Size-Dependent Response of CdSe Quantum Dots to Hydrostatic Pressure

Abstract

The size-dependent pressure response of oleatestabilized CdSe quantum dots (QDs) in paraffin is investigated using diamond anvil cell experiments and density functional theory (DFT). For QDs above 3.0 nm, the photoluminescence shows a blue-shift of around 43 meV/GPa, close to the value for bulk CdSe, but the shift increases strongly for nanocrystals less than 3 nm in size. Conversely, the absorption shift is 45 meV/GPa above 3.0 nm but weakens to 35 meV/GPa for particles 1.5 nm in size. No crystallographic phase transitions occur below 2 GPa, and the optical effects are reversible. DFT calculations confirm that shifts in the bulk modulus begin for sizes estimated to be 1/2 of the Bohr radius, which we term the extreme confinement regime.

Excitation-Dependent Fluorescence with Excitation-Selective Circularly Polarized Luminescence from Hierarchically Organized Atomic Nanoclusters

“…In this context, it is important to distinguish their fluorescence from the fluorescence of QDs, which are semiconducting nanoparticles constituting an indefinite number of atoms. While the fluorescence in atomic NCs originates from HOMO–LUMO transitions, akin to molecules, quantum confinement is the major origin of emission in QDs, whereas the size of the QD determines the energy difference between the conductance and valence bands, i.e., the emission of the QD. − As stated, atomic NCs, as opposed to other forms of nanoscale particles, have consistent structural integrity and their chemical composition can be expressed in terms of precise chemical formulas. Thus, any polydispersity that prevails in other common forms of nanoscale particles is hardly present for atomic NCs, and the structure–property relationship of atomic NCs can be defined reliably .…”

Temperature Dependence of the CdS Bandgap in the Extreme Confinement Regime

“…However, for d E g /d T , a reduction of 20% from the bulk value d E bulk /d T requires a particle size as small as 1.0 nm, which is significantly smaller than the Bohr radius. We refer to this as the EC regime, as shown for d E g /d P …”

“…However, recent studies have shown that some properties of QDs, such as the bandgap pressure coefficient (dE g /dP), 9 do not exhibit size dependence in the normal confinement regime but do so only in the "extreme confinement" (EC) regime. 9 The temperature dependence of the bandgap [E g (T)] is another fundamental property of semiconductors, and it provides insights into the underlying physical processes that affect the performance and reliability of semiconductor materials under different operating conditions. The strength of this temperature dependence can usually be described by its first temperature derivative, dE g /dT.…”

“…We refer to this as the EC regime, as shown for dE g /dP. 9 Analysis of eq 1 suggests that deviations are significant in the EC regime only when the temperature dependencies of both the effective masses and dielectric constant are negligible. A discussion of other common semiconductors, such as PbS, InP, and CsPbBr 3 , can be found in Figure S1.…”

Commemorating The Nobel Prize in Chemistry 2023 for the Discovery and Synthesis of Quantum Dots

“…Thanks to the noninjection-based approach, , a reaction can be readily stopped in the prenucleation stage, − which is almost impossible for the injection-based approach. , Prenucleation clusters that are relatively transparent in optical absorption were trapped. − They form via chemical self-assembly, that occurs prior to nucleation and growth of QDs. − These prenucleation clusters can transform to magic-size clusters (MSCs) and QDs. − Thus, a multistep nonclassical model should be taken into account to understand the nucleation and growth of colloidal QDs, instead of the one-step classical LaMer model . It is highly possible that MSCs and QDs are regulated differently in relation to quantum size effects because shape comes into play for the former. ,, On a side note, CdSe MSCs (with a size of ∼1.2 nm and optical absorption peaking at ∼415 nm) were produced in the hot-injection approach; the bandwidth of MSCs is narrower due to the almost complete absence of size distribution.…”