Synthesis, characterization and the photoinduced electron-transfer energetics of CdTe/CdSe type-II core/shell quantum dots

Abstract

The CdTe/CdSe type-II core/shell quantum dots (QDs) were chemically synthesized in a noncoordinating solvent. The optical properties and structures of the synthesized QDs were characterized by absorption spectroscopy (Abs), photoluminescence (PL) spectroscopy, PL-decay lifetime, X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDX). The PL peak of the CdTe/CdSe core/shell QDs could be tuned from 698 nm (1.77 eV) to 780 nm (1.59 eV) by changing the thickness of CdSe shell and fixing the size of CdTe core. The PL quantum yields (QYs) of these QDs were from 14.1% to 31.7% and their full width at half maximum (FWHM) of PL peaks was kept below 0.12 eV during the growth process of CdSe shell on CdTe core. Compared to CdTe cores, the CdTe/CdSe type-II core/shell QDs have much longer PL decay times, up to ~100 ns? Based on Marcus theory, the charge transfer (CT) of CdTe/CdSe 1–5 monolayers (MLs) type-II core/shell QDs has been studied and the effects of quantum confinement on the structure parameters have been revealed. The reorganization energies (RE) of the CdTe/CdSe (1–5 ML) type-II core/shell QDs for the electron transfer (ET) were in the range from 60 meV to 106 meV and was found that ET takes place in the Marcus inverted region (-ΔG0ET > λCT) which is typical for these QDs.