Semiconducting single-walled carbon nanotubes (SWCNTs) constitute an ideal platform for developing near-infrared biosensors, single photon sources, and nanolasers due to their distinct optical and electrical properties. Covalent doping of SWCNTs has recently been discovered as an efficient approach in enhancing their emission intensities. We perform pump−probe studies of SWCNTs that are covalently doped with sp 3 quantum defects and reveal strikingly different exciton formation dynamics and decay mechanisms in the presence of the defect sites. We show that, in highly doped SWCNTs, ultrafast trapping of excitons at the defect sites can outpace other photodynamic processes and lead to ground-state photobleaching of the quantum defects. Our fitting of the transient data with a kinetic model also reveals an upper limit in the quantum defect density for obtaining highly luminescent SWCNTs without causing irreversible damage. These findings not only deepen our understanding of the photodynamics in covalently doped SWCNTs but also reveal critical information for the design of bright near-infrared emitters that can be utilized in biological, quantum information, and nanophotonic applications.
Due
to their tunable bandgaps and strong spin-valley locking, transition
metal dichalcogenides constitute a unique platform for hosting single-photon
emitters. Here, we present a versatile approach for creating bright
single-photon emitters in WSe2 monolayers by the deposition
of gold nanostars. Our molecular dynamics simulations reveal that
the formation of the quantum emitters is likely caused by the highly
localized strain fields created by the sharp tips of the gold nanostars.
The surface plasmon modes supported by the gold nanostars can change
the local electromagnetic fields in the vicinity of the quantum emitters,
leading to their enhanced emission intensities. Moreover, by correlating
the emission energies and intensities of the quantum emitters, we
are able to associate them with two types of strain fields and derive
the existence of a low-lying dark state in their electronic structures.
Our findings are highly relevant for the development and understanding
of single-photon emitters in transition metal dichalcogenide materials.
We
have prepared nanocrystals of MoS2 across a range
of length scales by heating single crystals of the molecular precursor
(NH4)2Mo3S13·H2O. Rod-shaped crystals of the polysulfide precursor retain
their original morphology after heating at temperatures up to 1000
°C and undergo complete conversion to MoS2 while acting
as a template for the confined formation of MoS2 nanocrystals.
This solid state transformation proceeds with the release of gaseous
species without blowing the crystals apart and leads to formation
of pores embedded into a nanocrystalline assembly of the templated
nano-MoS2. The obtained assemblies of MoS2 nanocrystals
have the exact same shape of the original rod-shaped (NH4)2Mo3S13·H2O crystals
indicative of a pseudomorphic shape-retentive process. Such crystal-shaped
nanocrystal assemblies show electrical conductivity values similar
to a bulk MoS2 single crystal with electron carrier concentration
of 1.5 × 1014 cm–3 and mobility
of 7 cm2/(V s). The nanocrystals of MoS2 were
grown at temperatures ranging from 450 to 1000 °C, and the sizes,
shapes, morphologies, and their orientations can be engineered as
a function of heating rate, soaking time, and temperature. These findings
suggest a unique process for constrained templated nanocrystal growth
from an organized molecular precursor structure with control of bulk
morphology, size distribution, and orientation of nanocrystallites.
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