Effect of Cd0.5Zn0.5S shells on temperature-dependent luminescence kinetics of CdSe quantum dots

Abstract

CdSe/Cd_0.5Zn_0.5S core/shell quantum dots (QDs) with high photoluminescence (PL) efficiency up to 85% were fabricated in organic solutions at high temperature via an anisotropic shell growth on CdSe nanorods. The core/shell QDs with PL peak wavelengths from green to red were obtained by controlling the size of the cores and the thickness of the array Cd_0.5Zn_0.5S shells. Both the cores and the core/shell QDs revealed narrow size distributions which resulted in narrow PL spectra. Green-emitting CdSe cores with a Se-rich surface revealed a long average lifetime of ∼44 ns. After being coated with Cd_0.5Zn_0.5S shells, the average lifetime of QDs decreased drastically up to ∼23 ns. The average decay time of the core/shell QDs depended on their shell thickness. The temperature-dependent PL in a temperature range of 293 to 393 K was investigated for CdSe cores and highly luminescent CdSe/Cd_0.5Zn_0.5S core/shell QDs. Luminescent quenching occurred with increasing temperature for the cores even though the cores exhibited high crystallinity. In contrast, with increasing temperature, the emission PL peak wavelength of the core/shell QDs shifts towards lower energies, the PL bandwidth increases a little and the PL efficiencies decrease slightly. The red-shifted degree of the PL spectra with temperature is small (less than 10 nm).