We investigated the electronic properties of the molecular magnetic nanotoruses [FeIII 10LnIII 10(Me‐tea)10(Me‐teaH)10(NO3)10], examining the dependence on the lanthanide (Ln) of both the intra and intermolecular electronic channels. Using femtosecond absorption spectroscopy we show that the intramolecular electronic channels follow a three‐step process, which involves vibrational cooling and crossing to shallow states, followed by recombination. A comparison with the energy gaps showed a relationship between trap efficiency and gaps, indicating that lanthanide ions create trap states to form excitons after photo‐excitation. Using high‐resistance transport measurements and scaling techniques, we investigated the intermolecular transport, demonstrating the dominant role of surface‐limited transport channels and the presence of different types of charge traps. The intermolecular transport properties can be rationalized in terms of a hopping model, and a connection is provided to the far‐IR spectroscopic properties. Comparison between intra and intermolecular processes highlights the role of the excited electronic states and the recombination processes, showing the influence of Kramers parity on the overall mobility.
In the present study, we developed a fabrication process of an electrically driven single-photon LED based on InP QDs emitting in the red spectral range, the wavelength of interest coinciding with the high efficiency window of Si APDs. A deterministic lithography technique allowed for the pre-selection of a suitable QD, here exclusively operated under electrical carrier injection. The final device was characterized under micro-electroluminescence in direct current, as well as in pulsed excitation mode. In particular, under pulsed excitation of one device, single-photon emission of a spectral line, identified as an exciton, has been observed with g (2) raw (0) = 0.42 ± 0.02, where the non-zero g (2) -value is mainly caused by background contribution in the spectrum and re-excitation processes due to the electrical pulse length. The obtained results constitute an important step forward in the fabrication of electrically driven single-photon sources, where deterministic lithography techniques can be used to sensibly improve the device performances. In principle, the developed process can be extended to any desired emitter wavelength above 600 nm up to the telecom bands.
We report on the radiative interaction of two single quantum dots (QDs) each in a separate InP/GaInP-based microdisk cavity via resonant whispering gallery modes. The investigations are based on ab initio coupled disk modes. We apply optical spectroscopy involving a 4f -setup, as well as mode-selective real space imaging and photoluminescence mapping to discern single QDs coupled to a resonant microdisk mode. Excitation of one disk of the double cavity structure and detecting photoluminescene from the other yields proof of single photon emission of a QD excited by incoherent energy transfer from one disk to the other via a mode in the weak coupling regime. Finally, we present evidence of photons emitted by a QD in one disk that are transferred to the other disk by a resonant mode and are subsequently resonantly scattered by another QD.PACS numbers: 78.67. Hc, 42.50.Hz, 78.55.Cr The scientific development towards quantum technologies based on semiconductor solid-state devices has seen much progress in recent years. In particular, semiconductor quantum dots (QDs) put themselves forward for the implementation as qubits [1,2]. The coherent control of the interaction of two QDs in coupled quantum systems is a key element and promises, e.g., the implementation of parallel qubit operation for quantum information processing. To this end, Imamoglu et al. proposed [3] to utilize two spatially distant electron spins of QD excitons inside a microcavity coupled by a single cavity field to implement CNOT-operations.The coupling of two QDs in one cavity has been realized in micropillar [4] and photonic crystal cavities [5,6]. However, accomplishing selective tunability and individual addressability of each QD, which is essential for the manipulation of individual qubits in future applications, is technically challenging for closely spaced QDs. Consequently, the idea is to exploit the long-range interaction between QDs in coupled microcavity systems, i.e., photonic molecules (PMs) [7][8][9][10] where the energy transfer is mediated via a resonant cavity mode. It has been shown recently that the excitation of a two level system with quantum light instead of classical light could improve the quality of subsequently emitted single photons [11]. Thus, classical light could be used to excite a first QD which in turn excites a second QD with a stream of single photons. Using PMs to obtain an efficient coupling between the QDs presents an integrable and compact semiconductor solution. In addition, these PMs have also been theoretically investigated for entanglement of a pair of QDs [12,13], they enable the unconventional photon blockade [14,15], and serve as a starting point for the realization of driven-dissipative multi-cavity systems [16] and strong photon-photon correlations [17][18][19].An attractive type of cavity systems are whispering gallery mode (WGM) supporting microdisks (see exemplary SEM-picture in Fig. 1 a)). The WGMs propagate along the inner edge of the disk and couple to an adjacent microdisk cavity via the exponen...
On page 6280, A. K. Powell, A.‐N. Unterreiner, K. Goß, and co‐workers report an investigation of both intra‐ and intermolecular electron transfer processes in a family of nanotoroidal Fe(III)10Ln(III)10 cyclic coordination clusters. Photo‐induced intramolecular electron transport proceeds via exciton formation on the oxygen bridges. Intermolecular tranport is rationalized using a hopping model. In both cases, the Kramers parity of the lanthanide ion is important.
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