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Finding narrow-band light emitters for the visible spectral region remains an immense challenge. Such phosphors are in great demand for solid-state lighting and display application. In this context, green luminescence from tetrahedrally coordinated Mn(II) is an attractive research direction. While the oxide–ligand environment had been studied for decades, much less systematic efforts have been undertaken with regard to halide coordination, especially in the form of fully inorganic halide matrixes. In this study, we synthesized a series of hybrid organic–inorganic Mn(II) halides as well as a range of fully inorganic Zn halide hosts (chlorides, bromides, iodides) doped with Mn(II). In the latter, tetrahedral coordination is attained via substitutional doping owing to the tetrahedral symmetry of Zn sites. We find that the choice of the halide as well as subtle details of the crystal structure profoundly govern the photoluminescence peak positions (500–550 nm range) and emission line widths (40–60 nm) as well as radiative lifetimes (shorter for iodides) through the altered ligand-field effects and degrees of spin–orbit coupling. The photoluminescence quantum yields were as high as 70–90%. The major hurdle for the practical use of these compounds lies in their low absorption coefficients in the blue spectral regions.

For over 80 years, tailored molecular assemblies (e.g., H-and J-aggregates) have been of interest for the emergence of collective phenomena in their optical spectra 1 , coherent long-range energy transport 2,3 and their conceptual similarity with natural light-harvesting complexes 4,5 . Another highly versatile platform for creating controlled, aggregated states exhibiting collective phenomena arises from the organization of colloidal semiconductor nanocrystals (NCs) into long-range ordered superlattices (SLs) 6 . Cesium lead halide perovskite NCs 7-9 have recently emerged as highly appealing building blocks, owing to their high oscillator strength 10 , slow dephasing (long coherence times of up to 80 ps) 11,12 , minimal inhomogeneous broadening of emission lines, and a bright triplet exciton character with orthogonal dipole orientation 10 , potentially enabling an efficient omnidirectional coupling. Here we present perovskite-type (ABO3) binary and ternary NC SLs by a shapedirected co-assembly of steric-stabilized, highly luminescent cuboid-shaped CsPbBr3 NCs (occupying B-and/or O-sites) with spherical Fe3O4 or NaGdF4 NCs (A-sites) and truncated-cuboid PbS NCs (B-site). Such ABO3 SLs, as well as other newly obtained SL structures (binary NaCl-and AlB2-types), exhibit a high degree of orientational ordering of CsPbBr3 nanocubes. These novel perovskite mesostructures exhibit superfluorescence (SF) -a collective emission resulting in a burst of photons. SF is characterized, at high excitation density, by emission pulses with ultrafast (22 ps) radiative decay and Burnham-Chiao ringing behaviour with a strongly accelerated build-up time.

Formamidinium (FA)-based hybrid lead halide perovskites (FAPbX 3 , X = I or Br/I) have recently led to significant improvements in the performance of perovskite photovoltaics. The remaining major pitfall is the instability of α-FAPbI 3 , causing the phase transition from the desired three-dimensional cubic perovskite phase to a non-perovskite one-dimensional hexagonal lattice. In this work, we report the facile, inexpensive, solution-phase growth of cm-scale single crystals (SCs) of variable composition Cs x FA 1 − x PbI 3 − y Br y (x = 0-0.1, y = 0-0.6) which exhibit improved phase stability compared to the parent α-FAPbI 3 compound. These SCs possess outstanding electronic quality, manifested by a high-carrier mobility-lifetime product of up to 1.2 × 10 − 1 cm 2 V − 1 and a low dark carrier density that, combined with the high absorptivity of high-energy photons by Pb and I, allows the sensitive detection of gamma radiation. With stable operation up to 30 V, these novel SCs have been used in a prototype of a gamma-counting dosimeter.

Attaining pure single-photon emission is key for many quantum technologies, from optical quantum computing to quantum key distribution and quantum imaging. The past 20 years have seen the development of several solid-state quantum emitters, but most of them require highly sophisticated techniques (e.g., ultrahigh vacuum growth methods and cryostats for low-temperature operation). The system complexity may be significantly reduced by employing quantum emitters capable of working at room temperature. Here, we present a systematic study across ∼170 photostable single CsPbX 3 (X: Br and I) colloidal quantum dots (QDs) of different sizes and compositions, unveiling that increasing quantum confinement is an effective strategy for maximizing single-photon purity due to the suppressed biexciton quantum yield. Leveraging the latter, we achieve 98% single-photon purity (g (2) (0) as low as 2%) from a cavity-free, nonresonantly excited single 6.6 nm CsPbI 3 QDs, showcasing the great potential of CsPbX 3 QDs as room-temperature highly pure single-photon sources for quantum technologies.

Traditional fluorescence-based tags, used for anticounterfeiting, rely on primitive pattern matching and visual identification; additional covert security features such as fluorescent lifetime or pattern masking are advantageous if fraud is to be deterred. Herein, we present an electrohydrodynamically printed unicolour multi-fluorescent-lifetime security tag system composed of lifetime-tunable lead-halide perovskite nanocrystals that can be deciphered with both existing time-correlated single-photon counting fluorescence-lifetime imaging microscopy and a novel time-of-flight prototype. We find that unicolour or matching emission wavelength materials can be prepared through cation-engineering with the partial substitution of formamidinium for ethylenediammonium to generate “hollow” formamidinium lead bromide perovskite nanocrystals; these materials can be successfully printed into fluorescence-lifetime-encoded-quick-read tags that are protected from conventional readers. Furthermore, we also demonstrate that a portable, cost-effective time-of-flight fluorescence-lifetime imaging prototype can also decipher these codes. A single comprehensive approach combining these innovations may be eventually deployed to protect both producers and consumers.

Herein we demonstrate that solution-grown single crystals of semiconducting methylammonium lead halide perovskites (MAPbX 3 , where MA = CH 3 NH 3 + , X = Cl − , Br − and Br/I − ) can be used as semiconductor absorbers for full-colour imaging. A one-pixel photodetector prototype was constructed by stacking three layers of blue-, green-and red-sensitive MAPbCl 3 , MAPbBr 3 and MAPb(Br/I) 3 crystals, respectively. The prototype detector was demonstrated to recognize and faithfully reproduce coloured images by recombination of the signals from each individual colour channel. This layered structure concept, besides imparting a two-to three-fold reduction in the number of required pixels, also offers several other advantages over conventional technologies: three times more efficient light utilization (and thus higher sensitivity) than common Bayer scheme devices based on dissipative optical filters, colour moiré suppression and no need for de-mosaic image processing. In addition, the direct band gap structure of perovskites results in optical absorption that is several orders of magnitude greater than silicon. This opens a promising avenue towards the reduction of pixel-size in next-generation devices as compared with conventional silicon-based technologies.