Optical Materials: X最新文献

Nanotechnology research offers advancements in materials and industrial uses such as nano-electronics, medical sciences, fuel, biology, and technological innovation. The most often employed nanomaterial is Graphene oxide (GO), which has been regarded as a dominant progenitor for many specialized industries. The current work aims to establish a new, cost-effective, easy, and straightforward GO synthesis method. Laser spectroscopy and even traditional tools have been utilized for characterization. The prepared GO has been confirmed by XRD and FT-IR spectroscopy. Laser spectroscopy based on confocal microscopes like Raman micro-spectroscopy and fluorescence lifetime imaging microscopy (FLIM) has been used to ensure the synthesis of GO. Also, it could help in the detection of the prepared layer thickness. Raman spectroscopy detects the number of GO layers, which is one on average, while the Raman mapping shows a good distribution of GO on the substrate. Based on excitation with a 445 nm pulsed laser, FLIM shows that mono GO layers cover most of the surface while only a tiny area contains more than a single layer. The novel aspect of this work is the method of preparation and the way of utilizing both FLIM and Raman to detect the number of GO layers. The prepared GO could be used in many applications like solar cells and filtration.

In this work, vanadium pentoxide (V₂O₅) and titanium-modified V₂O₅ thin films were synthesized using the sol-gel spin coating route. The effect of Ti-doping concentration on the electrochromic optical properties and atomic/electronic structures of V₂O₅ smart thin films is examined. As the doping concentration of Ti increases, the surface roughness of the films is reduced. The structure of the films is analyzed using X-ray diffraction (XRD) and Raman spectroscopy, while the electrochromic modulation of atomic and electronic structures is elucidated through Raman and X-ray absorption spectroscopy (XAS) conducted during lithiation and delithiation. The XRD patterns demonstrate that an increase in Ti concentration leads to a more amorphous structure of the films and a shift of the main diffraction peak to a lower angle, attributable to the enlarged spacing between the stacking layers resulting from the incorporation of Ti ions. Soft X-ray absorption spectroscopy (XAS) and in situ hard XAS of the V L-edge, the O K-edge, and the V K-edge revealed a reduction in the charge state of V and local atomic structural symmetry modification upon lithated coloration and delithiated bleaching process. The critical insights provided by in situ XAS provides reveal that a small amount of Ti has the ability to modify the interlayer distance and local atomic structure of V₂O₅, thereby improving its electrochromic switching rate and stability when utilized in smart windows.

In this study the novel garnet-type Y_2.47Na_0.5Ln_0.03Al₅O₁₂, Y_2.97Ln_0.03Al_4.95V_0.05O₁₂, Y_2.92Na_0.05Ln_0.03Al_4.9833V_0.0167O₁₂ (Ln = Ce³⁺, Tb³⁺, Eu³⁺) phosphors were successfully synthesized by the sol-gel method for the first time. The structural, morphological and optical properties were characterized by using multiple characterization techniques. The XRD and FTIR results confirmed that all obtained phosphors are monophasic yttrium aluminium garnet compounds, i.e. the doping of Ce³⁺, Tb³⁺, Eu³⁺, Na⁺, V⁵⁺ ions does not induce any impurity phases, indicating the successful incorporation of these dopants into the YAG host. The formation of novel garnets was probed using ²⁷Al, ⁵¹V, ²³Na MAS NMR techniques. SEM micrographs revealed that almost in all cases, the surface of the obtained luminophores is porous and consists of homogeneously distributed irregular sphere-like shape particles, which tend to form larger agglomerates. The optical properties of obtained compounds were also investigated by recording their excitation and emission spectra and calculating the colour coordinates in the CIE 1931 colour space.

Tungstates play a major role in the, now for more than 60 years, ongoing scientific research of Eu(III) activated phosphors. Similarly, to other compounds featuring a closed shell transition metal anion like molybdates, vanadates, niobdates, tantalates, and tungstates are a family of materials that offer a wide range of potential host matrices for rare earth ions. Furthermore, tungstates provide several favourable characteristics like facile synthetic conditions via solid state synthesis, the possibility of high activator concentrations (low concentrations quenching), as well as intrinsic sensitization of lanthanides ions through a ligand-to-metal charge transfer (W⁶⁺/O²⁻). This review sets in by discussing the fundamentals of Eu(III) luminescence followed by a closer look at some general features of tungstates and their respective intrinsic luminescence. Various Eu(III) activated tungstates are explored in detail regarding their synthesis conditions and optical properties. Their compositional makeups and structures are correlated to the resulting optical properties. Potential strategies to improve the luminescent efficiency of new rare earth doped tungstates are derived from these correlations. In the closing section some general remarks regarding thermal quenching, concentration quenching, and charge transfer energies are discussed. Finally, comparisons to the related molybdates are drawn and the prospects of commercial application towards different fields of optical technologies are explored.

In this paper, we will address the several factors underlying the performance of scintillators in terms of light yield and energy resolution in the high-end medical imaging applications CT (Computed Tomography) and PET (Positron Emission Tomography. The state-of-the-art scintillators that are being applied in these modalities are discussed as well. We also address important scintillator properties like light yield, decay time and afterglow, energy resolution and the corresponding material- and activator choices. Finally, an outlook on these materials and technologies is presented.

New phenomena have been discovered at the nanoscale that allow us to manipulate light and design devices. Evanescent waves such as Surface Plasmon Polaritons are excited in dielectric–metal interfaces and propagate in the metal. If they reach other interfaces, they may be transmitted by the metal. It is a phenomenon known as Extraordinary Optical Transmission that occurs in nanostructures at the optical range. Depending on the metal it is possible to tune the wavelengths and incident angles where this phenomenon occurs. Gold, silver, aluminium and copper nanolayers are analysed on top of silicon (a-Si and c-Si) considering a sweep between 250 nm and 2500 nm. Considering a novel model based on Fresnel Coefficients in absorbing media, it is possible to improve energy harvesting in the ultraviolet–visible range, mainly due to the propagation of Surface Plasmon Polaritons. Then, the role of Surface Plasmon Polaritons in Air–Metal–Silicon nanostructures is analysed. The inclusion of the metal layer may decrease the reflectance by at least 10%, reaching values higher than 60%. The presented charts allow us to analyse the materials, wavelengths and incident angles where reflectance is decreased. There, the inclusion of metal layers brings benefits to the photodetection, since more energy is available in the absorbing layer. Considering this approach, the detection of specific wavelengths may be improved by introducing metals in the detectors.

Scintillators based on YVO₄:Er³⁺ and YVO₄:Er³⁺, Nd³⁺, synthesized through glucose-assisted sol-gel method and calcined under different temperatures were studied via X-ray excited optical luminescence (XEOL). The samples' crystalline structure was studied via X-ray powder diffraction and the crystallite size estimated by Scherrer's method. The results indicated the crystal purity phase in all samples, indexed as YVO₄, and crystallite size in nanometric order, which is in accordance with Transmission Electron Microscopy results that indicate the formation of nanoparticles with spherical shape tendency. The spectroscopic studies taken by XEOL demonstrated typical Er³⁺ and Nd³⁺ transitions were dominant on the emission spectra. An unusual host emission was also identified c.a. 340 and 600 nm and ascribed as an intrinsic host vanadate emission related with the material optical band gap (c.a. 3.5 eV) and/or associated with VO₄³⁻ to rare earth ions energy transfer. The scintillators kept the emission stability even exposed to ∼10¹⁰ photon/sec, which demonstrated their radiation hardness, which is an important feature to the application of YVO₄ based-materials as scintillators. Independently of the calcination temperature, glucose-assisted sol-gel method was reliable to produce YVO₄-based scintillators nanopowders with stable optical properties with potential to be applied in biological imaging and/or in theranostics.

Spherical silver nanoparticles (AgNps) show high scientific, economic, and biotechnological interest related to their photonic properties associated to the fascinating plasmonic absorption and antimicrobial activity, however, their synthesis using wet-chemical methods remains a challenge, in terms of control, repeatability, and reproducibility. Herein, we investigated two adapted strategies to produce water-suspended spheroidal and homogeneous AgNps by using sodium citrate (CT) and ascorbic acid (AA) as stabilizing and reducing agents, respectively. We also show the impact of experimental parameters such as reactional time, temperature, and precursor concentration, as well as their order/method of addition on the morphology and optical properties of AgNps that were intrinsically correlated through extinction spectra and transmission electron microscopy (TEM), additionally the activity of prepared AgNPs colloidal suspensions were tested against Staphylococcus aureus bacterium. The most controllable synthesis condition was achieved by methodology in which the silver precursor is added dropwise (one drop per second) to a solution at 70 °C containing CT and AA keeping the stirring for 20 min. The proposed methodology presented a high repeatability of the syntheses generating AgNps with regular size and shape (between 22 and 30 nm), being stable in water up to one year with slight changes in its plasmonic and morphological properties. A scale-up trial was also performed and the dropwise methodology allowed the obtention of spheroidal-AgNps suspensions five times more concentrated with the same morphological and optical control, which saves time and energy in the synthesis process. The AgNPs demonstrated a good antibacterial potential when the samples are freshly prepared, losing their activity as the samples age.

The point charge electrostatic model (PCEM) and the simple overlap model (SOM), both purely analytical crystal field models, are being briefly revisited, in order to show the evolution of their application to Eu doped compounds. Calculations are made through the method of equivalent nearest neighbours (MENN), and applied to the Eu(dipivaloylmethanate)₃1,10-phenanthroline [Eu(DPM)₃o-phen] complex, with the aim of discussing the Eu–O and Eu–N interactions. The charge of the Eu ion is calculated using the Batista-Longo improved model (BLIM) to give g_BLIM = 3,64e around the Eu-NN midpoint. The ⁷F₁ crystal-field levels and level splitting were satisfactorily reproduced with two charge factors, namely, g₁ = 0.495 and g₂ = 0.415, assuming the luminescent site in a tetragonal point symmetry slightly distorted. In particular, it is shown that the Eu³⁺, itself, is satisfied by attracting an amount of charge, which neutralize/stabilize its own site electrostatically, no matter what the ligating ions are. The Eu-NN overlap (ρ = <4f|2s2p>) is assumed to be 0.1, which is physically plausible both as a limit in respect to β, the SOM correction factor to the PCEM, and describes the covalent contribution to the Ln-NN interaction, the latter is the most important contribution of the SOM to the crystal-field theory of lanthanide containing compounds. An eloquent comparison with crystal-field levels of the Eu:LiYF₄ and Eu(btfa)₃(4,4-bipy)(EtOH) is made. Finally, this paper is, indeed, a very simple tribute to Professor Oscar L. Malta, as an acknowledgement of his deep contribution to the author's apprenticeship about crystal-field theory of systems containing lanthanides.