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We demonstrated a facile synthesis of highly luminescent blue emitting Cd 1− xZn xS/ZnS core/shell structured nanocrystals (NCs) in straightforward and reproducible manner. The alloyed Cd 1− xZn xS cores with homogeneity in both size and composition were prepared by introducing S precursors (S dissolved in the noncoordinating solvent (1-octadecene)) into the mixed solution of Cd−Oleate (Cd(OA) 2) and Zn−Oleate (Zn(OA) 2) at elevated temperature (300 °C). ZnS shells were successively overcoated on the prepared cores by the second injection of S precursors (S powder dissolved in tributylphosphine, TBPS) directly into the reactor with existing alloyed Cd 1− xZn xS NC cores without any purification steps. The prepared NCs exhibit strong band edge emission with high photoluminescent quantum yield (PL QY, up to 80%) and narrow spectral bandwidth (fwhm < 25 nm), which is believed to originate from the successful growth of ZnS shell layers on the Cd 1− xZn xS cores and the interfacial compatibility between Cd 1− xZn xS cores and the ZnS shell layers through the intradiffusion of Zn atoms from the ZnS shells into the Cd 1− xZn xS cores during the shell formation reaction. The emission wavelength (PL λ max.) of Cd 1− xZn xS/ZnS core/shell NCs was finely tuned from violet (415 nm) to blue (461 nm) by adjusting the amount of S precursors in the first injection (S in 1-octadecene) and thus changing actual Cd content ratio in the alloyed Cd 1− xZn xS cores (0.49 ≤ x≤ 0.76). Furthermore, multigram (3 g) scale production of Cd 1− xZn xS/ZnS core/shell NCs with narrow size distribution and spectral bandwidth was also demonstrated. [ABSTRACT FROM AUTHOR]

Gallium ion incorporation into silver indium gallium sulfide nanocrystals is investigated by various methods, including photoluminescence (PL) and X-ray photoelectron spectroscopy. The ZnS shell-growth enhances a PL quantum yield of up to 16%, with which the quantum dot light-emitting diode was successfully fabricated. [ABSTRACT FROM AUTHOR]

Herein, we report unique features of the assemblies of tetrapod-shaped colloidal nanocrystals (TpNCs) with lengthy arms applicable to flexible thin-film transistors. Due to the extended nature of tetrapod geometry, films made of the TpNC assemblies require reduced numbers of inter-NC hopping for the transport of charge carriers along a given channel length; thus, enhanced conductivity can be achieved compared to those made of typical spherical NCs without arms. Moreover, electrical conduction through the assemblies is tolerant against mechanical bending because interconnections between TpNCs can be well-preserved under bending. Interestingly, both the conductivity of the assemblies and their mechanical tolerance against bending are improved with an increase in the length of tetrapod arms. The arm length-dependency was demonstrated in a series of CdSe TpNC assemblies with different arm lengths (l = 0-90 nm), whose electrical conduction was modulated through electrolyte gating. From the TpNCs with the longest arm length included in the study (l = 90 nm), the film conductivity as high as 20 S/cm was attained at 3 V of gate voltage, corresponding to electron mobility of >10 cm²/(V s) even when evaluated conservatively. The high channel conductivity was retained (~90% of the value obtained from the flat geometry) even under high bending (bending radius = 5 mm). The results of the present study provide new insights and guidelines for the use of colloidal nanocrystals in solution-processed flexible electronic device applications. [ABSTRACT FROM AUTHOR]

Ratiometric pressure sensitive paints (r-PSPs) are all-optical probes for monitoring oxygen flows in the vicinity of complex or miniaturized surfaces. They typically consist of a porous binder embedding mixtures of a reference and a sensor chromophore exhibiting oxygen-insensitive and oxygen-responsive luminescence, respectively. Here, we demonstrate the first example of an r-PSP based on a single two-color emitter that removes limitations of r-PSPs based on chromophore mixtures such as different temperature dependencies of the two chromophores, cross-readout between the reference and sensor signals and phase segregation. In our approach, we utilize a novel "double-sensor" r-PSP that features two spectrally separated emission bands with opposite responses to the O2 pressure, which boosts the sensitivity with respect to traditional reference-sensor pairs. Specifically, we use two-color-emitting dot-in-bulk CdSe/CdS core/shell nanocrystals, exhibiting red and green emission bands from their core and shell states, whose intensities are respectively enhanced and quenched in response to the increased oxygen partial pressure that effectively tunes the position of the nanocrystal's Fermi energy. This leads to a strong and reversible ratiometric response at the single particle level and an over 100% enhancement in the pressure sensitivity. Our proof-of-concept r-PSPs further exhibit suppressed cross-readout thanks to zero spectral overlap between the core and shell luminescence bands and a temperature-independent ratiometric response between 0 and 70 °C. [ABSTRACT FROM AUTHOR]

The field of nanocrystal quantum dots (QDs) is already more than 30 years old, and yet continuing interest in these structures is driven by both the fascinating physics emerging from strong quantum confinement of electronic excitations, as well as a large number of prospective applications that could benefit from the tunable properties and amenability toward solution-based processing of these materials. The focus of this review is on recent advances in nanocrystal research related to applications of QD materials in lasing, light-emitting diodes (LEDs), and solar energy conversion. A specific underlying theme is innovative concepts for tuning the properties of QDs beyond what is possible via traditional size manipulation, particularly through heterostructuring. Examples of such advanced control of nanocrystal functionalities include the following: interface engineering for suppressing Auger recombination in the context of QD LEDs and lasers; Stokes-shift engineering for applications in large-area luminescent solar concentrators; and control of intraband relaxation for enhanced carrier multiplication in advanced QD photovoltaics. We examine the considerable recent progress on these multiple fronts of nanocrystal research, which has resulted in the first commercialized QD technologies. These successes explain the continuing appeal of this field to a broad community of scientists and engineers, which in turn ensures even more exciting results to come from future exploration of this fascinating class of materials. [ABSTRACT FROM AUTHOR]

We examine the effects of chlorine-passivation of Cd surface atoms on photocatalytic H2O reduction by CdSe NCs. Transient absorption spectroscopy reveals that Cl passivation removes electron trap states in CdSe NCs, which is also reflected in an increase of photoluminescence quantum yield, e.g., from 9 to 22% after the Cl treatment. Size-tunable energy states in CdSe NCs enable the systematic investigation of surface defects and their effect on the photocatalytic hydrogen generation rate. It turns out that, depending on band-edge energy levels, the surface trap states may enhance or inhibit photocatalysis. Cl-treated CdSe NCs larger than 2.7 nm show a higher hydrogen evolution rate than untreated CdSe NCs of the same size as Cl treatment removes trap states with energy below the H2O reduction potential. In contrast, the same Cl treatment does not increase the photocatalytic rate of CdSe NCs smaller than 2.7 nm because both the conduction band edge and trap states are above the water reduction potential. The size-dependence of the effect of Cl treatment suggests that electron trap states in CdSe may promote photocatalytic activity by enhancing charge separation. [ABSTRACT FROM AUTHOR]