Solid-state room-temperature lasing with tunability in a wide range of wavelengths is desirable for many applications. To achieve this, besides an efficient gain material with a tunable emission wavelength, a high quality-factor optical cavity is essential. Here, we combine a film of colloidal CdSe/CdZnS core−shell nanoplatelets with square arrays of nanocylinders made of titanium dioxide to achieve optically pumped lasing at visible wavelengths and room temperature. The all-dielectric arrays support bound states in the continuum (BICs), which result from lattice-mediated Mie resonances and boast infinite quality factors in theory. In particular, we demonstrate lasing from a BIC that originates from out-of-plane magnetic dipoles oscillating in phase. By adjusting the diameter of the cylinders, we tune the lasing wavelength across the gain bandwidth of the nanoplatelets. The spectral tunability of both the cavity resonance and nanoplatelet gain, together with efficient light confinement in BICs, promises low-threshold lasing with wide selectivity in wavelengths.

Although size tunable synthesis of PbS between 3 and 10 nm with emission in the NIR II region is well-known, there is no well-established method to produce smaller particles with emission below 1000 nm, which is easier to detect with less costly and more widely available Si and extented PMT-detectors. Here, we demonstrate synthesis of PbS QDs in sizes between 2.4 and 3.2 nm using PbCl 2 , elemental S, dodecanethiol (DT), and a toluene/ oleylamine mixture at low temperatures (65−80 °C). It was shown that addition of DT enhances the solubility of S and DT binds to the crystal surface during the growth, hence reducing the size with enhanced luminescence intensity. Use of toluene as a cosolvent reduces the viscosity and provides an additional reduction in the size. Using these variables, size tunable synthesis of highly luminescent QDs were achieved. Furthermore, we applied additional DT ligand exchange as a postprocess that increases the long-term stability of particles. The photoluminescence lifetime investigation provided insight into the luminescence properties of OLA/DT and DT-capped PbS QDs. Finally, we successfully expanded our synthesis method to the synthesis of small PbSe QDs.

Here, a facile approach to enhance the performance of solar-driven photoelectrochemical (PEC) water splitting is described by means of the synergistic effects of a hybrid network of plasmonic Au nanoparticles (NPs) decorated on multiwalled carbon nanotubes (CNTs). The device based on TiO 2-Au:CNTs hybrid network sensitized with colloidal CdSe/(CdSe x S 1−x) 5 /(CdS) 1 core/alloyed shell quantum dots (QDs) yields a saturated photocurrent density of 16.10 ± 0.10 mA cm −2 [at 1.0 V vs reversible hydrogen electrode (RHE)] under 1 sun illumination (AM 1.5G, 100 mW cm −2), which is ≈26% higher than the control device. The in-depth mechanism behind this significant improvement is revealed through a combined experimental and theoretical analysis for QDs/TiO 2-Au:CNTs hybrid network and demonstrates the multifaceted impact of plasmonic Au NPs and CNTs: i) hot-electron injection from Au NPs into CNTs and TiO 2 ; ii) near-field enhancement of the QDs absorption and carrier generation/separation processes by the plasmonic Au NPs; iii) enhanced photoinjected electron transport due to the highly directional pathways offered by CNTs. These results provide fundamental insights on the properties of QDs/TiO 2-Au:CNTs hybrid network, and highlights the possibility to improve the performance of other solar technologies.

Here, we discuss a simple low temperature process for the synthesis of small and stable PbS/CdS QDs with emission below 1100 nm. For this, small PbS QDs with emission below 1100 nm synthesized from PbCl 2 in oleylamine with 1-dodecanethiol, as reported by our group recently, were used. A thin CdS shell was grown on PbS at room temperature (RT) via cation exchange (CE), which is a self-limiting process providing about 100 nm blue shift in the emission maxima, hence is quite practical for reaction control and production of predictable particles. RTCE process provides 6−9 times stronger emission than original PbS with better optical stability. Annealing of the PbS/CdS QDs in solid state at mild temperatures (50−100 °C) improves crystallinity of the particles. Final ligand exchange on the annealed PbS/CdS with 1-dodecanethiol (DT) enhances the long-term stability of particles further. The optimum overall process is determined as RTCE followed by annealing at 50 °C for 1 h and finished with ligand exchange with DT. Influence of these processes on QD structure and optical properties were studied as well as stability in chloroform and petroleum products (diesel and gasoline) for possible optical tagging applications of such liquids. Overall, a simple, controllable, and scalable method is developed to produce highly stable, bright, size-tunable PbS/CdS QDs with emission detectable with low cost semiconductor detectors.

We demonstrate amplified spontaneous emission (ASE) in solution with ultralow thresholds of 30 μJ/cm 2 in red and of 44 μJ/cm 2 in green from engineered colloidal quantum well (CQW) heterostructures. For this purpose, CdSe/CdS core/crown CQWs, designed to hit the green region, and CdSe/CdS@Cd x Zn 1−x S core/crown@gradient-alloyed shell CQWs, further tuned to reach the red region by shell alloying, were employed to achieve highperformance ASE in the visible range. The net modal gain of these CQWs reaches 530 cm −1 for the green and 201 cm −1 for the red, 2−3 orders of magnitude larger than those of colloidal quantum dots (QDs) in solution. To explain the root cause for ultrahigh gain coefficient in solution, we show for the first time that the gain cross sections of these CQWs is ≥3.3 × 10 −14 cm 2 in the green and ≥1.3 × 10 −14 cm 2 in the red, which are two orders of magnitude larger compared to those of CQDs.