{
  "abstract": "Upconversion nanoparticles (UCNPs) are optically active materials with near-infrared excitation and tuneable anti-Stokes emission, typically resulting in visible emission. A route to routine and reliable synthesis of water-dispersible UCNPs for biomedical imaging applications is the polyethyleneimine (PEI)- assisted solvothermal autoclave synthesis; however, the properties of the resulting UCNPs remain understudied. Herein, we report how PEI molecular weight alters properties of core-only, red-emitting, water-dispersible PEI-UCNPs. In terms of brightness, 1.2 kDa PEI-UCNPs exhibited 5 times more intense upconversion luminescence (UCL) than 25 kDa PEI-UCNPs and a 29% longer UCL lifetime (LT) for the red emission band (~640-690 nm, 4 F 9/2 → 4 I 15/2 Er 3+ transition) in DI H 2 O. Dispersal in D 2 O increased emission across wavebands, with green emission ( 2 H 11/2 , 4 S 3/2 → 4 I 15/2 Er 3+ transition) increasing by 248 - 365% whereas red emission only increased between 38-64%. From our results, we infer that PEI may quench the UCL via high-energy NH vibrations. We also examined Förster Resonance Energy Transfer (FRET) between PEI-UCNPs and an electrostatically adsorbed fluorescent model dye, AlexaFluor647® (AF647). 25 kDa PEI-UCNPs achieved highest LT-estimated FRET efficiencies of ~11% in H 2 O and 16% in D 2 O, respectively. These findings highlight that polymer MW should be considered when optimising UCNP synthesis.",
  "abstract_shown": true,
  "affiliations": [
    "Department of Pure and Applied Chemistry, Technology and Innovation Centre, 99 George Street, Glasgow, UK, G1 1RD",
    "Department of Analytical Chemistry (Dpt.1, Federal Institute for Materials Research and Testing (BAM, Richard-Willstätter-Straße 11, Berlin, Germany, 12489",
    "Pure and Applied Chemistry",
    "University of Strathclyde",
    "Academic Centre for Materials and Nanotechnology, AGH University of Krakow, Mickiewicza 30, Krakow, Poland, 30-059",
    "Department of Engineering Physics",
    "McMaster University",
    "Chemistry, Durham University, South Road, Durham, United Kingdom, DH1 3LE"
  ],
  "article_type": null,
  "arxiv": null,
  "author_total": 9,
  "authors": [
    {
      "affs": [
        0
      ],
      "name": "Rebecca McGonigle",
      "orcid": "0009-0000-2964-2232"
    },
    {
      "affs": [
        1
      ],
      "name": "Christian Homann"
    },
    {
      "affs": [
        2,
        3
      ],
      "name": "Ciera Connelly"
    },
    {
      "affs": [
        4
      ],
      "name": "Marta Gajewska"
    },
    {
      "affs": [
        5,
        6
      ],
      "name": "Niko Hildebrandt"
    },
    {
      "affs": [
        7
      ],
      "name": "Robert Pal"
    },
    {
      "affs": [
        2,
        3
      ],
      "name": "Shiao Chow"
    },
    {
      "affs": [
        1
      ],
      "name": "Ute Resch-Genger"
    },
    {
      "affs": [
        0
      ],
      "name": "Lewis E. MacKenzie"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/09fjv4vddzbz0.bib",
  "cited_by": 0,
  "doi": "10.26434/chemrxiv.15004510/v2",
  "fulltext_url": null,
  "id": "09fjv4vddzbz0",
  "issns": [],
  "landing_url": "https://chemrxiv.org/doi/full/10.26434/chemrxiv.15004510/v2",
  "language": null,
  "licence": "CC-BY",
  "licence_label": "CC BY",
  "licence_source": "journal",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "openalex",
      "2505|Luminescence Properties of Advanced Materials"
    ]
  ],
  "openalex": "W7216395826",
  "pdf_url": "https://chemrxiv.org/doi/pdf/10.26434/chemrxiv.15004510/v2",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-02",
  "publisher": "American Chemical Society (ACS)",
  "ris": "https://research.draconitic.com/paper/09fjv4vddzbz0.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:17:22Z",
      "native_id": "10.26434/chemrxiv.15004510",
      "source": "chemrxiv",
      "url": "https://chemrxiv.org/doi/full/10.26434/chemrxiv.15004510/v2"
    }
  ],
  "subjects": [
    {
      "field": "chemistry",
      "origin": "openalex:2505|Luminescence Properties of Advanced Materials",
      "subfield": "materials-polymers"
    }
  ],
  "title": "Polyethyleneimine (PEI) molecular weight alters the photophysical and FRET properties of water dispersible NaYF4:Yb,Er upconversion nanoparticles",
  "title_text": "Polyethyleneimine (PEI) molecular weight alters the photophysical and FRET properties of water dispersible NaYF4:Yb,Er upconversion nanoparticles",
  "type": "preprint",
  "updated_at": "2026-10-30T12:17:22Z",
  "url": "https://research.draconitic.com/paper/09fjv4vddzbz0",
  "venue": "ChemRxiv",
  "versions": []
}