Exciton and multi-exciton dynamics in CdSe/Cd1-xZnxS quantum dots

The outstanding optical properties of Semiconductor Quantum Dots (QDs) have attracted much interest for over two decades. The development of synthetic methods for the production of core-shell QDs has opened the way to attaining almost ideal emitting properties. Their implementation in opto-electronic devices, such as light emitting diodes (LEDs) and lasers, requires a full understanding of the fine details of their photophysics. The exciton dynamics of core and coreshell QDs was extensively studied by means of pump and probe (P and P) and transient photoluminescence (TRPL) spectroscopies. Nevertheless, the wealth of possible exciton and multi-exciton decay mechanisms, operating on comparable time-scales, results in complex signals. In this work, the exciton dynamics of a complete CdSe/Cd 1-x Zn x S series is investigated, with a focus on exciton trapping processes. Insights into the energy distribution of exciton traps are unveiled by wavelength resolve QY measurements. Multicolor P and P measurements give a deeper insight into the dynamics of exciton trapping and Auger recombinations. An inversion method is proposed as a powerful tool for separating different contribution in complex P and P transients. The outcomes of this work clarify the role of core/shell interfaces and surfaces in modulating the optical properties and suggest possible routes for their improvement.