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.
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.
The decay of the majority of radioactive isotopes involves the emission of gamma ( gamma ) photons with energies of 50keV to 10MeV. Detectors of such hard radiation that are low-cost, highly ...sensitive and operate at ambient temperatures are desired for numerous applications in defence and medicine, as well as in research. We demonstrate that 0.3-1cm solution-grown single crystals (SCs) of semiconducting hybrid lead halide perovskites (MAPbI sub(3), FAPbI sub(3) and I-treated MAPbBr sub(3), where MA=methylammonium and FA=formamidinium) can serve as solid-state gamma-detecting materials. This possibility arises from a high charge-carrier mobility-lifetime ( mu tau ) product of 1.0-1.810 super(-2)cm super(2)V super(-1), a low dark carrier density of 10 super(9)-10 super(11)cm super(-3) (refs 3,4), a low density of charge traps of 10 super(9)-10 super(10)cm super(-3) (refs 4,5) and a high absorptivity of hard radiation by the lead and iodine atoms. We demonstrate the utility of perovskite detectors for testing the radiopurity of medical radiotracer compounds such as super(18)F-fallypride. Energy-resolved sensing at room temperature is presented using FAPbI sub(3) SCs and an super(241)Am source.
Formamidinium (FA)-based hybrid lead halide perovskites (FAPbX3 , 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-FAPbI3 , 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 Csx FA1-x PbI3-y Bry (x=0-0.1, y=0-0.6) which exhibit improved phase stability compared to the parent α-FAPbI3 compound. These SCs possess outstanding electronic quality, manifested by a high-carrier mobility-lifetime product of up to 1.2 × 10-1 cm2 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 CsPbX3 (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 CsPbI3 QDs, showcasing the great potential of CsPbX3 QDs as room-temperature highly pure single-photon sources for quantum technologies.
Lead halide perovskite nanocrystals (NCs) have emerged as next‐generation semiconductors capable of unifying superior photoemission properties, facile and inexpensive preparation, compositional and ...structural versatility. Among them, CsPbBr3 is a model system in theoretical and experimental studies owing to its intrinsic chemical stability. Nonetheless, knowledge of the precise magnitude and the size‐ and temperature‐dependent lattice and structural distortions is lacking, and the static/dynamic nature of disorder in NCs remains an open question. Herein, robust reciprocal space X‐ray total scattering analysis is applied and accurate lattice distortions, PbBr bond distances, and PbBrPb angles versus NCs size are extracted. The lattice anisotropy increases upon expansion on downsizing while, upon contraction on cooling, the lattice distortion behaves differently at intermediate (9 nm) and ultrasmall (5 nm) sizes and from the bulk. Bond distances (stretched by ≈1%) do not show any size dependence, whereas equatorial and axial angles denote more symmetric octahedral arrangements in the smallest sizes, where they differ by ≈2° compared to ≈8° in the bulk. Anomalously high atomic displacement parameters of axial bromine ions persisting down to cryogenic temperatures suggest statically disordered octahedral tilts. These results provide insights having important implications on size‐dependent emission properties and the exciton fine structure.
Halide perovskite quantum dots (QDs) are of great interest as novel light sources. Herein, the structural study of CsPbBr3 QDs reveals variations of lattice anisotropy and octahedral tilts over a size range of 5–20 nm and over a temperature range of 6–300 K. The findings are relevant for understanding the size/temperature dependence of the QDs exciton fine structure.
Atomically defined assemblies of dye molecules (such as H and J aggregates) have been of interest for more than 80 years because of the emergence of collective phenomena in their optical spectra
, ...their coherent long-range energy transport, their conceptual similarity to natural light-harvesting complexes
, and their potential use as light sources and in photovoltaics. Another way of creating versatile and controlled aggregates that exhibit collective phenomena involves the organization of colloidal semiconductor nanocrystals into long-range-ordered superlattices
. Caesium lead halide perovskite nanocrystals
are promising building blocks for such superlattices, owing to the high oscillator strength of bright triplet excitons
, slow dephasing (coherence times of up to 80 picoseconds) and minimal inhomogeneous broadening of emission lines
. So far, only single-component superlattices with simple cubic packing have been devised from these nanocrystals
. Here we present perovskite-type (ABO
) binary and ternary nanocrystal superlattices, created via the shape-directed co-assembly of steric-stabilized, highly luminescent cubic CsPbBr
nanocrystals (which occupy the B and/or O lattice sites), spherical Fe
O
or NaGdF
nanocrystals (A sites) and truncated-cuboid PbS nanocrystals (B sites). These ABO
superlattices, as well as the binary NaCl and AlB
superlattice structures that we demonstrate, exhibit a high degree of orientational ordering of the CsPbBr
nanocubes. They also exhibit superfluorescence-a collective emission that results in a burst of photons with ultrafast radiative decay (22 picoseconds) that could be tailored for use in ultrabright (quantum) light sources. Our work paves the way for further exploration of complex, ordered and functionally useful perovskite mesostructures.
We establish the formula representing cubic nanocrystals (NCs) as hard cubes taking into account the role of the ligands and describe how these results generalize to any other NC shapes. We derive ...the conditions under which the hard cube representation breaks down and provide explicit expressions for the effective size. We verify the results from the detailed potential of mean force calculations for two nanocubes in different orientations as well as with spherical nanocrystals. Our results explicitly demonstrate the relevance of certain ligand conformations, i.e., “vortices”, and show that edges and corners provide natural sites for their emergence. We also provide both simulations and experimental results with single component cubic perovskite nanocrystals assembled into simple cubic superlattices, which further corroborate theoretical predictions. In this way, we extend the Orbifold Topological Model (OTM) accounting for the role of ligands beyond spherical nanocrystals and discuss its extension to arbitrary nanocrystal shapes. Our results provide detailed predictions for recent superlattices of perovskite nanocubes and spherical nanocrystals. Problems with existing united atom force fields are discussed.
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