3 research outputs found
Solution Synthesis and Optical Properties of Transition-Metal-Doped Silicon Nanocrystals
A new synthetic method was developed
to produce a range of transition-metal
(Mn, Ni, and Cu) doped silicon nanocrystals (Si NCs). The synthesis
produces monodisperse undoped and doped Si NCs with comparable average
sizes as shown by transmission electron microscopy (TEM). Dopant composition
was confirmed by EDX (energy dispersive X-ray spectroscopy). The optical
properties of undoped and doped were compared and contrasted using
absorption (steady-state and transient) and photoluminescence spectroscopy.
Doped Si NCs demonstrated unique dopant-dependent optical properties
compared to undoped Si NCs such as enhanced subgap absorption, and
40 nm shifts in the emission. Transient absorption (TA) measurements
showed that photoexcitations in doped Si NCs relaxed via dopant states
not present in undoped Si NCs
Solution Synthesis and Optical Properties of Transition-Metal-Doped Silicon Nanocrystals
A new synthetic method was developed
to produce a range of transition-metal
(Mn, Ni, and Cu) doped silicon nanocrystals (Si NCs). The synthesis
produces monodisperse undoped and doped Si NCs with comparable average
sizes as shown by transmission electron microscopy (TEM). Dopant composition
was confirmed by EDX (energy dispersive X-ray spectroscopy). The optical
properties of undoped and doped were compared and contrasted using
absorption (steady-state and transient) and photoluminescence spectroscopy.
Doped Si NCs demonstrated unique dopant-dependent optical properties
compared to undoped Si NCs such as enhanced subgap absorption, and
40 nm shifts in the emission. Transient absorption (TA) measurements
showed that photoexcitations in doped Si NCs relaxed via dopant states
not present in undoped Si NCs
The Evolution of Quantum Confinement in CsPbBr<sub>3</sub> Perovskite Nanocrystals
Colloidal
nanocrystals (NCs) of lead halide perovskites are considered
highly promising materials that combine the exceptional optoelectronic
properties of lead halide perovskites with tunability from quantum
confinement. But can we assume that these materials are in the strong
confinement regime? Here, we report an ultrafast transient absorption
study of cubic CsPbBr<sub>3</sub> NCs as a function of size, compared
with the bulk material. For NCs above ∼7 nm edge length, spectral
signatures are similar to the bulk material–characterized by
state-filling with uncorrelated charges–but discrete new kinetic
components emerge at high fluence due to bimolecular recombination
occurring in a discrete volume. Only for the smallest NCs (∼4
nm edge length) are strong quantum confinement effects manifest in
TA spectral dynamics; focusing toward discrete energy states, enhanced
bandgap renormalization energy, and departure from a Boltzmann statistical
carrier cooling. At high fluence, we find that a hot-phonon bottleneck
effect slows carrier cooling, but this appears to be intrinsic to
the material, rather than size dependent. Overall, we find that the
smallest NCs are understood in the framework of quantum confinement,
however for the widely used NCs with edge lengths >7 nm the photophysics
of bulk lead halide perovskites are a better point of reference