title: Novel and easy access to highly luminescent Eu and Tb doped ultra-small CaF2, SrF2and BaF2nanoparticles - structure and luminescence.
abstract: A universal fast and easy access at room temperature to transparent sols of nanoscopic Eu3+and Tb3+doped CaF2, SrF2and BaF2particles via the fluorolytic sol-gel synthesis route is presented. Monodisperse quasi-spherical nanoparticles with sizes of 3-20 nm are obtained with up to 40% rare earth doping showing red or green luminescence. In the beginning luminescence quenching effects are only observed for the highest content, which demonstrates the unique and outstanding properties of these materials. From CaF2:Eu10 via SrF2:Eu10 to BaF2:Eu10 a steady increase of the luminescence intensity and lifetime occurs by a factor of ≈2; the photoluminescence quantum yield increases by 29 to 35% due to the lower phonon energy of the matrix. The fast formation process of the particles within fractions of seconds is clearly visualized by exploiting appropriate luminescence processes during the synthesis. Multiply doped particles are also available by this method. Fine tuning of the luminescence properties is achieved by variation of the Ca-to-Sr ratio. Co-doping with Ce3+and Tb3+results in a huge increase (>50 times) of the green luminescence intensity due to energy transfer Ce3+→ Tb3+. In this case, the luminescence intensity is higher for CaF2than for SrF2, due to a lower spatial distance of the rare earth ions.
authors.affiliation: Humboldt-Universität zu Berlin, Institut für Chemie, Brook-Taylor-Str. 2, D-12489 Berlin, Germany. erhard.kemnitz@chemie.hu-berlin.de.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Ritter
authors.affiliation: Humboldt-Universität zu Berlin, Institut für Chemie, Brook-Taylor-Str. 2, D-12489 Berlin, Germany. erhard.kemnitz@chemie.hu-berlin.de.
authors.forename: Philipp
authors.initials: P
authors.lastname: Haida
authors.affiliation: Humboldt-Universität zu Berlin, Institut für Chemie, Brook-Taylor-Str. 2, D-12489 Berlin, Germany. erhard.kemnitz@chemie.hu-berlin.de.
authors.forename: Friedrich
authors.initials: F
authors.lastname: Fink
authors.affiliation: Humboldt-Universität zu Berlin, Institut für Chemie, Brook-Taylor-Str. 2, D-12489 Berlin, Germany. erhard.kemnitz@chemie.hu-berlin.de and Nanofluor GmbH, Rudower Chaussee 29, D-12489 Berlin, Germany.
authors.forename: Thoralf
authors.initials: T
authors.lastname: Krahl
authors.affiliation: Bundesanstalt für Materialforschung und -prüfung (BAM), Fachbereich Chemische und optische Sensorik, Richard-Willstätter-Str. 11, D-12489 Berlin, Germany.
authors.forename: Kornelia
authors.initials: K
authors.lastname: Gawlitza
authors.affiliation: Bundesanstalt für Materialforschung und -prüfung (BAM), Fachbereich Chemische und optische Sensorik, Richard-Willstätter-Str. 11, D-12489 Berlin, Germany.
authors.forename: Knut
authors.initials: K
authors.lastname: Rurack
authors.affiliation: Humboldt-Universität zu Berlin, Institut für Chemie, Brook-Taylor-Str. 2, D-12489 Berlin, Germany. erhard.kemnitz@chemie.hu-berlin.de.
authors.forename: Gudrun
authors.initials: G
authors.lastname: Scholz
authors.affiliation: Humboldt-Universität zu Berlin, Institut für Chemie, Brook-Taylor-Str. 2, D-12489 Berlin, Germany. erhard.kemnitz@chemie.hu-berlin.de and Nanofluor GmbH, Rudower Chaussee 29, D-12489 Berlin, Germany.
authors.forename: Erhard
authors.identifier: http://orcid.org/0000-0002-5300-3905
authors.initials: E
authors.lastname: Kemnitz