Role of ZnS Segment on Charge Carrier Dynamics and Photoluminescence Property of CdSe@CdS/ZnS Quantum Rods

Abstract

Growing a wide band gap shell on bare core and/or core@shell materials is a fascinating idea for improving the photoluminescence (PL) efficiency and stability. An epitaxially grown shell adds another degree of complexity to the system and modulates the excited-state relaxation dynamics, which remain poorly understood. Employing time-resolved PL and femtosecond transient absorption (TA) spectroscopy, we present a thorough study on charge carrier dynamics of CdSe@CdS and CdSe@CdS/ZnS quantum rods (QRs). Various excitation wavelengths were used to identify the contribution of individual segment toward the optical properties of the QRs. Our femtosecond TA measurements provide a clear evidence of excitation migration from CdS as well as ZnS to CdSe core within few picoseconds of photoexcitation. The excitons recombine faster in the CdSe moiety of the CdSe@CdS/ZnS than that of the CdSe@CdS QRs via an extra decay path. The interband trap states that are created via the formation of extended defects because of la...