Interpreting the Ultraviolet Absorption in the Spectrum of 415 nm-Bandgap CdSe Magic-Size Clusters

Abstract

Colloidal semiconductor magic-size clusters (MSCs), a crucial link between molecular and bulk materials, have attracted attention in the past three decades. However, the identification of their nonbandgap electronic transitions via optical absorption has been challenging due to the possible presence of other-bandgap ensembles in synthetic batches. For CdSe MSC-415, referred to as the optical absorption (1S(e)-1S(h)) in nanometers of wavelength, we report our exploration on the origin of two commonly documented absorption peaks at 381 and 351 nm. We show that the evolution of the two peaks does not synchronize with that of the ∼415 nm peak and seems to be respectively related to the disappearance of MSC-391 and MSC-361. Accordingly, these two peaks detected are probably not due to higher order electronic transitions in MSC-415. The present study shows the necessity of re-evaluating previous experimental results and of developing advanced theoretical models to better understand the quantized energy levels of MSCs.

Thermally-induced reversible structural isomerization in colloidal semiconductor CdS magic-size clusters

“…An in-depth understanding of the structural isomerism would be essential to design and engineer advanced miniaturized devices, whose switching kinetics could be accelerated or delayed as per the requirement of individual applications. We anticipate that the present work will inspire and motivate more studies (including modeling) on structural transformations of colloidal NCs 47 , 60 .…”

Room-temperature formation of CdS magic-size clusters in aqueous solutions assisted by primary amines

“…The multistep model, designated by nonclassical nucleation theory, accounts for the presence of intermediates in the pre-nucleation stage . Such intermediates have been illustrated in several materials systems including calcium-based inorganics [4][5][6][7][8] , organics [9][10][11] , polymers [12][13][14] , metals [15][16][17] , and semiconductor quantum dots (QDs) [18][19][20][21][22][23][24][25][26][27][28] .…”

“…For organic-phase approaches to semiconductor metal (M) chalcogenide (E) QDs, a two-pathway model has been proposed for the pre-nucleation stage [18][19][20][21][22][23][24][25][26][27][28] . One pathway involves the formation of monomers and fragments, which result in QDs as per the LaMer model of the CNT.…”

One-Step Approach to Single-Ensemble CdS Magic-Size Clusters with Enhanced Production Yields

“…5,6 The two pathways are connected by an intrinsic MSC to PC to QD pathway, which is consistent with the experimental observation that the growth of QDs is accompanied by the decrease of MSCs. [7][8][9][10][11][12] Semiconductor ME MSCs have generally been acknowledged to be side products in the production of colloidal semiconductor ME QDs. [10][11][12] For samples sequentially extracted from hot-injection or non-hot-injection reaction batches, MSCs display sharp optical absorption peaking usually at particular wavelengths, while QDs exhibit relatively broad optical absorption that continuously redshifts as their size increases.…”

“…5 Also, the peak position is affected by dispersion environments including temperatures, such as a few nanometer redshifts for CdSe MSC-415 at 30 to 60 C. 9 Accordingly, MSC-311 capped by methyl carboxylate ligands (resulted from the Cd(MA) 2 + S + HPPh 2 reaction) did not display a thermally-induced transformation to CdS MSC-322, as readily as MSC-311 capped by oleate ligands did, which was from the Cd(OA) + S + HPPh reaction. This may be reasonably attributed to the fact that 2methyloctadecanoic acid has a stronger coordination effect towards Cd than oleic acid does.…”