Although metal-halide perovskites have recently revolutionized research in optoelectronics through a unique combination of performance and synthetic simplicity, their low-dimensional counterparts can ...further expand the field with hitherto unknown and practically useful optical functionalities. In this context, we present the strong temperature dependence of the photoluminescence lifetime of low-dimensional, perovskite-like tin-halides and apply this property to thermal imaging. The photoluminescence lifetimes are governed by the heat-assisted de-trapping of self-trapped excitons, and their values can be varied over several orders of magnitude by adjusting the temperature (up to 20 ns °C
). Typically, this sensitive range spans up to 100 °C, and it is both compound-specific and shown to be compositionally and structurally tunable from -100 to 110 °C going from C(NH
)
SnBr
to Cs
SnBr
and (C
N
H
I)
SnI
. Finally, through the implementation of cost-effective hardware for fluorescence lifetime imaging, based on time-of-flight technology, these thermoluminophores have been used to record thermographic videos with high spatial and thermal resolution.
Colloidal lead halide perovskite nanocrystals (NCs) have recently emerged as a novel class of bright emitters with pure colors spanning the entire visible spectral range. Contrary to conventional ...quantum dots, such as CdSe and InP NCs, perovskite NCs feature unusual, defect-tolerant photophysics. Specifically, surface dangling bonds and intrinsic point defects such as vacancies do not form midgap states, known to trap carriers and thereby quench photoluminescence (PL). Accordingly, perovskite NCs need not be electronically surface-passivated (with, for instance, ligands and wider-gap materials) and do not noticeably suffer from photo-oxidation. Novel opportunities for their preparation therefore can be envisaged. Herein, we show that the infiltration of perovskite precursor solutions into the pores of mesoporous silica, followed by drying, leads to the template-assisted formation of perovskite NCs. The most striking outcome of this simple methodology is very bright PL with quantum efficiencies exceeding 50%. This facile strategy can be applied to a large variety of perovskite compounds, hybrid and fully inorganic, with the general formula APbX3, where A is cesium (Cs), methylammonium (MA), or formamidinium (FA), and X is Cl, Br, I or a mixture thereof. The luminescent properties of the resulting templated NCs can be tuned by both quantum size effects as well as composition. Also exhibiting intrinsic haze due to scattering within the composite, such materials may find applications as replacements for conventional phosphors in liquid-crystal television display technologies and in related luminescence down-conversion-based devices.
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.
Fully inorganic, perovskite‐derived zero‐dimensional Cs4SnBr6 exhibits room‐temperature broad‐band photoluminescence from self‐trapped excitons, centered at 540 nm with a quantum yield of 15±5 % (298 K; near 100 % at 200 K), and a large Stokes shift of ca.1.2 eV. A compositional series, Cs4−xAxSn(Br1−yIy)6 (A=Rb, K; x≤1, y≤1), was obtained wherein the emission peak ranges from 500 nm to 620 nm.
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.
Colloidal lead halide perovskite nanocrystals are of interest as photoluminescent quantum dots (QDs) whose properties depend on the size and shape. They are normally synthesized on subsecond time ...scales through hard-to-control ionic metathesis reactions. We report a room-temperature synthesis of monodisperse, isolable, spheroidal APbBr
3
QDs (“A” indicates cesium, formamidinium, and methylammonium) that are size tunable from 3 to >13 nanometers. The kinetics of both nucleation and growth are temporally separated and substantially slowed down by the intricate equilibrium between the precursor (PbBr
2
) and the APbBr
3
solute, with the latter serving as a monomer. QDs of all these compositions exhibit up to four excitonic transitions in their linear absorption spectra, and we demonstrate that the size-dependent confinement energy for all transitions is independent of the A-site cation.
Slowing nanoparticle growth
Inorganic materials with more covalent bonding, such as cadmium selenide, form uniform nanoparticles under fast growth conditions, but perovskites such as cesium lead bromide (CsPbBr
3
) are more ionic and grow rapidly to form larger nanoparticles. Akkerman
et al
. controlled the nanoparticles’ growth kinetics by using trioctylphosphine oxide, which solubilized the PbBr
2
precursor, bound to the cation-PbBr
3
monomer (solute), and weakly coordinated to the crystal nuclei surfaces. Nanoparticles with diameters from 3 to 13 nanometers were stabilized and isolated in high yield with lecithin, a long-chain zwitterion. Four well-resolved excitonic transitions with size-dependent confinement energies were seen for cesium as well as organic cations. —PDS
Monodisperse lead-halide perovskite nanocrystals are synthesized through slow and temporally separated nucleation and growth.
Lead-halide perovskite APbX3 (A = Cs or organic cation; X = Cl, Br, I) nanocrystals (NCs) are the subject of intense research due to their exceptional characteristics as both classical and quantum ...light sources. Many challenges often faced with this material class concern the long-term optical stability, a serious intrinsic issue connected with the labile and polar crystal structure of APbX3 compounds. When conducting spectroscopy at a single particle level, due to the highly enhanced contaminants (e.g., water molecules, oxygen) over the NC ratio, deterioration of NC optical properties occurs within tens of seconds with typically used excitation power densities (1–100 W/cm2) and in ambient conditions. Here, we demonstrate that choosing a suitable polymer matrix is of paramount importance for obtaining stable spectra from a single NC and for suppressing the dynamic photoluminescence blueshift. In particular, polystyrene (PS), the most hydrophobic among four tested polymers, leads to the best optical stability, one to two orders of magnitude higher than that obtained with poly(methyl methacrylate), a common polymeric encapsulant containing polar ester groups. Molecular mechanics simulations based on a force-field approximation corroborate the hypothesis that PS affords for a denser molecular packing at the NC surface. These findings underscore the often-neglected role of the sample preparation methodologies for the assessment of the optical properties of perovskite NCs at a single-particle level and guide the further design of robust single photon sources.
Abstract
The lead halide perovskites demonstrate huge potential for optoelectronic applications, high energy radiation detectors, light emitting devices and solar energy harvesting. Those materials ...exhibit strong spin-orbit coupling enabling efficient optical orientation of carrier spins in perovskite-based devices with performance controlled by a magnetic field. Here we show that elaborated time-resolved spectroscopy involving strong magnetic fields can be successfully used for perovskites. We perform a comprehensive study of high-quality lead halide perovskite CsPbBr
3
crystals by measuring the exciton and charge carrier
g
-factors, spin relaxation times and hyperfine interaction of carrier and nuclear spins by means of coherent spin dynamics. Owing to their ‘inverted’ band structure, perovskites represent appealing model systems for semiconductor spintronics exploiting the valence band hole spins, while in conventional semiconductors the conduction band electrons are considered for spin functionality.
Lead halide perovskites (CH3NH3PbX3, where X = I, Br) and other metal halide complexes (MX n , where M = Pb, Cd, In, Zn, Fe, Bi, Sb) have been studied as inorganic capping ligands for colloidal ...nanocrystals. We present the methodology for the surface functionalization via ligand-exchange reactions and the effect on the optical properties of IV–VI, II–VI, and III–V semiconductor nanocrystals. In particular, we show that the Lewis acid–base properties of the solvents, in addition to the solvent dielectric constant, must be properly adjusted for successful ligand exchange and colloidal stability. High luminescence quantum efficiencies of 20–30% for near-infrared emitting CH3NH3PbI3-functionalized PbS nanocrystals and 50–65% for red-emitting CH3NH3CdBr3- and (NH4)2ZnCl4-capped CdSe/CdS nanocrystals point to highly efficient electronic passivation of the nanocrystal surface.
In the past years, halide capping became one of the most promising strategies to passivate the surface of colloidal quantum dots (CQDs) in thin films to be used for electronic and optoelectronic ...device fabrication. This is due to the convenient processing, strong n-type characteristics, and ambient stability of the devices. Here, we investigate the effect of three counterions (ammonium, methylammonium, and tetrabutylammonium) in iodide salts used for treating CQD thin films and shed light on the mechanism of the ligand exchange. We obtain two- and three-dimensional square-packed PbS CQD superlattices with epitaxial merging of nearest neighbor CQDs as a direct outcome of the ligand-exchange reaction and show that the order in the layer can be controlled by the nature of the counterion. Furthermore, we demonstrate that the acidity of the environment plays an important role in the substitution of the carboxylates by iodide ions at the surface of lead chalcogenide quantum dots. Tetrabutylammonium iodide shows lower reactivity compared to methylammonium and ammonium iodide due to the nonacidity of the cation, which eventually leads to higher order but also poorer carrier transport due to incomplete removal of the pristine ligands in the QD thin film. Finally, we show that single-step blade-coating and immersion in a ligand exchange solution such as the one containing methylammonium iodide can be used to fabricate well performing bottom-gate/bottom-contact PbS CQD field effect transistors with record subthreshold swing.
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