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As one of Cd-free semiconductor nanocrystals, Zn-based nanocrystals are widely studied due to their wide band gap to be a candidate for blue- and green-emitting materials. Herein, ZnInGaSe nanocrystals were synthesized with the controlled stoichiometry from the intermediate of ZnInGaSe magic size clusters. The approach via the magic size clusters greatly increases the amount of Ga in ZnInGaSe NCs. After the growth of the ZnS shell, ZnInGaSe/ZnS core/shell nanocrystals exhibited improved green emission. Furthermore, Cu as the impurity was introduced into ZnInGaSe NCs to reduce the vacancy defects to promote the photoluminescence. Finally, a photoluminescence quantum yield of 35.7% was obtained in Cu:ZnInGaSe/ZnS core/shell nanocrystals. The donor–acceptor recombination mechanism was proposed to explain the optical properties in ZnInGaSe NCs. Cu:ZnInGaSe nanocrystals were utilized in light-emitting diodes, showing the potential of ZnInGaSe nanocrystals for optoelectronic devices. [ABSTRACT FROM AUTHOR]

Herein, a novel molecular SO2‐Bri‐DSB based on the sulfone‐bridged distyrylbenzene derivative is synthesized, and its organic crystal is fabricated. It has a very high photoluminescence (PL) quantum efficiency in the solution and crystalline state, i.e., dual‐state emission (DSE), and the corresponding PL mechanism is clarified in detail using the transient absorption and transient PL test. The PL behaviors in the monomolecular state and organic crystal are compared. In addition, the optical anisotropy of the SO2‐Bri‐DSB crystal is thoroughly investigated using various polarization‐dependent spectroscopy techniques. The time evolution of anisotropy is composed of a step behavior caused by the anisotropy of the electronic transition and a slow enhancing process with a lifetime of 4.86 ns, which is governed by the change in emission lifetime due to the anisotropy. The space‐resolved evolution of the optical anisotropy is investigated using the polarization‐dependent light wave‐guiding test and exhibits that the emission anisotropy gradually decreases with length, and it has a longer effective propagation length than the polarization emission signal. The findings provide insight into the intrinsic optical anisotropy of single‐molecular crystals and indicate that these materials have enormous potential in the domains of polarization lighting and display. [ABSTRACT FROM AUTHOR]

Currently, the performance of quantum‐dot light‐emitting diodes (QLEDs) based on environmental‐friendly Cu─In─Zn─S quantum dots (QDs) still lags far behind that of Cd‐QDs‐based devices. Here it is demonstrated that the unique trap‐related recombination in Cu─In─Zn─S QDs is mainly responsible for the low device efficiency. The luminous efficiency of Cu─In─Zn─S‐based QLEDs is rather sensitive to the temperature and hole‐transporting layers (HTLs) due to the susceptible thermal‐related trappingdetrapping processes of holes in radiative Cu‐related traps. The holes in Cu‐related traps can be quenched by escaping to the valence band of the QDs or/and transferring to the adjacent HTLs. An HTL with low highest occupied molecular orbitals is desired to enhance the hole injection and hinder the aforementioned hole transfer. As a result, a high device efficiency of 6.0 cd A−1 is achieved at room temperature, which is attributed to suppressed HTL‐induced emission quenching and efficient valence‐band‐dominated hole injection from HTL to the QDs. The device efficiency is further increased to 13.2 cd A−1 at 150K by suppressing thermal‐induced quenching. [ABSTRACT FROM AUTHOR]

A clear understanding on the fundamental working mechanisms of quantum‐dot light emitting diodes (QLEDs), especially the blue devices, is always sought after. Here the electroluminescence (EL) turn‐on mechanism of blue QLEDs is unraveled by structure engineering of the hole‐transport layers (HTLs). It is demonstrated that the EL turn‐on in blue QLEDs is highly dependent on the charge‐transport polarity of the HTLs. Energy transfer between HTLs and the blue quantum dots (QDs) occurs for the QLEDs based on bipolar HTLs, and, in contrast, charge injection is responsible for EL turn‐on of the blue devices consisting of unipolar HTLs. In addition, large hole‐injection barrier results in serious accumulation of holes at the interface of HTLs/QDs, then inducing serious electrons leakage into the HTLs, thereby leading to poor device efficiency under low driving current. It is suggested here that confining the carriers to the quantum dots and reducing the hole‐injection barrier remain two critical aspects to optimize the performance of blue QLEDs. [ABSTRACT FROM AUTHOR]

Inorganic semiconductor nanocrystals (NCs) are considered potential emitters for next-generation displays due to their special quantum size confinement effect. Herein, Cd-free AgInZnS (AIZS) NCs were produced via the cation exchange reaction from AgIn5S8 NCs for light-emitting diodes as green emitters. AIZS NC-based light-emitting diodes showed a maximum current efficiency of 6.34 cd/A and an external quantum efficiency of 1.3%, which are the highest values for AIZS NC-based light-emitting diodes for green emitters so far. The composition of AIZS NCs produced with different ligands can vary the band gap structure of AIZS NCs, affecting the balance of charge injections in the device to induce different performances of AIZS NC-based light-emitting diodes. [ABSTRACT FROM AUTHOR]

In order to improve the optoelectronic performance of π-conjugated molecules with electronic donors and electronic acceptors, people often choose multi-branch molecule structures, which can enhance the charge transfer ability. In this work, the photo-physical characteristics of (E)-4-(2-(3-methylquinoxalin-2-yl)vinyl)-N,N-diphenylaniline (QTPA1) and 4,4′-((1E,1′E)-quinoxaline-2,3-diylbis(ethene-2,1-diyl))bis(N,N-diphenylaniline) (QTPA2) in monodisperse systems and aggregated states were investigated in detail, showing that the photoluminescence quantum yield (PLQY) of oligomers is apparently enhanced in high-polarity solutions and decreased in low-polarity solvents instead, after the oligomer is linked with a conjugated branch. Based on the pump–probe and pump–dump–probe, this unusual phenomenon is assigned to the polarity-dependent intramolecular charge transfer (CT) mechanism of oligomers induced by the conjugated branch. In the PL of aggregated state and the two-photon fluorescence (TPF), increasing the conjugated branch has a positive effect on the PL characteristics that the PL performance of QTPA2 is higher than that of the aggregated QTPA1. In the aggregated state, QTPA2 has a larger degree of π electron conjugation, which suppresses intramolecular vibrations and reduces the energy loss caused by non-radiative processes. In addition, the two-photon absorption section of QTPA2 keeps higher in comparison with that of QTPA1 owing to the enhancement of the intramolecular dipole intensity, leading to the enhancement of TPF. This research could elucidate the physical mechanism underlying the optoelectronic performance and help us develop novel organic optoelectronic materials with high performance. [ABSTRACT FROM AUTHOR]

From a copper target, laser-ablated plasma was investigated by spectral- and temporal-resolved emission spectroscopy. With the presence of a 0.8 T steady magnetic field, the emission of the expanding plasma showed significant enhancements of the spectral lines for all neutral, singly, and doubly ionized species. The relative enhancements for different species have been studied with temporal-resolved measurement by comparing the spectra obtained with and without the magnetic field. The enhanced emission from the plasma plume is attributed to an increase of the radiative recombination rate in the plasma due to magnetic confinement. The temporal evolution of the plasma parameters, including electron temperature and electron density, was deduced and discussed for the cases with and without a magnetic field. OCIS codes: 300.6365, 300.2140, 300.6350, 300.6320, 350.5400.

Currently, blue quantum‐dot light‐emitting diodes (QLEDs) remain the bottleneck limiting the development of QLED‐based applications. To achieve high‐performance blue QLEDs, poly‐N‐vinylcarbazole (PVK) is usually employed as the hole‐transport layer (HTL) to reduce the hole injection barrier. However, fabrication of efficient blue QLEDs with PVK HTL remains challenging and empirical/accidental. Here, it is demonstrated that PVK layer can trap electrons and hence resulting in low device efficiency. This is why the performance of blue QLEDs is highly dependent on the PVK batch received from the manufacturers. As an interlayer, ZnSe/ZnS quantum dots (QDs) are inserted between PVK and blue ZnCdSe/ZnS QD emitters. The resulted device presents an external quantum efficiency of 20.6% under 2920 cd m−2, enhanced by ≈35% compared with that of PVK‐alone device. The remarkable enhancement is owing to the QD interlayer that not only suppresses the electron trapping in PVK, increasing the probability of exciton recombination within the emissive layer, but also facilitates the hole injection, improving the charge balance in blue devices. [ABSTRACT FROM AUTHOR]