Here, we foster the combined use of conventional techniques to obtain a comprehensive structural and chemical characterization of kesterites (Cu2ZnSnS4, Copper-Zinc-Tin Sulfide, CZTS), a class of light-absorbing materials employed in sustainable thin-film solar cells, with magnetometry and Electron paramagnetic resonance (EPR) spectroscopy, to identify the nature of their paramagnetic centers. Iron-doped (CZFTS) and non-doped nanocrystals were synthesized by hot-injection method and then treated at 450 degrees C. The structural analysis evidenced that while the raw CZTS and CZFTS nanocrystals do not show any secondary phase, a minority phase is present in the annealed samples. The complementary distribution of the metal ions in both CZTS and CZFTS was also assessed. Magnetometry and EPR spectroscopy pointed out the formation of paramagnetic vacancies following the high temperature treatment and the successful doping with Iron. This work highlighted the unique capability of a multipronged approach to detect paramagnetic defects in kesterite nanocrystals, which are otherwise challenging to identify using single techniques.

Abstract Photonic properties in a plasmonic nanocrystal are directly impacted by carrier density, carrier effective mass, and carrier damping behavior. Postprocessing of as-prepared Cd2SnO4 (CTO) by solvothermal annealing is shown to enhance the localized surface plasmon (LSPR) optical quality through a time-dependent LSPR shift and LSPR narrowing. The change in the LSPR is complex but postulated to be driven by surface reconstruction leading to incorporation of Sn, reduction in size, and defect evolution. The changes in the CTO produce a shift to higher frequency for the LSPR and loss of a high energy shoulder with an exponential rate of k ∼ 1.0 h–1. The improved plasmonic quality factor is due to the overall increase in carrier density and loss of the shoulder during solvothermal annealing. During annealing, an increase in the depletion layer width and a decrease in Sn activation in CTO with k ∼ 0.5 h–1 are also observed. Postprocessing of isolated plasmonic metal oxide nanocrystals through solvo-thermal annealing may represent a convenient strategy to enhance LSPR quality factors, providing a pathway to improving photonic properties in this class of materials.

Kesterites, Cu2ZnSnS4 (Copper-Zinc-Tin Sulfide, CZTS) are a class of light-absorbing materials employed in sustainable thin-film solar cells due to the lack of toxic elements and critical raw materials. However, they are affected by the presence of secondary phases, antisite defects and vacancies, which degrade their efficiency. Here, we foster the combined use of conventional techniques to obtain a comprehensive structural and chemical characterization of these materials (X-Ray Diffraction, micro-Raman scattering, Diffuse Reflectance spectroscopy and Scanning Transmission Electron Microscopy), with magnetometry and Electron paramagnetic resonance (EPR) spectroscopy, to identify the nature of their paramagnetic centers. As a case study, we undertook a synthetic approach incorporating iron as a substitute for zinc into the composition. CZTS and Cu2(Zn1-xFex)SnS4 (Copper-Zinc-Iron-Tin Sulfide, CZFTS) nanocrystals were synthesized by hot-injection method and then thermally treated at 450°C, a process typically implemented to improve the performance in optoelectronic devices. The structural analysis evidenced that while the raw CZTS and CZFTS nanocrystals do not show any secondary phase, a minority phase is present in the annealed samples. The complementary distribution of the metal ions in both CZTS and CZFTS was also assessed. Magnetometry and EPR spectroscopy pointed out the formation of paramagnetic vacancies following the high temperature treatment and the successful doping with Iron. Remarkably, this work highlighted the unique capability of EPR spectroscopy to detect paramagnetic defects in kesterite nanocrystals, which are otherwise challenging to identify using other techniques. The exploitation of EPR can thus unveil new opportunities to optimize materials features for optoelectronics and photovoltaics.

Tunable flat optics are essential for advancing compact photonic devices. Here we show a numerical study of a reflective magneto-optical metasurface with a dynamically tunable focal length. The structure comprises bismuth iron garnet nanodisks in a Gires-Tournois resonator configuration. The magneto-optical properties of the garnet modulate the reflected phase response via an external magnetic field, allowing focusing at different focal lengths. Full-wave simulations demonstrate that the metasurface exhibits distinct focusing characteristics depending on the applied magnetic field direction for a fixed right circularly polarized incident wave at 1.550 μm. Specifically, switching the external field from +0.2 T to -0.2 T changes the focal length by a factor of approximately two (from 7.16 mm to 13.76 mm). These findings demonstrate that magneto-optical metasurfaces offer a flexible, viable approach for non-mechanical, tunable focusing in compact reflective optical components.

We experimentally demonstrate the enhancement of magneto-optical properties in the visible and near infrared spectral regime by employing Gires-Tournois (GT) resonant architectures based on cobalt. Two distinct systems are investigated: a planar GT cavity composed of a thin Co layer, a silica spacer, and another thin cobalt layer coating a thick aluminium substrate; and a GT metasurface with the same multilayer architecture, but where the top continuous cobalt layer is replaced by a periodic array of cobalt disk-shaped meta-atoms. Through a careful sample realization and characterization, we experimentally demonstrate that both structures achieve about an order of magnitude increase in the polar Magneto-Optical Kerr Effect (p-MOKE) to 200 nm cobalt film. This result is analyzed by means of a combination of analytical models and numerical simulations. This enhancement is mainly attributed to constructive interference within the GT cavity and to the synergistic effects of localized surface plasmon resonances, surface lattice resonances and optical cavity modes in the metasurface. These results establish a promising platform for the development of compact, magneto-optically tunable nanophotonic devices with potential applications in nonreciprocal photonics, active optical modulation, and sensing technologies.

Magneto‐optics, a research area that studies the interaction between magnetic fields and light, has recently made remarkable progress due to a better understanding of light–matter interactions at the nanoscale. The integration of magnetic and plasmonic functionalities with nanometric resolution offers exciting opportunities, especially due to the ability of plasmonic phenomena to enhance magneto‐optical responses. In this respect, wet‐chemistry methods are particularly useful in fine‐tuning the magnetic and plasmonic properties of nanocrystals, enabling the creation of a large library of hybrid colloidal systems with enhanced magneto‐optical features. Here, recent advancements in these magnetoplasmonic hybrid nanomaterials are explored and special focus on a key area of interest, that is, the nascent field of chiral plasmonics is put. Metal nanocrystals with intrinsic chiroptical features can lead to a combination of chiral plasmonics and magneto‐optics effects when interacting with the magnetic counterpart, paving the way toward the establishment of a systematic and comprehensive roadmap for the predesign and fabrication of chiral magnetoplasmonic systems. The implications of this progress are profound, offering both fundamental insights and promising technological applications.

Static metasurfaces offer precise control over light but lack reconfigurability, limiting their use in dynamic applications. Introducing tunability via external stimuli, such as magnetic fields, enables active control of their optical response, broadening their functionality. In this computational study, we present the design of a metal–dielectric–metal magnetoplasmonic metasurface with improved magnetic field tunability, surpassing the magneto-optical response of unstructured ferromagnetic materials. This improvement arises from the synergistic effect of localized plasmon excitation, surface lattice resonance, and Fabry–Pérot cavity modes. The design approach presented here consists in matching the characteristic resonance frequencies of the three phenomena by iteratively adjusting the structural parameters of the metasurface: nanostructure size, lattice period, and cavity layer thickness. This optimization led to a substantial enhancement in the reflectance modulation induced by an external magnetic field, with the overall contrast exceeding that of an unstructured cavity by more than an order of magnitude across various regions of the visible to near-infrared spectrum, under relatively low magnetic fields. This unique capability makes the system a promising tool for magnetic field-sensitive optical modulation of reflected light intensity, with potential applications as a laser amplitude modulator.

Multilayered metal-dielectric nanostructures display both strong plasmonic behavior and hyperbolic optical dispersion. The latter is responsible for the appearance of two separated radiative and non-radiative channels in the extinction spectrum of these structures. This unique property can open a wealth of opportunities towards the development of multifunctional systems that simultaneously can behave as optimal scatterers and absorbers at different wavelengths, an important feature to achieve multiscale control light-matter interactions in different spectral regions for different types of applications, such as optical computing or detection of thermal radiation. Nevertheless, the temperature dependence of the optical properties of these multilayered systems has never been investigated. In this work we study how radiative and non-radiative processes in hyperbolic meta-antennas can probe temperature changes of the surrounding medium. We show that, while radiative processes are essentially not affected by a change in the external temperature, the non-radiative ones are strongly affected by a temperature variation. By combining experiments and temperature dependent effective medium theory, we find that this behavior is connected to enhanced damping effects due to electron-phonon scattering. Contrary to standard plasmonic systems, a red-shift of the non-radiative mode occurs for small variations of the environment temperature. Our study shows that to probe temperature changes it is essential to exploit non-radiative processes in systems supporting plasmonic excitations, which can be used as very sensitive thermometers via linear absorption spectroscopy.

Here we report on the Magneto-Chiral Dichroism (MChD) detected through visible and near-infrared light absorption of two enantiomeric pairs of Er III and Tm III chiral complexes featuring a propeller-like molecular structure. The magnetic properties show typical features of isolated paramagnetic ions associated with 4 I 15/2 and 3 H 6 ground state terms. MChD spectroscopy shows high g MChD dissymmetry factors of ca. 0.12 T −1 and 0.05 T −1 ( T =4.0 K and B =1.0 T) for Er III and Tm III , respectively, associated with the magnetic-dipole allowed 4 I 13/2 ← 4 I 15/2 and 3 H 5 ← 3 H 6 transitions. MChD signals of the two complexes were detected up to room temperature and under magnetic fields up to 5.0 T. For the first time, the MChD results are discussed in the context of the Richardson theory of lanthanide optical activity and provide clear indications on the strongest MChD-active electronic transitions of lanthanide complexes.

We develop here a comprehensive experimental approach to independently determine charge carrier parameters, namely, carrier density and mass, in plasmonic indium tin oxide nanocrystals. Typically, in plasmonic nanocrystals, only the ratio between these two parameters is accessible through optical absorption experiments. The multitechnique methodology proposed here combines single particle and ensemble optical and magneto-optical spectroscopies, also using 119Sn solid-state nuclear magnetic resonance spectroscopy to probe the surface depletion layer. Our methodology overcomes the limitations of standard fitting approaches based on absorption spectroscopy and ultimately gives access to carrier effective mass directly on the NCs, discarding the use of literature value based on bulk or thin film materials. We found that mass values depart appreciably from those measured on thin films; consequently, we found carrier density values that are different from reported literature values for similar systems. The effective mass was found to deviate from the parabolic approximation at a high carrier density. Finally, the dopant activation and defect diagram for ITO NCs for tin doping between 2.5 and 15% are determined. This approach can be generalized to other plasmonic heavily doped semiconductor nanostructures and represents, to the best of our knowledge, the only method to date to characterize the full Drude parameter space of 0-D nanosystems.

Copper-poor Cu2ZnSnS4 (copper zinc tin sulfide, CZTS) inorganic semiconducting nanoparticles were synthesized by an environmentally friendly low-temperature (100 degrees C) synthetic path, which allows precise control of the Sn content without any relevant presence of Zn- and Sn-related secondary phases. The resulting nanoparticles are polycrystalline and quasi-spherical, with an average diameter of 10 nm. The shape and composition were assessed using a multitechnique approach based on X-ray photoelectron spectroscopy (XPS), energy-dispersive fluorescence X-ray spectroscopy (EDXRF), inductively coupled plasma atomic emission spectrometry (ICP-AES), and high-resolution transmission electron microscopy (HR-TEM). The presence of paramagnetic species associated with Cu2+ cations was highlighted by electron paramagnetic resonance (EPR) spectroscopy, pinpointing the presence of significant exchange interactions between Cu2+ ions. The mixed oxidation state of Cu induces the generation of free holes, which are confined in the nanoparticles, giving rise to a plasmonic resonance. The plasmonic properties were investigated as a function of Sn doping through vis-NIR absorption spectroscopy combined with magnetic circular dichroism (MCD). This approach enabled the extraction of charge carriers' density and mass, a key step for further optimization of CZTS-based photovoltaic devices.

Magnetic circularly polarized luminescence (MCPL), i.e. the possibility of generating circularly polarized luminescence in the presence of a magnetic field in achiral or racemic compounds, is a technique of rising interest. Here we show that the far-red spin-flip (SF) transitions of a molecular Cr(iii) complex give intense MCD (magnetic circular dichroism) and in particular MCPL (g MCPL up to 6.3 × 10-3 T-1) even at magnetic fields as low as 0.4 T. Cr(iii) doublet states and SF emission are nowadays the object of many investigations, as they may open the way to several applications. Due to their nature, such transitions can be conveniently addressed by MCPL, which strongly depends on the zero field splitting and Zeeman splitting of the involved states. Despite the complexity of the nature of such states and the related photophysics, the obtained MCPL data can be rationalized consistently with the information recovered with more established techniques, such as HFEPR (high-frequency and -field electron paramagnetic resonance). We anticipate that emissive molecular Cr(iii) species may be useful in magneto-optical devices, such as magnetic CP-OLEDs.

Multilayered metal-dielectric nanostructures display both a strong plasmonic behavior and hyperbolic optical dispersion. The latter is responsible for the appearance of two separated radiative and nonradiative channels in the extinction spectrum of these structures. This unique property can open plenty of opportunities toward the development of multifunctional systems that simultaneously can behave as optimal scatterers and absorbers at different wavelengths, an important feature to achieve multiscale control of light-matter interactions in different spectral regions for different types of applications, such as optical computing or detection of thermal radiation. Nevertheless, the temperature dependence of the optical properties of these multilayered systems has never been investigated. In this work, we study how radiative and nonradiative processes in hyperbolic meta-antennas can probe temperature changes of the surrounding medium. We show that, while radiative processes are essentially not affected by a change in the external temperature, the nonradiative ones are strongly affected by a temperature variation. By combining experiments and temperature-dependent effective medium theory, we find that this behavior is connected to enhanced damping effects due to electron-phonon scattering. Contrary to standard plasmonic systems, a red-shift of the nonradiative mode occurs for small variations of the environment temperature. Our study shows that, to probe temperature changes, it is essential to exploit nonradiative processes in systems supporting plasmonic excitations, which can be used as very sensitive thermometers via linear absorption spectroscopy.

The similar reactivity of lanthanides generally leads to statistically populated polynuclear complexes, making the rational design of ordered hetero-lanthanide compounds extremely challenging. Here we report on the site selectivity in hetero-lanthanide tetranuclear complexes afforded by the relatively simple ditopic pyterpyNO ligand (4'-(4-pyridil)-2,2':6',2"-terpyridine N-oxide). The sequential room temperature reaction of RE2(tta)(6)(pyterpyNO)(2) (where RE=Y, (1); Eu, (2), Dy, (3) Htta=2-thenoyltrifluoroacetone) with La(tta)(3)dme (dme=dimethoxyethane) yielded Y2La2(tta)(12)(pyterpyNO)(2) (4), Dy2La2(tta)(12)(pyterpyNO)(2) (5) and Eu2La2(tta)(12)(pyterpyNO)(2) (6). Single crystals X-ray diffraction studies showed that 4, 5 and 6 are isostructural, featuring a tetranuclear structure with two different metal coordination sites with coordination numbers 8 (CN8) and 9 (CN9). The two smaller cations are mainly bridged by the O-donor atoms of the NO groups of two pyterpyNO ligands (CN8), while the larger lanthanum centres are bound by a terpyridine unit (CN9). Size selectivity has been studied with structural and magnetic studies in the solid state and through F-19 NMR and photoluminescence studies in solution, showing a direct dependence on the difference of ionic radii of the ions and yielding a 91 % selectivity for 4. Furthermore, F-19 NMR, X-ray and PL studies pointed out that the nature of the product is independent from the synthetic route for compound Eu2Y2(tta)(12)(pyterpyNO)(2) (7), keeping the ion selectivity also for a self-assembly reaction. Unexpectedly, these studies have evidenced that selectivity is not exclusively governed by electrostatic interactions related to size dimensions.

Abstract Cesium lead bromide perovskite (CsPbBr3) nanocrystals have raised impressive interest as efficient and stable optoelectronic materials. Size and morphology play important roles in the final performances of these materials and advanced characterization studies are needed to elucidate structural and surface properties. In this work, CsPbBr3 cubic nanocrystals were obtained by colloidal synthesis and characterized by multinuclear Solid State NMR (SSNMR), complemented by X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and optical spectroscopy. The multinuclear NMR approach allowed the different components of the nanocubes to be separately observed. In particular, the surface ligands and their interactions with the nanocubes surface were investigated by 1H and 13C NMR experiments, while the structural investigation of the perovskite nanocubes was addressed by exploiting 207Pb and 133Cs spectral properties in comparison with bulk CsPbBr3. Static 207Pb NMR spectra indicated a possible contribution of chemical shift anisotropy from the 207Pb nuclei of the outer layer. The 133Cs NMR spectra showed signals with different chemical shifts for cesium atoms in at least three regions of the nanocubes, from the inner core to the surface, which were interpreted in terms of cubic layers with different distances from the surface using a simple geometrical model. This interpretation was also supported by 133Cs longitudinal relaxation time measurements.

Chiral materials formed by aggregated organic compounds play a fundamental role in chiral optoelectronics, photonics and spintronics. Nonetheless, a precise understanding of the molecular interactions involved remains an open problem. Here we introduce magnetic circular dichroism (MCD) as a new tool to elucidate molecular interactions and structural parameters of a supramolecular system. A detailed analysis of MCD together with electronic circular dichroism spectra combined to ab initio calculations unveils essential information on the geometry and energy levels of a self-assembled thin film made of a carbazole di-bithiophene chiral molecule. This approach can be extended to a generality of chiral organic materials and can help rationalizing the fundamental interactions leading to supramolecular order. This in turn could enable a better understanding of structure–property relationships, resulting in a more efficient material design.

Plasmonics represents a unique approach to confine and enhance electromagnetic radiation well below the diffraction limit, bringing a huge potential for novel applications, for instance, in energy harvesting, optoelectronics, and nanoscale biochemistry. To achieve novel functionalities, the combination of plasmonic properties with other material functions has become increasingly attractive. In this Perspective, we review the current state of the art, challenges, and future opportunities within the field of magnetoplasmonics in confined geometries, an emerging area aiming to merge magnetism and plasmonics to either control localized plasmons, confined electromagnetic-induced collective electronic excitations, using magnetic properties, or vice versa. We begin by highlighting the cornerstones of the history and principles of this research field. We then provide our vision of its future development by showcasing raising research directions in hybrid magnetoplasmonic systems to overcome radiation losses and novel materials for magnetoplasmonics, such as transparent conductive oxides and hyperbolic metamaterials. Finally, we provide an overview of recent developments in plasmon-driven magnetization dynamics, nanoscale opto-magnetism, and acousto-magnetoplasmonics. We conclude by giving our personal vision of the future of this thriving research field.

Nanoalloys combining magnetic and plasmonic properties are interesting systems for catalysis and photo-catalysis, magneto-optics, nanomagnetism and fundamental studies. Nevertheless, their synthesis is chal-lenging due to the immiscibility of Au and 3d magnetic metals at mild temperatures in equilibrium conditions. In this work we prepared through colloidal chemistry synthesis Au3LixM1-x (M = Fe, Ni or Co) nanoalloys and studied the synthetic conditions that affect the transition between a disordered and an ordered L12 intermetallic alloy crystal phase. We found that Au seeds act as templates for the formation of the intermetallic nanoalloys, and that lithium (coming from the Butyllithium reducing agent injected after the seeds formation) plays a fundamental role in the stabilization of the intermetallic phase. By tuning the synthetic parameters, we were able to tune the Fe content in Au3LixFe1-x intermetallic nanoalloys from 0.6 to 2.6 %, also tuning the magnetic moment of the nanoalloys. All the synthesized nanoalloys were able to sustain a plasmonic resonance in the visible range, which is blue shifted and broadened with respect to Au NPs. Our results can open colloidal syn-thesis to novel crystal phases and nanomaterials combining plasmonic and magnetic functionalities at the nanoscale.

Tuning the plasmonic response with an external magnetic field is extremely promising to achieve active magneto-plasmonic devices, such as next generation refractometric sensors or tunable optical components. Noble metal nanostructures represent an ideal platform for studying and modeling magnetoplasmonic effects through the interaction of free electrons with external magnetic fields, even though their response is relatively low at the magnetic field intensities commonly applied in standard magneto-optical spectroscopies. Here we demonstrate a large magnetoplasmonic response of silver nanoparticles by performing magnetic circular dichroism spectroscopy at high magnetic fields, revealing a linear response to the magnetic field up to 30 T. The exploitation of such high fields allowed us to probe directly the field-induced splitting of circular plasmonic modes by performing absorption spectra with static circular polarizations, giving direct experimental evidence that the magneto-optical activity of plasmonic nanoparticles arises from the energy shift of field-split circular magnetoplasmonic modes.

The engineering of the surface of nanomaterials with bioactive molecules allows controlling their biological identity thus accessing functional materials with tuned physicochemical and biological profiles suited for specific applications. Then, the manufacturing process, by which the nanomaterial surface is grafted, has a significant impact on their development and innovation. In this regard, we report herein the grafting of sugar headgroups on a graphene oxide (GO) surface by exploiting a green manufacturing process that relies on the use of vibrational ball mills, a grinding apparatus in which the energy is transferred to the reacting species through collision with agate spheres inside a closed and vibrating vessel. The chemical composition and the morphology of the resulting glyco-graphene oxide conjugates (glyco-GO) are assessed by the combination of a series of complementary advanced techniques (i.e. UV-vis and Raman spectroscopy, transmission electron microscopy, and Magic Angle Spinning (MAS) solid-state NMR (ssNMR) providing in-depth insights into the chemical reactivity of GO in a mechanochemical route. The conjugation of monosaccharide residues on the GO surface significantly improves the antimicrobial activity of pristine GO against P. aeruginosa. Indeed, glyco-GO conjugates, according to the monosaccharide derivatives installed into the GO surface, affect the ability of sessile cells to adhere to a polystyrene surface in a colony forming assay. Scanning electron microscopy images clearly show that glyco-GO conjugates significantly disrupt an already established P. aeruginosa biofilm.