Enhanced Valley Splitting of Exciton Emission in Colloidal PbSe Quantum Dots When the Interdot Distance Coincides with Onset of Förster Resonance Energy Transfer

Energy-Transfer-Induced Enhanced Valley Splitting of Excitonic Emission of Inorganic CdTe@ZnS QDs in the Presence of Organic J-Aggregates: A Spectroscopic Insight into the Efficient Exciton (Inorganic)–Exciton (Organic) Coupling

“…In order to understand the variation of the emission bands of QDs in detail, the PL spectra of QDs were deconvoluted satisfactorily by fitting with two Gaussian bands (Figure a–d), which indicates the existence of multiple emitting states. Since the present QDs had a unimodal distribution in size (Figure S2a,b), the two emission bands were certainly not caused due to the presence of two coexisting groups of QDs with different diameters …”

“…This observation is a clear indication of the fact that the electronic coupling that leads to FRET is also closely related to the enhanced valley splitting of the QD emission band. It is relevant to mention here that recently Omata and co-workers have shown that electronic coupling leading to FRET may enhance the valley splitting. This observation is very interesting in the sense that valley splitting can be tuned by simply controlling the FRET process from QDs to J-aggregates without applying any external field.…”

“…The valence band maxima and conduction band minima of Cd-chalcogenides are both situated at the Γ-point in the Brillouin zone . Since there are four Γ-points per face-centered cubic Brillouin zone, the fundamental bandgap becomes 8-fold degenerate (considering spin degeneracy). , This 8-fold fundamental bandgap in turn yield a 64-fold degenerate lowest exciton state (1S h –1S e ). , This degeneracy can partially be lifted by a number of effects, such as intra-band coupling, inter-valley couplings, electron–hole exchange, etc. , These effects are primarily responsible for creating a fine exciton structure . The electron–hole exchange may also lead to an intricate exciton fine structure consisting of several bright and dark states .…”

“…38,39 Very recently, Omata and co-workers have shown that strong exciton−exciton coupling between PbSe QDs can lead to valley splitting of the QD emission, and they have also shown that the interdot distance can control the extent of valley splitting. 40 From the above discussions, one can realize that information available on strong coupling phenomena is not large, rather very limited. More importantly, no information is available in the literature where an organic exciton (Frankel) is shown to participate in the valley splitting of an inorganic excitonic (Wannier−Mott) emission band.…”

“…Strong coupling usually involves two systems, where one needs to be strongly confined and another needs to possess a strong transition dipole moment. − The strength of such coupling can be given as g = μ e | E vac |∝ μ e /√ V , where g is the coupling strength, E vac is the vacuum field, and V is the mode volume. , In recent times, strongly coupled nanoscale assemblies with coupling between local surface plasmon resonance and excitons, excitons with photons, etc., ,,, have attracted considerable attention from academia and industry owing to their potential applications in fields of artificial light harvesting, thresholdless lasing, sensing, quantum information processing, optical computing, etc. − In fact, it has been recently proposed that strong coupling between two suitable interacting systems such as exciton–exciton, exciton–plasmon, exciton–photon, and photon–plasmon can produce future-generation materials for various optoelectronic applications. − Strong coupling has also been demonstrated in hybrid nanosystems comprising plasmonic nanoparticles and cyanine dye J-aggregates . Interestingly, it has been demonstrated that strong coupling can also lead to an interesting process known as valley splitting, where the observed emission band gets split into two distinct emission bands due to the lifting of the degeneracy of the two existing excitonic states of the emitting species (QDs). , The valley splitting phenomenon has been observed in the plasmonic absorption band of nanomaterials in the presence of inorganic excitons (QDs), , organic excitons (aggregates), , and also in the presence of two-dimensional transition-metal dichalcogenides. , Very recently, Omata and co-workers have shown that strong exciton–exciton coupling between PbSe QDs can lead to valley splitting of the QD emission, and they have also shown that the interdot distance can control the extent of valley splitting . From the above discussions, one can realize that information available on strong coupling phenomena is not large, rather very limited.…”