Lanthanide-doped upconversion nanoparticles: synthesis and applications

Abstract

Lanthanide-ion-doped upconversion nanoparticles (UCNPs) have emerged as a new class of luminescent materials that offer excellent chemical stability, good biocompatibility, narrow bandwidth, long luminescence times, good resistance to photobleaching and photoblinking. ^1,2 Most importantly, UCNPs can up-convert two or more low energy photons into one high energy photon because of their intra-configurational 4f electron transitions. ^1,2 Therefore, UCNPs are of great interest in many fields including photocatalysis, biomedicine and sensing.³

In this project the main aim was to explore the UCNPs synthesis under different conditions and their functionalization with organic and inorganic materials. We observed that the synthesis played a critical role in determining the structure, phase, and upconversion (UC) luminescence of the resulting materials. Different parameters including the role of oleic acid (OA) and the effect of the host lattice and the fluoride source were studied. Furthermore, different coatings materials were formed around the surface of the core UCNPs and were fully characterized.

With a view of developing a universal protocol for the silanization of UCNPs, we investigated the silica coating around different sizes and morphologies of UCNPs. We created an approach based on a calibration curve. The employment of this approach proved to produce uniform and individual silica coating of the UCNPs, which were employed for further functionalization with oligonucleotides and gold.

The synthesis and the photocatalysis activity of the UCNPs coated by TiO₂ were studied. Results showed efficient photocatalytic activity under UV as well as IR irradiation, using redox dyes (DCPIP and Resazurin). Different effects on the photocatalytic activity such as annealing effect, loading effect, and recyclability were also studied.

Additionally, we functionalized the surface of the UCNPs with IR-806 dyes in order to enhance the UC luminescence properties and to provide new insights on the energy migration and surface effects of the UCNPs. Hence, the UC and downconversion (DC) luminescence properties were individually investigated in the dye-sensitized UCNPs in comparison to the non-sensitized UCNPs.

Encouraged by the principle of dye sensitizing in UCNPs, we additionally investigated whether new IR dyes could be used to cover different part of the IR spectrum. We proposed a new IR-dye molecule (IR-1076) in order to alleviate the well-known concentration quenching that exist in UCNPs. Although the work is still ongoing, we expect that the strategy could be used to produce UCNPs with higher dopant concentrations, hence enhancing the UC and DC luminescence properties.

More information

Identifiers

ORCID for Antonios Kanaras: orcid.org/0000-0002-9847-6706

Catalogue record

Export record