Developing high-performance visible-to-UV photon upconversion systems based on triplet-triplet annihilation photon upconversion (TTA-UC) is highly desired, as it provides a potential approach for UV light-induced photosynthesis and photocatalysis. However, the quantum yield and spectral range of visible-to-UV TTA-UC based on nanocrystals (NCs) are still far from satisfactory. Here, three different sized CdS NCs are systematically investigated with triplet energy transfer to four mediators and four annihilators, thus substantially expanding the available materials for visibleto-UV TTA-UC. By improving the quality of CdS NCs, introducing the mediator via a direct mixing fashion, and matching the energy levels, a high TTA-UC quantum yield of 10.4% (out of a 50% maximum) is achieved in one case, which represents a record performance in TTA-UC based on NCs without doping. In another case, TTA-UC photons approaching 4 eV are observed, which is on par with the highest energies observed in optimized organic systems. Importantly, the in-depth investigation reveals that the direct mixing approach to introduce the mediator is a key factor that leads to close to unity efficiencies of triplet energy transfer, which ultimately governs the performance of NC-based TTA-UC systems. These findings provide guidelines for the design of high-performance TTA-UC systems toward solar energy harvesting.

BPNSs can be mechanically peeled off from bulk BP crystals using scotch-tape. [37] Although this method can produce high quality 2D BPNSs in a simple and cost-effective manner, the obtained BPNSs show inhomogeneous size, poor repeatability, and extremely low production yield. To obtain BPNSs in a high yield, several alternative methods were employed including metal assisted mechanical exfoliation [102] and exfoliation using polydimethylsiloxane (PDMS) stamp, [70] viscoelastic stamp using blue Nitto tape, [103] and poly(methyl methacrylate)/poly(vinyl alcohol) stack. [104] In another approach, Zhu and co-workers reported a large-scale preparation of relatively stable BPNSs through high energy solid-state mechanical ball milling of bulk BP in the presence of an additive LiOH. [105] The high-energy mechanical milling facilitates the generation of free radicals at the edges by breaking the PP bonds and thus leads to the formation of stable hydroxyl functionalized BPNSs. In addition, this method has been widely utilizing as an efficient method to synthesize functionalized BPNSs for various applications. [106,107] Adv. Sci. 2020, 7, 1902359 3.20-3.73 Å a 1L 2L 3L Bulk Armchair b

Assembling different kinds of 2D nanosheets into heterostructures presents a promising way of designing novel artificial materials with new and improved functionalities by combining the unique properties of each component. In the past few years, black phosphorus nanosheets (BPNSs) have been recognized as a highly feasible 2D material with outstanding electronic properties, a tunable bandgap, and strong in‐plane anisotropy, highlighting their suitability as a material for constructing heterostructures. In this study, recent progress in the construction of BPNS‐based heterostructures ranging from 2D hybrid structures to 3D networks is discussed, emphasizing the different types of interactions (covalent or noncovalent) between individual layers. The preparation methods, optical and electronic properties, and various applications of these heterostructures—including electronic and optoelectronic devices, energy storage devices, photocatalysis and electrocatalysis, and biological applications—are discussed. Finally, critical challenges and prospective research aspects in BPNS‐based heterostructures are also highlighted.

The preparation of a supramolecular nanocomposite containing BODIPY, tryptophan and gold nanoparticles capable of photosensitized generation of singlet oxygen is reported.