Quantum Yield Measurements Research Articles

Novel phthalocyanines bearing fluoro-methylquinolin substituents: Synthesis, characterization, photophysical and photochemical properties

The novel 4-((6-fluoro-2-methylquinolin-4-yl)oxy)phthalonitrile (3a), 3-((6-fluoro-2-methylquinolin-4-yl)oxy)phthalonitrile (3b), tetra 6-fluoro-2-methylquinolin-4-yl)oxy substituted zinc(II) phthalocyanines (4a and 4b) and their water soluble derivatives (5a and 5b) were prepared. The proposed structures of novel compounds were comfirmed via FT-IR, 1HNMR , UV–Vis and MALDI-TOF mass data. The aggregation tendency, fluorescence quantum yield, singlet oxygen quantum yield and photodegradation measurements were performed to examine the photodynamic therapy potential of both peripherally tetra substituted zinc(II) phthalocyanines (4a and 4b) and the water soluble quaternized tetra substituted zinc(II) phthalocyanines (5a and 5b). The result showed that both the novel tetra 6-fluoro-2-methylquinolin-4-yl)oxy substituted zinc(II) phthalocyanines (4a and 4b) and their water soluble derivatives (5a and 5b) could be used as photosensitizer agents in PDT thanks to their lack of aggregation tendency, having sufficient fluorescence emission for monitoring and produce high amount of singlet oxygen to destroy cancerous tissues and having moderate photostability.

Inhibition sensitivity of invitro firefly bioluminescence quantum yields to Zn2+ and Cd2+ concentrations in aqueous solutions.

To elucidate the inhibition effects of Zn2+ and Cd2+ on the luciferin-luciferase reaction, we performed quantitative measurements of quantum yields and spectral shapes for invitro firefly bioluminescence in aqueous solutions containing ZnSO4, ZnCl2, CdSO4, and CdCl2 at different concentrations. Particular care was taken toward the equilibrium between metal ions and enzyme proteins, anion difference, solubility, and uncertainty evaluation. The bioluminescence quantum yields decreased almost linearly to the concentration of Zn2+ and Cd2+ below 0.25 mM. No obvious difference was found between the chloride and sulfate anion solutions. We defined inhibition sensitivity as the decrease in relative quantum yield versus the concentration of metal ions, and they were determined to be 1.48 ± 0.13 and 1.13 ± 0.16/mM for Zn2+ and Cd2+, respectively. We estimated the detection limit of inhibition effects as the concentration of metal ions that decrease relative quantum yields by 10%, which were 0.07 mM (4 ppm) and 0.09 mM (10 ppm) for Zn2+ and Cd2+, respectively. The shape of the bioluminescence spectra changed sensitively with the increase in Zn2+ concentrations. The bioluminescence peak energy for 0.10-mM Zn2+ was ~2.2 eV, while that for 0.25-mM Zn2+ was ~2.0 eV. The shape of the spectra changed less sensitively with the increase in Cd2+concentrations, and the peak energy was at ~2.2 eV for Cd2+ concentrations of 0.10 and 0.25 mM.

Synthesis and optimization of chitosan-incorporated semisynthetic polymer/α-Fe2O3 nanoparticle hybrid polymer to explore optimal efficacy of fluorescence resonance energy transfer/charge transfer for Co(II) and Ni(II) sensing

Initially, four synthetic fluorescent polymers (SFPs) are synthesized from α-methacrylic acid and methanolacrylamide monomers carrying –C(=O)OH and –C(=O)NH subfluorophores, respectively. Among SFPs, ∼1:1 incorporation of subfluorophores in the optimum SFP3 is explored by spectroscopic analyses. Subsequently, chitosan is incorporated in SFP3 to produce five semi-synthetic fluorescent polymers (SSFPs). The maximum incorporation of chitosan in SSFP4 is supported by different spectroscopies. In SSFP4, strong electrostatic interactions among polar functionalities of chitosan and synthetic polymer favor resonance-associated charge transfer (RCT) from SSFP4-(amide) to SSFP4-(canonical). Finally, three hybrid fluorescent polymers (HFPs) are fabricated encapsulating iron-oxide nanoparticle within SSFP4. The maximum proportion of hematite (α-Fe2O3) phase in HFPs is explored by spectroscopic, magnetometric, microscopic, and light scattering studies. HFP2 shows local/RCT/fluorescence resonance energy transfer (FRET) emission at 393/460/570 nm. In HFP2, FRET, RCT, and ratiometric pH-sensing within 3.0–6.5 phenomena are explored by solvent polarity effects, time-correlated single photon counting, quantum yield measurements, alongside I431/I460 vs pH plots. RCT and FRET emissions of HFP2 are utilized for selective sensing of Co(II)/Ni(II) with limits of detection of 4.990 ppb (460 nm)/4.353 ppb (570 nm) and 45.041 ppb (428 nm)/29.617 ppb (527 nm) in organic and aqueous solutions, respectively.

The Photoredox Paradox: Electron and Hole Upconversion as the Hidden Secrets of Photoredox Catalysis.

Although photoredox catalysis is complex from a mechanistic point of view, it is also often surprisingly efficient. In fact, the quantum efficiency of a puzzlingly large portion of photoredox reactions exceeds 100% (i.e., the measured quantum yields (QYs) are >1). Hence, these photoredox reactions can be more than perfect with respect to photon utilization. In several documented cases, a single absorbed photon can lead to the formation of >100 molecules of the product, behavior known to originate from chain processes. In this Perspective, we explore the underlying reasons for this efficiency, identify the nature of common catalytic chains, and highlight the differences between HAT and SET chains. Our goal is to show why chains are especially important in photoredox catalysis and where the thermodynamic driving force that sustains the SET catalytic cycles comes from. We demonstrate how the interplay of polar and radical processes can activate hidden catalytic pathways mediated by electron and hole transfer (i.e., electron and hole catalysis). Furthermore, we illustrate how the phenomenon of redox upconversion serves as a thermodynamic precondition for electron and hole catalysis. After discussing representative mechanistic puzzles, we analyze the most common bond forming steps, where redox upconversion frequently occurs (and issometimes unavoidable). In particular, we highlight the importance of 2-center-3-electron bonds as a recurring motif that allows a rational chemical approach to the design of redox upconversion processes.

Experimental and theoretical investigations on the photophysical and electronic properties of new synthesized organic small molecule for optoelectronic applications

In the present work, we report the chemical synthesis of a newly π-conjugated system using a Wittig reaction. The chemical structure of the synthesized molecule named 1,4-Bis((E)-2-(1-methyl-pyrrol-2-yl)vinyl)benzene (BisPyrBz) was supported by Fourier transform infrared spectroscopy. The optical properties were investigated first using optical absorption (O.A) and steady-state photoluminescence (PLs) tools. Otherwise, transient photoluminescence (TRPL) and quantum yield measurements (PLQY) are present in a diluted solution and condensed state. Theoretical investigations on the synthesized molecule were performed using density functional density (DFT). Experimental and theoretical data show the formation of a planar π-conjugated system. The obtained molecule presents a blue emission with high PLQY, at around 35 % in the solution state. The emission is red-shifted to the green color, with a drastic decrease of the PLQY to around 1 % indicating a possible aggregation-caused quenching behavior in the condensed state. The use of the synthesized BisPyrBz as a π linker in a newly designed A-π-D small molecule permits to obtain a newly near-infrared absorbing material with a weak energy gap Eg = ELUMO − EHOMO, which is at around 1.93 eV, and a weak optical band gap which is estimated to be 1.67 eV.

Coumarin-Phosphazenes: Enhanced Photophysical Properties from Hybrid Materials.

Phosphazenes have drawn a great deal of interest over the past 20 years as a potentially useful building block for the fabrication of fluorescent materials. The main objective of this work is to explore novel derivatives produced by coumarins, a class of chemicals well-known for their photophysical importance, and cyclophosphazenes. UV absorbance, fluorescence emission, quantum yield, and lifetime measurements were conducted to comprehend the optical properties. Furthermore, single-crystal X-ray analysis and theoretical calculations were carried out to confirm the structure of the molecule. The obtained findings collectively confirm the commendable optical properties exhibited by the studied compounds. Moreover, a detailed study of the crystal packing arrangement of DPP-Et-Kum-Et compound crystallized in the P21/n monoclinic space group revealed the presence of stacking interactions between the nonplanar conjugated benzene rings of the coumarins and the rigid diphenyl groups attached to the phosphazene ring. The crystal structure of the DPP-Kum-Me-Me compound is mainly based on classical C-H···O intermolecular hydrogen bonding interactions with an average distance of 2.52 Å. Importantly, the calculated absorption spectra of the compounds are in close agreement with the experimental data, further supporting their interesting electronic properties. Given that the DPP-Et-Kum-Et and DPP-Kum-Et compounds have the theoretically lowest band gaps (4.31 and 4.30 eV, respectively), the activation energies of these compounds were determined by an impedance analyzer using dc conductance values measured at different temperatures. The calculated activation energies for DPP-Et-Kum-Et and DPP-Kum-Et are 104.49 and 100.92 meV, respectively. The results demonstrate that both theoretical and experimental calculations are in agreement with each other and that the DPP-Kum-Et compound has the lowest conductivity.

Fluorophore multimerization on a PEG backbone as a concept for signal amplification and lifetime modulation

Fluorescent labels have strongly contributed to many advancements in bioanalysis, molecular biology, molecular imaging, and medical diagnostics. Despite a large toolbox of molecular and nanoscale fluorophores to choose from, there is still a need for brighter labels, e.g., for flow cytometry and fluorescence microscopy, that are preferably of molecular nature. This requires versatile concepts for fluorophore multimerization, which involves the shielding of dyes from other chromophores and possible quenchers in their neighborhood. In addition, to increase the number of readout parameters for fluorescence microscopy and eventually also flow cytometry, control and tuning of the labels’ fluorescence lifetimes is desired. Searching for bright multi-chromophoric or multimeric labels, we developed PEGylated dyes bearing functional groups for their bioconjugation and explored their spectroscopic properties and photostability in comparison to those of the respective monomeric dyes for two exemplarily chosen fluorophores excitable at 488 nm. Subsequently, these dyes were conjugated with anti-CD4 and anti-CD8 immunoglobulins to obtain fluorescent conjugates suitable for the labeling of cells and beads. Finally, the suitability of these novel labels for fluorescence lifetime imaging and target discrimination based upon lifetime measurements was assessed. Based upon the results of our spectroscopic studies including measurements of fluorescence quantum yields (QY) and fluorescence decay kinetics we could demonstrate the absence of significant dye-dye interactions and self-quenching in these multimeric labels. Moreover, in a first fluorescence lifetime imaging (FLIM) study, we could show the future potential of this multimerization concept for lifetime discrimination and multiplexing.

Nonlinear Optical Activity of a Chiral Organic-Inorganic ([(NH3CH2CH2)3NH])2[MnBr5]Br5 Photoluminescent and Piezoelectric Crystal.

The family of Mn-based organic-inorganic hybrids has greatly expanded due to their advantages in applications. They also show superior bright and size-tunable photoluminescence and can be considered a perfect alternative to toxic lead-based compounds. In this work, we present the detailed structural, optical, and electrical characterization of ([(NH3CH2CH2)3NH])2[MnBr5]Br5. The title compound exhibits a unique type of inorganic arrangement created by the trigonal bipyramids. It crystallizes in noncentrosymmetric space group R32, indicating its optical activity, piezoelectricity, and second-order optical nonlinearity proven by the second harmonic of light measurements. The studied crystals exhibit intense photoluminescence originating from the Mn(II) ion 4T1(G) → 6A1 transition. The measured lifetime of the photoluminescence emission is ≤1.5 ms, while the measured quantum yield for both powder and crystal samples reaches ∼70%.

Improvement of the Quality of Wild Rocket (Diplotaxis tenuifolia) with Respect to Health-Related Compounds by Enhanced Growth Irradiance.

For healthier human nutrition, it is desirable to provide food with a high content of nutraceuticals such as polyphenolics, vitamins, and carotenoids. We investigated to what extent high growth irradiance influences the content of phenolics, α-tocopherol and carotenoids, in wild rocket (Diplotaxis tenuifolia), which is increasingly used as a salad green. Potted plants were grown in a climate chamber with a 16 h day length at photosynthetic photon flux densities varying from 20 to 1250 μmol m-2 s-1. Measurements of the maximal quantum yield of photosystem II, FV/FM, and of the epoxidation state of the violaxanthin cycle (V-cycle) showed that the plants did not suffer from excessive light for photosynthesis. Contents of carotenoids belonging to the V-cycle, α-tocopherol and several quercetin derivatives, increased nearly linearly with irradiance. Nonintrusive measurements of chlorophyll fluorescence induced by UV-A and blue light relative to that induced by red light, indicating flavonoid and carotenoid content, allowed not only a semiquantitative measurement of both compounds but also allowed to follow their dynamic changes during reciprocal transfers between low and high growth irradiance. The results show that growth irradiance has a strong influence on the content of three different types of compounds with antioxidative properties and that it is possible to determine the contents of flavonoids and specific carotenoids in intact leaves using chlorophyll fluorescence. The results may be used for breeding to enhance healthy compounds in wild rocket leaves and to monitor their content for selection of appropriate genotypes.

Interlaboratory Comparison on Absolute Photoluminescence Quantum Yield Measurements of Solid Light Converting Phosphors with Three Commercial Integrating Sphere Setups.

Scattering luminescent materials dispersed in liquid and solid matrices and luminescent powders are increasingly relevant for fundamental research and industry. Examples are luminescent nano- and microparticles and phosphors of different compositions in various matrices or incorporated into ceramics with applications in energy conversion, solid-state lighting, medical diagnostics, and security barcoding. The key parameter to characterize the performance of these materials is the photoluminescence/fluorescence quantum yield (Φf), i.e., the number of emitted photons per number of absorbed photons. To identify and quantify the sources of uncertainty of absolute measurements of Φf of scattering samples, the first interlaboratory comparison (ILC) of three laboratories from academia and industry was performed by following identical measurement protocols. Thereby, two types of commercial stand-alone integrating sphere setups with different illumination and detection geometries were utilized for measuring the Φf of transparent and scattering dye solutions and solid phosphors, namely, YAG:Ce optoceramics of varying surface roughness, used as converter materials for blue light emitting diodes. Special emphasis was dedicated to the influence of the measurement geometry, the optical properties of the blank utilized to determine the number of photons of the incident excitation light absorbed by the sample, and the sample-specific surface roughness. While the Φf values of the liquid samples matched between instruments, Φf measurements of the optoceramics with different blanks revealed substantial differences. The ILC results underline the importance of the measurement geometry, sample position, and blank for reliable Φf data of scattering the YAG:Ce optoceramics, with the blank's optical properties accounting for uncertainties exceeding 20%.

Isochemical crystallization in condensed borate LaMgB5O10 glass-ceramics doped with optical probe Eu3.

The isochemical glass-ceramics doped with Eu3+ were prepared by the heat treatment of lanthanum magnesium borate glass. The crystalline phase was chemically identical to a glass matrix and consisted of condensed borate LaMgB5O10. The isochemical crystallization process begins with the formation of rings by BO4 groups. The emergence of ordered crystalline phase gives rise to intense charge transfer absorption of Eu3+, allowing the efficient luminescence under UV. The analysis of Judd-Ofelt parameters and comparison to purely crystalline samples obtained by solid-state synthesis reveal a switch of parameter relations from Ω2 > Ω4 for glass to Ω2 < Ω4 for crystals but also a maximum value of Ω6 for glass-ceramic sample, which indicates enhanced structural rigidity and results in superior luminescence output. The quantum yield measurements confirmed higher luminescence efficiency for glass-ceramics compared to both pure glass and pure crystalline samples.

Quantum yield in induced-junction silicon photodiodes at wavelengths around 400 nm

The quantum yield in silicon has previously been assumed to be of significance only in the ultraviolet spectral range. Due to the low internal losses of induced-junction silicon photodiodes and their predictability it is possible for the first time to make more accurate estimation of the quantum yield. We report on measurement of quantum yield in induced-junction silicon photodiodes. The results show that the quantum yield can be larger than unity even at wavelengths around 450 nm. A model of the quantum yield has been fitted to the experimental data and can be implemented in the spectral responsivity models to maintain high accuracy predictability to around 160 ppm down to 360 nm.

The operation of PEPCK increases light harvesting plasticity in C4 NAD-ME and NADP-ME photosynthetic subtypes: A theoretical study.

The repeated emergence of NADP-malic enzyme (ME), NAD-ME and phosphoenolpyruvatecarboxykinase (PEPCK) subtypes of C4 photosynthesis are iconic examples of convergent evolution, which suggests that these biochemistries do not randomly assemble, but are instead specific adaptations resulting from unknown evolutionary drivers. Theoretical studies that are based on the classic biochemical understanding have repeatedly proposed light-use efficiency as a possible benefit of the PEPCK subtype. However, quantum yield measurements do not support this idea. We explore this inconsistency here via an analytical model that features explicit descriptions across a seamless gradient between C4 biochemistries to analyse light harvesting and dark photosynthetic metabolism. Our simulations show that the NADP-ME subtype, operated by the most productive crops, is the most efficient. The NAD-ME subtype has lower efficiency, but has greater light harvesting plasticity (the capacity to assimilate CO2 in the broadest combination of light intensity and spectral qualities). In both NADP-ME and NAD-ME backgrounds, increasing PEPCK activity corresponds to greater light harvesting plasticity but likely imposed a reduction in photosynthetic efficiency. We draw the first mechanistic links between light harvesting and C4 subtypes, providing the theoretical basis for future investigation.

Efficient fluorescence probe for detection of naproxen in pharmaceutical formulations and water samples using MPA-capped CdTe/ZnS core-shell nanocrystal-neutral red: Experimental and computational studies

The distinct optical properties of surface-engineered quantum dots, featuring high fluorescent quantum yields and biocompatibility, render them valuable tools for precise and selective sensing and biosensing applications spanning diverse fields, including medicine, environmental monitoring, and diagnostics. In this study, we have successfully fabricated a new “OFF-ON” fluorescent probe based on 3-mercaptopropionic acid (MPA) - capped CdTe/ZnS QDs and neutral red (NR) for the determination of Naproxen (NAP) in pharmaceutical formulations and water samples. The as-prepared MPA-TGA-CdTe/ZnS QDs exhibit a robust photoluminescent emission, peaking at 544 nm upon excitation with a 380 nm wavelength. The quantum yield measurement for the TGA-CdTe QDs was ascertained to be 29.3 %. The findings displayed that the fluorescence emission of MPA-TGA-CdTe/ZnS quantum dots (QDs) could be significantly quenched by increasing neutral red concentration, which can be attributed to the formation of non-fluorescent NR- MPA-TGA-CdTe/ZnS QDs complex (NR-MPA energy level 1.15 Kcal/mol). Upon the addition of naproxen, there was a noticeable enhancement in fluorescence intensity because of the formation of the strong complex between naproxen and NR (NR-NAP energy level: −1.54 Kcal/mol), leading to the detachment of NR from the surface of quantum dots. Consequently, the MPA-TGA-CdTe/ZnS QDs became activated, resulting in the restoration of fluorescence intensity of MPA-TGA-CdTe/ZnS QDs. The enhancement of fluorescence intensity exhibited a direct relationship with the concentration of naproxen, following a linear trend within the concentration range of 2.00 × 10−1 to 27.3 µmol/L with the detection limits of 7.0 × 10−2 µmol/L. Moreover, computational studies were also used to validate the MPA-TGA-CdTe/ZnS QDs turn-off-ON sensor for sensing naproxen. The interactions of NAP, NR, and MPA-TGA-CdTe/ZnS QDs made a solid base for controlling the fluorescent reversibility of QDs. The as-prepared quantum dots were subjected to cytotoxicity studies using an MTT assay and AAS technique. These findings revealed that MPA-TGA-CdTe/ZnS QDs have greater biocompatibility and lower toxicity, making them attractive for biological applications. The recoveries of naproxen detection using the proposed fluorescent probe in various pharmaceutical formulations and water samples ranged from 97.4 % to 102 %, with a relative standard deviation of less than 5 %.

Surface saturation current densities of perovskite thin films from Suns‐photoluminescence quantum yield measurements

AbstractWe present a simple yet powerful analysis of Suns‐photoluminescence quantum yield measurements that can be used to determine the surface saturation current densities of thin film semiconductors. We apply the method to state‐of‐the‐art polycrystalline perovskite thin films of varying absorber thickness. We show that the non‐radiative bimolecular recombination in these samples originates from the surfaces. To the best of our knowledge, this is the first study to demonstrate and quantify non‐linear (bimolecular) surface recombination in perovskite thin films.

Carbon dots on LAPONITE® hybrid nanocomposites: solid-state emission and inter-aggregate energy transfer.

This study delves into the photoluminescent characteristics of solid-state hybrid carbon dots/LAPONITE® (CDLP). These hybrid materials were synthesized using the hydrothermal method with a precise pH control set at 8.5. The LAPONITE® structure remains intact without structural collapse, and we detected the possible deposition of carbon dots (CDs) aggregates on the clay mineral's edges. The use of different concentrations of citric acid (10-, 6-, 2- and 1-times weight/weight of LAPONITE® mass, maintaining the 1 : 1 molar ratio with ethylenediamine) during synthesis results in different CDs concentrations in CDLP-A (low precursors concentration) and CDLP-D (high concentration) with an amorphous structure and average size around 2.8-3.0 nm. The CDLP displayed visible photoluminescence emission in aqueous and powder, which the last underwent quenching according to lifetimes and quantum yield measurements. Low-temperature measurements revealed an enhancement of the non-radiative pathways induced by aggregation. Energy transfer modelling based on Förster-Dexter suggests an approximate mean distance of 9.5 nm between clusters of CDs.

Novel red emitting Phosphor-in-Glass (PiG) based on Na6CaP2O9: Eu3+ phosphor as an inorganic colour converter for w-LED applications

A set of transparent, red-emitting, nUV excitable phosphor-in-glass (PiG) of different phosphor concentrations was fabricated via low temperature co-sintering process by incorporating Na6CaP2O9:Eu3+ phosphor into the multicomponent borosilicate glass. Structural and morphological properties were estimated through XRD, FTIR, HR-TEM and FE-SEM. The electron microscope images confirm the successful incorporation of phosphor into the amorphous glass with negligible glass-phosphor interaction. The luminescent characteristics of the prepared samples were investigated via UV–Vis transmittance spectra, photoluminescence spectra, JO theory, decay analysis and quantum yield measurement. The transmittance spectra reveal exceptional transparency of the samples in the visible region. The PiGs emit prominently at 614 nm under 393 nm excitation with a lifetime in the millisecond range. Chromaticity coordinates corresponding to red emission under 393 nm excitation are (0.634, 0.366). These results contemplate the fabricated PiGs as a potential red emissive inorganic colour converter in lighting and display devices.

Determining wavelength-dependent quantum yields of photodegradation: importance of experimental setup and reference values for actinometers.

Accurate quantum yields are crucial for modeling photochemical reactions in natural and engineered treatment systems. Quantum yields are usually determined using a single representative light source such as xenon lamps to mimic sunlight or UVC light for water treatment. However, photodegradation modeling can be improved by understanding the wavelength dependence of quantum yields and the potential errors introduced by the experimental setup. In this study, we investigated the effects of experimental setup on measured quantum yields using four photoreactor systems and up to 11 different light sources. When using a calibrated spectroradiometer to measure incident irradiance on an open solution surface, apparent quantum yields were up to two times higher if light reflection and light screening were not accounted for in the experimental setup. When the experimental setup was optimized to allow for accurate irradiance measurements, quantum yields were reproducible across photoreactors. The optimized experimental setup was then used to determine quantum yields of uridine, atrazine, p-nitroanisole (PNA), sulfamethoxazole, and diclofenac across the UV spectrum. No significant wavelength dependence of quantum yields was observed for sulfamethoxazole and diclofenac, in contrast to wavelength-dependent quantum yields for uridine, atrazine, and PNA. These reference values can be used for determining wavelength-dependent quantum yields of other compounds of interest. Additionally, more accurate results can be obtained when using (1) an actinometer with similar light absorption and photoreactivity compared to that of the target chemical, (2) optically transparent actinometer solutions that can account for light reflection within reaction vessels, and (3) a quantum yield that corresponds to the spectrum of the selected light source.

How to recognize clustering of luminescent defects in single-wall carbon nanotubes.

Semiconducting single-wall carbon nanotubes (SWCNTs) are a promising material platform for near-infrared in vivo imaging, optical sensing, and single-photon emission at telecommunication wavelengths. The functionalization of SWCNTs with luminescent defects can lead to significantly enhanced photoluminescence (PL) properties due to efficient trapping of highly mobile excitons and red-shifted emission from these trap states. Among the most studied luminescent defect types are oxygen and aryl defects that have largely similar optical properties. So far, no direct comparison between SWCNTs functionalized with oxygen and aryl defects under identical conditions has been performed. Here, we employ a combination of spectroscopic techniques to quantify the number of defects, their distribution along the nanotubes and thus their exciton trapping efficiencies. The different slopes of Raman D/G+ ratios versus calculated defect densities from PL quantum yield measurements indicate substantial dissimilarities between oxygen and aryl defects. Supported by statistical analysis of single-nanotube PL spectra at cryogenic temperatures they reveal clustering of oxygen defects. The clustering of 2-3 oxygen defects, which act as a single exciton trap, occurs irrespective of the functionalization method and thus enables the use of simple equations to determine the density of oxygen defects and defect clusters in SWCNTs based on standard Raman spectroscopy. The presented analytical approach is a versatile and sensitive tool to study defect distribution and clustering in SWCNTs and can be applied to any new functionalization method.

Alleviating nanostructural phase impurities enhances the optoelectronic properties, device performance and stability of cesium-formamidinium metal-halide perovskites.

The technique of alloying FA+ with Cs+ is often used to promote structural stabilization of the desirable α-FAPbI3 phase in halide perovskite devices. However, the precise mechanisms by which these alloying approaches improve the optoelectronic quality and enhance the stability have remained elusive. In this study, we advance that understanding by investigating the effect of cationic alloying in CsxFA1-xPbI3 perovskite thin-films and solar-cell devices. Selected-area electron diffraction patterns combined with microwave conductivity measurements reveal that fine Cs+ tuning (Cs0.15FA0.85PbI3) leads to a minimization of stacking faults and an increase in the photoconductivity of the perovskite films. Ultra-sensitive external quantum efficiency, kelvin-probe force microscopy and photoluminescence quantum yield measurements demonstrate similar Urbach energy values, comparable surface potential fluctuations and marginal impact on radiative emission yields, respectively, irrespective of Cs content. Despite this, these nanoscopic defects appear to have a detrimental impact on inter-grains'/domains' carrier transport, as evidenced by conductive-atomic force microscopy and corroborated by drastically reduced solar cell performance. Importantly, encapsulated Cs0.15FA0.85PbI3 devices show robust operational stability retaining 85% of the initial steady-state power conversion efficiency for 1400 hours under continuous 1 sun illumination at 35 °C, in open-circuit conditions. Our findings provide nuance to the famous defect tolerance of halide perovskites while providing solid evidence about the detrimental impact of these subtle structural imperfections on the long-term operational stability.