Colloidal lead halide perovskite nanocrystals (NCs) have recently emerged as versatile photonic sources. Their processing and optoelectronic applications are hampered by the loss of colloidal stability and structural integrity due to the facile desorption of surface capping molecules during isolation and purification. To address this issue, herein, we propose a new ligand capping strategy utilizing common and inexpensive long-chain zwitterionic molecules such as 3-(N,N-dimethyloctadecylammonio)propanesulfonate, resulting in much improved chemical durability. In particular, this class of ligands allows for the isolation of clean NCs with high photoluminescence quantum yields (PL QYs) of above 90% after four rounds of precipitation/redispersion along with much higher overall reaction yields of uniform and colloidal dispersible NCs. Densely packed films of these NCs exhibit high PL QY values and effective charge transport. Consequently, they exhibit photoconductivity and low thresholds for amplified spontaneous emission of 2 μJ cm–2 under femtosecond optical excitation and are suited for efficient light-emitting diodes.

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The spatial localization of charge carriers to promote the formation of bound excitons and concomitantly enhance radiative recombination has long been a goal for luminescent semiconductors. Zero‐dimensional materials structurally impose carrier localization and result in the formation of localized Frenkel excitons. Now the fully inorganic, perovskite‐derived zero‐dimensional SnII material Cs4SnBr6 is presented that exhibits room‐temperature broad‐band photoluminescence centered at 540 nm with a quantum yield (QY) of 15±5 %. A series of analogous compositions following the general formula Cs4−xAxSn(Br1−yIy)6 (A=Rb, K; x≤1, y≤1) can be prepared. The emission of these materials ranges from 500 nm to 620 nm with the possibility to compositionally tune the Stokes shift and the self‐trapped exciton emission bands.

bolometric detectors, owing to advancements in MEMS-technologies (Micro-Electro-Mechanical Systems) 6,7 , have already entered the consumer electronics market, and are able to record thermal images with both high speed and high resolution. However, their thermographic performance, based on measurements of IR radiation intensity, is inherently limited by the transparency and emissivity/reflectivity of an observed object and, more importantly, by any material and medium (window, coating, matrix, solvent etc.) situated within the path between the detector and an object ( Fig. 1). As one of the major consequences, IR thermography cannot be easily combined with conventional optical microscopy or other enclosed optical systems such as cryostats or microfluidic cells.An alternative method for remote thermography, which is unhindered by enclosures or IRabsorptive media, utilizes temperature sensitive luminophores (i.e. fluorophores or phosphors) with PL in the visible spectral range (Fig. 1c) that are deposited onto, or incorporated into, the object of interest as temperature probes [8][9][10][11][12][13][14][15][16] . To probe an object's temperature, the luminophore is then excited by an ultraviolet or visible (UV-Vis) pulsed source (e.g. laser or light-emitting diode) and the temperature-dependent PL lifetime decay is then analyzed by time-resolving detectors.This PL-lifetime approach exhibits several benefits: the excitation power and, consequently the PL intensity, can be adjusted to a value appropriate for the dynamic range of the detector.Additionally, the use of UV-Vis light, rather than mid-to long-wavelength IR radiation, allows for the direct integration of this method with conventional optical spectroscopy and microscopy applied in biological studies and materials research. Furthermore, higher spatial resolutions can be obtained with visible light (400-700 nm) as the diffraction-limit is ca. 20-times sharper than for LWIR (7-14 µm); this potentially extends the utility of remote thermography to intracellular, in vitro, and in vivo studies 17 .

Interest in hybrid organic-inorganic lead halide compounds with perovskite-like two-dimensional crystal structures is growing due to the unique electronic and optoelectronic properties of these compounds. Herein, we demonstrate the synthesis, thermal and optical properties, and calculations of the electronic band structures for one- and two-layer compounds comprising both cesium and guanidinium cations: Cs[C(NH)]PbI (I), Cs[C(NH)]PbBr (II), and Cs[C(NH)]PbBr (III). Compounds I and II exhibit intense photoluminescence at low temperatures, whereas compound III is emissive at room temperature. All of the obtained substances are stable in air and do not thermally decompose until 300 °C. Since Cs and C(NH) are increasingly utilized in precursor solutions for depositing polycrystalline lead halide perovskite thin films for photovoltaics, exploring possible compounds within this compositional space is of high practical relevance to understanding the photophysics and atomistic chemical nature of such films.

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.

Lead halide perovskites of APbX3 type [A = Cs, formamidinium (FA), methylammonium; X = Br, I] in the form of ligand-capped colloidal nanocrystals (NCs) are widely studied as versatile photonic sources. FAPbBr3 and CsPbBr3 NCs have become promising as spectrally narrow green primary emitters in backlighting of liquid-crystal displays (peak at 520–530 nm, full width at half-maximum of 22–30 nm). Herein, we report that wet ball milling of bulk APbBr3 (A = Cs, FA) mixed with solvents and capping ligands yields green luminescent colloidal NCs with a high overall reaction yield and optoelectronic quality on par with that of NCs of the same composition obtained by hot-injection method. We emphasize the superiority of oleylammonium bromide as a capping ligand used for this procedure over the standard oleic acid and oleylamine. We also show a mechanically induced anion-exchange reaction for the formation of orange-emissive CsPb(Br/I)3 NCs.

The Landé or g-factors of charge carriers are decisive for the spin-dependent phenomena in solids and provide also information about the underlying electronic band structure. We present a comprehensive set of experimental data for values and anisotropies of the electron and hole Landé factors in hybrid organic-inorganic (MAPbI3, MAPb(Br0.5Cl0.5)3, MAPb(Br0.05Cl0.95)3, FAPbBr3, FA0.9Cs0.1PbI2.8Br0.2, MA=methylammonium and FA=formamidinium) and all-inorganic (CsPbBr3) lead halide perovskites, determined by pump-probe Kerr rotation and spin-flip Raman scattering in magnetic fields up to 10 T at cryogenic temperatures. Further, we use first-principles density functional theory (DFT) calculations in combination with tight-binding and k ⋅ p approaches to calculate microscopically the Landé factors. The results demonstrate their universal dependence on the band gap energy across the different perovskite material classes, which can be summarized in a universal semi-phenomenological expression, in good agreement with experiment.