{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,1]],"date-time":"2026-09-01T16:14:55Z","timestamp":1788279295311,"version":"build-2803163510"},"reference-count":84,"publisher":"MDPI AG","issue":"17","license":[{"start":{"date-parts":[[2026,9,1]],"date-time":"2026-09-01T00:00:00Z","timestamp":1788220800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100015661","name":"Ioffe Institute","doi-asserted-by":"publisher","award":["FFUG-2024-0019"],"award-info":[{"award-number":["FFUG-2024-0019"]}],"id":[{"id":"10.13039\/501100015661","id-type":"DOI","asserted-by":"publisher"}]},{"award":["FFUG-2024-0019"],"award-info":[{"award-number":["FFUG-2024-0019"]}],"id":[{"id":"https:\/\/ror.org\/05dkdaa55","id-type":"ROR","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Nanomaterials"],"abstract":"<jats:p>We present the results of a study of europium-grafted detonation nanodiamond using X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), and photoluminescence techniques. The material was prepared by mixing an aqueous solution of europium(III) nitrate hexahydrate, Eu(NO3)3\u00b76H2O, with a nanodiamond suspension, resulting in ion exchange between Eu3+ ions and protons of surface carboxyl groups and direct grafting of the nanodiamond surface with Eu3+ ions. However, after two years of storage under ambient conditions, the compound exhibits the reduction of ~13% of Eu3+ ions to the paramagnetic Eu2+ state. This unusual finding is discussed in the context of our XPS, EPR, NMR, and photoluminescence data. We propose that this effect can be associated with surface defects and sp2-hybridized graphene-like fragments that act as electron donors to Eu3+ ions. The observed spontaneous partial reduction of Eu3+ to Eu2+ during long-term storage demonstrates that the oxidation state of surface-grafted europium is not completely stable under ambient conditions. This finding is important because even a partial change in the Eu valence may modify the optical and magnetic properties of Eu-grafted nanodiamonds intended for luminescent, sensing, and quantum applications.<\/jats:p>","DOI":"10.3390\/nano16171104","type":"journal-article","created":{"date-parts":[[2026,9,1]],"date-time":"2026-09-01T15:08:43Z","timestamp":1788275323000},"page":"1104","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Unexpected Reduction of Eu3+ Ions to Eu2+ on a Nanodiamond Surface: An XPS, NMR, EPR, and Photoluminescence Study"],"prefix":"10.3390","volume":"16","author":[{"given":"Natalya","family":"Froumin","sequence":"first","affiliation":[{"name":"Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Beer-Sheva 8410501, Israel"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0574-1911","authenticated-orcid":false,"given":"Alexander","family":"Shames","sequence":"additional","affiliation":[{"name":"Department of Physics, Ben-Gurion University of the Negev, Beer-Sheva 8410501, Israel"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0120-5847","authenticated-orcid":false,"given":"Anastasiya","family":"Chizhikova","sequence":"additional","affiliation":[{"name":"Ioffe Institute, St. Petersburg 194021, Russia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Maxim","family":"Uchaev","sequence":"additional","affiliation":[{"name":"Ioffe Institute, St. Petersburg 194021, Russia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0285-8495","authenticated-orcid":false,"given":"Alexander","family":"Panich","sequence":"additional","affiliation":[{"name":"Department of Physics, Ben-Gurion University of the Negev, Beer-Sheva 8410501, Israel"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,9,1]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"075101","DOI":"10.1088\/0954-3899\/41\/7\/075101","article-title":"Discovery of the 151Eu \u03b1 Decay","volume":"41","author":"Casali","year":"2014","journal-title":"J. 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