No abstract

Polymorphism and anisotropy are fundamental phenomena of crystalline materials. However, the structure-dependent photoluminescent (PL) anisotropy in polymorphic organic crystals has remained unexplored. Herein, two polymorphic nanocrystals, green-emitting nanorods (PtD-g) and yellow-emitting nanoplates (PtD-y), were obtained from a platinum­(II)−β-diketonate complex. The PtD-y crystals display remarkable PL anisotropy with an anisotropy ratio of up to 0.87 whereas the emission of the PtD-g crystals is nearly unpolarized. The polarization properties are rationalized on the different molecular packing of these crystals. By light-harvesting energy transfer, the PtD-y crystals are successfully used to amplify the emission polarization of a red-emitting platinum acceptor (PtA) doped into the donor crystalline matrix, which is otherwise weakly polarized as pure crystals.

Metal halide perovskites have emerged as promising candidates for solution-processed blue light-emitting diodes (LEDs). However, halide phase segregationand the resultant spectral shiftat LED operating voltages hinders their application. Here we report true-blue LEDs employing quasi-two-dimensional cesium lead bromide with a narrow size distribution of quantum wells, achieved through the incorporation of a chelating additive. Ultrafast transient absorption spectroscopy measurements reveal that the chelating agent helps to control the quantum well thickness distribution. Density functional theory calculations show that the chelating molecule destabilizes the lead species on the quantum well surface and that this in turn suppresses the growth of thicker quantum wells. Treatment with γ-aminobutyric acid passivates electronic traps and enables films to withstand 100°C for 24 h without changes to their emission spectrum. LEDs incorporating γ-aminobutyric acid-treated perovskites exhibit blue emission with Commission Internationale de l'Éclairage coordinates of (0.12, 0.14) at an external quantum efficiency of 6.3%.

Real-time visualization of assembly processes and sophisticated signal processing at the nanoscale are two challenging topics in photonic nanomaterials. Here, high-quality light-harvesting crystalline nanorods were developed by the coassembly of two polypyridyl Ir(III) and Ru(II) metallophosphors, behaving as the antenna chromophore and energy acceptor, respectively. By using a one-pot or stepwise growth condition, homogeneous and multiblock heterojunction nanorods were prepared, respectively. These nanostructures display multicolor phosphorescence from green to red due to the efficient triplet energy transfer and light-harvesting capability at low acceptor doping ratios. Heterojunction nanorods show gradient emission-color switches during different growth stages, in which the real-time stepwise assembly can be vividly visualized using fluorescence microscopy techniques. Triplet excitons were successfully manipulated in both homogeneous and heterojunction nanorods to realize waveguided green, orange, and red emissions and advanced photonic signal logics and encoding/decoding on single multiblock heterojunction nanorod.

Metal borides/borates have been considered promising as oxygen evolution reaction catalysts; however, to date, there is a dearth of evidence of long-term stability at practical current densities. Here we report a phase composition modulation approach to fabricate effective borides/borates-based catalysts. We find that metal borides in-situ formed metal borates are responsible for their high activity. This knowledge prompts us to synthesize NiFe-Boride, and to use it as a templating precursor to form an active NiFe-Borate catalyst. This boride-derived oxide catalyzes oxygen evolution with an overpotential of 167 mV at 10 mA/cm2 in 1 M KOH electrolyte and requires a record-low overpotential of 460 mV to maintain water splitting performance for over 400 h at current density of 1 A/cm2. We couple the catalyst with CO reduction in an alkaline membrane electrode assembly electrolyser, reporting stable C2H4 electrosynthesis at current density 200 mA/cm2 for over 80 h.

Highly-ordered GaAs/AlGaAs quantum-dot arrays (QDA) were grown by molecular-beam epitaxy on GaAs (001) using masks of anodic nanochannel alumina (NCA). The QDA replicated the hexagonal lattice pattern of the NCA masks with period spacing of 100 nm. The circular disk-like dots were defined by the nanohole channels of NCA masks with size adjustable between 45 and 85 nm. Both single- and double-well GaAs/AlGaAs QDA exhibited strong photoluminescence. The single-well QDA showed a narrow peak at 1.64 eV with full width at half maximum of only 16 meV, indicating good size uniformity and crystal quality for the QDA. NCA masked epitaxial growth is thus shown to be a promising general approach for fabricating various heterostructure QDA, including both strained and lattice-matched heterostructures.

Electrical‐to‐optical signal conversion is widely employed in information technology and is implemented using on‐chip optical modulators. State‐of‐the‐art modulator technologies are incompatible with silicon manufacturing techniques: inorganic nonlinear crystals such as LiNbO3 are integrated with silicon photonic chips only using complex approaches, and hybrid silicon–LiNbO3 optical modulators show either low bandwidth or high operating voltage. Organic perovskites are solution‐processed materials readily integrated with silicon photonics; and organic molecules embedded within the perovskite scaffold allow in principle for high polarizability. However, it is found that the large molecules required for high polarizability also require an increase of the size of the perovskite cavity: specifically, using the highly polarizable DR2+ (R = H, F, Cl) in the A site necessitates the exploration of new X‐site options. Only by introducing BF4– as the X‐site molecule is it possible to synthesize (DCl)(NH4)(BF4)3, a material exhibiting a linear EO coefficient of 20 pm V–1, which is 10 times higher than that of metal halide perovskites and is a 1.5 fold enhancement compared to reported organic perovskites. The EO response of the organic perovskite approaches that of LiNbO3 (reff ≈ 30 pm V–1) and highlights the promise of rationally designed organic perovskites for use in efficient EO modulators.

Thermal-responsive phosphorescent nanotubes have been fabricated from the co-assembly of two neutral iridium complexes, which behave as the antenna chromophores and energy acceptors, respectively, in these highly ordered crystalline superstructures. By tuning the acceptor doping ratio in a range of 0 to 0.5 %, these tubes display color-tunable phosphorescence from green to red at room temperature, and it is attributed to the highly efficient light-harvesting and energy transfer within these materials. For the same reason, the acceptor emission in the nanotubes is amplified more than 800 times with respect to its pure non-emissive solid sample. The doped tubes show reversible thermal-responsiveness, in which the energy transfer was completely suppressed at 77 K and reactivated at room temperature. These processes were characterized by the in situ emission color (green, orange, and red) and spectral changes and lifetime measurements of isolated nanotubes. The temperature-controlled exciton dynamics are responsible for the luminescent thermochromism in these crystalline materials.