The narrow, near infrared (NIR) emission from lanthanide ions has attracted great interest, particularly with regard to developing tools for bioimaging, where the long lifetimes of lanthanide excited states can be exploited to address problems arising from autofluorescence and sample transparency. Despite the promise of lanthanide-based probes for near-IR imaging, few reports on their use are present in the literature. Here, we demonstrate that images can be recorded by monitoring NIR emission from lanthanide complexes using detectors, optical elements and a microscope that were primarily designed for the visible part of the spectrum.

Organic−inorganic metal halide perovskites have recently attracted increasing attention as highly efficient light harvesting materials for photovoltaic applications. The solution processability of these materials is one of their major advantages on the route toward fabrication of low-cost solar cells and optoelectronic devices. However, the precise control of crystallization and morphology of organometallic perovskites deposited from solutions, considered crucial for enhancing the final photovoltaic performance, still remains challenging. In this context, here, we report on growing microcrystalline deposits of methylammonium lead triiodide perovskite, CH3NH3PbI3 (MAPbI3), by one-step solution casting on cylinder-shaped quartz substrates (rods) having diameters in the range of 80 to 1800 μm. We show that the substrate curvature has a strong influence on morphology of the obtained polycrystalline deposits of MAPbI3. Specifically, a marked size reduction of MAPbI3 microcrystallites concomitant with an increased crystal packing density was observed with increasing the substrate curvatures. In contrast, although the crystallite width and length markedly decreased for substrates with higher curvatures, the photoluminescence (PL) spectral peak positions did not significantly evolve for MAPbI3 deposits on substrates with different diameters. The crystallite size reduction and a denser coverage of microcrystalline MAPbI3 deposits on cylinder-shaped substrates with higher curvatures were attributed to two major contributions, both related to the annealing step of the MAPbI3 deposits. In particular, the diameter-dependent variability of the heat capacities and the substrate curvature-enhanced solvent evaporation rate seemed to contribute the most to the crystallization process and the resulting morphology changes of MAPbI3 deposits on cylinder-shaped quartz substrates with various diameters. The longitudinal geometry of cylinder-shaped substrates provided also a facile solution for checking the PL response of the deposits of MAPbI3 exposed to the flow of various gaseous media, such as oxygen (O2), nitrogen (N2), and argon (Ar). Specifically, under excitation with λexc = 546 nm, the rapid and pronounced decreases and increases of PL signals were observed under intermittent subsequent exposures to O2 and N2, respectively. Overall, the approach reported herein inspires novel, cylinder-shaped geometries of MAPbI3 deposits, which can find applications in low-cost photo-optical devices, including gas sensors.

Because of their excellent photoelectric properties, organic−inorganic metal halide perovskites (MHPs), such as methylammonium lead triiodide, CH 3 NH 3 PbI 3 (MAPbI 3 ), and methylammonium lead tribromide, CH 3 NH 3 PbBr 3 (MAPbBr 3 ), are of great interest for the emerging MHPs-based photovoltaic technology. Despite extensive research efforts focused on physicochemical aspects of both MAPbI 3 and MAPbBr 3 , the impact of environmental extremes, including various gaseous media, on their photoelectric properties remains poorly understood. In this context, here, the MHPs-based gas-sensing elements were grown by one-step solution process on the outer surface of cylindrical in shape quartz substrates with diameters varying in the range of 80−1100 μm. The elongated cylinder-shaped geometry and high surface-to-volume ratios of the thus-prepared deposits revealed advantageous for designing miniature, light-transparent gas-flow chambers and made it possible to investigate the photoluminescence (PL) and photocurrent (PC) responses of both MHPs exposed to the precisely controlled recurrent flow of either O 2 or N 2 . In addition, we could also collect the PL responses for the deposits of MAPbI 3 and MAPbBr 3 , positioned side-by-side close to each other and therefore simultaneously exposed to identical environmental conditions. Specifically, we found that under exposure to O 2 the PL responses of MAPbI 3 and MAPbBr 3 were markedly opposite; i.e., the PL decreased for MAPbI 3 , whereas it increased for MAPbBr 3 . In contrast, under the exposure to N 2 , the PL of MAPbI 3 increased, while it decreased for MAPbBr 3 . A considerably differential behavior was also found for the PC responses. In particular, under recurrent exposures to both gaseous media, the PL and PC responses of MAPbBr 3 correlated, whereas for MAPbI 3 they anticorrelated. In conclusion, the distinctly opposite PL and PC responses of polycrystalline deposits of MAPbI 3 and MAPbBr 3 to O 2 and N 2 reported herein point to markedly contrasting properties of the surface carrier traps and defects for these two MHPs. This study also evidences that a side-by-side arrangement of elongated cylindrically shaped substrates coated with two different MHPs, due to their differential responses to exposure to O 2 or N 2 , can function as a simple differential gas detector.

Optoelectronic devices and solar cells based on organometallic hybrid perovskites have to operate over a broad temperature range, which may contain their structural phase transitions. For instance, the temperature of 330 K, associated with the tetragonal–cubic transformation, may be crossed every day during the operation of solar cells. Therefore, the analysis of thermal cycling effects on structural and electronic properties is of significant importance. This issue is addressed in the case of methylammonium lead iodide (CH3NH3PbI3) across both structural phase transitions (at 160 and 330 K). In situ synchrotron radiation X‐ray diffraction (XRD) data recorded between 140 and 180 K show the emergence of a boundary phase between the orthorhombic and tetragonal phases, which becomes more abundant with successive thermal cycles. At high temperatures, around 330 K, an incommensurately modulated tetragonal phase is formed upon repeated crossings of the phase boundary between tetragonal and cubic phases. These alterations, which indicate a gradual evolution of the material under operating conditions of photovoltaic devices, are further documented by electrical resistivity and heat capacity measurements.

The exotic properties of quantum spin liquids (QSLs) have continually been of interest since Anderson’s 1973 ground-breaking idea. Geometrical frustration, quantum fluctuations, and low dimensionality are the most often evoked material’s characteristics that favor the long-range fluctuating spin state without freezing into an ordered magnet or a spin glass at low temperatures. Among the few known QSL candidates, organic crystals have the advantage of having rich chemistry capable of finely tuning their microscopic parameters. Here, we demonstrate the emergence of a QSL state in [EDT-TTF-CONH2]2+[BABCO−] (EDT-BCO), where the EDT molecules with spin-1/2 on a triangular lattice form layers which are separated by a sublattice of BCO molecular rotors. By several magnetic measurements, we show that the subtle random potential of frozen BCO Brownian rotors suppresses magnetic order down to the lowest temperatures. Our study identifies the relevance of disorder in the stabilization of QSLs.