Spectrally Resolved Dynamics of Synthesized CdSe/ZnS Quantum Dot/Silica Nanocrystals for Photonic Down-Shifting Applications

Photonic structures capable of luminescence down-shifting (LDS) have strong application potential in several areas of optoelectronics. Such structures can be formed by overcoating quantum dots (QDs) with integrable, transparent layers. In this paper, silica was grown on CdSe/ZnS QDs to form QD/silica nanocrystals (NCs) in a microemulsion synthesis process. The synthesized structures were structurally and optically characterized to understand the growth mechanism, luminescence properties, and the influence of process parameters on excitonic decay and lifetime. Process conditions were established to have single QDs at the centers of the silica particles. The effects of temperature, excitation duration, size of QDs, and type of ligands on decay dynamics were established. Temperature- and time-resolved excitonic decay study of QD/silica NCs suggested carrier-trapping at the QD/silica interface and the exciton-phonon coupling to be the two main nonradiative processes limiting the luminescence efficiency. The synthesized NCs displayed intense photoluminescence (PL) with slight decrease in lifetime. The PL efficiency of the NCs improved for longer illumination. The NC structures that safely embed QDs in transparent medium are good candidates for LDS applications in photovoltaic, imaging, and detection devices.