeformed materials were recorded as a function of pumping power density, using a pulsed excitation laser at 375 nm (LDH series). These provide information on the carrier lifetimes in the material, which clearly decrease with increasing power, probably due to stimulated emission. The crumpled graphene is thought to form a virtual cavity for emitted photons by scattering.

To learn more, read the paper in Optics Express (2022): All-carbon stretchable and cavity-free white lasers

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