Article pubs.acs.org/JPCC
Plasmonic Fluorescence Enhancement of DBMBF2 Monomers and DBMBF2−Toluene Exciplexes using Al-Hole Arrays Thomas M. Schmidt,† Vladimir E. Bochenkov,†,‡ Juan Diego A. Espinoza,§ Edsger C. P. Smits,§ Aziz M. Muzafarov,∥ Yuriy N. Kononevich,∥ and Duncan S. Sutherland*,† †
Aarhus UniversityiNANO, Gustav Wieds Vej 14, 8000 Aarhus, Denmark Department of Chemistry, Lomonosov Moscow State University, 119991 Moscow, Russia § Holst Centre/TNO, High Tech Campus 31, 5656AE Eindhoven, The Netherlands ∥ N. S. Enikolopov Institute of Synthetic Polymer Materials of the Russian Academy of Sciences, 117393 Moscow, Russia ‡
ABSTRACT: The optical properties of aluminum hole arrays fabricated via colloidal lithography were investigated. By tuning the hole diameter and hole spacing independently, their influence on the Bloch wave−surface plasmon polariton (BWSPP) and localized surface plasmon resonances resonances (LSPR) could be identified. The aluminum hole arrays were used to enhance the fluorescence of a dibenzoylmethanatoboron difluoride (DBMBF2) dye. The dye exhibits the advantageous property of forming an exciplex with aromatic compounds. The interaction of DBMBF2 monomer fluorescence and DBMBF2−toluene exciplexes with Al hole arrays is studied. Furthermore, the respective roles of the BW-SPPs and LSPRs were studied through tuning of the plasmon resonances from the UV excitation wavelength (λext = 385 nm) through the visible emission range (400−550 nm). Monomer emission was predominately enhanced by BW-SPPs while exciplex emission showed a contribution from both BW-SPPs and LSPRs. Fluorescence enhancement of 3.8 was observed for DBMBF2−toluene exciplex emission from 26 nm thick polymer films. Aluminum hole arrays are shown to be attractive structures for fluorescence enhancing applications with excitation in the UV and stable oxide coatings.
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nm.9 Despite higher optical losses, aluminum is preferred over silver for applications in spectral regions below 380 nm and where oxygen is present in the environment. The oxide formed on Al is, in contrast to Ag, self-limiting giving a stable and reproducible oxide thickness (∼3−4 nm)12 with robust plasmonic properties. In addition, Al presents resonances in the near UV, making it an interesting material for fluorescence enhancement of biological molecules that have optical absorptions and/or emission in the UV region.9,13,14 A key phenomenon observed for metal enhanced fluorescence is the competition between the metal quenching mechanism (seen at
