High-resolution remote thermography using luminescent low-dimensional tin-halide perovskites

While 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 (PL) lifetime of low-dimensional, perovskite-like tin-halides, and apply this property to thermal imaging with a high precision of 0.05 {\deg}C. The PL 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 {\deg}C-1). Typically, this sensitive range spans up to one hundred centigrade, and it is both compound-specific and shown to be compositionally and structurally tunable from -100 to 110 {\deg} C going from [C(NH2)3]2SnBr4 to Cs4SnBr6 and (C4N2H14I)4SnI6. Finally, through the innovative implementation of cost-effective hardware for fluorescence lifetime imaging (FLI), based on time-of-flight (ToF) technology, these novel thermoluminophores have been used to record thermographic videos with high spatial and thermal resolution.Comment: 25 pages, 4 figure

Lead-Free Low-Dimensional Main Group Metal Halides: New Self-Trapped Excitonic Emitters and Their Applications

Metal-halide based semiconductors have been in the limelight for the past few years as a result of the outstanding performance of devices in a variety of optoelectronic applications utilizing lead-halide perovskites. Lead-free materials based on Sb, Sn, or Bi with a three-dimensional (3D) framework, on the other hand, have yet to provide a true alternative. This thesis instead explores the field of low-dimensional, specifically zero-dimensional (0D), lead-free metal-halides as luminescent materials. These 0D materials contain disconnected metal-halide octahedra, which drastically alters their optoelectronic properties compared to fully connected 3D structures and, prior to 2017, the library of such 0D metal-halides was exceedingly small. This work began with the study of the optical properties of one known yet uninvestigated incongruently melting phase — Cs4SnBr6. This material was found to exhibit broad yet efficient room temperature photoluminescence (RT PL), which occurs as a result of the recombination of self-trapped excitons (STEs). The STE emission in this phase was then found to be compositionally tunable within the Cs4-xAxSn(Br1-yIy)6 (A=Rb,K; x,y≤1) family. The discovery of this and other phases by the community prompted a closer look at the optical properties of various additional Sn-based 0D and 1D materials such as (C4H14N2I)4SnI6 and [C(CH2)3]2SnBr4. In doing so, it became evident that their PL lifetimes were extremely temperature dependent (~ 20 ns/K). This opened the door to using 0D metal-halides as remote-optical thermometric and thermographic luminophores i.e. materials which can be used to optically determine temperature. In addition to this thermal sensitivity, this emission process was found to be intrinsic and incredibly robust with no changes to the PL lifetime observed between synthetic batches or after partial degradation or partial oxidation. These two factors together allowed for a thermometric precision of ±13 mK. Although this was quite impressive, the fact of the matter remained that these are still tin-based materials and they will, inevitably, fully oxidize. This inspired the dimensional reduction of the pnictogen halides to discover new, oxidatively stable 0D materials for remote-optical thermometry. This resulted in the Rb7Bi3-3xSb3xCl16 (x≤1) family of materials, which also exhibit STE PL with a similar thermal sensitivity as the tin-based materials. Furthermore, these structures contain edge-shared octahedral dimers, which were determined to be the source of RT PL and the luminescent properties of structures containing them have not been previously investigated. This work also led to the discovery of a new set of mixed-valent materials with the composition Rb23MIII7SbV2Cl54 (MIII = Bi, Sb). These 0D structures contain octahedra of with xi various oxidation states (3+ and 5+) and exhibit intense colors as a result of intervalent/mixed-valent charge transfer. While non-luminescent even at 12 K, these materials do exhibit relatively high mobility-lifetime products under X-ray illumination, suggesting that the site-to-site tunneling through this structure may provide a potentially useful tool for new X-ray and hard-radiation detector materials. In summary, the work presented here has resulted in several, substantial contributions to the low-dimensional metal-halide community, which include the synthesis and characterization of several new materials as well as the identification and successful demonstration of remote-optical thermometry/thermography as a new application for this class of materials. This dissertation serves as an effective foundation for further research in the field by giving other researchers an overview of the field as well as insights into potentially interesting avenues for investigation, both for materials as well as possible applications

Efficient Lone-Pair-Driven Luminescence: Structure–Property Relationships in Emissive 5s2 Metal Halides

Low-dimensional metal halides have been the focus of intense investigations in recent years following the success of hybrid lead halide perovskites as optoelectronic materials. In particular, the light emission of low-dimensional halides based on the 5s2 cations Sn2+ and Sb3+ has found utility in a variety of applications complementary to those of the three-dimensional halide perovskites because of its unusual properties such as broadband character and highly temperature-dependent lifetime. These properties derive from the exceptional chemistry of the 5s2 lone pair, but the terminology and explanations given for such emission vary widely, hampering efforts to build a cohesive understanding of these materials that would lead to the development of efficient optoelectronic devices. In this Perspective, we provide a structural overview of these materials with a focus on the dynamics driven by the stereoactivity of the 5s2 lone pair to identify the structural features that enable strong emission. We unite the different theoretical models that have been able to explain the success of these bright 5s2 emission centers into a cohesive framework, which is then applied to the array of compounds recently developed by our group and other researchers, demonstrating its utility and generating a holistic picture of the field from the point of view of a materials chemist. We highlight those state-of-the-art materials and applications that demonstrate the unique capabilities of these versatile emissive centers and identify promising future directions in the field of low-dimensional 5s2 metal halides

White CsPbBr 3

Inorganic lead halide perovskites have gained immense scientific interest for optoelectronic applications. In this work, we present a one‐dimensional polymorph of cesium lead bromide (δ‐CsPbBr3) synthesized through a simple anion‐exchange reaction, wherein distorted edge‐sharing PbBr6 octahedra form 1D chains isolated by Cs ions. δ‐CsPbBr3 was characterized by Raman spectroscopy, X‐ray diffraction, 207Pb and 133Cs solid‐state NMR, and by optical emission and absorption spectroscopies. This non‐perovskite material irreversibly transforms into the well‐known three‐dimensional perovskite phase (γ‐CsPbBr3) upon heating to above 151 °C. The indirect bandgap was determined by absorption measurements and calculation to be 2.9 eV. δ‐CsPbBr3 exhibits broadband yellow photoluminescence with a quantum yield of 3.2 %±0.2 % at room temperature and 95 %±5 % at 77 K, and this emission is attributed to the recombination of self‐trapped excitons. This study emphasizes that the metastable δ‐CsPbBr3 may be a persistent, concomitant phase in Cs−Pb‐Br‐containing materials systems, such as those used in solar cells and LEDs, and it showcases the characterization tools used for its detection.ISSN:0018-019XISSN:1522-267

White CsPbBr3: Characterizing the One‐Dimensional Cesium Lead Bromide Polymorph

Inorganic lead halide perovskites have gained immense scientific interest for optoelectronic applications. In this work, we present a one‐dimensional polymorph of cesium lead bromide (δ‐CsPbBr3) synthesized through a simple anion‐exchange reaction, wherein distorted edge‐sharing PbBr6 octahedra form 1D chains isolated by Cs ions. δ‐CsPbBr3 was characterized by Raman spectroscopy, X‐ray diffraction, 207Pb and 133Cs solid‐state NMR, and by optical emission and absorption spectroscopies. This non‐perovskite material irreversibly transforms into the well‐known three‐dimensional perovskite phase (γ‐CsPbBr3) upon heating to above 151 °C. The indirect bandgap was determined by absorption measurements and calculation to be 2.9 eV. δ‐CsPbBr3 exhibits broadband yellow photoluminescence with a quantum yield of 3.2 %±0.2 % at room temperature and 95 %±5 % at 77 K, and this emission is attributed to the recombination of self‐trapped excitons. This study emphasizes that the metastable δ‐CsPbBr3 may be a persistent, concomitant phase in Cs−Pb‐Br‐containing materials systems, such as those used in solar cells and LEDs, and it showcases the characterization tools used for its detection.ISSN:0018-019XISSN:1522-267

Lead-Halide Scalar Couplings in 207Pb NMR of APbX3 Perovskites (A = Cs, Methylammonium, Formamidinium; X = Cl, Br, I)

Understanding the structure and dynamics of newcomer optoelectronic materials - lead halide perovskites APbX3 [A = Cs, methylammonium (CH3NH3+, MA), formamidinium (CH(NH2)2+, FA); X = Cl, Br, I] - has been a major research thrust. In this work, new insights could be gained by using 207Pb solid-state nuclear magnetic resonance (NMR) spectroscopy at variable temperatures between 100 and 300 K. The existence of scalar couplings 1JPb-Cl of ca. 400 Hz and 1JPb-Br of ca. 2.3 kHz could be confirmed for MAPbX3 and CsPbX3. Diverse and fast structure dynamics, including rotations of A-cations, harmonic and anharmonic vibrations of the lead-halide framework and ionic mobility, affect the resolution of the coupling pattern. 207Pb NMR can therefore be used to detect the structural disorder and phase transitions. Furthermore, by comparing bulk and nanocrystalline CsPbBr3 a greater structural disorder of the PbBr6-octahedra had been confirmed in a nanoscale counterpart, not readily captured by diffraction-based techniques.ISSN:2045-232

Microcarrier-Assisted Inorganic Shelling of Lead Halide Perovskite Nanocrystals

The conventional strategy of synthetic colloidal chemistry for bright and stable quantum dots has been the production of epitaxially matched core/shell heterostructures to mitigate the presence of deep trap states. This mindset has been shown to be incompatible with lead halide perovskite nanocrystals (LHP NCs) due to their dynamic surface and low melting point. Nevertheless, enhancements to their chemical stability are still in great demand for the deployment of LHP NCs in light-emitting devices. Rather than contend with their attributes, we propose a method in which we can utilize their dynamic, ionic lattice and uniquely defect-tolerant band structure to prepare non-epitaxial salt-shelled heterostructures that are able to stabilize these materials against their environment, while maintaining their excellent optical properties and increasing scattering to improve out-coupling efficiency. To do so, anchored LHP NCs are first synthesized through the heterogeneous nucleation of LHPs onto the surface of microcrystalline carriers, such as alkali halides. This first step stabilizes the LHP NCs against further merging, and this allows them to be coated with an additional inorganic shell through the surface-mediated reaction of amphiphilic Na and Br precursors in apolar media. These inorganically shelled NC@carrier composites offer significantly improved chemical stability toward polar organic solvents, such as γ-butyrolactone, acetonitrile, N-methylpyrrolidone, and trimethylamine, demonstrate high thermal stability with photoluminescence intensity reversibly dropping by no more than 40% at temperatures up to 120 °C, and improve compatibility with various UV-curable resins. This mindset for LHP NCs creates opportunities for their successful integration into next-generation light-emitting devices.ISSN:1936-0851ISSN:1936-086

A novel strategy to characterize the pattern of β-lactam antibiotic-induced drug resistance in Acinetobacter baumannii

Abstract Carbapenem-resistant Acinetobacter baumannii (CRAb) is an urgent public health threat, according to the CDC. This pathogen has few treatment options and causes severe nosocomial infections with > 50% fatality rate. Although previous studies have examined the proteome of CRAb, there have been no focused analyses of dynamic changes to β-lactamase expression that may occur due to drug exposure. Here, we present our initial proteomic study of variation in β-lactamase expression that occurs in CRAb with different β-lactam antibiotics. Briefly, drug resistance to Ab (ATCC 19606) was induced by the administration of various classes of β-lactam antibiotics, and the cell-free supernatant was isolated, concentrated, separated by SDS-PAGE, digested with trypsin, and identified by label-free LC–MS-based quantitative proteomics. Thirteen proteins were identified and evaluated using a 1789 sequence database of Ab β-lactamases from UniProt, the majority of which were Class C β-lactamases (≥ 80%). Importantly, different antibiotics, even those of the same class (e.g. penicillin and amoxicillin), induced non-equivalent responses comprising various isoforms of Class C and D serine-β-lactamases, resulting in unique resistomes. These results open the door to a new approach of analyzing and studying the problem of multi-drug resistance in bacteria that rely strongly on β-lactamase expression

Guanidinium-Formamidinium Lead Iodide: A Layered Perovskite-Related Compound with Red Luminescence at Room Temperature

Two-dimensional hybrid organic–inorganic lead halides perovskite-type compounds have attracted immense scientific interest due to their remarkable optoelectronic properties and tailorable crystal structures. In this work, we present a new layered hybrid lead halide, namely [CH(NH2)2][C(NH2)3]PbI4, wherein puckered lead-iodide layers are separated by two small and stable organic cations: formamidinium, CH(NH2)2+, and guanidinium, C(NH2)3+. This perovskite is thermally stable up to 255 °C, exhibits room-temperature photoluminescence in the red region with a quantum yield of 3.5%, and is photoconductive. This study highlights a vast structural diversity that exists in the compositional space typically used in perovskite photovoltaics.ISSN:0002-7863ISSN:1520-512

Hybrid 0D Antimony Halides as Air-Stable Luminophores for High-Spatial-Resolution Remote Thermography

Luminescent organic-inorganic low-dimensional ns(2) metal halides are of rising interest as thermographic phosphors. The intrinsic nature of the excitonic self-trapping provides for reliable temperature sensing due to the existence of a temperature range, typically 50-100 K wide, in which the luminescence lifetimes (and quantum yields) are steeply temperature-dependent. This sensitivity range can be adjusted from cryogenic temperatures to above room temperature by structural engineering, thus enabling diverse thermometric and thermographic applications ranging from protein crystallography to diagnostics in microelectronics. Owing to the stable oxidation state of Sb3+, Sb(III)-based halides are far more attractive than all major non-heavy-metal alternatives (Sn-, Ge-, Bi-based halides). In this work, the relationship between the luminescence characteristics and crystal structure and microstructure of TPP2SbBr5 (TPP = tetraphenylphosphonium) is established, and then its potential is showcased as environmentally stable and robust phosphor for remote thermography. The material is easily processable into thin films, which is highly beneficial for high-spatial-resolution remote thermography. In particular, a compelling combination of high spatial resolution (1 mu m) and high thermometric precision (high specific sensitivities of 0.03-0.04 K-1) is demonstrated by fluorescence-lifetime imaging of a heated resistive pattern on a flat substrate, covered with a solution-spun film of TPP2SbBr5.ISSN:0935-9648ISSN:1521-409