Recently, hBN has become an interesting platform for quantum optics due to the peculiar defect-related luminescence properties. In this work, multicolor radiative emissions are engineered and tailored by position-controlled low-energy electron irradiation. Varying the irradiation parameters, such as the electron beam energy and/or area dose, we are able to induce light emissions at different wavelengths in the green-red range. In particular, the 10 keV and 20 keV irradiation levels induce the appearance of broad emission in the orange-red range (600-660 nm), while 15 keV gives rise to a sharp emission in the green range (535 nm). The cumulative dose density increase demonstrates the presence of a threshold value. The overcoming of the threshold, which is different for each electron beam energy level, causes the generation of non-radiative recombination pathways.

Materials able to produce free radicals have gained increasing attention for environmental and biomedical purposes. Free radicals, such as the superoxide anion (O2o-), act as secondary mes-sengers in many physiological pathways, such as cell survival. Therefore, the production of free radicals over physiological levels has been exploited in the treatment of different types of cancer, including osteosarcoma (OS). In most cases, the production of radical oxygen species (ROS) by materials is light-induced and requires the use of chemical photosensitisers, making it difficult and expensive to produce. Here, for the first time, we propose photoluminescent hybrid ZrO2-acetylacetonate nanoparticles (ZrO2-acac NPs) able to generate O2o- without light activation as an adjuvant for the treatment of OS. To increase the uptake and ROS generation in cancer cells, we modify the surface of ZrO2-acac NPs with hyaluronic acid (HA), which recognizes and binds to the surface antigen CD44 overexpressed on OS cells. Since these nanoparticles emit in the visible range, their uptake into cancer cells can be followed by a label-free approach. Overall, we show that the generation of O2o- is toxic to OS cells and can be used as an adjuvant treatment to increase the efficacy of conventional drugs.

Air quality monitoring is an increasingly debated topic nowadays. The increasing spillage of waste products released into the environment has contributed to the increase in air pollution. Consequently, the production of increasingly performing devices in air monitoring is increasingly in demand. In this scenario, the attention dedicated to workplace safety monitoring has led to the developing and improving of new sensors. Despite technological advancements, sensors based on nanostructured materials are difficult to introduce into the manufacturing flow due to the high costs of the processes and the approaches that are incompatible with the microelectronics industry. The synthesis of a low-cost ultra-thin silicon nanowires (Si NWs)-based sensor is here reported, which allows us the detection of various dangerous gases such as acetone, ethanol, and the ammonia test as a proof of concept in a nitrogen-based mixture. A modified metal-assisted chemical etching (MACE) approach enables to obtain ultra-thin Si NWs by a cost-effective, rapid and industrially compatible process that exhibit an intense light emission at room temperature. All these gases are common substances that we find not only in research or industrial laboratories, but also in our daily life and can pose a serious danger to health, even at small concentrations of a few ppm. The exploitation of the Si NWs optical and electrical properties for the detection of low concentrations of these gases through their photoluminescence and resistance changes will be shown in a nitrogen-based gas mixture. These sensing platforms give fast and reversible responses with both optical and electrical transductions. These high performances and the scalable synthesis of Si NWs could pave the way for market-competitive sensors for ambient air quality monitoring.

Halide perovskites exhibiting broad band emission have attracted increasing attention since their discovery in 2014 because of their potential in lighting applications. Here, we report a new bromoplumbate organic-inorganic perovskite (C4-E)(2)PbBr4 where C4-E+ is the ethyl-butyrate-ammonium cation crystallizing in the polar space group Ccm2(1) at room temperature. This layered perovskite undergoes two reversible structural transitions at 45 degrees C and 180 degrees C assigned to a structural change and a rare congruent melting, respectively. Its emission properties are morphology dependent since crystals exhibit whitish emission due to a broad band (BB) extending in the whole visible range beside two excitonic emissions (HE and LE), while as thin films obtained by spin-coating the HE excitonic emission is by far the main component. PL measurements performed at different incident angles and different configurations, together with fluorescence microscopy analysis, reveal that the LE emission originates from the edges of crystals and HE from the bulk. PL measurements along with the temperature also revealed the effects of the structural transition on the two excitonic peaks, being partially quenched and red-shifted to 100-130 meV for temperatures above 45 degrees C, while minor changes of the BB emission was observed through the transition. This acentric material exhibits a strong SHG signal at room temperature, similar to the one exhibited by urea.

The preparation and characterization of three new complexes, namely [Pt(1,3-bis(4-triphenylamine-pyridin-2-yl)-4,6-difluoro-benzene)Cl] ([PtL1Cl]), [Pt(1,3-bis(4-triphenylamine-pyridin-2-yl)-5-triphenylamine-benzene)Cl] ([PtL2Cl]), and [Pt(1,3-bis(4-triphenylamine-pyridin-2-yl)-5-mesityl-benzene)Cl] ([PtL3Cl]), is reported. All of them are highly luminescent in dilute deaerated dichloromethane solution (?lum = 0.88-0.90, in the yellow-green region; the ?max,em in nm for the monomers are: 562, 561 and 549 for [PtL1Cl], [PtL2Cl] and [PtL3Cl], respectively).[PtL1Cl] is the most appealing, being characterized by a very long lifetime (103.9 ?s) and displaying intense NIR emission in concentrated deaerated solution (?lum = 0.66) with essentially no "contamination" by visible light < 600 nm. This complex allows the fabrication of both yellow-green and deep red/NIR OLEDs; OLED emissions are in the yellow-green (CIE = 0.38, 0.56) and deep red/NIR (CIE = 0.65, 0,34) regions, for [PtL1Cl] 8 wt% (with 11% ph/e EQE) and pure [PtL1Cl] (with 4.3% ph/e EQE), respectively.

A one dimensional (1D) perovskite-type (C6H7NBr)3[CdBr5] (abbreviated 4-BAPC) was synthesized by slow evaporation at room temperature (RT). 4-BAPC crystalizes in the monoclinic system with the space group P21/c. The 1D inorganic chains are formed by corner sharing CdBr6 octahedra. Thermal measurement shows that 4-BAPC is stable up to 190 °C. Optical characterization demonstrates that the grown crystal is an indirect bandgap material with a bandgap value of 3.93 eV, which is consistent with theoretical calculations. The electronic structure, calculated using density functional theory, reveals that the valence band originates from a combination of Br-4p orbitals and Cd-4d orbitals, whereas the conduction band originates from the Cd-5s orbitals. The photoluminescence spectroscopy shows that the obtained material exhibits a broad-band white light emission with extra-high CRI of 98 under lambda-exc=380 nm. This emission is mainly resulting from the self-trapped exciton recombinations within the inorganic CdBr6 octahedron, and the fluorescence within the organic conjugated ammonium salt.

Carbon quantum dots (CQD) were prepared from three different precursors and by three bottom-up synthesis methods: classical pyrolysis of citric acid (CAP), microwave irradiation of glucose (GM), and hydrothermal treatment of glucosamine hydrochloride (GAH). CQD were further functionalized using various nitrogen-containing compounds: 6-aminohexanoic acid, 1,6-diaminohexane, N-octylamine, dimethylamine, and tryptophan. Special attention was dedicated to investigate how the combination of synthetic method and starting material affected the nature and properties of CQD. The analysis indicated that CAP were good candidates for covalent post-functionalization, GM allowed an easy passivation, and GAH permitted the direct introduction of nitrogen into the core. The size distribution showed a core-shell structure for CQD functionalized with an aminoacid by microwave irradiation, whereas the thermal decomposition evidenced the degradation of functionalizing molecules and the presence of pyridinic and pyrrolic nitrogen after hydrothermal synthesis. Photoluminescence spectra revealed important differences between the synthesis techniques, related to the occurrence of surface states, and the highest fluorescence quantum yield for hydrothermally prepared CQD. These approaches led to CQD with properties that can be exploited in many fields from energy conversion to sensing.

The influence of the thermomechanical effects on the optical properties of germanium microstructures is investigated. Finite element method (FEM) calculations allow a complete spatial assessment of mechanical deformations induced by a silicon nitride (SiN) stressor layer deposited on Ge micropillars. Simulated strain maps are confirmed by experimental maps obtained by Raman spectroscopy. The theoretical investigation on strain-dependent band structure, including the presence of a strain gradient along the longitudinal direction, is exploited to fully capture photoluminescence spectroscopy experiments. Finally, the joint effect of temperature and strain on the fundamental bandgap is also quantified.

The power conversion efficiency of the formamidinium tin iodide (FASI) solar cells constantly increases, with the current record power conversion efficiency approaching 15%. The literature reports a broad anomaly distribution of the photoluminescence (PL) peak position. The PL anomaly is particularly relevant to photovoltaic applications since it directly links the material's bandgap and subgap defects energy, which are crucial to extracting its full photovoltaic potential. Herein, the PL of FASI polycrystalline thin film and powder is studied. It is found that a distribution of PL peak positions in line with the distribution available in the literature systematically. The distribution in PL is linked to the octahedral tilting and Sn off-centering within the perovskite lattice, influenced by the procedure used to prepare the material. Our finding paves the way toward controlling the energy distribution of tin perovskite and thus preparing highly efficient tin halide perovskite solar cells.

An altered fluffy type A Ca-Al-rich inclusion in the CR2 Renazzo carbonaceous chondrite was examined by combined Raman, scanning electron microscopy with energy dispersion system (SEM-EDS) and cathodoluminescence (CL) mapping. Blue CL at 450 nm and orange emission at 600 nm were related to anorthite and calcite, respectively. Raman spectra were highly fluorescent, and only the stronger peaks of anorthite, clinopyroxene and calcite were observed. Raman-induced fluorescence emission was measured using the 632-nm Raman laser source, up to 850 nm, and used to chart the mineral phases. A fluorescence structured peak at 690 nm, split in three subpeaks at 678, 689 and 693 nm, was found; it is likely related to the fluorescence emission of Cr3+ from a fassaitic pyroxene in anorthite. Secondary pyroxene in the Wark-Lovering rim does not show the peak at 690 nm; the different fluorescence emission from the secondary rim and the pyroxene patches within anorthite could be a marker to spot the primary pyroxene. From combined imaging, the events in the altered chondrite could be sequenced. Starting from a pristine assemblage of spinel and melilite, with little fassaite, several alteration episodes occurred. Alteration in secondary anorthite, which could be mapped by the blue CL emission at 450 nm, was followed by alkalization, with rims of sodalite and nepheline, and subsequent formation of secondary clinopyroxene, encircling the inclusion. Widespread calcite alteration, present also in the matrix between chondrules, was the last recorded event.

Titanium dioxide (TiO2) is a functional semiconductor metal oxide that plays amajor role in themany applicative fields,mostly includingwater remediation, surface functionalization and photoanodes for photoelectrochemical reactors. TiO2 is also one of the known chemoresistive materials that can be adopted as sensitive layers in solid state gas sensors. TiO2 has a peculiarly property in the fact that it exhibits two different photoluminescence (PL) spectra, depending on the crystalline polymorph considered (rutile or anatase), and that the PLemission of these two phases reacts differently as exposed to molecular oxygen (O2).We showsome representative results of this phenomenon, discussing the possibility to exploit it actual applications.

Metal-organic frameworks (MOFs) are a class of porous coordination networks extraordinarily varied in physicochemical characteristics such as porosity, morphologies, and compositions. These peculiarities make MOFs widely exploited in a large array of applications, such as catalysis, chemicals and gas sensing, drug delivery, energy storage, and energy conversion. MOFs can also serve as nanostructured precursors of metal oxides with peculiar characteristics and controlled shapes. In this work, starting from MIL125-(Ti), a 1,4-benzenedicarboxylate (BDC)-based MOF with Ti as metallic center, mesoporous TiO2 powders containing both anatase and rutile crystalline phases were produced. A challenging utilization of these porous MOF-derived Ti-based oxides is the optically-based quantitative detection of molecular oxygen (O2) in gaseous and/or aqueous media. In this study, the photoluminescence (PL) intensity changes during O2 exposure of two MOF-derived mixed-phase TiO2 powders were probed by exploiting the opposite response of rutile and anatase in VIS-PL and NIR-PL wavelength intervals. This result highlights promising future possibilities for the realization of MOF-derived doubly-parametric TiO2-based optical sensors.

A comparative study is presented on the photoluminescence (PL) response toward molecular oxygen (O2) in tin dioxide (SnO2), zinc oxide (ZnO) and titanium dioxide (TiO2) nanoparticles. The findings show that both PL enhancement and PL quenching can be observed on different materials, arguably depending on the spatial localization of the defects responsible for the PL emission in each different oxide. No significant results are evidenced for SnO2 nanoparticles. ZnO with red/orange emission shown an O2-induced PL enhancement, suggesting that the radiative emission involves holes trapped in surface vacancy oxygen centers. While the ZnO results are scientifically interesting, its performances are inferior to the ones shown by TiO2, which exhibits the most interesting response in terms of sensitivity and versatility of the response. In particular, O2 concentrations in the range of few percent and in the range of a few tenths of a part per million are both detectable through the same mixed-phase TiO2 sample, whose rutile phase gives a reversible and fast response to larger (0.4-2%) O2 concentration while its anatase phase is usable for detection in the 25-75 ppm range. The data for rutile TiO2 suggest that its surfaces host deeply trapped electrons at large densities, allowing good sensitivities and, more notably, a relatively unsaturated response at large concentrations. Future work is expected to improve the understanding and modeling of the photophysical framework that lies behind the observations.

Over the past 10 years, carbon dots (CDs) synthesized from renewable raw materials have received considerable attention in several fields for their unique photoluminescent properties. Moreover, the synthesis of CDs fully responds to the principles of circular chemistry and the concept of safe-by-design. This review will focus on the different strategies for incorporation of CDs in organic light-emitting devices (OLEDs) and on the study of the impact of CDs properties on OLED performance. The main current research outcomes and highlights are summarized to guide users towards full exploitation of these materials in optoelectronic applications.

The unique combination of organic and inorganic layers in 2D layered perovskites offers promise for the design of a variety of materials for mechatronics, flexoelectrics, energy conversion, and lighting. However, the potential tailoring of their properties through the organic building blocks is not yet well understood. Here, different classes of organoammonium molecules are exploited to engineer the optical emission and robustness of a new set of Ruddlesden-Popper metal-halide layered perovskites. It is shown that the type of molecule regulates the number of hydrogen bonds that it orms with the edge-sharing [PbBr6]4- octahedra layers, leading to strong differences in the material emission and tunability of the color coordinates, from deep-blue to pure-white. Also, the emission intensity strongly depends on the length of the molecules, thereby providing an additional parameter to optimize their emission efficiency. The combined experimental and computational study provides a detailed understanding of the impact of lattice distortions, compositional defects, and the anisotropic crystal structure on the emission of such layered materials. It is foreseen that this rational design can be extended to other types of organic linkers, providing a yet unexplored path to tailor the optical and mechanical properties of these materials and to unlock new functionalities.

Plasmon-exciton coupling is gaining increasing interest for enhancing the performance of optoelectronic, photonic and photo-catalytic devices. Herein we evaluate the interaction of excitons in zinc oxide tetrapods with surface plasmons of gold nanostructures with different morphologies. The gold nanostructures are grown in situ on ZnO tetrapods by means of a photochemical process, resulting in clean interfaces. The modification of the synthesis parameters results in different morphologies, as isolated nanoparticles, nano-domes or nanoparticles aggregates. Plasmon-exciton interaction is evaluated by means of cathodoluminescence spectroscopy and mapping at the nanoscale. The ZnO excitonic emission is strongly blue-shifted and broadened in close proximity of the gold nanostructures. This effect is explained by the formation of a Schottky barrier that is strongly mediated by the morphology of metal nanostructures

Metamorphic InAs/InGaAs quantum dots (QDs) have been proposed as active elements for optoelectronic light-emitting devices operating in the infrared range. However, advanced structure design to allow efficient and stable enhancement of quantum yield at room temperature are still needed. Here, we compare a metamorphic InAs/In0.15Ga0.85As QD heterostructure with and without GaAs confining barriers, to investigate the effect of introducing GaAs barriers on the photo- and thermo-electrical properties. GaAs confining barriers allow to enhance the QD photoluminescence intensity at 1.3 mu m, i.e. second telecommunication window, by more than two orders of magnitude at room temperature and at 80 K. We also discuss the effect of GaAs barriers on the carrier transport and on defect-related levels detected by means of photocurrent and deep level thermally stimulated current spectroscopies. GaAs confining barriers decrease the thermal escape rate of electrons confined in QD and wetting layer, thereby highly increasing the radiative recombination and also quenching the photocurrent. At low temperatures, the barriers also reduce the capture of electrons generated in InGaAs by the QD layer and, on the other hand, prevent the trapping of electrons outside the QD layer, decreasing carrier lifetimes. The deep levels identified as point and extended defects have been detected in the InGaAs layers. There are no new types of defects introduced in the structure by the addition of the barriers, but this causes a weakly increased density of traps near QDs. Our results show that InAs/InGaAs QDs with GaAs confining barriers can be efficient light emitters with only a slight increase of defects in the structure. Hence, such advanced design for metamorphic QDs can be of relevant interest for applications in energy-efficient QD lasers, optical amplifiers and single-photon emitters operating at 1.3-1.55 mu m.

We report a comprehensive investigation on stacking faults (SFs) in the 3C-SiC cross-section epilayer. 3C-SiC growth was performed in a horizontal hot-wall chemical vapour deposition (CVD) reactor. After the growth (85 microns thick), the silicon substrate was completely melted inside the CVD chamber, obtaining free-standing 4 inch wafers. A structural characterization and distribution of SFs was performed by mu-Raman spectroscopy and room-temperature mu-photoluminescence. Two kinds of SFs, 4H-like and 6H-like, were identified near the removed silicon interface. Each kind of SFs shows a characteristic photoluminescence emission of the 4H-SiC and 6H-SiC located at 393 and 425 nm, respectively. 4H-like and 6H-like SFs show different distribution along film thickness. The reported results were discussed in relation with the experimental data and theoretical models present in the literature.

The development of non-toxic fluorescent agents alternative to heavy metal-based semiconductor quantum dots represents a relevant topic in biomedical research and in particular in the bioimaging field. Herein, highly luminescent Si-H terminal microporous silicon nanoparticles with mu s-lived photoemission are chemically modified with a two step process and successfully used as label-free probes for in vivo time-gated luminescence imaging. In this context,Hydra vulgarisis used as model organism for in vivo study and validity assessment. The application of time gating allows to pursue an effective sorting of the signals, getting rid of the most common sources of noise that are fast-decay tissue autofluorescence and excitation scattering within the tissue. Indeed, an enhancement by a factor similar to 20 in the image signal-to-noise ratio can be estimated.

The stability of 2D organic-inorganic perovskites to solvents is key to enable the production of pervoskite devices with standard lithography techniques. Systematic studies of resiliance indicate that solvent polarity plays a central role.