Colloidal Quantum Dots (QDs) have attracted the attention of the scientific and industrial communities for their wide range of applications including display technology, bioimaging, light harvesting, quantum computing, and miniature lasers. QDs are suited for these application due to: one pot synthesis with abundant precursors and solvents, size-tunable optical response, and high photostability. The ability of QDs’ to harvest and emit light is sensitive to its surface morphology and environment. Thus, QDs’ optical properties can be manipulated by surface modification. In particular, it was observed that the quantum yield of photoluminesces (QYPL) of cadmium chalcogenides QDs can increases by 55.7 times when treated with hydride-generating compounds. Investigating the mechanism for the enhancement in the QYPL is complicated due to complex surface chemistry. Here, we report on the effect of hydride anion (H-) on the morphology, electronic structure, and optical spectra of small Cd-Se clusters investigated by density functional theory (DFT) and time-dependent DFT. Results of our calculations reveal that H- interaction with the QDs’ surface gives rise to two main chemical changes: removal surface Se anions as H2Se, and coordinates with surface Cd cations. When H- removes surface Se anions the surface becomes Cd-enriched. Future treatment results in surface Cd passivated by H- which leads to a significant increase in the oscillator strength of the first excited singlet state (S1) compared to the original QDs. The increase in oscillator strength indicates the elimination of hole and electron trap states from the band gap of the QDs, thereby decreasing the contribution of non-radiative electron-hole recombination and the increase QYPL of cadmium chalcogenides QDs.

DFT insights into brightening of II-VI quantum dots by hydride treatment

2019 Spring National Meeting

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