Morphology and dopant-dependent optical characteristics of novel composite 1D and 3D-based heterostructures of CdSe nanocrystals and LaPO4:Re (Re = Eu, Ce, Tb) metal phosphate nanowires

作者：Han Jinkyu; Wang Lei; Wong Stanislaus S^*

来源：RSC Advances, 2014, 4(66): 34963-34980.

DOI：10.1039/c4ra05933f

In this report, we synthesize and structurally characterize novel semiconducting nanoscale composite heterostructures composed of zero-dimensional (0D) CdSe nanocrystals coupled with both one-and three-dimensional (1D and 3D) rare earth metal-doped LaPO4 metal phosphate materials. Subsequent optical characterization has demonstrated a clear dependence of the intrinsic charge and energy transfer processes in these systems on both (i) morphology and (ii) the presence of dopants. Specifically, similar to 4.5 nm CdSe quantum dots (QDs) have been successfully anchored onto (a) high-aspect ratio rare-earth activated LaPO4 nanowires, measuring similar to 7 nm in diameter and similar to 1.3 mu m in length, prepared by a modified hydrothermal protocol, and (b) well-dispersed urchin-like 3D architectures of LaPO4:Re (Re = Ce, Tb, Eu) (diameter similar to 500 nm), fabricated using a large-scale, solution-precipitation approach in the presence of 6-mercaptohexanoic acid, used as a self-assembly facilitating agent. We have proposed a growth mechanism of our 3D sub-micron LaPO4-based architectures, based on a detailed time-dependent scanning electron microscopy visualization study. In terms of properties, our results show that our 1D and 3D heterostructures evince both PL quenching and a shorter average lifetime of CdSe QDs as compared with unbound CdSe QDs. We suggest that a photo-induced charge transfer process occurs from CdSe QDs to LaPO4: Eu through the mediation of water molecules in the intrinsic LaPO4 structure. Conversely, analogous CdSe QD-3D LaPO4: Eu heterostructures exhibit noticeably less PL quenching and longer lifetimes as compared with 1D composites since it appears that not only charge transfer from CdSe QDs to LaPO4:Eu but also energy transfer from LaPO4:Eu to CdSe QDs are substantially more efficient processes with 3D as compared with 1D heterostructures, possibly due to the nearly 3 times higher coverage density of QDs on the surfaces of the underlying 3D LaPO4 motif, thereby contributing to its more effective absorption capability of LaPO4: Eu emission. Moreover, the magnitude of the PL signal and the corresponding lifetimes in the CdSe QD (0D)-LaPO4 (3D) heterostructures are dependent upon the rare-earth dopant tested itself. Data are additionally explained in the context of the inherent energy level alignments of both CdSe QDs and LaPO4:Re (Re Ce, Tb, and Eu) systems.

• 出版日期2014