Design, synthesis and photophysical properties of InP/CdS/CdSe and CdTe/CdS/CdSe (core/shell/shell) quantum dots for photon upconversion

Complex core/multi-shell quantum dot (QD) configurations can be used to tailor light absorption and emission properties. We present a core/shell/shell/shell structure designed to implement efficient photon upconversion. We report on the design and characterization of two intermediate products that could progress to implement this design: InP/CdS/CdSe and CdTe/CdS/CdSe. Products were synthesized by adapting established procedures for the colloidal synthesis of nanoparticles in solution. Transmission electron microscopy (TEM) and x-ray diffraction (XRD) were used to determine particle size, crystallinity, and band alignment. The photophyscial properties of the intermediate products were characterized using steady-state absorption and photoluminescence (PL) spectroscopy. The results suggest that the core/multi-shell structure successfully confines an optically-generated hole in the QD core while allowing the electron to escape to the outer shell. This independent control over carrier transfer dynamics provides the tools necessary to implement efficient photon upconversion.