M.D. Leistikow

Size-dependent oscillator strength and quantum efficiency of CdSe quantum dots controlled via the local density of states

We study experimentally time-resolved emission of colloidal CdSe quantum dots in an environment with a controlled local density of states (LDOS). The decay rate is measured versus frequency and as a function of distance to a mirror. We observe a linear relation between the decay rate and the LDOS, allowing us to determine the size-dependent quantum efficiency and oscillator strength. We find that the quantum efficiency decreases with increasing emission energy mostly due to an increase in nonradiative decay. We manage to obtain the oscillator strength of the important class of CdSe quantum dots. The oscillator strength varies weakly with frequency in agreement with behavior of quantum dots in the strong confinement limit. Surprisingly, previously calculated tight-binding results differ by a factor of 5 with the measured absolute values. Results from pseudopotential calculations agree well with the measured radiative rates. Our results are relevant for applications of CdSe quantum dots in spontaneous emission control and cavity quantum electrodynamics

Signature of a three-dimensional photonic band gap observed on silicon inverse woodpile photonic crystals

We have studied the reflectivity of CMOS-compatible three-dimensional silicon inverse woodpile photonic crystals at near-infrared frequencies. Polarization-resolved reflectivity spectra were obtained from two orthogonal crystal surfaces using an objective with a high numerical aperture. The spectra reveal broad peaks with maximum reflectivity of 67% that are independent of the spatial position on the crystals. The spectrally overlapping reflectivity peaks for all directions and polarizations form the signature of a broad photonic band gap with a relative bandwidth up to 16%. This signature is supported with stop gaps in plane-wave band-structure calculations and with the frequency region of the expected band gap.

Experimental signature of a broad 3D photonic band gap in silicon nanostructures

Three-dimensional photonic crystals radically control propagation and emission of light [1, 2]. Photonic crystals are ordered composite materials with a spatially varying dielectric constant that has a periodicity of the order of the wavelength of light. In specific three-dimensional crystals, a common frequency range for all polarizations is formed for which light is not allowed to propagate in any direction, called the photonic band gap. It is an outstanding challenge to create these crystals and experimentally demonstrate the photonic band gap.

Size dependent oscillator strength of CdSe quantum dots determined by nanophotonic control

Control over spontaneous emission of quantum dots is important for many applications, especially as light sources in photonic materials and nanostructures[1–3]. Colloidal CdSe quantum dots have recently generated enormous interest because of the tunability of their emission energy with particle diameter over the entire visible range. The strength of the interaction of a quantum dot with the light field is determined by the oscillator strength, making the oscillator strength a crucial parameter for successful inhibition and enhancement of spontaneous emission.