A Real‐Time In Situ Demonstration of Direct and Indirect Transformation Pathways in CdTe Magic‐Size Clusters at Room Temperature

Abstract

The transformations of colloidal semiconductor magic‐size clusters (MSCs) are expected to occur with only discrete, step‐wise redshifts in optical absorption. Here, we challenge this assumption presenting a novel, conceptually different transformation, for which the redshift is continuous. In the room‐temperature transformation from CdTe MSC‐448 to MSC‐488 (designated by the peak wavelengths in nanometer), the redshift of absorption monitored in situ displays distinctly continuous and/or step‐wise behavior. Based on conclusive evidence provided by real‐time experiments, the former transformation is apparently direct and intra‐cluster with a relatively large energy barrier. The latter transformation is indirect and assisted by MSC precursor compounds (PCs). The former transformation follows the latter often, being predominant at a relatively high temperature. The present findings encourage a reconsideration of the absorption redshift reported previously for transformations of binary II–VI MSCs, together with the pathway associated without the increase of cluster mass.

Transformations of Magic-Size Clusters via Precursor Compound Cation Exchange at Room Temperature

“…The uninterrupted pattern is similar to that reported for the intracluster isomerization from CdTe MSC-448 to MSC-488. 36,37 After the addition of Cd(OA) 2 to a dispersion containing ZnSe MSC-299 at RT, the CE reaction (Step 2) that transfers the ZnSe PC to the CdSe PC takes place immediately. Step 2 facilitates Step 1 via which ZnSe MSC-299 transforms to its counterpart ZnSe PC-299.…”

“…In addition to the present CE reaction, we have demonstrated that the binary ME PC can experience another four chemical reactions. They are isomerization to binary ME MSCs, [2][3][4][5][14][15][16]18,34,35 substitution reactions followed by isomerization to binary or ternary MSCs (Figure S1B), 17,[34][35][36][37]53,54 addition reactions followed by isomerization to photoluminescent MSCs (Figure S1B), 55 and fragmentation to QDs. 2,56 For the reaction of M and E precursors to ME QDs, the E precursor dominates the selfassembly of the M and E precursors that results in the formation of the ME PC with similar stoichiometry.…”