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Light harvesting devices based on metal halide perovskite nanocrystals (NCs) rely on the application of ligand washing or ligand exchange processes to transform pristine, glassy NC solids into electronically active NC arrays. A less explored route combines such treatments with the fabrication of NC heterojunctions with organic semiconductors to promote charge transfer through conductive pathways within the blends. Herein, optical spectroscopy and photoconductivity is implemented for a detailed investigation of the charge generation and charge extraction process in blends of green CsPbBr3NCs or red CsPb(Br,I)3NCs capped with short octylamine/octanoic-acid ligands with the fullerene derivative phenyl-C70-butyric acid methyl ester (PC70BM). Incorporation of the fullerene results in efficient quenching of the NC photoluminescence (PL) and the emergence of a fast subnanosecond decay channel in the transient PL, which is consistent with efficient interfacial dissociation of the NC excitons via electron transfer to the PC70BM. Importantly, the photocurrent in lateral devices with gold contacts is improved by up to 2 orders of magnitude upon fullerene incorporation, with optimum concentration of 20% per weight PC70BM for both green and red absorbing NCs. Short, post synthetic thermal annealing up to 100 °C further improves charge extraction due to better material blending and film quality, increasing by an additional order of magnitude the photo response of the devices.

Nanocrystal superlattices (NC SLs) have long been sought as promising metamaterials, with nanoscale-engineered properties arising from collective and synergistic effects among the constituent building blocks. Lead halide perovskite (LHP) NCs come across as outstanding candidates for SL design, as they demonstrate collective light emission, known as superfluorescence, in single- and multicomponent SLs. Thus far, LHP NCs have only been assembled in single-component SLs or coassembled with dielectric NC building blocks acting solely as spacers between luminescent NCs. Here, we report the formation of multicomponent LHP NC-only SLs, i.e., using only CsPbBr3NCs of different sizes as building blocks. The structural diversity of the obtained SLs encompasses the ABO6, ABO3, and NaCl structure types, all of which contain orientationally and positionally locked NCs. For the selected model system, the ABO6-type SL, we observed efficient NC coupling and Förster-like energy transfer from strongly confined 5.3 nm CsPbBr3NCs to weakly confined 17.6 nm CsPbBr3NCs, along with characteristic superfluorescence features at cryogenic temperatures. Spatiotemporal exciton dynamics measurements reveal that binary SLs exhibit enhanced exciton diffusivity compared to single-component NC assemblies across the entire temperature range (from 5 to 298 K). The observed coherent and incoherent NC coupling and controllable excitonic transport within the solid NC SLs hold promise for applications in quantum optoelectronic devices.

•Four ORC designs are examined in terms of energy, exergy, and economics.•ORC with quasi-isothermal expansion performs better thermodynamically.•ORC with quasi-isothermal expansion is the most economically viable cycle.•Electrical and exergy efficiencies by up to 9.8%, and 53.9%•The payback period achieves values up to 1.3 years.

Nanocrystal (NC) self-assembly is a versatile platform for materials engineering at the mesoscale. The NC shape anisotropy leads to structures not observed with spherical NCs. This work presents a broad structural diversity in multicomponent, long-range ordered superlattices (SLs) comprising highly luminescent cubic CsPbBr3NCs (and FAPbBr3NCs) coassembled with the spherical, truncated cuboid, and disk-shaped NC building blocks. CsPbBr3nanocubes combined with Fe3O4or NaGdF4spheres and truncated cuboid PbS NCs form binary SLs of six structure types with high packing density; namely, AB2, quasi-ternary ABO3, and ABO6types as well as previously known NaCl, AlB2, and CuAu types. In these structures, nanocubes preserve orientational coherence. Combining nanocubes with large and thick NaGdF4nanodisks results in the orthorhombic SL resembling CaC2structure with pairs of CsPbBr3NCs on one lattice site. Also, we implement two substrate-free methods of SL formation. Oil-in-oil templated assembly results in the formation of binary supraparticles. Self-assembly at the liquid–air interface from the drying solution cast over the glyceryl triacetate as subphase yields extended thin films of SLs. Collective electronic states arise at low temperatures from the dense, periodic packing of NCs, observed as sharp red-shifted bands at 6 K in the photoluminescence and absorption spectra and persisting up to 200 K.

The 1:1:1 reaction of DyCl3·6H2O, K3[Co(CN)6] and bpyO2in H2O has provided access to a complex with formula [DyCo(CN)6(bpyO2)2(H2O)3]·4H2O (1) in a very good yield, while [DyFe(CN)6(bpyO2)2(H2O)3]·4H2O (2) was also precipitated (also in a high yield) using K3[Fe(CN)6] instead of K3[Co(CN)6]. Their structures have been determined by single-crystal X-ray crystallography and characterized based on elemental analyses and IR spectra. Combined direct current (dc) and alternating current (ac) magnetic susceptibility revealed slow magnetic relaxation upon application of a dc field. μ-SQUID measurements and CASSCF calculations revealed high-temperature relaxation dynamics for both compounds. Low-temperature magnetic studies show the relaxation characteristics for 1, while for compound 2the dynamics corresponds to an antiferromagnetically coupled Dy···Fe pair. High-resolution optical studies have been carried out to investigate the performance of compounds 1and 2as luminescence thermometers. For 1, a maximum thermal sensitivity of 1.84% K–1at 70 K has been calculated, which is higher than the acceptable sensitivity boundary of 1% K–1for high-performance luminescence thermometers in a broad range of temperature between 40 and 140 K. Further optical studies focused on the chromaticity diagram of compound 1revealed a temperature shift from warm white (3200 K) at 10 K toward a more natural white color near 4000 K at room temperature.

Colloidal quantum dots (CQDs) are typically decorated with organic molecules that provide surface passivation and colloidal solubility. An alternate but less studied surface functionalization approach viainorganic complexes can produce stable CQDs with attractive transport and optical properties. Further development of such all-inorganic CQD solids is dependent on the deeper understanding of the energetic and dynamic interactions of the new ligands with the CQD excitons. Herein, a series of four metal chalcogenide (MCC) ligands of the KzXS4type were attached to PbS CQDs. Out of the four MCC complexes studied, we find that only K4GeS4ligands yield robust PbS CQD films with bright photoluminescence (PL) in the solid state. A systematic spectroscopic investigation of the K4GeS4-capped CQD films provides evidence of the temperature-dependent ligand-mediated exciton delocalization and trapping processes. At low temperatures, efficient trapping at ligand-induced states is found to occur within ∼6 ns after photoexcitation, followed by a considerably slower exciton back transfer to the CQD core. At elevated temperatures, the CQD films become photoconductive, providing evidence of exciton dissociation viacarrier transfer within adjacent dots. The addition of a thin CdS shell suppresses the delocalization and trapping of excitons, resulting in brighter emission and significantly slower transient absorption and PL dynamics.

Materials with optical gain in the infrared are of paramount importance for optical communications, medical diagnostics, and silicon photonics. The current technology is based either on costly III–V semiconductors that are not monolithic to silicon CMOS technology or Er-doped fiber technology that does not make use of the full fiber transparency window. Colloidal quantum dots (CQDs) offer a unique opportunity as an optical gain medium in view of their tunable bandgap, solution processability, and CMOS compatibility. The 8-fold degeneracy of infrared CQDs based on Pb-chalcogenides has hindered the demonstration of low-threshold optical gain and lasing, at room temperature. We demonstrate room-temperature, infrared, size-tunable, band-edge stimulated emission with a line width of ∼14 meV. Leveraging robust electronic doping and charge-exciton interactions in PbS CQD thin films, we reach a gain threshold at the single exciton regime representing a 4-fold reduction from the theoretical limit of an 8-fold degenerate system, with a net modal gain in excess of 100 cm–1.

Disentangling temporally overlapping charge carrier recombination events in organic bulk heterojunctions by optical spectroscopy is challenging. Here, a new methodology for employing delayed luminescence spectroscopy is presented. The proposed method is capable of distinguishing between recombination of spatially separated charge carriers and trap-assisted charge recombination simply by monitoring the delayed luminescence (afterglow) of bulk heterojunctions with a quasi time-integrated detection scheme. Applied on the model composite of the donor poly(6,12-dihydro-6,6,12,12-tetraoctyl-indeno[1,2-b]fluorene-alt-benzothiadiazole) (PIF8BT) polymer and the acceptor ethyl–propyl perylene diimide (PDI) derivative, that is, PIF8BT:PDI, the luminescence of charge-transfer (CT) states created by nongeminate charge recombination on the ns to μs timescale is observed. Fluence-dependent, quasi time-integrated detection of the CT luminescence monitors exclusively emissive charge recombination events, while rejecting the contribution of other early-time emissive processes. Trap-assisted and bimolecular charge recombination channels are identified based on their distinct dependence on fluence. The importance of the two recombination channels is correlated with the layer’s order and electrical properties of the corresponding devices. Four different microstructures of the PIF8BT:PDI composite obtained by thermal annealing are investigated. Thermal annealing of PIF8BT:PDI shrinks the PDI domains in parallel with the growth of the PIF8BT domains in the blend. Common to all states studied, the delayed CT luminescence signal is dominated by trap-assisted recombination. Yet, the minor fraction of fully separated charge recombination in the overall CT emission increases as the difference in the size of the donor and acceptor domains in the PIF8BT:PDI blend becomes larger. Electric field-induced quenching measurements on complete PIF8BT:PDI devices confirm quantitatively the dominance of emissive trap-limited charge recombination and demonstrates that only 40% of the PIF8BT/PDI CT luminescence comes from the recombination of fully-separated charges, taking place within 200 ns after photoexcitation. The method is applicable to other nonfullerene acceptor blends beyond the system discussed here, if their CT state luminescence can be monitored.

The slowdown of carrier cooling in lead halide perovskites (LHP) may allow the realization of efficient hot carrier solar cells. Much of the current effort focuses on the understanding of the mechanisms that retard the carrier relaxation, while proof-of-principle demonstrations of hot carrier harvesting have started to emerge. Less attention has been placed on the impact that the energy and momentum relaxation slowdown imparts on the spontaneous and stimulated light-emission process. LHP nanocrystals (NCs) provide an ideal testing ground for such studies as they exhibit bright emission and high optical gain, while the carrier cooling bottleneck is further pronounced compared to their bulk analogues due to confinement. Herein, the luminescent properties of CsPbBr3, FAPbBr3, and FAPbI3NCs in the strong photoexcitation regime are investigated. In the former two NC systems, amplified spontaneous emission is found to dominate over the radiative recombination at average carrier occupancy per nanocrystal larger than 5–10. On the other hand, under the same photoexcitation conditions in the FAPbI3NCs, a longer lived population of hot carriers results in a competition between hot luminescence, stimulated emission, and defect recombination. The dynamic interplay between the aforementioned three emissive channels appears to be influenced by various experimental and material parameters that include temperature, material purity, film morphology, and excitation pulse width and wavelength.

Prolonged consumption of water contaminated with fluoride ions (F–) at concentrations exceeding 1.5 ppm can lead to considerable health implications, particularly in children and developing embryos. With irreversible and potentially severe forms of fluoride (F–) toxicity such as skeletal fluorosis being endemic in at least 25 countries, constructing affordable, remote-access, reliable water-sampling methods for F–contamination is an important goal. In this work, we present a novel lanthanide-based luminescent metal–organic framework, named SION-105, with a boron (B) receptor site whose interactions with F–in aqueous solutions are simultaneously electrostatic and specific in nature because of its carefully designed structural environment. This allows the material to be easily regenerated and used over 10 cycles, setting it apart from most existing molecular and polymeric F–sensors. SION-105has been combined with a portable prototype sampling device that was designed and built in-house to measure F–concentrations in natural groundwater samples taken from three different countries, with the results showing excellent agreement with ion chromatography analysis.

Natural minerals are widely used in numerous environmental applications, mainly as sorbents in ion exchange and sorption processes. Minerals, such as zeolites and clays, can be found all over the world, but they are mined containing a variety of different impurities; this prevents their accurate characterization. The present study examines various methods used for the characterization of three common natural silicate minerals, one zeolite (clinoptilolite) and two clays (montmorillonite and vermiculite). Their characterization was performed through a series of analytical measurements so as to gather all the information needed regarding their structural properties. Therefore, “similar” minerals such as clinoptilolite vs. heulandite and vermiculite vs. hydrobiotite can be distinguished; revealing important properties when comes to their practical application. The methods used in the present study are X-ray powder diffraction (XRD), X-ray fluorescence, Fourier transform infrared (FTIR) spectroscopy, TG/DTG/DTA and N2-porosimetry (BET). An extensive literature review of the natural silicate minerals has been conducted and the relevant results and methods are comparatively reported. The analytical results enabled the distinguish of the examined minerals. XRD, FTIR, TG/DTG/DTA showed that all three minerals have characteristic bands that can be used to easily distinguish from others.

The efficient harvesting of hot carrier energy in semiconductors is typically inhibited by their ultrafast thermalization process. Recently, highly promising experiments reported on the slowdown of the intraband relaxation in hybrid metal halide perovskites. In this work, we report on the presence of long-lived hot carriers in weakly confined colloidal nanocrystals (NCs) of formamidinium lead iodide perovskite (FAPbI3). The effect is apparent from the excitation-dependent lengthening of the rise time and broadening of the high-energy tail of the transient absorption bleaching signal, yielding a retardation of the carrier relaxation by 2 orders of magnitude compared to typical time scales in colloidal semiconductor NCs. Three distinct cooling stages are observed, occurring at sub-picosecond, ∼5 ps, and ∼40 ps time scales, which we attribute to scattering from LO-phonons, contribution from a hot phonon bottleneck effect and Auger heating, respectively. Thermalization appears also influenced by the FAPbI3NCs purity, with trapping at unreacted precursor impurities further reducing the carrier energy loss rate.

AbstractBentonite is a clay mineral often used in ion exchange processes due to its high ion exchange capacity. In the present study, a commercially available in Greece market bentonite was obtained and characterized by XRD, XRF, FTIR, BET, and TG/DTA analysis. Monmorillonite was the main component of bentonite sample (>80%). Ion exchange equilibria of Zn2+, Cr3+, and Mn2+on bentonite was examined by use of batch equilibrium isotherms, distribution coefficients, and maximum exchange levels (MELs) under the same normality for all metals (0.01 N) at 25 ± 2°C. The equilibrium isotherms for the metals studied exhibit a favorable-type isotherm. Selectivity series deduced from equilibrium isotherms are Cr3+ > Zn2+ > Mn2+, and the same occurs for MELs. The Langmuir and Freundlich models were applied and fitted the equilibrium data for the metal ion uptake. A detailed literature review on heavy metals-bentonite equilibrium is provided.

Bentonite is a clay mineral often used in ion exchange processes due to its high ion exchange capacity. In the present study, a commercially available in Greece market bentonite was obtained and characterized by XRD, XRF, FTIR, BET, and TG/DTA analysis. Monmorillonite was the main component of bentonite sample (>80%). Ion exchange equilibria of Zn2+, Cr3+, and Mn2+on bentonite was examined by use of batch equilibrium isotherms, distribution coefficients, and maximum exchange levels (MELs) under the same normality for all metals (0.01 N) at 25 ± 2°C. The equilibrium isotherms for the metals studied exhibit a favorable-type isotherm. Selectivity series deduced from equilibrium isotherms are Cr3+ > Zn2+ > Mn2+, and the same occurs for MELs. The Langmuir and Freundlich models were applied and fitted the equilibrium data for the metal ion uptake. A detailed literature review on heavy metals-bentonite equilibrium is provided.

Two fly ashes (FAs) originating from Kardia and Megalopolis power plants are used for the first time to amend the acid mining drainage (AMD) from the abandoned Ermioni and the active Kassandra Greek mining sites. The fly ashes employed are of type C, with Kardia fly ash (KFA) being mostly calcareous and Megalopolis’ (MFA) mostly siliceous. Both FAs were tested for their pH-regulating and metal-ions-removal efficiency. Regarding the acidity reduction both FAs proved equally efficient; by regulating the FA to AMD solution ratio, final pH values between 6 and 12.5 were attained using KFA while weakly acidic (pH = 6) to neutral solutions were produced in the case of MFA. Except for chromium ions, both FAs, also, proved equally effective in (heavy-)metal-removal for loadings higher than 5 g/50 mL acid waters. KFA, particularly, cleaned up the acid mine drainage solution from all metals even at a 0.5 g/50 mL loading. For KFA, metal removal was attributed to precipitation while in the case of MFA retention was found to occur via adsorption and/or complexation as well. Both FAs and AMD are largely produced as side effects of the two major Greek economic activities, i.e., electricity production and mining; using FAs to assess the AMD environmental impact can contribute to circular economy and, therefore, is of significant financial interest for Greece.

The heat-to-electricity conversion efficiency of concentrated solar power plants may be enhanced, for lower cost electricity generation, by using high-temperature (750oC) supercritical CO2as a working fluid to drive the turbines in these plants. Unfortunately, such operation has been inhibited by the reduction in thermomechanical performance at >550oC of metal alloys used, or considered for use, in compact heat exchangers for heat transfer to supercritical CO2. Co-continuous, melt-infiltration-processed SiC/Si composites possess an attractive combination of high-temperature mechanical and thermal properties for use in such compact heat exchangers. However, the corrosion behavior of melt-infiltration-processed, equivolume SiC/Si composites in CO2at 750°C has not been reported. In this work, the oxidation kinetics of SiC/Si composites, fabricated by Si liquid infiltration into porous SiC preforms, have been examined in CO2 and in air at 750°C for up to 700 h. Continuous, thin, slow-growing external amorphous SiO2 scales formed on the SiC/Si composites during oxidation in both gases, without detectable oxide formation at internal (subsurface) SiC/Si interfaces. Corrosion-induced SiC formation in CO2, and Si3N4 formation in air, were also not detected below the SiO2 scales. The weight gains were small, with a significantly lower rate of weight gain detected in CO2 than in air. SiO2 scales formed on SiC in both gases were thinner than the scales formed on Si. The SiO2 scales formed on Si in air were notably thicker than the scales formed on Si in CO2, whereas SiO2 scales formed on SiC in air and CO2 were of similar thickness.