We present an experimental and theoretical study of the fluorescence rate of a single molecule as a function of its distance to a laser-irradiated gold nanoparticle. The local field enhancement leads to an increased excitation rate whereas nonradiative energy transfer to the particle leads to a decrease of the quantum yield (quenching). Because of these competing effects, previous experiments showed either fluorescence enhancement or fluorescence quenching. By varying the distance between molecule and particle we show the first experimental measurement demonstrating the continuous transition from fluorescence enhancement to fluorescence quenching. This transition cannot be explained by treating the particle as a polarizable sphere in the dipole approximation.

https://www.photonics.ethz.ch/fileadmin/user_upload/FILES2SHARE/anger06a.pdf

Enhancement and quenching of single-molecule fluorescence.

Quantum dots embedded in photonics nanostructures provide unprecedented control over the interaction between light and matter. This review gives an overview of the theoretical principles involved, as well as applications ranging from high-precision quantum electrodynamics experiments to quantum-information processing.

Interfacing single photons and single quantum dots with photonic nanostructures

Control of spontaneously emitted light lies at the heart of quantum optics. It is essential for diverse applications ranging from miniature lasers and light-emitting diodes, to single-photon sources for quantum information, and to solar energy harvesting. To explore such new quantum optics applications, a suitably tailored dielectric environment is required in which the vacuum fluctuations that control spontaneous emission can be manipulated. Photonic crystals provide such an environment: they strongly modify the vacuum fluctuations, causing the decay of emitted light to be accelerated or slowed down, to reveal unusual statistics, or to be completely inhibited in the ideal case of a photonic bandgap. Here we study spontaneous emission from semiconductor quantum dots embedded in inverse opal photonic crystals. We show that the spectral distribution and time-dependent decay of light emitted from excitons confined in the quantum dots are controlled by the host photonic crystal. Modified emission is observed over large frequency bandwidths of 10%, orders of magnitude larger than reported for resonant optical microcavities. Both inhibited and enhanced decay rates are observed depending on the optical emission frequency, and they are controlled by the crystals’ lattice parameter. Our experimental results provide a basis for all-solid-state dynamic control
of optical quantum systems.

Controlling the dynamics of spontaneous emission from quantum dots by photonic crystals

We describe the recent experimental progress in the control of spontaneous emission by manipulating optical modes with photonic crystals. It has been clearly demonstrated that the spontaneous emission from light emitters embedded in photonic crystals can be suppressed by the so-called photonic bandgap, whereas the emission efficiency in the direction where optical modes exist can be enhanced. Also, when an artificial defect is introduced into the photonic crystal, a photonic nanocavity is produced that can interact with light emitters. Cavity quality factors, or Q factors, of up to 2 million have been realized while maintaining very small mode volumes, and both spontaneous-emission modification (the Purcell effect) and strong-coupling phenomena have been demonstrated. The use of photonic crystals and nanocavities to manipulate spontaneous emission will contribute to the evolution of a variety of applications, including illumination, display, optical communication, solar energy and even quantum-information systems.

Spontaneous-emission control by photonic crystals and nanocavities

We observe large spontaneous emission rate modification of individual InAs quantum dots (QDs) in a 2D photonic crystal with a modified, high-$Q$ single-defect cavity. Compared to QDs in a bulk semiconductor, QDs that are resonant with the cavity show an emission rate increase of up to a factor of 8. In contrast, off-resonant QDs indicate up to fivefold rate quenching as the local density of optical states is diminished in the photonic crystal. In both cases, we demonstrate photon antibunching, showing that the structure represents an on-demand single photon source with a pulse duration from 210 ps to 8 ns. We explain the suppression of QD emission rate using finite difference time domain simulations and find good agreement with experiment.

Controlling the spontaneous emission rate of single quantum dots in a two-dimensional photonic crystal.

/pdf/controlling-the-dynamics-of-spontaneous-emission-from-4o2jd27pmr.pdf

We observe experimentally that ensembles of quantum dots in three-dimensional (3D) photonic crystals reveal strongly nonexponential time-resolved emission. These complex emission decay curves are analyzed with a continuous distribution of decay rates. The log-normal distribution describes the decays well for all studied lattice parameters. The distribution width is identified with variations of the radiative emission rates of quantum dots with various positions and dipole orientations in the unit cell. We find a striking sixfold change of the width of the distribution by varying the lattice parameter. This interpretation qualitatively agrees with the calculations of the 3D projected local density of states. We therefore conclude that fluorescence decay of ensembles of quantum dots is highly nonexponential to an extent that is controlled by photonic crystals.

/pdf/strongly-nonexponential-time-resolved-fluorescence-of-4nbpo0y89h.pdf

Strongly nonexponential time-resolved fluorescence of quantum-dot ensembles in three-dimensional photonic crystals

We have measured spontaneous emission decay rates from an ensemble of quantum dots in strongly interacting inverse-opal photonic crystals. The decay traces are successfully modelled with a log-normal distribution of decay rates. The most-frequent decay rate varies by a factor of three as a function of the crystal lattice parameter, in agreement with the theoretical photonic density of states. The distribution width varies by a factor of six and can be identified with the spatial variation of the local density of states that is probed by quantum dots at various positions in the unit cell. This is the first experimental evidence for a position-dependent emission rate in photonic crystals.

Spontaneous-emission rate distributions in photonic crystals controlled by position-dependent local density of states

We have measured time-resolved spontaneous emission from quantum dots in 3D photonic crystals. Due to the spatially dependent local density of states, the distribution of decay rates varies strongly with the photonic crystal lattice parameter.

/pdf/dynamics-of-spontaneous-emission-controlled-by-local-density-2eclfslnf1.pdf

A. Floris van Driel

Papers

Controlling the dynamics of spontaneous emission from quantum dots by photonic crystals

Controlling the dynamics of spontaneous emission from quantum dots by photonic crystals

Strongly nonexponential time-resolved fluorescence of quantum-dot ensembles in three-dimensional photonic crystals

Spontaneous-emission rate distributions in photonic crystals controlled by position-dependent local density of states

Dynamics of spontaneous emission controlled by local density of states in photonic crystals