Sensitization, energy transfer and infra-red emission decay modulation in Yb3+-doped NaYF4 nanoparticles with visible light through a perfluoroanthraquinone chromophore

Haizhou Lu,Ignacio Hernández,William P Gillin,Jianxu Hu,Peter B Wyatt,Mark A Green,Huanqing Ye,Xianjin Cui,Philip J Blower,Andrei N Khlobystov,Hang Gu,Yu Peng

doi:10.1038/s41598-017-05350-9

Abstract

Infra-red emission (980 nm) of sub 10 nm Yb3+-doped NaYF4 nanoparticles has been sensitized through the excitation of 2-hydroxyperfluoroanthraquinone chromophore (1,2,3,4,5,6,7-heptafluro-8-hydroxyanthracene-9,10-dione) functionalizing the nanoparticle surface. The sensitization is achieved with a broad range of visible light excitation (400–600 nm). The overall near infra-red (NIR) emission intensity of Yb3+ ions is increased by a factor 300 as a result of the broad and strong absorption of the chromophore compared with ytterbium’s intrinsic absorption. Besides the Yb3+ NIR emission, the hybrid composite shows organic chromophore-based visible emission in the orange-red region of the spectrum. We observe the energy migration process from the sensitized Yb3+ ions at the surface to those in the core of the particle using time-resolved optical spectroscopy. This highlights that the local environments for emitting Yb3+ ions at the surface and center of the nanoparticle are not identical, which causes important differences in the NIR emission dynamics. Based on the understanding of these processes, we suggest a simple strategy to control and modulate the decay time of the functionalized Yb3+-doped nanoparticles over a relatively large range by changing physical or chemical parameters in this model system.

Highlights

Trivalent lanthanide-doped luminescent nanoparticles have attracted considerable attention in the recent years due to their potential in optical and biological applications as a consequence of their small size and the characteristic lanthanide-based f-f transitions
The synthesis of Yb3+-doped NaYF4 nanoparticles and the functionalization of ligand capped Yb3+-doped NaYF4 are described in detail in the Methods section
Since we observe a minor increase of the PL upon direct excitation, but it is considerably smaller than upon excitation in the chromophore, we interpret this result as a significant increase in the sensitization efficiency

Summary

Introduction

Trivalent lanthanide-doped luminescent nanoparticles have attracted considerable attention in the recent years due to their potential in optical and biological applications as a consequence of their small size and the characteristic lanthanide-based f-f transitions These systems incorporate the lanthanide emissions’ high monochromaticity (their energy is relatively independent of the matrix), and potentially high efficiency and long lifetime together www.nature.com/scientificreports/. It has revealed efficient up-conversion (near infra-red to visible) suitable for biological and optical applications[1,2,3,4,5,6], the β structure showing the highest measured up-converting quantum efficiency[7] For both biological and other optical applications, such as lasers or telecommunications, the presence of lanthanides with NIR absorption and emission is appealing. A number of alternatives, including fluorination[21, 22] or chlorination[12] of the organic groups have been proposed, some of them resulting in considerable increases of the emission with relatively high emission efficiencies and correlated long lifetimes allowing, for instance, NIR to visible upconversion in organic environments[22]

Methods

Results

Conclusion