Single-wall carbon nanotubes (SWCNT) fluoresce in the nearinfrared (NIR) region and have been assembled with biopolymers such as DNA to form highly sensitive molecular (bio)sensors. They change their fluorescence when they interact with analytes. Despite the progress in engineering these sensors, the underlying mechanisms are still not understood. Here, we identify processes and rate constants that explain the photophysical signal transduction by exploiting sp 3 quantum defects in the sp 2 carbon lattice of SWCNTs. As a model system, we use ssDNA-coated (6,5)-SWCNTs, which increase their NIR emission (E 11 , 990 nm) up to +250% in response to the important neurotransmitter dopamine. In contrast, SWCNTs coated with DNA but with a low number of NO 2 -aryl sp 3 quantum defects decrease both their E 11 (−35%) and defect-related E 11 * emission (−50%) at 1130 nm. Consequently, the interaction with the analyte does not change the radiative exciton decay pathway alone. Furthermore, the fluorescence response of pristine SWCNTs increases with SWCNT length, suggesting that exciton diffusion is affected. The quantum yield of pristine (6,5)-SWCNTs increases in response to the analyte from 0.6 to 1.3% and points to a change in non-radiative rate constants. These experimental results for dopamine and other analytes are explained by a Monte Carlo simulation of exciton diffusion, which supports a change in two non-radiative decay pathways together with an increase in exciton diffusion (three-rate constant model). The combination of such SWCNTs with defects and without defects enables the assembly of ratiometric biosensors with opposing responses at different wavelengths. In summary, we demonstrate how perturbation of a nanomaterial with quantum defects reveals the photophysical mechanism and reverses optical responses of biosensors.

Different techniques that enable the selective microstructure design of aerogels without the use of additives are presented. For this, aerogels were prepared from platinum nanoparticle solutions using the cryoaerogelation method, and respective impacts of different freezing times, freezing media, and freezing temperatures were investigated with electron microscopy as well as inductively coupled plasma optical emission spectroscopy. The use of lower freezing temperatures, freezing media with higher heat conductivities, and longer freezing periods led to extremely different network structures with enhanced stability. In detail, materials were created in the shape of lamellar, cellular, and dendritic networks. So far, without changing the building blocks, it was not possible to create the selective morphologies of resulting aerogels in cryoaerogelation. Now, these additive-free approaches enable targeted structuring and will open up new opportunities in the future cryoaerogel design.

Colloidal two-dimensional (2D) lead chalcogenide nanoplatelets (NPLs) represent highly interesting materials for near- and short wave-infrared applications including innovative glass fiber optics exhibiting negligible attenuation. In this work, we demonstrate...

Strongly quantum-confined 2D colloidal PbS nanoplatelets (NPLs) are highly interesting materials for near-infrared optoelectronic applications. Here, we use ultrafast transient optical absorption spectroscopy to study the characteristics and dynamics of photoexcited excitons in ultrathin PbS NPLs with a cubic (rock-salt) structure. The NPLs are synthesized at near room temperature from lead oleate and thiourea precursors and show an optical absorption onset at 680 nm (1.8 eV) as well as photoluminescence at 720 nm (1.7 eV). By treating PbS NPLs with CdCl 2 in a postsynthetic step, their photoluminescence quantum yield is strongly enhanced from 1.4 % to 19.4 %.The surface treatment leads to an increased lead to sulfur ratio in the structures and associated reduced non-radiative recombination. Exciton-phonon interactions in pristine and CdCl 2 treated PbS NPLs at frequencies of 1.8 and 2.2 THz are apparent from coherent oscillations in the measured transient absorption spectra. This study is an important step forward in unraveling and controlling the optical properties of IV-VI semiconductor NPLs.

This paper analyzes the electrochemical and physicochemical properties of activated carbons developed from coffee husk through different activation routes.