Off-resonance surface plasmon enhanced spontaneous emission from CdTe quantum dots

Abstract

Surface plasmon ͑SP͒ enhanced photoluminescence ͑PL͒ from CdTe quantum dots ͑QDs͒ on monolayers of Au nanoparticles is investigated under both resonant and nonresonant conditions. Enhancement of the QD PL intensity is observed when the emission spectrum is redshifted with respect to the SP absorption resonance. Coupling to the SPs results in a redshift and broadening of the PL spectrum, and an increase in the PL decay rate. The largest coupling is observed for QD monolayers with peak emission at 667 nm, producing a ten fold increase in PL intensity. No change in PL intensity and decay rate is observed at the SP resonance. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2422906͔ Surface plasmons ͑SPs͒ excited on thin metallic structures/nanoparticles play a major role in photoluminescence ͑PL͒ enhancement 1-4 and PL quenching. 5,6 These effects have been attributed to enhanced excitation field, 2-5 modified radiative and nonradiative decay rates, 7-9 and coupling to SPs. 3,4,7,8 In a metal-emitter system, the exact conditions under which enhancement or quenching of the PL will occur are still under debate. We report on the offresonance enhancement of the quantum dot ͑QD͒ emission and the importance of SP scattering.The structures, grown using a layer-by-layer technique, 10,11 are comprised of 3 monolayers ͑ML͒ of Au NPs ͑diameter ϳ7 nm͒ on a quartz substrate, followed by a polyelectrolyte ͑PE͒ spacer layer and capped by 2 ML of CdTe thioglycolic acid stabilized QDs.12-14 The 3 ML of Au NPs and 2 ML of QDs on quartz substrates are deposited using positively charged polyethyleneimine as the counterpart. The spacer is comprised of bilayers of positively charged poly͑diallyldimethylammonium chloride͒ and negatively charged poly͑sodium 4-styrene sulfonate͒, with thicknesses of approximately 1.4 and 11.7 nm for one and nine PE bilayers, respectively.15 Room temperature PL spectra are recorded with the excitation wavelength of 400 nm using a Perkin-Elmer fluorescence spectrometer. The time-resolved PL decays were measured using a PicoQuant Microtime200 time-resolved confocal microscope system with 150 ps resolution. Excitation is provided by 480 nm picosecond pulses at a 10 MHz repetition rate from an LDH-480 laser head controlled by a PDL-800B driver ͑PicoQuant͒.The PL spectra for CdTe QD monolayers, with peak emissions at 556, 612, 667, and 757 nm, were recorded as a function of QD-metal separation. The PL intensity enhancement factor is determined by a comparison with the PL peak intensity in the absence of the Au NP layer. A tenfold PL peak intensity enhancement was observed for QDs emitting at 667 nm, whereas a fourfold increase was noted for those emitting at 612 and 757 nm and essentially no discernible change was observed for the 556 nm QDs, as shown in Fig. 1. The PL peak wavelength and the full width at half maximum ͑FWHM͒ as a function of the number of PE bilayers, for the 667 and 556 nm QDs, are shown in Fig. 2 ͑the data for the 612 and 757 nm QDs, are not shown for clarity but are discussed below͒. R...

Experimental and Theoretical Investigation of the Distance Dependence of Localized Surface Plasmon Coupled Förster Resonance Energy Transfer

“…5,6 The near-field of the plasmonic structure can modify the emission of a fluorophore. [7][8][9][10][11][12] Depending on the plasmonic properties of the metallic nanoparticle (MNP) it can lead to quenching or enhancement of the fluorophore emission. The modified emission can be a consequence of many processes such as NRET to the MNP, scattering and absorption by the MNP, and changes in the emitter's radiative and nonradiative decay rates.…”

Surface plasmon enhanced Förster resonance energy transfer between the CdTe quantum dots

“…The distance dependent acceptor QDs' PL lifetime intensities are also shown in the figure as an inset. The dotted line is a reference one, which is the acceptor QDs' intensity from the mixed dots, when they are on the 6 When the layer of mixed QDs is in very close to the Au NPs, i.e., up to eight PE bilayers, the acceptor QDs' intensities are quenched due to the nonradiative energy transfer from the QDs to the Au NPs. Here, we note that the pure monolayer of acceptor QDs' PL lifetime intensities with the Au NPs is not shown the distance dependence.…”

“…3 Efforts to improve the FRET process have been focused on structures with reduced donor-acceptor QDs' separation, improved spectral overlap of the donor emission and acceptor absorption spectra, and increased packing density of the layers. 4 Metal nanoparticles ͑NPs͒ have been used to modify some of the fundamental optical processes such as Raman scattering 5 and radiative processes 6 in chemical species in a characteristic way. In this letter, we present the experimental evidence for the enhanced FRET between the CdTe QDs at nanoscale proximity to Au NPs, motivated by the previous theoretical studies, which indicated the potential to accelerate the FRET process between the donor and acceptor molecules 7 and QDs ͑Ref.…”

“…11 3 monolayers of Au NPs are deposited on a quartz substrate using polyethyleneimine as a counterpart. As a second step, polyelectrolyte ͑PE͒ bilayers comprised of 4,6,8,10,12,14, and 16 spacer layers are selfassembled on top of the Au NP layers for studying the distance dependence of the FRET process. Each bilayer thickness is approximately 1.4 nm.…”

Strain-driven alignment of In nanocrystals on InGaAs quantum dot arrays and coupled plasmon-quantum dot emission

“…1-3 More recently, the coupling of a QD to the plasmon resonance of a metal nanoparticle or nanoparticle array has attracted much attention, representing the ultimate electromagnetic resonator with subwavelength size. Such hybrid QD-metal nanoparticle structures enable the enhancement of the QD emission, [4][5][6][7] control of the polarization of emitted light, 8 modification of the far field radiation pattern, 9 and other interesting collective optical phenomena. 10,11 So far, fabricating those structures relied on chemical self-assembly 12 or top-down processing, 8 the latter being without control of the position of the QDs with respect to the metal nanostructures which is required to fully exploit their unique properties.…”