Spectroscopy of CdTe/CdSe Type-II Nanostructures: Morphology, Lattice Mismatch, and Band-Bowing Effects

We compare the spectroscopy of two different morphologies of CdTe/CdSe type-II nanocrystals. Core/tetrapod and spherical core/shell particles are grown from identicalCdTe cores, and both morphologies exhibit type-II spectroscopic behavior. The two morphologies show very different oscillator strengths for the lowest (luminescent) transition; the core/tetrapod particles exhibit larger oscillator strengths for the same amount of spectral shift. A model is presented that explains this difference and accurately predicts emission wavelengths and relative oscillator strengths for the spherical particles. This model uses an elastic continuum treatment to consider strain induced by lattice mismatch at the core/shell interface. The CdTe–CdSe lattice mismatch results in a calculated core pressure of about 2.9 GPa for the particles with the thickest shells. This pressure causes a change in the CdTe conduction band energy of about 0.24 eV and a change in the CdTe lattice parameter of 2.3%. The change in the lattice pa...