Search Results (26)

Multimodal nanocomposites that combine optical and magnetic functionalities are of great interest for applications such as imaging and temperature sensing. Ternary CuInS₂ (CIS)-based quantum dots (QDs) offer low toxicity, strong near-infrared (NIR) emission, and high photostability, making them promising for optical nanothermometry and imaging. In this study, CIS QDs were synthesized using an aqueous cysteine-mediated approach. Manganese ferrite (MnFe₂O₄) nanoparticles were prepared as the magnetic component due to their non-toxicity and superparamagnetic properties. To integrate both functionalities, QDs and magnetic nanoparticles (MNPs) were encapsulated in silica and then combined to form multimodal CIS/MnFe₂O₄/SiO₂ nanocomposites. The structure and morphology of the materials were characterized by TEM and XRD, while their optical properties were examined using UV–Vis, photoluminescence (PL) spectroscopy. This design ensured optical isolation, preventing fluorescence quenching while maintaining colloidal stability. The obtained composites exhibited PL in the NIR region and a thermosensitivity of 2.04%/°C. TEM analysis confirmed uniform silica shell formation and successful integration of both components within the composite. The materials also retained the superparamagnetic behavior of MnFe₂O₄, making them suitable for combined optical and magnetic functionalities. These results demonstrate the potential of CIS/MnFe₂O₄/SiO₂ nanocomposites as multifunctional platforms for optical imaging, temperature monitoring, and magnetically modulated effects. Full article

NiO films were successfully deposited by sol–gel spin coating on Si, glass, and ITO-covered glass substrates. The impact of the film thickness (the different number of layers), annealing temperatures (from 300 to 500 °C), and the substrate type on the crystal structure, film morphology, optical, and vibrational properties was investigated. X-ray diffraction (XRD) revealed a polycrystalline structure and the appearance of the cubic NiO phase. Field Emission Scanning Electron Microscopy (FESEM) was applied to explore the surface morphology of NiO films, deposited on glass and ITO substrates. The oxidation states of Ni were determined by X-ray photoelectron spectroscopy (XPS). The presence of Ni²⁺ and Ni³⁺ states was supposed. UV–VIS–NIR spectroscopy revealed that NiO films possessed a high average transparency of up to 74.6% in the visible spectral range when they were deposited on glass substrates, and up to 76.9% for NiO films on ITO substrates. The thermal treatments and the film thickness slightly affected the film transparency in the spectral range of 450–700 nm. The work function (WF) of the samples was determined. This research showed that good properties of sol–gel NiO films can be compared to the properties of those films produced using complicated and expensive techniques. Full article

This study investigates the effects of different tungsten (W) doping contents on the optical transmittance, surface roughness, residual stress, and microstructure of evaporated vanadium dioxide (VO₂) thin films. W-doped VO₂ thin films with varying tungsten concentrations were fabricated using electron beam evaporation combined with ion-assisted deposition techniques, and deposited on silicon wafers and glass substrates. The optical transmittances of undoped and W-doped VO₂ thin films were measured by UV/VIS/NIR spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The root mean square surface roughness was measured using a Linnik microscopic interferometer. The residual stress in various W-doped VO₂ films was evaluated using a modified Twyman–Green interferometer. The surface morphological and structural characterization of the W-doped VO₂ thin films were performed by field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). Raman spectroscopy was used to analyze the structure and vibrational modes of different W-doped VO₂ thin films. These results show that the addition of tungsten significantly alters the structural, optical, and mechanical properties of VO₂ thin films. Full article

The fast detection of Extra Virgin Olive Oil (EVOO) adulteration with poorer quality and lower price vegetable oils is important for the protection of consumers and the market of olive oil from fraudulent activities, the latter exhibiting an increasing trend worldwide during the last few years. In this work, two optical spectroscopic techniques, namely, Laser-Induced Breakdown Spectroscopy (LIBS) and UV-Vis-NIR absorption spectroscopy, are employed and are assessed for EVOO adulteration detection, using the same set of olive oil samples. In total, 184 samples were studied, including 40 EVOOs and 144 binary mixtures with pomace, soybean, corn, and sunflower oils, at various concentrations (ranging from 10 to 90% w/w). The emission data from LIBS, related to the elemental composition of the samples, and the UV-Vis-NIR absorption spectra, related to the organic ingredients content, are analyzed, both separately and combined (i.e., fused), by Linear Discriminant Analysis (LDA), Support Vector Machines (SVMs), and Logistic Regression (LR). In all cases, very highly predictive accuracies were achieved, attaining, in some cases, 100%. The present results demonstrate the potential of both techniques for efficient and accurate olive oil authentication issues, with the LIBS technique being better suited as it can operate much faster. Full article

This paper reports on the successful preparation of a low absorption–emission thermal control coating on the surface of LAZ933 magnesium–lithium alloy using the micro-arc oxidation method. This study analyzed the microstructure, phase composition, and thermal control properties of the coating using Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), UV–visible near-infrared spectroscopy (UV-VIS-NIR) and infrared emissivity measurements. The results indicate that the hemispherical emissivity of the coating remains unaffected with an increase in temperature and holding time, while the solar absorption ratio gradually increases. The thermal control performance of the coating after a high-temperature experiment was found to be related to the diffusion of the Li metal element in the magnesium lithium alloy matrix, as determined by X-ray photoelectron spectroscopy (XPS), flame graphite furnace atomic absorption spectrometry (GFAAS) and Glow Discharge Optical Emission Spectroscopy (GD-OES). As the holding time is extended, the coating structure gradually loosens under thermal stress. The Li metal element in the substrate diffuses outward and reacts with O₂, H₂O and CO₂ in the air, forming LiO₂, LiOH, Li₂CO₃ and other products. This reaction affects the coating’s solar absorption ratio in the end. Full article

This study examines the impact of varying oxygen flow rates on the properties of Cu₂O thin films deposited via radio frequency (RF) magnetron sputtering. X-ray diffraction (XRD) analysis showed a phase transition from cubic Cu₂O to a mixed Cu₂O and CuO phase, eventually forming a Cu₄O₃ tetragonal structure as oxygen content increased. The surface morphology and cross-sectional structure of Cu₂O thin films observed through field emission scanning electron microscopy (FE-SEM) were found to vary significantly depending on the oxygen flow rate. X-ray photoelectron spectroscopy (XPS) indicated notable variations in the chemical states of copper and oxygen. The Cu 2p spectra revealed peaks around 933 eV and 953 eV for all samples, with the S01 sample (deposited with only argon gas) exhibiting the lowest intensity. The S02 sample showed the highest peak intensity, which then gradually decreased from S03 to S06. The O 1s spectra followed a trend with peak intensity being highest in S02 and decreasing with further oxygen flow rates, indicating the formation of complex oxides such as Cu₄O₃. UV-Vis-NIR spectroscopy results demonstrated a decrease in transmittance and optical band gap energy with increasing oxygen content, suggesting a decline in crystallinity and an increase in defects and impurities. These findings underscore the critical role of precise oxygen flow rate control in tailoring the structural, morphological, compositional, and optical properties of Cu₂O thin films for specific electronic and optical applications. Full article

In this study, we investigated the impact of polyvinyl alcohol (PVA) incorporation on the optical properties and oxygen detection performance of a titanium dioxide/methylene blue (TiO₂/MB) nanocomposite colorimetric indicator for packaging applications. The nanocomposite was synthesized via mechanical milling of TiO₂ nanoparticles with MB and citric acid. PVA, at varying concentrations (0, 3, 9, and 14 wt%), was introduced during the wet milling process to produce a homogeneous composite film. Spin coating was employed to fabricate TiO₂/MB nanocomposite films for oxygen detection evaluation. The influence of PVA loading on the films’ chemical functionalities and surface morphologies was assessed using Fourier-transform infrared spectroscopy (FTIR) and field-emission scanning electron microscopy (FE-SEM). The indicator’s activation process, involving a color change between bleached and colored states, and its recovery time were monitored via optical imaging and UV-VIS-NIR spectrophotometry. The results revealed that a PVA content of 9 wt% yielded well-defined films with enhanced stability of the TiO₂/MB nanocomposite’s oxygen detection performance. Full article

The present paper deals with a new two-in-one zero-dimensional (0D) organic–inorganic hybrid compound namely (C₆H₁₀N₂)₄[CdBr₆][CdBr₄]₂. This molecular crystal structure contains isolated CdBr₄ tetrahedra and CdBr₆ octahedra. The optical characterization by UV–Vis–NIR spectroscopy shows that the (C₆H₁₀N₂)₄[CdBr₆][CdBr₄]₂ exhibits a large gap energy of 4.97 eV. Under UV excitation, this hybrid material shows a bright cold white light emission (WLE) at room temperature. The photoluminescence (PL) analysis suggests that the WLE originates from the organic molecules. Density of states (DOS) analysis using the density functional theory (DFT) demonstrates that the calculated HOMO(Br)→LUMO(organic) absorption transition (4.1 eV) does not have significant intensity, while, the transition involving the valence band (VB) and the second and third conduction bands (CB) around 5 eV are allowed, which is in good agreement with the experimental gap value. The interesting theoretical result is that the LUMO(organic)→HOMO(Br) emission is allowed, which confirms the important role of the organic molecule in the emission mechanism, in good agreement with the experimental PL analysis. Full article

A series including single and mixed Ni-Co aluminates was obtained using the precursor method, with malic acid as a ligand. The malate precursors (polynuclear coordination compounds) were isolated and characterized by Fourier Transform Infrared (FTIR), Ultraviolet/Visible/Near Infrared (UV–Vis–NIR) spectroscopy, and thermal analysis. The UV–Vis–NIR spectra of the synthesized complex compounds highlighted the presence of Co²⁺ and Ni²⁺ in an octahedral environment. The thermal decomposition of these precursors led to Co_1−xNi_xAl₂O₄ (x = 0, 0.1, 0.25, 0.5, 0.75, 0.9, and 1) spinels. The effect of Ni²⁺ substitution on the structure, morphology, and optical properties of the obtained oxides was studied with the help of different characterization tools. XRD, FTIR, and Raman spectra evidenced the formation of the spinel phase. The size of the crystallites and the agglomeration degree of the particles decrease when the nickel content increases. The band gap (BG) value is not significantly influenced by the Ni substitution. The fluorescence spectra recorded for all samples show a similar pattern, but different intensities of the emission bands. Full article

The blending approach (also known as the ex-situ approach) was used for the deposition of thin composite films comprising poly(vinyl alcohol-graft-methyl acrylate) (PVA-g-PMA) and silver nanoparticles (AgNPs). Firstly, the copolymer aqueous dispersion was synthesized through the redox polymerization of methyl acrylate (MA) on poly(vinyl alcohol) (PVA) using ammonium cerium (IV) nitrate as the initiator. Then, AgNPs were synthesized through a “green” method using the water extract of lavender based on by-products of the essential oil industry, and then they were blended with the polymer. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) were used to determine nanoparticle size, along with their stability over time in suspension, during the 30-day period. Thin films of the PVA-g-PMA copolymer, with different AgNP volume fractions varying between 0.008 and 0.260%, were deposited via the spin-coating method on Si substrates, and their optical properties were explored. UV-VIS-NIR spectroscopy and non-linear curve fitting were used for the determination of the refractive index, extinction coefficient, and thickness of the films, while photoluminescence measurements at room temperature were conducted for studying the emission of the films. The concentration dependence of film thickness was observed and showed that thickness increased linearly from 31 nm to 75 nm when the nanoparticles’ weight content increased from 0.3 wt% to 2.3 wt%. The sensing properties toward acetone vapors were tested in a controlled atmosphere by measuring reflectance spectra before and during exposure to the analyte molecules in the same film spot; the swelling degree of films was calculated and compared to the corresponding undoped samples. It was shown that the concentration of AgNPs of 1.2 wt% in the films is optimal for the enhancement of the sensing response toward acetone. The influence of AgNPs on the films’ properties was revealed and discussed. Full article

In this paper, as-synthesized and oleic acid (OA)-surface-treated zinc oxide (ZnO) nanocrystals were successfully synthesized and investigated for cool-nanopigment applications. ZnO nanocrystals were synthesized using the thermal decomposition method. The OA-surface-treated ZnO sample was obtained with an OA:ZnO ratio of 1:1. The structural, optical and morphological properties of the samples were characterized via X-ray diffraction (XRD), Fourier transform infrared (FTIR), UV-VIS-NIR diffused reflectance spectroscopy (DRS) and field-emission scanning electron microscopy (FE-SEM) techniques. ZnO nanocrystals possess a well-known zincate phase of ZnO, as confirmed for the as-synthesized sample with a reduction in the integrity of the ZnO crystalline structure upon the application of the OA coating. XRD peaks broadening and decreasing in crystallite size were obtained upon the surface modification of the ZnO by OA. The average crystallite size decreased from 31.5 to 17.4 nm, and the surface area changed from 23.37 to 7.48 m²/g upon OA treatment. These changes were attributed to the well-capping of the ZnO nanoparticles by OA, and, furthermore, OA increased the dispersion of the nanoparticles. The optical band gap of the investigated samples demonstrated a blue shift from 3.06 eV to 3.22 eV upon treatment. Both samples showed high NIR reflectance ($R_{NIR}^{\ast }$) values, which makes them well qualified for use as cool nanopigments. Additionally, the as-synthesized sample showed an $R_{NIR}^{\ast }$ value higher than that of the treated sample. Full article

Nowadays, scientists are interested in inorganic luminescence materials that can be excited with UV or NIR radiation and emit in the visible range. Such inorganic materials can be successfully used as luminescent or anti-counterfeiting pigments. In this work, we report the synthesis and optical properties investigation of solely Tm³⁺ doped and Yb³⁺/Tm³⁺ co-doped K₂Gd(PO₄)(WO₄) phosphors. The single-phase samples were prepared using a solid-state reaction method. The Tm³⁺ concentration was changed from 0.5% to 5%. Downshifting and upconversion emission studies were performed under 360 nm and 980 nm excitation, respectively. Yb³⁺ ions were used as sensitizers in the K₂Gd(PO₄)(WO₄) phosphors to transfer the captured energy to Tm³⁺ ions. It turned out that under UV excitation, phosphors emitted in the blue spectral area regardless of the presence or absence of Yb³⁺. However, a very strong deep-red (~800 nm) emission was observed when Yb³⁺ and Tm³⁺-containing samples were excited with a 980 nm wavelength laser. It is interesting that the highest upconversion emission in the UV/Visible range was achieved for 20% Yb³⁺, 0.5% Tm³⁺ doped sample, whereas the sample co-doped with 20% Yb³⁺, 2% Tm³⁺ showed the most intensive UC emission band in the NIR range. The materials were characterized using powder X-ray diffraction and scanning electron microscopy. Optical properties were studied using steady-state and kinetic downshifting and upconversion photoluminescence spectroscopy. Full article

Herein, spectrally selective single-layered CuO nanocoatings were successfully demonstrated via green synthesis and deposited on stainless steel (SS) substrates using a spin coater at 700, 800, 900, and 1000 rpm. The morphological, structural, and compositional analyses of the obtained nanocoatings were studied using SEM, XRD, EDX, and Raman spectroscopy. The SEM images show nanorod-like structure surfaces with dense surface morphology. The XRD patterns confirmed the presence of peaks indexed to a monoclinic structural phase of CuO. The EDX spectra clearly revealed the presence of Cu and O elements, and XPS spectra showed peaks of Cu2p and O1s core levels, which are typical characteristics of Cu (II) and O(II), respectively, in CuO. The Raman spectra showed peaks at 305, 344, and 642 cm⁻¹ attributed to Raman active (A_g+2B_g) modes for Cu-O stretching. Rutherford backscattering spectrometry (RBS) determined the content of the elements and the changes in the thicknesses of the coatings with the rotational speed (RS) of the spin coater. The elemental content of Cu and O atoms were, respectively, 54 and 46%. The thicknesses were calculated to be 1.406 × 10¹⁸ atoms/cm² (296.3 nm), 1.286 × 10¹⁸ atoms/cm² (271.0 nm), 1.138 × 10¹⁸ atoms/cm² (239.8 nm), and 0.985 × 10¹⁵ atoms/cm² (207.5 nm) at 700, 800, 900 and 1000 rpm, respectively. The optical properties of the CuO nanocoatings were characterized using UV–Vis–NIR and FTIR spectrometers; its vital solar selectivity parameters of solar absorptance (α) and emissivity (ε) were evaluated in the ranges of 0.3–2.5 and 2.5–20 µm wavelengths, respectively. The obtained coatings exhibited solar parameters (α = 0.90, and ε = 0.31) associated with 700 rpm due to an intrinsic and interference-induced absorption as well as higher attenuation of light. Full article

The property of persistent luminescence shows great potential for anti-counterfeiting technology and imaging by taking advantage of a background-free signal. Current anti-counterfeiting technologies face the challenge of low security and the inconvenience of being limited to visible light emission, as emitters in the NIR optical windows are required for such applications. Here, we report the preparation of a series of Zn_1+xGa_2−2xSn_xO₄ nanoparticles (ZGSO NPs) with persistent luminescence in the first and second near-infrared window to overcome these challenges. ZGSO NPs, doped with transition-metal (Cr³⁺ and/or Ni²⁺) and in some cases co-doped with rare-earth (Er³⁺) ions, were successfully prepared using an improved solid-state method with a subsequent milling process to reach sub-200 nm size particles. X-ray diffraction and absorption spectroscopy were used for the analysis of the structure and local crystal field around the dopant ions at different Sn⁴⁺/Ga³⁺ ratios. The size of the NPs was ~150 nm, measured by DLS. Doped ZGSO NPs exhibited intense photoluminescence in the range from red, NIR-I to NIR-II, and even NIR-III, under UV radiation, and showed persistent luminescence at 700 nm (NIR-I) and 1300 nm (NIR-II) after excitation removal. Hence, these NPs were evaluated for multi-level anti-counterfeiting technology. Full article

Solar energy presents the greatest potential by which to produce heat energy with reduced carbon emissions for power generation. To increase its harvesting and conversion, it is necessary to understand fundamental concepts and develop new materials. Although many processes can obtain selective absorbing surfaces (SAS) for application in solar energy exploitation, including electroplating methods, those processes have not sufficiently investigated the substrate’s treatment impact. The present work investigates 304 stainless steel (SS304) substrates treatment influence on the film’s (coatings) optical properties of SAS based on CrO₃ electroplating. For this purpose, three main steps featured in the methodology: substrates treatment, coatings deposition, and physical-chemical characterization. The former was performed by detergent cleaning (DC), acid treatment (AT), and electropolishing (EP). Then, coatings were electroplated towards chromium deposition on the substrates with different deposition times. Finally, films were characterized by Profilometry, UV-Vis-NIR, and IR regions Spectroscopy and Scanning Electron Microscopy (SEM). The results indicated that, in terms of surface treatments on the substrate, the electropolished (EP) substrates presented average roughness values of 35 nm, reflectivity of 5.09%, and clear morphological difference (SEM) when compared to other treatments in this study (DC and AT). A SAS was successfully obtained, and the electropolished substrates (EP) presented coatings with better optical performance than other samples (DC and AT), with absorptivity values around 98% and emissivity of approximately 7%. A relationship between substrate treatment, its roughness, and the impacts on the optical selectivity of SASs was observed. Therefore, electropolishing is presented as a promising treatment for the SASs substrates. Full article