Quantification of the Activator and Sensitizer Ion Distributions in NaYF4:Yb3+, Er3+ Upconverting Nanoparticles Via Depth‐Profiling with Tender X‐Ray Photoemission. Issue 29 (22nd June 2022)

• Record Type: Journal Article
• Authors: Clark, Pip C. J.; Andresen, Elina; Sear, Michael J.; Favaro, Marco; Girardi, Leonardo; van de Krol, Roel; Resch‐Genger, Ute; Starr, David E.
• Is Part Of: Small. Volume 18:Issue 29(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-06-22
• Subjects: core@shell -- depth profile -- dopant distributions -- interfaces -- nanoparticles -- photoelectron spectroscopy -- upconversion; Nanotechnology -- Periodicals; Nanoparticles -- Periodicals; Microtechnology -- Periodicals; 620.5
• DOI: 10.1002/smll.202107976
• Languages: English
• ISSNs: 1613-6810

Abstract

Abstract: The spatial distribution and concentration of lanthanide activator and sensitizer dopant ions are of key importance for the luminescence color and efficiency of upconverting nanoparticles (UCNPs). Quantifying dopant ion distributions and intermixing, and correlating them with synthesis methods require suitable analytical techniques. Here, X‐ray photoelectron spectroscopy depth‐profiling with tender X‐rays (2000–6000 eV), providing probe depths ideally matched to UCNP sizes, is used to measure the depth‐dependent concentration ratios of Er 3+ to Yb 3+, [Er 3+ ]/[Yb 3+ ], in three types of UCNPs prepared using different reagents and synthesis methods. This is combined with data simulations and inductively coupled plasma‐optical emission spectroscopy (ICP‐OES) measurements of the lanthanide ion concentrations to construct models of the UCNPs' dopant ion distributions. The UCNP sizes and architectures are chosen to demonstrate the potential of this approach. Core‐only UCNPs synthesized with XCl3 ·6H2 O precursors (β‐phase) exhibit a homogeneous distribution of lanthanide ions, but a slightly surface‐enhanced [Er 3+ ]/[Yb 3+ ] is observed for UCNPs prepared with trifluroacetate precursors (α‐phase). Examination of Yb‐core@Er‐shell UCNPs reveals a co‐doped, intermixed region between the single‐doped core and shell. The impact of these different dopant ion distributions on the UCNP's optical properties is discussed to highlight their importance for UCNP functionality and the design of efficient UCNPs. Abstract : Hard X‐ray photoemission spectroscopy, HAXPES, depth‐profiling combined with data simulations reveals the dopant ion distributions in three types of upconverting nanoparticles, UCNPs. The range of UCNP sizes and architectures studied highlight this approach's ability to extract chemical speciation, dopant ion distributions, and dopant intermixing. Correlation with UCNP optical properties promises to guide strategies to increase UCNP brightness and tune their spectral properties.