title: Characterizing Photon Reabsorption in Quantum Dot-Polymer Composites for Use as Displacement Sensors.
abstract: The reabsorption of photoluminescence within a medium, an effect known as the inner filter effect (IFE), has been well studied in solutions, but has garnered less attention in regards to solid-state nanocomposites. Photoluminescence from a quantum dot (QD) can selectively excite larger QDs around it resulting in a net red-shift in the reemitted photon. In CdSe/CdS core/shell QD-polymer nanocomposites, we observe a large spectral red-shift of over a third of the line width of the photoluminescence of the nanocomposites over a distance of 100 μm resulting from the IFE. Unlike fluorescent dyes, which do not show a large IFE red-shift, QDs have a component of inhomogeneous broadening that originates from their size distribution and quantum confinement. By controlling the photoluminescence broadening as well as the sample dispersion and concentration, we show that the magnitude of the IFE within the nanocomposite can be tuned. We further demonstrate that this shift can be exploited in order to spectroscopically monitor the vertical displacement of a nanocomposite in a fluorescence microscope. Large energetic shifts in the measured emission with displacement can be maximized, resulting in a displacement sensor with submicrometer resolution. We further show that the composite can be easily attached to biological samples and is able to measure deformations with high temporal and spatial precision.
authors.affiliation: Department of Chemistry, University of California , Berkeley, California 94720, United States.|Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Matthew A
authors.identifier: 0000-0003-1401-8415
authors.initials: MA
authors.lastname: Koc
authors.affiliation: Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.|Department of Materials Science and Engineering, University of California , Berkeley, California 94720, United States.
authors.forename: Shilpa N
authors.identifier: 0000-0001-5641-8930
authors.initials: SN
authors.lastname: Raja
authors.affiliation: Department of Chemistry, University of California , Berkeley, California 94720, United States.|Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Lindsey A
authors.initials: LA
authors.lastname: Hanson
authors.affiliation: Department of Chemistry, University of California , Berkeley, California 94720, United States.|The Hamburg Centre for Ultrafast Imaging, University of Hamburg , Luruper Chaussee 149, 22761 Hamburg, Germany.
authors.forename: Son C
authors.initials: SC
authors.lastname: Nguyen
authors.affiliation: Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.|Molecular Foundry, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Nicholas J
authors.identifier: 0000-0001-5434-1191
authors.initials: NJ
authors.lastname: Borys
authors.affiliation: Department of Chemistry, University of California , Berkeley, California 94720, United States.
authors.forename: Alexander S
authors.initials: AS
authors.lastname: Powers
authors.affiliation: Biological Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Siva
authors.initials: S
authors.lastname: Wu
authors.affiliation: Department of Chemistry, University of California , Berkeley, California 94720, United States.|Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.|JX Nippon Oil & Energy Corporation, 8 , Chidori-cho, Naka-ku, Yokohama-shi, Kanagawa 231-0815, Japan.
authors.forename: Kaori
authors.initials: K
authors.lastname: Takano
authors.affiliation: Department of Chemistry, University of California , Berkeley, California 94720, United States.|Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Joseph K
authors.initials: JK
authors.lastname: Swabeck
authors.affiliation: Department of Chemistry, University of California , Berkeley, California 94720, United States.|Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Jacob H
authors.identifier: 0000-0003-3658-1487
authors.initials: JH
authors.lastname: Olshansky
authors.affiliation: Department of Mechanical Engineering, University of California , Berkeley, California 94720, United States.
authors.forename: Liwei
authors.initials: L
authors.lastname: Lin
authors.affiliation: Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.|Department of Materials Science and Engineering, University of California , Berkeley, California 94720, United States.|Department of Mechanical Engineering, University of California , Berkeley, California 94720, United States.
authors.forename: Robert O
authors.identifier: 0000-0002-0501-6998
authors.initials: RO
authors.lastname: Ritchie
authors.affiliation: Department of Chemistry, University of California , Berkeley, California 94720, United States.|Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.|Department of Materials Science and Engineering, University of California , Berkeley, California 94720, United States.|Kavli Energy NanoScience Institute , Berkeley, California 94720, United States.
authors.forename: A Paul
authors.identifier: 0000-0001-6895-9048
authors.initials: AP
authors.lastname: Alivisatos
keywords: fluorescence; inner filter effect; nanocomposite; photoluminescence; photon recycling; quantum dots; sensor