Tuning Lanthanide Luminescence in Nanostructured Host Materials

鑭系摻雜納米結構的發光調控

Student thesis: Doctoral Thesis

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Award date4 Jul 2022

Abstract

As a special class of luminescent materials, lanthanide-doped nanocrystals (NCs) demonstrate unique optical properties stemming from localized electronic transitions within the 4f orbitals of lanthanide dopant ions. By selectively incorporating multiple lanthanide ions into different regions of a host crystal at well-defined concentrations, lanthanide-doped NCs can produce tunable emissions spanning ultraviolet (UV) and near-infrared (NIR). In addition, the parity-forbidden nature of 4f transitions in lanthanide ions renders ultralong excited-state lifetimes of up to several milliseconds, which permits convenient optical modulation in the time domain. Despite the excellent optical performance of lanthanide ions, the emission modulations in different host materials and the promising applications need to be explored.

This thesis begins with a literature review of strategies for tuning lanthanide luminescence in nanostructured materials for various applications. By incorporating otherwise incompatible lanthanide ions into separate layers of a core–shell nanostructure, the interactions of dopant ions can be precisely controlled for realizing unprecedented luminescence processes. Nanostructural engineering also allows integration and coupling with QDs/dye molecules and plasmon structures for synergistic optical modulation. Besides, luminescence nanothermometry, bioimaging and therapy, information storage and encryption, and bio-applications enabled by these advanced nanomaterials will also be discussed.

In chapter 4, we report a wet-chemistry synthesis and characterization of CaS NCs doped with various amounts of Ce3+ ions. We discover a doping-induced evolution of NC size (39 to 14 nm) and emission color (green to yellow). Our mechanistic investigations, corroborated by theoretical calculations, reveal that the changes in NC properties are correlated with the modifications of charge density and local structure at the nanocrystal surface. Owing to the altered surface structure, we identify a dark Ce state that selectively extinct light emission of the CaS:Ce NCs. We demonstrate that the doping-induced surface effects can be offset by coating the CaS:Ce NCs with an undoped CaS shell, giving rise to a shell-thickness-dependent emission. Our findings suggest an effective strategy for extended control over NC size and light emission via aliovalent doping.

In chapter 5, a core–shell–shell nanostructure composed of NaGdF4:Yb/Tm@NaGdF4:Nd@NaYF4 is developed to realize Yb3+-sensitized upconversion and downshifting luminescence in Nd3+ ions. The unusual photon conversion property stems from a gadolinium sublattice mediated Yb3+ → Tm3+ → Gd3+ → Nd3+ energy transfer pathway. The energy transfer processes are investigated by varying the dopant concentration and distribution, in conjunction with time decay measurements.

In chapter 6, we present an erythrocyte-delivered and NIR photoactivatable PtIV nanoprodrug for advanced cancer treatment, based on the use of an Nd3+-sensitized core–shell–shell upconversion nanoplatform. Compared with small molecule PtIV prodrugs, this nanoprodrug exhibits significantly enhanced stability, prolonged circulation in the blood, and minimized side effects. The hitchhiking of the nanoprodrug on erythrocytes dramatically increases Pt accumulation in the tumor. Upon irradiation, the nanoprodrug releases oxaliplatin in a controllable manner, resulting in significant antitumor activity against breast tumors in vivo, as evidenced by the complete elimination of tumors from a single-dose injection. Additionally, this nanoprodrug is associated with remarkably enhanced immunopotentiation. Our study highlights an efficient strategy to overcome the shortcomings of traditional Pt-based chemotherapy via the erythrocyte-mediated delivery of an NIR-activatable nanoprodrug of oxaliplatin, a clinically used anticancer drug.

    Research areas

  • Lanthanide doping, Emission tuning, Alkaline-earth NCs, Core–shell, Upconversion, Photodynamic therapy