Author: Guo, Shuai
Title: Nd³⁺-sensitized UCNPs with superior luminescent properties, anisotropic growth and luminescent janus system
Degree: Ph.D.
Year: 2017
Subject: Hong Kong Polytechnic University -- Dissertations
Nanoparticles
Pages: 267 pages : color illustrations
Language: English
Abstract: In this thesis, we have generalized the research work that focus on construction, synthesis and characterization, luminescent properties study of Nd³⁺-sensitized upconversion nanoparticles: Firstly, we have developed the Nd³⁺-harvest-transfer-sensitization trinity system (Nd³⁺­Trinity system), which is used to coating on the NaGdF₄:Yb, X(Er/Tm/Ho) or the EMU [NaGdF₄:Yb,Tm@NaGdF₄:Yb,X(Eu/Tb) or NaGdF₄:Yb,X(Eu/Tb)@NaGdF₄:Yb,Tm] cores, to develop the Nd³⁺-sensitized UCNPs with excitation of 808 nm laser to avoid the over-heating effect caused by the traditionally used 980 nm laser as well as shielding all the quenching factors in the Nd³⁺-sensitized UCNPs with well design of the Nd³⁺-Trinity system. And the UCNPs with Nd³⁺-Trinity system coating have shown superior luminescent properties, including the enhanced luminescence intensity, prolonged lifetime, deeper luminescence penetration, larger partition of red emission. Furthermore, we have generalized that the enhanced luminescence intensity comes from the higher absorption of Nd³⁺ ions to 808 nm laser; the prolonged lifetime is proposed to be result in the 1056 nm photon selectively participation in the ETU process; deeper luminescence penetration is in consequence of the avoidance of the over-heating effect by the utilization of the 808 nm laser as the photo-luminescence source, larger partition of red emission is proposed to be influenced by the cross-relaxation of the Nd³⁺-X(Er/Tm/Ho)³⁺. Secondly, when Nd³⁺-harvest-transfer-sensitization trinity system is coated on the NaYF₄:Yb, X(Er/Tm/Ho), the phenomenon of the anisotropic growth is observed, which could be generalized as a longitudianl growth of the NaYF₄:Yb, X(Er/Tm/Ho) by the preference of the oleate binding to the (001) facets, as well as the etching of the NaYF₄ cores which result in the NaYF₄ cores dissolving. Furthermore, the layer-by-layer coating of the multiple shells of the Nd³⁺-Trinity system, intensifies the anisotropic growth, which has influence on the luminescent properties. Lastly, we have put forward the concept of the "Luminescent Janus" nanoparticles, which could be illustrated as the same UCNPs, that displays various luminescent properties, which is mainly the emission band, by the particular excitation source (808 nm c.w. or pulsed laser, 980 nm c.w. or pulsed laser). Also, we have developed three types of "Luminescent Janus" nanoparticles, which are driven by the energy migration upconversion (EMU) system with excitation of 808 nm/980 nm pulsed laser, to realize the RGB (red-green-blue)/full-color tenability.
Access: open access

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