3 research outputs found
Precise Control of Quantum Confinement in Cesium Lead Halide Perovskite Quantum Dots via Thermodynamic Equilibrium
Cesium lead halide
(CsPbX<sub>3</sub>) nanocrystals have emerged
as a new family of materials that can outperform the existing semiconductor
nanocrystals due to their superb optical and charge-transport properties.
However, the lack of a robust method for producing quantum dots with
controlled size and high ensemble uniformity has been one of the major
obstacles in exploring the useful properties of excitons in zero-dimensional
nanostructures of CsPbX<sub>3</sub>. Here, we report a new synthesis
approach that enables the precise control of the size based on the
equilibrium rather than kinetics, producing CsPbX<sub>3</sub> quantum
dots nearly free of heterogeneous broadening in their exciton luminescence.
The high level of size control and ensemble uniformity achieved here
will open the door to harnessing the benefits of excitons in CsPbX<sub>3</sub> quantum dots for photonic and energy-harvesting applications
Effects of Direct Solvent-Quantum Dot Interaction on the Optical Properties of Colloidal Monolayer WS<sub>2</sub> Quantum Dots
Because of the absence
of native dangling bonds on the surface
of the layered transition metal dichalcogenides (TMDCs), the surface
of colloidal quantum dots (QDs) of TMDCs is exposed directly to the
solvent environment. Therefore, the optical and electronic properties
of TMDCS QDs are expected to have stronger influence from the solvent
than usual surface-passivated QDs due to more direct solvent-QD interaction.
Study of such solvent effect has been difficult in colloidal QDs of
TMDC due to the large spectroscopic heterogeneity resulting from the
heterogeneity of the lateral size or (and) thickness in ensemble.
Here, we developed a new synthesis procedure producing the highly
uniform colloidal monolayer WS<sub>2</sub> QDs exhibiting well-defined
photoluminescence (PL) spectrum free from ensemble heterogeneity.
Using these newly synthesized monolayer WS<sub>2</sub> QDs, we observed
the strong influence of the aromatic solvents on the PL energy and
intensity of monolayer WS<sub>2</sub> QD beyond the simple dielectric
screening effect, which is considered to result from the direct electronic
interaction between the valence band of the QDs and molecular orbital
of the solvent. We also observed the large effect of stacking/separation
equilibrium on the PL spectrum dictated by the balance between inter
QD and QD-solvent interactions. The new capability to probe the effect
of the solvent molecules on the optical properties of colloidal TMDC
QDs will be valuable for their applications in various liquid surrounding
environments
Synthesis and Optical Properties of One Year Air-Stable Chiral Sb(III) Halide Semiconductors
Chiral hybrid metal-halide semiconductors (MHS) pose
as ideal candidates
for spintronic applications owing to their strong spin–orbit
coupling (SOC), and long spin relaxation times. Shedding light on
the underlying structure–property relationships is of paramount
importance for the targeted synthesis of materials with an optimum
performance. Herein, we report the synthesis and optical properties
of 1D chiral (R-/S-THBTD)SbBr5 (THBTD = 4,5,6,7-tetrahydro-benzothiazole-2,6-diamine) semiconductors
using a multifunctional ligand as a countercation and a structure
directing agent. (R-/S-THBTD)SbBr5 feature direct and indirect band gap characteristics, exhibiting
photoluminescence (PL) light emission at RT that is accompanied by
a lifetime of a few ns. Circular dichroism (CD), second harmonic generation
(SHG), and piezoresponse force microscopy (PFM) studies validate the
chiral nature of the synthesized materials. Density functional theory
(DFT) calculations revealed a Rashba/Dresselhaus (R/D) spin splitting,
supported by an energy splitting (ER)
of 23 and 25 meV, and a Rashba parameter (αR) of
0.23 and 0.32 eV·Å for the R and S analogs, respectively. These values are comparable to
those of the 3D and 2D perovskite materials. Notably, (S-THBTD)SbBr5 has been air-stable for a year, a record
performance among chiral lead-free MHS. This work demonstrates that
low-dimensional, lead-free, chiral semiconductors with exceptional
air stability can be acquired, without compromising spin splitting
and manipulation performance