AUTHOR=Agbo Peter , Kanady Jacob S. , Abergel Rebecca J. 

TITLE=Infrared Photon Pair-Production in Ligand-Sensitized Lanthanide Nanocrystals

JOURNAL=Frontiers in Chemistry

VOLUME=8

YEAR=2020

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2020.579942

DOI=10.3389/fchem.2020.579942

ISSN=2296-2646

ABSTRACT=<p>This report details spectroscopic characterizations of rare-earth, core-shell nanoparticles decorated with the <italic>f</italic>-element chelator 3,4,3-LI(1,2-HOPO). Evidence of photon downconversion is corroborated through detailed power dependence measurements, which suggest two-photon decay paths are active in these materials, albeit only representing a minority contribution of the sum luminescence, with emission being dominated by normal, Stokes' shifted fluorescence. Specifically, ultraviolet ligand photosensitization of Nd<sup>3+</sup> ions in a NaGdF<sub>4</sub> host shell results in energy transfer to a Nd<sup>3+</sup>/Yb<sup>3+</sup>-doped NaGdF<sub>4</sub> nanoparticle core. The population and subsequent decay of core, Yb<sup>3+</sup><sup>2</sup><italic>F</italic><sub>5/2</sub> states result in a spectral shift of 620 nm, manifested in a NIR emission displaying luminescence profiles diagnostic of Yb<sup>3+</sup> and Nd<sup>3+</sup> excited state decays. Emphasis is placed on the generality of this material architecture for realizing ligand-pumped, multi-photon downconversion, with the Nd<sup>3+</sup>/Yb<sup>3+</sup> system presented here functioning as a working prototype for a design principle that may be readily extended to other lanthanide pairs.</p>