Enhanced Upconversion and Photoconductive Nanocomposites of Lanthanide-Doped Nanoparticles Functionalized with Low-Vibrational-Energy Inorganic Ligands

01 November 2024, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Upconverting nanoparticles (UCNPs) convert near-infrared (IR) light into higher-energy visible light, allowing them to be used in applications such as biological imaging, nano-thermometry, and photodetection. It is well known that the upconversion luminescent efficiency of UCNPs can be enhanced by using a host material with low phonon energies, but the use of low-vibrational-energy inorganic ligands and non-epitaxial shells has been relatively underexplored. Here, we investigate the functionalization of lanthanide-doped NaYF4 UCNPs with low-vibrational-energy Sn2S64- ligands. Raman spectroscopy and elemental mapping are employed to confirm the binding of Sn2S64- ligands to UCNPs. This binding enhances upconversion efficiencies up to a factor of 16, consistent with an increase in the luminescent lifetimes of the lanthanide ions. Annealing Sn2S64--capped UCNPs results in the formation of a nanocomposite comprised of UCNPs embedded within an interconnected matrix of SnS2, enabling each UCNP to be electrically accessible through the semiconducting SnS2 matrix. This facilitates the integration of UCNPs into electronic devices, which we demonstrate through the fabrication of a UCNP-SnS2 photodetector that detects UV and near-IR light. Our findings show the promise of using low-phonon inorganic capping agents to enhance the properties of UCNPs while assisting their integration in optoelectronic devices.

Keywords

upconverting nanoparticles
upconversion
nanocomposite
colloidal nanocrystals
inorganic ligands
photodetector
ligand chemistry
lanthanide-doped
fluorescence

Supplementary materials

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Supplementary Information
Description
Chemicals used, synthesis of lanthanide-doped NaYF4 UCNPs core, UCNP shell growth procedure, characterization techniques, Raman DFT calculations, photoconductivity measurements, laser scanning microscopy setup, dynamic light scattering before and after Sn2S64- ligand exchange, nanoscale EDS spectrum, microscale EDS mapping and spectrum, kinetics of UCL enhancement, effect of Sn2S64- on avalanching UCNPs, TEM/STEM images of UCNPs.
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