Ultrafast photophysical process of bi-exciton Auger recombination in CuInS2 quantum dots studied by transient-absorption spectroscopy

Highly efficient near-infrared light-emitting diodes based on Zn:CuInSe2/ZnS//ZnS quantum dots with double shell engineering

Near-infrared (NIR) quantum dot-based light-emitting diodes (QLEDs) developed rapidly in the fields of biomedical applications, telecommunications, sensing and diagnostics. However, it remains an enormous challenge for the synthesis of high-quality NIR QD materials with low toxicity or non-toxicity, high photoluminescence (PL) quantum yields (QYs) and high stability. Herein, we used a facile method to synthesize large-sized (8 nm) and thick-shell NIR Zn:CuInSe₂/ZnS//ZnS QDs by engineering a double ZnS shell. The resulting NIR QDs exhibited high PL QYs of 80%, and excellent photochemical stability, which could be ascribed to the decreased lattice mismatch of the core/shell interface by the introduced Zn element into CuInSe₂ cores and the energetic defect passivation of the double ZnS shell engineering. Furthermore, the high-quality Zn:CuInSe₂/ZnS//ZnS QDs based LEDs exhibited the maximum external quantum efficiency (EQE) of 3.0%, 4.0% and 2.5% for PL peaks located at 705, 719 and 728 nm, respectively. This efficiency is comparable to that of the outstanding PbS- and InAs-based NIR QLEDs, as well as the avoidance of toxic heavymetal and/or hazardous reagents in this work. The synthesized high-quality Zn:CuInSe₂/ZnS//ZnS QDs could be expected to promote the potential applications of heavy-metal-free QDs in the NIR fields.

Spectral analysis on the acceptor concentration-dependent fluorescence resonance energy transfer process in CuInS2@ZnS-SQ complexes

Owing to the broad spectral response and flexible choices of donors and acceptors, fluorescence resonance energy transfer (FRET) system based on quantum dots (QDs) is a potential candidate for enhancing performance of solar cells and other optoelectronic devices. Thus it is necessary to develop such FRET systems with high efficiency and understand the involved photophysical dynamics. Here, with type I CuInS₂@ZnS core-shell quantum dots as the energy donor, series of CuInS₂@ZnS-SQ complexes are synthesized by adjusting the acceptor (squaric acid, SQ) concentration. The FRET dynamics of the samples is systematically investigated by virtue of steady-state emission, time-resolved fluorescence decay, and transient absorption measurements. The experimental results display a positive correlation between the energy transfer efficient (η). The best energy transfer efficient achieved from experimental data is 52%. This work provides better understanding of the photophysical dynamics in similar complexes and facilitates further development of new photoelectronic devices based on relevant FRET systems.

Impurity effects on binding energy, diamagnetic susceptibility and photoionization cross-section of chalcopyrite AgInSe2nanotadpole

Recently the interest in chalcopyrite semiconductor nanostructures has increased because of their non-toxicity and their wide direct bandgap. Likewise, structures with non-trivial geometry are particularly interesting because of their electronic, optical, and magnetic properties. In the current article, the finite element method was used in conjunction with the effective mass approximation to theoretically investigate the properties of a chalcopyrite AgInSe₂nanotadpole in the presence of an hydrogen like shallow off-center impurity. The morphology of the nanotadpole gives it excellent hydrodynamic properties and is ideal for a wide range of applications. The probability densities for various impurity positions and energy levels were obtained. The results suggested a strong dependence of the behavior of the electron on the impurity positions and the orientation of the wave function. The investigation of the nanotadpole's energy spectra and their comparison with the cylindrical and spherical quantum dots suggest that the spectrum has degenerate states similar to the spherical case, however at some ranges, the levels behave similarly to the cylindrical case. The binding energy's dependence on the nanotadpole's size and the impurity position was obtained. The dependence of the diamagnetic susceptibility on the impurity position was calculated. An extensive investigation of the photoionization cross-section was carried out for the ground and the first two excited states as the initial states and the first twenty excited states as the final states.

Förster resonance energy transfer outpaces Auger recombination in CdTe/CdS quantum dots-rhodamine101 molecules system upon compression

Förster resonance energy transfer (FRET) and Auger recombination in quantum dots (QDs)-molecules system are important mechanisms for affecting performance of their optoelectronic and photosynthesis devices. However, exploring an effective strategy to promote FRET and suppress Auger recombination simultaneously remains a daunting challenge. Here, we report that FRET process is promoted and Auger recombination process is suppressed in CdTe/CdS QDs-Rhodamine101 (Rh101) molecules system upon compression. The greatly improved FRET is attributed to the shortened donor-acceptor distance and increased the number of molecules attached to QDs induced by pressure. The reduced Auger recombination is ascribed to the formation of an alloy layer at the core/shell interface. The FRET can occur 70 times faster than Auger recombination under a high pressure of 0.9 GPa. Our findings demonstrate that high pressure is a robust tool to boost FRET and simultaneously suppress Auger recombination, and provides a new route to QDs-molecules applications.