Exciton

About: Exciton is a research topic. Over the lifetime, 31603 publications have been published within this topic receiving 810642 citations.

Unified picture of electron and hole relaxation pathways in semiconductor quantum dots

Abstract: Size dependent electron and hole relaxation dynamics were measured in colloidal CdSe quantum dots with state-to-state specificity. These experiments reveal the electron and hole state-to-state relaxation dynamics with a precision of $\ensuremath{\sim}10\phantom{\rule{0.3em}{0ex}}\mathrm{fs}$, allowing quantitative evaluation of the manifold of pathways by which an exciton relaxes in strongly confined quantum dots. These experiments corroborate previously observed confinement induced femtosecond Auger relaxation channels for electrons, but with sufficient precision to quantitatively and unambiguously determine the size dependence of the Auger mechanism. These experiments also show that the hole energy loss rate increases for smaller quantum dots, contradicting known relaxation mechanisms for holes. We propose a confinement enhanced mechanism for hole relaxation in colloidal quantum dots, overcoming the predicted phonon bottleneck for holes. The relative contributions of the relaxation pathways are identified for electrons and for holes. These state selective experiments produce a unified picture of the manifold of relaxation pathways available to both electrons and holes in strongly confined colloidal quantum dots.

Observation of the one‐exciton to two‐exciton transition in a J aggregate

Abstract: We report on the first observation of the one‐exciton to two‐exciton transition in J aggregates. A theoretical analysis supports our interpretation.

The ground exciton state of formamidinium lead bromide perovskite nanocrystals is a singlet dark state

Abstract: Lead halide perovskites have emerged as promising new semiconductor materials for high-efficiency photovoltaics, light-emitting applications and quantum optical technologies. Their luminescence properties are governed by the formation and radiative recombination of bound electron-hole pairs known as excitons, whose bright or dark character of the ground state remains unknown and debated. While symmetry analysis predicts a singlet non-emissive ground exciton topped with a bright exciton triplet, it has been predicted that the Rashba effect may reverse the bright and dark level ordering. Here, we provide the direct spectroscopic signature of the dark exciton emission in the low-temperature photoluminescence of single formamidinium lead bromide perovskite nanocrystals under magnetic fields. The dark singlet is located several millielectronvolts below the bright triplet, in fair agreement with an estimation of the long-range electron-hole exchange interaction. Nevertheless, these perovskites display an intense luminescence because of an extremely reduced bright-to-dark phonon-assisted relaxation.

Overcoming the energy gap law in near-infrared OLEDs by exciton–vibration decoupling

Abstract: The development of high-performance near-infrared organic light-emitting diodes is hindered by strong non-radiative processes as governed by the energy gap law Here, we show that exciton delocalization, which serves to decouple the exciton band from highly vibrational ladders in the S0 ground state, can bring substantial enhancements in the photoluminescence quantum yield of emitters, bypassing the energy gap law Experimental proof is provided by the design and synthesis of a series of new Pt(ii) complexes with a delocalization length of 5–9 molecules that emit at 866–960 nm with a photoluminescence quantum yield of 5–12% in solid films The corresponding near-infrared organic light-emitting diodes emit light with a 930 nm peak wavelength and a high external quantum efficiency up to 214% and a radiance of 416 W sr−1 m−2 Both theoretical and experimental results confirm the exciton–vibration decoupling strategy, which should be broadly applicable to other well-aligned molecular solids Pt(ii) complexes allow the fabrication of efficient near-infrared organic light-emitting diodes that operate beyond the 900 nm region