Limits...
Ultrafast spontaneous emission source using plasmonic nanoantennas.

Hoang TB, Akselrod GM, Argyropoulos C, Huang J, Smith DR, Mikkelsen MH - Nat Commun (2015)

Bottom Line: The antennas consist of silver nanocubes coupled to a gold film separated by a thin polymer spacer layer and colloidal core-shell quantum dots, a stable and technologically relevant emitter.We show an increase in the spontaneous emission rate of a factor of 880 and simultaneously a 2,300-fold enhancement in the total fluorescence intensity, which indicates a high radiative quantum efficiency of ∼50%.The nanopatch antenna geometry can be tuned from the visible to the near infrared, providing a promising approach for nanophotonics based on ultrafast spontaneous emission.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Physics, Duke University, Durham, North Carolina 27708, USA. [2] Center for Metamaterials and Integrated Plasmonics, Duke University, Durham, North Carolina 27708, USA.

ABSTRACT
Typical emitters such as molecules, quantum dots and semiconductor quantum wells have slow spontaneous emission with lifetimes of 1-10 ns, creating a mismatch with high-speed nanoscale optoelectronic devices such as light-emitting diodes, single-photon sources and lasers. Here we experimentally demonstrate an ultrafast (<11 ps) yet efficient source of spontaneous emission, corresponding to an emission rate exceeding 90 GHz, using a hybrid structure of single plasmonic nanopatch antennas coupled to colloidal quantum dots. The antennas consist of silver nanocubes coupled to a gold film separated by a thin polymer spacer layer and colloidal core-shell quantum dots, a stable and technologically relevant emitter. We show an increase in the spontaneous emission rate of a factor of 880 and simultaneously a 2,300-fold enhancement in the total fluorescence intensity, which indicates a high radiative quantum efficiency of ∼50%. The nanopatch antenna geometry can be tuned from the visible to the near infrared, providing a promising approach for nanophotonics based on ultrafast spontaneous emission.

No MeSH data available.


Related in: MedlinePlus

Fluorescence enhancement of QDs coupled to NPAs.(a) QD fluorescence intensity as a function of average incident laser power in three cases—on a glass slide, on a Au film and coupled to individual NPAs (NPAs 1–3). The solid lines are fits to a power law, with the power exponent, p, showing a nearly linear scaling. The vertical dashed line indicates the power at which subsequent measurements in this paper are performed under pulsed excitation. (b) Histogram showing the distribution of the fluorescence enhancement factors of the 11 measured NPAs.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4525280&req=5

f3: Fluorescence enhancement of QDs coupled to NPAs.(a) QD fluorescence intensity as a function of average incident laser power in three cases—on a glass slide, on a Au film and coupled to individual NPAs (NPAs 1–3). The solid lines are fits to a power law, with the power exponent, p, showing a nearly linear scaling. The vertical dashed line indicates the power at which subsequent measurements in this paper are performed under pulsed excitation. (b) Histogram showing the distribution of the fluorescence enhancement factors of the 11 measured NPAs.

Mentions: To quantitatively estimate the enhancement in the fluorescence intensity of the QDs coupled to a single plasmonic NPA, we conducted a series of experiments on three different samples: (i) a sample containing QDs coupled to NPAs as described above; (ii) a sample of QDs adhered on top of a PAH layer on a Au film but without any nanocubes; and (iii) a sample with QDs adhered to a PAH layer on a glass slide. To ensure the same surface density of QDs, all samples are prepared with the same concentration of QDs in solution and had the same surface chemistry (PAH) before spin coating the QDs. For excitation, a 535-nm Ti:sapphire laser is used with a pulse length of ∼150 fs, which is passed through a pulse picker to reduce the repetition rate from 80 to 40 MHz. The excitation laser is focused to a diffraction-limited spot, ∼300 nm in diameter and the QD fluorescence is collected in an epifluorescence configuration and measured by an avalanche photodiode (see Methods). Figure 3a shows the dependence of the QD fluorescence intensity on the laser excitation power for the three samples described above. The fluorescence intensity from the QDs coupled to a single NPA is substantially higher than from the QDs on a PAH layer on a glass slide or on a Au film. For QDs on a PAH layer on a Au film without any nanocubes, we find that the fluorescence is quenched by ∼70% compared with QDs on glass. This quenching is attributed to short-range non-radiative energy transfer between the QDs and the Au film4041. The emission intensity from QDs coupled to a single NPA shows linear scaling with excitation power density in the range of 0.01–10 kW cm−2. At higher excitation power densities, permanent photobleaching of the QDs occurs before saturation of the excited state population can be reached. All subsequent measurements in this paper are conducted at an excitation power density of Iex,0=1 kW cm−2. For structures with a polymer gap layer and no QDs, we found that the NPA scattering resonance was unmodified and stable for average excitation power densities with the femtosecond laser of up to 10 MW cm−2.


Ultrafast spontaneous emission source using plasmonic nanoantennas.

Hoang TB, Akselrod GM, Argyropoulos C, Huang J, Smith DR, Mikkelsen MH - Nat Commun (2015)

Fluorescence enhancement of QDs coupled to NPAs.(a) QD fluorescence intensity as a function of average incident laser power in three cases—on a glass slide, on a Au film and coupled to individual NPAs (NPAs 1–3). The solid lines are fits to a power law, with the power exponent, p, showing a nearly linear scaling. The vertical dashed line indicates the power at which subsequent measurements in this paper are performed under pulsed excitation. (b) Histogram showing the distribution of the fluorescence enhancement factors of the 11 measured NPAs.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4525280&req=5

f3: Fluorescence enhancement of QDs coupled to NPAs.(a) QD fluorescence intensity as a function of average incident laser power in three cases—on a glass slide, on a Au film and coupled to individual NPAs (NPAs 1–3). The solid lines are fits to a power law, with the power exponent, p, showing a nearly linear scaling. The vertical dashed line indicates the power at which subsequent measurements in this paper are performed under pulsed excitation. (b) Histogram showing the distribution of the fluorescence enhancement factors of the 11 measured NPAs.
Mentions: To quantitatively estimate the enhancement in the fluorescence intensity of the QDs coupled to a single plasmonic NPA, we conducted a series of experiments on three different samples: (i) a sample containing QDs coupled to NPAs as described above; (ii) a sample of QDs adhered on top of a PAH layer on a Au film but without any nanocubes; and (iii) a sample with QDs adhered to a PAH layer on a glass slide. To ensure the same surface density of QDs, all samples are prepared with the same concentration of QDs in solution and had the same surface chemistry (PAH) before spin coating the QDs. For excitation, a 535-nm Ti:sapphire laser is used with a pulse length of ∼150 fs, which is passed through a pulse picker to reduce the repetition rate from 80 to 40 MHz. The excitation laser is focused to a diffraction-limited spot, ∼300 nm in diameter and the QD fluorescence is collected in an epifluorescence configuration and measured by an avalanche photodiode (see Methods). Figure 3a shows the dependence of the QD fluorescence intensity on the laser excitation power for the three samples described above. The fluorescence intensity from the QDs coupled to a single NPA is substantially higher than from the QDs on a PAH layer on a glass slide or on a Au film. For QDs on a PAH layer on a Au film without any nanocubes, we find that the fluorescence is quenched by ∼70% compared with QDs on glass. This quenching is attributed to short-range non-radiative energy transfer between the QDs and the Au film4041. The emission intensity from QDs coupled to a single NPA shows linear scaling with excitation power density in the range of 0.01–10 kW cm−2. At higher excitation power densities, permanent photobleaching of the QDs occurs before saturation of the excited state population can be reached. All subsequent measurements in this paper are conducted at an excitation power density of Iex,0=1 kW cm−2. For structures with a polymer gap layer and no QDs, we found that the NPA scattering resonance was unmodified and stable for average excitation power densities with the femtosecond laser of up to 10 MW cm−2.

Bottom Line: The antennas consist of silver nanocubes coupled to a gold film separated by a thin polymer spacer layer and colloidal core-shell quantum dots, a stable and technologically relevant emitter.We show an increase in the spontaneous emission rate of a factor of 880 and simultaneously a 2,300-fold enhancement in the total fluorescence intensity, which indicates a high radiative quantum efficiency of ∼50%.The nanopatch antenna geometry can be tuned from the visible to the near infrared, providing a promising approach for nanophotonics based on ultrafast spontaneous emission.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Physics, Duke University, Durham, North Carolina 27708, USA. [2] Center for Metamaterials and Integrated Plasmonics, Duke University, Durham, North Carolina 27708, USA.

ABSTRACT
Typical emitters such as molecules, quantum dots and semiconductor quantum wells have slow spontaneous emission with lifetimes of 1-10 ns, creating a mismatch with high-speed nanoscale optoelectronic devices such as light-emitting diodes, single-photon sources and lasers. Here we experimentally demonstrate an ultrafast (<11 ps) yet efficient source of spontaneous emission, corresponding to an emission rate exceeding 90 GHz, using a hybrid structure of single plasmonic nanopatch antennas coupled to colloidal quantum dots. The antennas consist of silver nanocubes coupled to a gold film separated by a thin polymer spacer layer and colloidal core-shell quantum dots, a stable and technologically relevant emitter. We show an increase in the spontaneous emission rate of a factor of 880 and simultaneously a 2,300-fold enhancement in the total fluorescence intensity, which indicates a high radiative quantum efficiency of ∼50%. The nanopatch antenna geometry can be tuned from the visible to the near infrared, providing a promising approach for nanophotonics based on ultrafast spontaneous emission.

No MeSH data available.


Related in: MedlinePlus