Temperature Dependence of the CdS Bandgap in the Extreme Confinement Regime

Abstract

A non-empirical equation describing the effect of size on the temperature dependence of the optical bandgap of CdS (dE g/dT) is obtained on the basis of the Brus equation. Intriguingly, we find that dE g/dT diverges strongly from bulk values only within the “extreme confinement” (EC) regime. We conducted both experimental and theoretical investigations of the absorption spectra of CdS clusters and quantum dots as a function of temperature above room temperature. Our results show that the value of dE g/dT obtained from absorption spectra in the EC regime is 2.5 times higher than in the strong confinement regime. Notable ligand sensitivities are also observed for dE g/dT in the case of CdS clusters. Ab initio molecular dynamics simulations and density functional theory calculations reveal that thermal fluctuations are the crucial factor influencing the bandgap temperature coefficient. Our results help resolve some long-standing debates regarding the dE g/dT behavior of semiconductor quantum dots.

Formation and Transformation of CdS Clusters during the Prenucleation Stage and in a Dilute Dispersion at Room Temperature

“…Our findings bring insights into the formation (via chemical self-assembly) − and isomerization of semiconductor clusters, the knowledge of which may shed light onto those formed in the prenucleation stage of other materials such as calcium-based inorganics, , organics, − polymers, − and metals. , It is our conviction that this study represents a fundamental advance in the scientific understanding of the prenucleation stage, the “black box” or “forbidden region” of QDs in which the molecule-to-cluster transition occurs and “molecular chemistry meets solid state science” . Hopefully the concept of extreme quantum confinement for MSCs will be perfected, , to provide us the very theoretical explanation for the isomerization among CdS MSCs (including MSC-311, MSC-322, MSC-345, and MSC-360), together with that reported among CdSe MSCs (which include MSC-350/360, MSC-380/390, and MSC-415), , CdTe MSCs (which include MSC-371, MSC-417, MSC-448, and MSC-488), − and between CdTeSe MSC-399 and MSC-422 …”

“…With regard to quantum confinement, MSCs and QDs have different effects because shape comes into play for MSCs. 11,12 A two-pathway model is implemented to comprehend the growth relationship between II−VI metal chalcogenide (ME) MSCs and QDs (Scheme S1). 7,13−15 One pathway is classical, associated with the monomer (Mo) formation between M and E precursors via M−E covalent bond formation.…”

“…40,41 It is our conviction that this study represents a fundamental advance in the scientific understanding of the prenucleation stage, the "black box" or "forbidden region" of QDs in which the molecule-to-cluster transition occurs and "molecular chemistry meets solid state science". 42 Hopefully the concept of extreme quantum confinement for MSCs will be perfected, 11,12 to provide us the very theoretical explanation for the isomerization among CdS MSCs (including MSC-311, MSC-322, MSC-345, and MSC-360), together with that reported among CdSe MSCs (which include MSC-350/360, MSC-380/390, and MSC-415), 43,44 CdTe MSCs (which include MSC-371, MSC-417, MSC-448, and MSC-488), 20−22 and between CdTeSe MSC-399 and MSC-422. 23 ■ ASSOCIATED CONTENT * sı Supporting Information…”

“…Such an exploration is in outstanding demand in order to advance our synthetic capability of MSCs with a high degree of control and theoretical understanding of the extreme quantum confinement of MSCs. With regard to quantum confinement, MSCs and QDs have different effects because shape comes into play for MSCs. , …”