Colloidal quantum wells combine the advantages of size-tunable electronic properties with vast reactive surfaces that could allow one to realize highly emissive luminescent-sensing varnishes capable of detecting chemical agents through their reversible emission response, with great potential impact on life sciences, environmental monitoring, defence and aerospace engineering. Here we combine spectroelectrochemical measurements and spectroscopic studies in a controlled atmosphere to demonstrate the ‘reversed oxygen-sensing’ capability of CdSe colloidal quantum wells, that is, the exposure to oxygen reversibly increases their luminescence efficiency. Spectroelectrochemical experiments allow us to directly relate the sensing response to the occupancy of surface states. Magneto-optical measurements demonstrate that, under vacuum, heterostructured CdSe/CdS colloidal quantum wells stabilize in their negative trion state. The high starting emission efficiency provides a possible means to enhance the oxygen sensitivity by partially de-passivating the particle surfaces, thereby enhancing the density of unsaturated sites with a minimal cost in term of luminescence losses.

Lead halide perovskite nanocrystals (NCs) are emerging as optically active materials for solution-processed optoelectronic devices. Despite the technological relevance of tracing rational guidelines for optimizing their performances and stability beyond their intrinsic resilience to structural imperfections, no in-depth study of the role of selective carrier trapping and environmental conditions on their exciton dynamics has been reported to date. Here we conduct spectro-electrochemical (SEC) experiments, side-by-side to oxygen sensing measurements on CsPbBr NCs for the first time. We show that the application of EC potentials controls the emission intensity by altering the occupancy of defect states without degrading the NCs. Reductive potentials lead to strong (60%) emission quenching by trapping of photogenerated holes, whereas the concomitant suppression of electron trapping is nearly inconsequential to the emission efficiency. Consistently, oxidizing conditions result in minor (5%) brightening due to suppressed hole trapping, confirming that electron traps play a minor role in nonradiative decay. This behavior is rationalized through a model that links the occupancy of trap sites with the position of the NC Fermi level controlled by the EC potential. Photoluminescence measurements in controlled atmosphere reveal strong quenching by collisional interactions with O, which is in contrast to the photobrightening effect observed in films and single crystals. This indicates that O acts as a scavenger of photoexcited electrons without mediation by structural defects and, together with the asymmetrical SEC response, suggests that electron-rich defects are likely less abundant in nanostructured perovskites than in the bulk, leading to an emission response dominated by direct interaction with the environment.

The latest trend in solar cell technology is to develop photon managing processes that adapt the solar emission to the spectral range at which the devices show the largest intrinsic effi ciency. Triplet-triplet annihilationassisted photon upconversion (sTTA-UC) is currently the most promising process to blue-shift sub-bandgap photons at solar irradiance, even if the narrow absorption band of the employed chromophores limits its application. In this work, we demonstrate how to obtain broadband sTTA-UC at sub-solar irradiance, by enhancing the system's light-harvesting ability by way of an ad-hoc synthesized family of chromophores with complementary absorption properties. The overall absorptance is boosted, thus doubling the number of upconverted photons and signifi cantly reducing the irradiance required to achieve the maximum upconversion yield. An outstanding yield of ≈10% is obtained under broadband air mass (AM) 1.5 conditions, which allows a DSSC device to operate by exploiting exclusively sub-bandgap photons.

Excimers are evanescent quasi-particles that typically form during collisional intermolecular interactions and exist exclusively for their excited-state lifetime. We exploited the distinctive structure of metal quantum clusters to fabricate permanent excimer-like colloidal superstructures made of ground-state noninteracting gold cores, held together by a network of hydrogen bonds between their capping ligands. This previously unknown aggregation state of matter, studied through spectroscopic experiments and ab initio calculations, conveys the photophysics of excimers into stable nanoparticles, which overcome the intrinsic limitation of excimers in single-particle applications-that is, their nearly zero formation probability in ultra-diluted solutions. In vitro experiments demonstrate the suitability of the superstructures as nonresonant intracellular probes and further reveal their ability to scavenge reactive oxygen species, which enhances their potential as anticytotoxic agents for biomedical applications.

Sensitized triplet–triplet annihilation based photon up‐conversion (TTA‐UC) greatly improves the scope and applicability of fluorescence bioimaging by enabling anti‐Stokes detection at low powers, thus eliminating the background autofluorescence and limiting the potential damage of the living tissues. Here the authors present a facile, one‐step protocol to prepare dual dye‐doped, TTA‐UC active nanomicelles starting from the commercially available surfactant Kolliphor EL, a component of several FDA approved preparations. These nanosized micelles show an unprecedented up‐conversion yield of 6.5% under 0.1 W cm−2 excitation intensity in an aqueous, nondeaerated dispersion. The supramolecular architecture obtained preserves the embedded dyes from oxygen quenching, allowing satisfactory anti‐Stokes fluorescence imaging of 3T3 cells. This is the first example of efficient multicomponent up‐converters prepared using highly biocompatible materials approved by the international authority, paving the way for the development of new complex and multifunctional materials for advanced theranostics.