Carbon dots have emerged as promising luminescent materials for solid-state lighting and color-conversion applications; however, their photoluminescence efficiency in the solid state is often limited by aggregation-induced quenching phenomena. In this work, we systematically investigate the role of the molar precursor ratio on the optical properties of green-emitting carbon dots, with the aim of establishing a direct link between synthesis parameters, photoluminescence optimization, and device-level performance. By carefully tuning the precursor ratio during synthesis, a significant enhancement of photoluminescence intensity and a strong suppression of solid-state quenching are achieved while preserving spectral stability in the green region. The optimized carbon dots exhibit improved radiative recombination and favorable optical characteristics for solid-state integration. Building on these results, the carbon dots are successfully employed as color-conversion layers in the fabrication of green light-emitting diodes, demonstrating efficient green emission under electrical excitation. This study highlights precursor ratio engineering as a simple and effective strategy to tailor carbon dot photoluminescence and provides a clear pathway from materials optimization to the realization of green color-conversion LED devices.

Alpha-phase molybdenum trioxide (alpha-MoO3) has recently attracted much attention in the nanophotonics community because of its strong ability to excite surface phonon polaritons (SPhPs), exploitable in many applications ranging from the sensing of biomolecules to the realization of polarizers and filters in the mid-infrared. In this paper, we report on fabrication, characterization and optimization of alpha-phase MoO3 thin films grown by pulsed laser deposition. Different process conditions were tested through structural and optical characterization to obtain the most suitable films for mid-infrared photonic applications.

SrMoO3 (SMO) thin films offer exceptional UV transparency and metallic conductivity, making them ideal transparent electrodes for UV-C LEDs. However, their deposition is challenged by thermodynamic instability, where trace oxygen triggers oxidation to insulating SrMoO4. This study employs pulsed laser deposition (PLD) under either high vacuum or oxygen, or argon atmosphere, to grow epitaxial SMO on lattice-matched (001) LSAT and (110) GdScO3 substrates. Structural and electrical characterization reveals that oxygen pressures induce SrMoO4 formation, increasing sheet resistance. Critically, post-deposition vacuum annealing at 850 degrees C decomposes SrMoO4 inclusions, reducing resistance by three orders of magnitude. These results establish oxygen suppression during growth and corrective annealing as essential strategies for realizing high-conductivity SMO electrodes in UV-C optoelectronics.

This study presents a comprehensive analysis of the optical and electronic properties of thin films of molybdenum oxide and tungsten oxide to implement hole-selective contact for heterojunction solar cells. These contacts are currently viewed as an alternative for the fabrication of doping-free solar cells. However, the spreading of this technology is still limited due to the development of S-shaped J-V curves, which affect the electrical performance of the cells, and further optimization in the material deposition process is therefore crucial to overcome these challenges. To improve transition metal oxide-based heterojunction technology, this work investigates the impact of oxygen vacancies on electrical performance, particularly their role in S-shaped J-V curves. Defect density evaluation through nondestructive techniques like photothermal deflection spectroscopy together with a detailed experimental characterization is presented in this paper to highlight the structural and optical properties of the films. Prototypes of solar cells incorporating hole-selective contacts with tungsten and molybdenum oxide are prepared to show S-shaped J-V characteristics under AM 1.5 illumination. An equivalent circuit modeling was used for understanding the electrical characteristics of the prototypes. Furthermore, this approach offers insights into the optimization of the performances of devices.

Alpha-phase molybdenum trioxide ($\alpha-\text{MoO}_{3}$) has recently attracted much attention in the nanophotonics community because of its strong ability to excite surface phonon polaritons (SPhPs), exploitable in many applications ranging from the sensing of biomolecules to the realization of polarizers and filters in the mid-infrared. In this paper, we report on fabrication, characterization and optimization of alpha-phase $\text{MoO}_{3}$ thin films grown by pulsed laser deposition. Different process conditions were tested through structural and optical characterization to obtain the most suitable films for mid-infrared photonic applications.

We present chemical beam vapor deposition (CBVD) as a valuable technique for the fabrication of good quality HfO2-based memristors. This deposition technique gives the opportunity to rapidly screen material properties in combinatorial mode and to reproduce the optimized conditions homogenously on large substrates. Cu/HfO2/Pt memory devices with three different oxide thicknesses were fabricated and electrically characterized. A bipolar resistive switching and forming free behavior was seen in all the tested devices. Lower switching voltages than similar devices fabricated by employing different deposition techniques were observed. The conduction mechanism in the low resistance state can be ascribed to filamentary copper, while a trap-controlled space charge limited current conduction was observed in the high resistance state. The comparative evaluation of devices with different oxide thicknesses allows to infer that devices with thicker HfO2 film (25 nm) are more performing in terms of ROFF/RON ratio (106), and reproducible resistive switching over more than 100 cycles in both low and high resistance states. Thinner oxide devices (20 nm and 16 nm), despite similar long retention time (104 s), and lower SET/RESET voltages show instead a smaller memory window and a switching instability. These results, compared also with other reported in literature for similar memristive structures realized with other deposition techniques, show that CBVD can be considered as a promising technique for realizing HfO2-based non-volatile memory devices with good performance.

The development of mid-infrared nanophotonics relies on the availability of new materials combining metal- and insulator-like optical features. We systematically studied the phase transition of thermochromic vanadium dioxide (VO2) using substitutional tungsten doping at room temperature. Our results reveal that vanadium dioxide thin films, doped with tungsten and grown via pulsed laser deposition techniques on sapphire substrates, can be precisely engineered to exhibit tailored infrared phonon and plasmon polaritonic responses. By controlling the extent of tungsten concentration, starting from VO2-WO3 cold-pressed powder targets, we demonstrate the ability to continuously adjust both the amplitude and frequency of optical phonon resonances. Furthermore, we observe tunable free-electron response due to varying tungsten concentrations. The adopted fabrication technique makes it possible to create multilayer structures by alternating layers with different concentrations of tungsten. Our results pave the way for the development of tunable mid-infrared metamaterial devices operating at room-temperature.

We report on a promising approach to realize bifacial silicon carbide (SiC) based ultraviolet (UV) photodetectors with no metallic electrodes. The ohmic contact regions, consisting of a few conductive carbon-rich layers, while maintaining the necessary UV sensitivity for the photodetector’s operation, are directly realized using a nanosecond-pulsed excimer laser. By combining structural, optical, and electrical characterization, we demonstrate how this treatment allows the formation of ohmic contacts, on both front and rear side, using fluence higher than 1.6 J/cm 2 and 3.2 J/cm 2 , respectively.

In this work, a study about how to produce color conversion layer for Light Emitting Diodes (LEDs) in a simple, fast and cost-effective way, using carbon dots (CDs) made from urea (U) and citric acid (CA), is reported. In our method, an auto generated matrix of urea and other subproducts such as cyanuric acid, incorporates the CDs, drastically reducing their intrinsic photoluminescence self-quenching in solid state form.

Abstract In this paper we report a rapid, low cost and easy way to produce solid-state luminescent carbon-dots (CDs) as color converters for light-emitting diodes (LEDs). CD precursor (urea and citric acid) molar ratio in aqueous solution is varied with the aim to find out the best conditions for an efficient color conversion and reducing photoluminescence quenching without any additional treatments, and to produce color conversion LEDs in a simple and green way.

The temperature tunability of complex dielectric constants of vanadium dioxide (VO2) makes it a promising phase-change material for use in active, dynamic, tunable photonics applications. Specifically, the semiconductor-to-metal phase transition in VO2 enables reversible, broadband, and large complex refractive index variation and paves the way for a plethora of applications. Although the critical temperature for phase-transition is 68 °C for VO2 films, its transition temperature can be reduced to room temperature by tungsten-doping of vanadium dioxide. Such a degree of freedom in controlling the critical temperature through tungsten doping provides further tunability of the thermochromic behavior. In this work, we investigate a variety of W-doped VO2 thin films deposited by laser ablation of targets with increasing W doping content and report detailed infrared characterization together with numerical simulations. Our experimental results indicate that the perfect absorption can be achieved at different temperatures, within the VO2 insulator-to-metal phase transition process, as a function of W doping content. Tunable subwavelength layers allow perfect absorption under different temperature conditions around λ = 12 µm. We show that a high dynamic range of reflectivity can be achieved when the temperature is increased above the phase transition temperature. Furthermore, we observe perfect absorption at 11.8 µm at room temperature for a W content of 0.75%. We believe that W-doped VO2 thin films with tunable and controllable perfect absorption will open the way for a class of promising thermo-optical devices including thermos-photovoltaics, infrared filters, radiative cooling devices, and thermal emitters.

We investigated infrared reflectivity of undoped and Tungsten (W) doped Vanadium dioxide (VO2) films at varying temperatures. Undoped VO2 exhibited a clear phase transition at 100°C, achieving near 0% reflectivity, or perfect light absorption. As W doping concentration increased, the phase-transition temperature decreased, maintaining the zero-reflectivity condition. Only a 0.75% W doping enabled room temperature perfect absorption without heating the film.

This paper reviews the state-of-the-art technologies, characterizations, materials (precursors and encapsulants), and challenges concerning multicolor and white light-emitting diodes (LEDs) based on carbon dots (CDs) as color converters. Herein, CDs are exploited to achieve emission in LEDs at wavelengths longer than the pump wavelength. White LEDs are typically obtained by pumping broad band visible-emitting CDs by an UV LED, or yellow–green-emitting CDs by a blue LED. The most important methods used to produce CDs, top-down and bottom-up, are described in detail, together with the process that allows one to embed the synthetized CDs on the surface of the pumping LEDs. Experimental results show that CDs are very promising ecofriendly candidates with the potential to replace phosphors in traditional color conversion LEDs. The future for these devices is bright, but several goals must still be achieved to reach full maturity.

III-N light-emitting-diodes (LEDs) are subject of intense investigations, thanks to their high efficiency and great reliability. The quality of the semiconductor material has a significant impact on the electro-optical performance of LEDs: for this reason, a detailed characterization of defect properties and the modeling of the impact of defects on device performance are of fundamental importance. This presentation addresses this issue, by discussing a set of recent case studies on the topic; specifically, we focus on the experimental characterization of defects, and on the modeling of their impact on the electro-optical characteristics of the devices.

The application of titanium dioxide (TiO2) in the photovoltaic (PV) field is gaining traction as this material can be deployed in doping-free heterojunction solar cells with the role of electron selective contact. For modeling-based optimization of such contact, knowledge of the titanium oxide defect density of states (DOS) is crucial. In this paper, we report a method to extract the defect density through nondestructive optical measures, including the contribution given by small polaron optical transitions. The presence of both related to oxygen-vacancy defects and polarons is supported by the results of optical characterizations and the evaluation of previous observations resulting in a defect band fixed at 1 eV below the conduction band edge of the oxide. Solar cells employing pulsed laser deposited-TiO2 electron selective contacts were fabricated and characterized. The J-V curve of these cells showed, however, an S-shape, then a detailed analysis of the reasons for such behavior was carried out. We use a model involving the series of a standard cell equivalent circuit with a Schottky junction in order to explain these atypical performances. A good matching between the experimental measurements and the adopted theoretical model was obtained. The extracted parameters are listed and analyzed to shed light on the reasons behind the low-performance cells.

Thin layers of MoOx have been deposited by thermal evaporation followed by post-deposition annealing. The density of states distributions of the MoOx films were extracted deconvoluting the absorption spectra, measured by a photothermal deflection spectroscopy setup, including the small polaron contribution. Results revealed a sub-band defect distribution centered 1.1 eV below the conduction band; the amplitude of this distribution was found to increase with post-deposition annealing temperature and film thickness.

Recent studies demonstrated that the performance of InGaN/GaN quantum well (QW) light emitting diodes (LEDs) can be significantly improved through the insertion of an InGaN underlayer (UL). The current working hypothesis is that the presence of the UL reduces the density of non-radiative recombination centers (NRCs) in the QW itself: during the growth of the UL, surface defects are effectively buried in the UL, without propagating towards the QW region. Despite the importance of this hypothesis, the concentration profile of defects in the quantum wells of LEDs with and without the UL was never investigated in detail. This paper uses combined capacitance-voltage and steady-state photocapacitance measurements to experimentally identify the defects acting as NRCs and to extract a depth-profile of the traps, thus proving the incorporation upon indium-reaction. Specifically: (i) we demonstrate that LEDs without UL have a high density (9.2 × 1015 cm−3) of defects, compared to samples with UL (0.8 × 1015 cm−3); (ii) defects are located near midgap (E C-1.8 eV, corresponding to E i-E T ∼ 0.3 eV), thus acting as efficient NRCs; (iii) crucially, the density of defects has a peak within the QWs, indicating that traps are segregated at the first grown InGaN layers; (iv) we propose a model to calculate trap distribution in the QW, and we demonstrate a good correspondence with experimental data. These results provide unambiguous demonstration of the role of UL in limiting the propagation of defects towards the QWs, and the first experimental characterization of the properties of the related traps.

A cheap, compact and customisable characterisation system for memristor devices, working between +/- 10 V, is presented. SPICE (Simulation Program with Integrated Circuit Emphasis) simulations are performed to verify the circuit feasibility and a proper software is developed to drive the system. The potentiality of the realised system is tested by performing several electrical measurements on both Cu/HfO2/Pt memristors and two-terminals com-mercial devices.