title: Tip enhancement of upconversion photoluminescence from rare earth ion doped nanocrystals.
abstract: We present tip-enhanced upconversion photoluminescence (PL) images of Er(3+)- and Yb(3+)-doped NaYF4 nanocrystals on glass substrates with subdiffraction spatial resolution. Tip-sample distance dependent measurements clearly demonstrate the near-field origin of the image contrast. Time-resolved PL measurements show that the tip increases the spontaneous emission rate of the two emission channels of Er(3+) in the visible region. Very efficient enhancement of upconversion PL is discussed in the context of the two-photon nature of the excitation process and homoenergy transfer between the ions within the nanocrystals. Comparison between different nanocrystals and tips shows a strong influence of the tip shape on the image contrast that becomes particularly relevant for the larger dimensions of the investigated nanocrystals.
authors.affiliation: †Department Chemie and CeNS, Ludwig-Maximilians-Universität München, 81377 München, Germany.
authors.forename: Nina
authors.initials: N
authors.lastname: Mauser
authors.affiliation: ‡Institute of Physics, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka 5, 87-100 Torun, Poland.
authors.forename: Dawid
authors.initials: D
authors.lastname: Piatkowski
authors.affiliation: †Department Chemie and CeNS, Ludwig-Maximilians-Universität München, 81377 München, Germany.
authors.forename: Tobia
authors.initials: T
authors.lastname: Mancabelli
authors.affiliation: §Institute of Physical and Theoretical Chemistry, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland.
authors.forename: Marcin
authors.initials: M
authors.lastname: Nyk
authors.affiliation: ‡Institute of Physics, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka 5, 87-100 Torun, Poland.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Mackowski
authors.affiliation: †Department Chemie and CeNS, Ludwig-Maximilians-Universität München, 81377 München, Germany.
authors.forename: Achim
authors.initials: A
authors.lastname: Hartschuh
keywords: optical antenna; rare earth ion doped crystals; tip-enhanced near-field optical microscopy; upconverted luminescence