Facet-selective growth and optical properties of CdTe/CdSe tetrapod-shaped nanocrystal heterostructures

Selective CdSe tip growth on CdTe tetrapod-shaped colloidal seeds has been achieved for a Cd:surfactant molar ratio of 1:2, where surfactant is oleic acid. The average length of tetrapod arms increased from 12 to 21 nm while arm width remained constant of 3 nm. Formation of CdSe tips shifts the excitonic absorption maximum to the near-infrared region and the appearance of low-intensity absorption feature corresponding to a charge-transfer band. At the same time, luminescence band splits into a narrow (about 100 meV width) CdTe excitonic subband and a 230-meV-wide charge-transfer subband, with splitting energy increasing up to 260 meV depending on CdSe tip length. The intensity ratio of charge transfer to excitonic luminescence increases exponentially with splitting energy rise. Considerable modification of the photoluminescence spectrum has been observed with temperature variation in the range of 10–60 °C.