UV Reflectance Spectroscopy Research Articles

On the optical properties of monoclinic Na3AlF6 and Na3AlF6:Mn4+

Mn4+ activated luminescent materials have attracted much attention as colour converters for light sources and displays. In particular, alkali metal hexafluorometallates, such as K2SiF6:Mn4+ or K2TiF6:Mn4+, emit light in the red spectral region if pumped by phosphor converted LEDs (pcLED). In accordance with Zhu et al. we applied the cation-exchange method in order to synthesize Mn4+ doped Na3AlF6. Na3AlF6:Mn4+ exhibits efficient red photoluminescence peaking at 627 nm, which can be assigned to the 2Eg → 4A2g intraconfigurational transition of Mn4+ ([Ar]3d.3 configuration) within the [MnF6]2- octahedra on the aluminum site in the cryolite host structure. Photoluminescence properties, such as temperature dependence of the PL intensity and luminescence lifetime are presented. Additionally, the band structure of the undoped host material has been treated with Density Functional Theory (DFT). The theoretical results have been evaluated experimentally with diffuse UV reflectance spectroscopy. Finally, luminous efficacy and color rendering values of simulated warm white emitting pcLEDs comprising a dichromatic phosphor blend employing Na3AlF6:Mn4+ as the red emitting component are calculated and compared to the performance of warm white emitting pcLEDs comprising K2SiF6:Mn4+ as red emitting component.

Coal-based graphene as a promoter of TiO2 catalytic activity for the photocatalytic degradation of organic dyes

Graphene oxide (GO) obtained from coal-based graphite by the Hummers method was hydrothermally treated to obtain reduced GO (rGO). TiO2 was mixed with aqueous suspensions of GO and rGO and dried at 70 °C to obtain GO-TiO2 and rGO-TiO2 with 95 wt% TiO2. TiO2 was also combined with a GO suspension by hydrothermal treatment to obtain rGO-hTiO2 with 95 wt% TiO2. The three hybrids were used as catalysts for the photocatalytic degradation of rhodamine B (Rh B) and methyl orange (MO). Of the three materials, rGO-hTiO2 had the highest catalytic activity for the degradation of Rh B and MO under visible light irradiation. The reasons for having the best catalytic activity are that the incorporation of rGO into TiO2 helps increase its adsorption capacities for Rh B and MO as evidenced by adsorption in dark, and a narrowing of the TiO2 band gap as revealed by diffuse UV reflectance spectroscopy. This reduces the rate of recombination of electron-hole pairs by there being intimate contact between the TiO2 particles and rGO, forming Ti-O-C bonds as confirmed by XPS, with the TiO2 particles being uniformly decorated on the rGO sheets.

UV Hyperspectral Imaging as Process Analytical Tool for the Characterization of Oxide Layers and Copper States on Direct Bonded Copper.

Hyperspectral imaging and reflectance spectroscopy in the range from 200–380 nm were used to rapidly detect and characterize copper oxidation states and their layer thicknesses on direct bonded copper in a non-destructive way. Single-point UV reflectance spectroscopy, as a well-established method, was utilized to compare the quality of the hyperspectral imaging results. For the laterally resolved measurements of the copper surfaces an UV hyperspectral imaging setup based on a pushbroom imager was used. Six different types of direct bonded copper were studied. Each type had a different oxide layer thickness and was analyzed by depth profiling using X-ray photoelectron spectroscopy. In total, 28 samples were measured to develop multivariate models to characterize and predict the oxide layer thicknesses. The principal component analysis models (PCA) enabled a general differentiation between the sample types on the first two PCs with 100.0% and 96% explained variance for UV spectroscopy and hyperspectral imaging, respectively. Partial least squares regression (PLS-R) models showed reliable performance with R2c = 0.94 and 0.94 and RMSEC = 1.64 nm and 1.76 nm, respectively. The developed in-line prototype system combined with multivariate data modeling shows high potential for further development of this technique towards real large-scale processes.

Synthesis and characterization of Fe(III)-Fe(II)-Mg-Al smectite solid solutions and implications for planetary science

AbstractThis study demonstrates the synergies and limits of multiple measurement types for the detection of smectite chemistry and oxidation state on planetary surfaces to infer past geochemical conditions. Smectite clay minerals are common products of water-rock interactions throughout the solar system, and their detection and characterization provides important clues about geochemical conditions and past environments if sufficient information about their composition can be discerned. Here, we synthesize and report on the spectroscopic properties of a suite of smectite samples that span the intermediate compositional range between Fe(II), Fe(III), Mg, and Al end-member species using bulk chemical analyses, X-ray diffraction, Vis/IR reflectance spectroscopy, UV and green-laser Raman spectroscopy, and Mössbauer spectroscopy. Our data show that smectite composition and the oxidation state of octahedral Fe can be reliably identified in the near infrared on the basis of combination and fundamental metal-OH stretching modes between 2.1–2.9 μm, which vary systematically with chemistry. Smectites dominated by Mg or Fe(III) have spectrally distinct fundamental and combination stretches, whereas Al-rich and Fe(II)-rich smectites have similar fundamental minima near 2.76 μm, but have distinct combination M-OH features between 2.24 and 2.36 μm. We show that with expanded spectral libraries that include intermediate composition smectites and both Fe(III) and Fe(II) oxidation states, more refined characterization of smectites from MIR data is now possible, as the position of the 450 cm–1 absorption shifts systematically with octahedral Fe content, although detailed analysis is best accomplished in concert with other characterization methods. Our data also provide the first Raman spectral libraries of smectite clays as a function of chemistry, and we demonstrate that Raman spectroscopy at multiple excitation wavelengths can qualitatively distinguish smectite clays of different structures and can enhance interpretation by other types of analyses. Our sample set demonstrates how X-ray diffraction can distinguish between dioctahedral and trioctahedral smectites using either the (02,11) or (06,33) peaks, but auxiliary information about chemistry and oxidation state aids in specific identifications. Finally, the temperature-dependent isomer shift and quadrupole splitting in Mössbauer data are insensitive to changes in Fe content but reliability differentiates Fe within the smectite mineral structure.

Preparation of SiO2/α-Fe2O3 Composite from Rice Husk and Iron Sand as a Photocatalyst for Degradation of Acid Black 1 Dye

The SiO2/α-Fe2O3 composite was successfully synthesized using impregnation method by using rice husk ash as silica (SiO2) sources. Hematite (α-Fe2O3) was derived from iron sand which was extracted using hydrochloric acid and ammonium hydroxide as co-precipitation agent. The synthesized SiO2/α-Fe2O3 composite was characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and diffuse reflectance (DR) UV spectroscopy. The performance of as prepared SiO2/α-Fe2O3 composite was evaluated on photodegradation of acid black 1 (AB 1) dye under UV light irradiation. The results showed that SiO2/α-Fe2O3 composite exhibits high photocatalytic acitivity for degradation of acid black 1 with degradation efficiency up to 85.86% within 120 minutes. The photocatalytic activity of SiO2/α-Fe2O3 composite was higher than that of bare α-Fe2O3. The SiO2/α-Fe2O3composite also can remove textile wastewater containing AB1 dye up to 82.96%. This results suggest that SiO2/α-Fe2O3 composite holds a great potential for degradation of dyes and various application in wastewater treatment.

Single wall carbon nanotubes growth over cobalt-iron mesoporous MCM-41 bimetallic catalyst under methane chemical vapor deposition, an experimental and DFT evaluation

Cobalt and iron MCM-41 catalysts were synthesized through an in-situ incorporation process starting from commercial iron and cobalt nitrates. The incorporation was confirmed by diffuse reflectance UV spectroscopy (DRS-UV) inspecting the cobalt and iron silicate-like photon absorption features and comparing with pure MCM-41-Co and MCM-41-Fe catalysts. Additionally it was found that the incorporation of cobalt and iron does not compromise the mesoporous structure of MCM-41 as confirmed by N2 adsorption isotherms. All catalysts showed high surface areas (∼1100 m2g−1). Catalysts performance was conducted in a simple methane chemical vapor deposition (CVD) set up at 800 °C to produce single wall carbon nanotubes (SWCNT) under a constant flow of methane for 30 min. CVD products were characterized by thermogravimetric analysis (TGA) and Raman spectroscopy, finding that the iron content in the catalysts favors the selectivity and yield of graphitic-like structures, and confirming the presence of SWCNT by the appearance of a characteristic radial breathing mode (RBM) signals. These results were supported by Density Functional Theory (DFT) simulations of the methane dissociation (CH4 +TM → H3C –TMH) over Con (n = 1–5) and ComFe (m = 1–4), finding a different activation energy trend where ComFe (m = 1–4) clusters have the lower activation energy. The DFT study also revealed a charge difference (δC − δTM) higher in the case of dissociation over ComFe (m = 1–4) which may lead to an electrostatic stabilization of the transition metal, diminishing the activation energy of those clusters and leading to a faster carbon uptake.

Physicochemical characterization and molecular modeling study of host–guest systems of aripiprazole and functionalized cyclodextrins

Aripiprazole (ARP), an innovative atypical antipsychotic drug, exhibits very low aqueous solubility, affecting its dissolution and absorption and high lipophilicity. Its complexation with cyclodextrins (CDs) was designed to improve drug solubility and consequently its bioavailability. The inclusion complexes of aripiprazole with two β-cyclodextrin derivative, namely random methyl-β-cyclodextrin (RAMEB) and heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin, were obtained and investigated both in solution and in solid state. The kneading method was used to prepare the inclusion complexes, and they were characterized with different analytical techniques, including thermal analysis, powder X-ray diffractometry, universal attenuated total reflectance Fourier-transform IR spectroscopy and UV spectroscopy. The stoichiometry of both APR/CDs inclusion complexes was found as 1:2 by employing continuous variation method. Benesi–Hildebrand equation was used for the apparent constant stability determination. Structural studies of the inclusion complexes were carried out using molecular modeling techniques in order to explain the complexation mechanism. The results of the studies demonstrate that the physicochemical properties of the kneaded products are different from ARP, testifying the inclusion complexes formation between aripiprazole and CDs when the kneading method is used. The solubility of the drug substance was improved upon complexation with CDs; higher increase in ARP solubility was noticed in the presence of RAMEB.

Development of structural colored cotton fabric via the layer-by-layer electrostatic self-assembling of SiO2 nanoparticles

SiO2 nanoparticles were synthesized by the Stober method. Their diameters were finely tuned from 250 to 580 nm by varying the NH3·H2O and tetraethyl orthosilicate (TEOS) concentrations. SiO2 particles with different diameters were assembled onto the surface of cotton fabric via the layer-by-layer electrostatic self-assembling method to achieve structural colored fabrics. The surface morphologies of the synthesized SiO2 particles and structural colored cotton fabrics were analyzed by scanning electron microscopy. The chemical composition of SiO2 particles was analyzed by Fourier transform infrared spectroscopy and X-ray diffraction. The thermal properties and color properties of structural color fabrics were analyzed by thermogravimetric analysis, UV reflectance spectroscopy and spectrophotometer.

Gd3Li3Te2O12:U6+,Eu3+: A Tunable Red Emitting Garnet Showing Efficient U6+ to Eu3+ Energy Transfer at Room Temperature

Since the invention of fluorescent light sources, there is strong interest in Eu3+ activated phosphors as they are able to provide a high color rendering index (CRI) and luminous efficacy, which will also hold for phosphor converted light emitting diodes. Due to an efficient U6+ to Eu3+ energy transfer in Gd3Li3Te2O12:U6+,Eu3+, this inorganic composition shows red photoluminescence peaking at 611 nm. That means Eu3+ photoluminescence can be nicely sensitized via excitation into the U6+ excitation bands. Therefore, photoluminescence properties, such as temperature dependent emission and emission lifetime measurements, are presented. Charge transfer bands were investigated in detail. Additionally, density functional theory calculations reveal the band structure of the pure, i.e., non-doped host material. Obtained theoretical results were evaluated experimentally by the aid of diffuse UV reflectance spectroscopy.

Facile fabrication of NiTiO3/graphene nanocomposites for photocatalytic hydrogen generation

Nickel titanate on reduced graphene oxide (NiTiO3/rGO) were elaborated by facile microwave ignition method. The prepared nanomaterials were controlled using different ratios of GO to NiTiO3. The synthesized photocatalysts were characterized by X-Ray Diffraction (XRD), Raman Spectroscopy, Infrared Spectroscopy, Transmission Electron Microscopy (TEM), and UV-Reflectance Spectroscopy. The results demonstrate that photocatalytic performance of the photocatalysts for hydrogen generation increases up to 8383 μmol/(h.g) with increasing graphene content up to 5%). However, further increase in graphene content above this optimum level has decreased the performance of photocatalyst. The enhanced photocatalytic performance for hydrogen evolution is attributed to extension of its absorption edge to the visible light region, directly related to retard recombination of electron-hole pairs due to synergistic effects of NiTiO3 and graphene which leads to more efficient utilization of the solar energy.

Effect of crystal plane orientation in tuning the photocatalytic activity of zinc oxide particles

Crystal plane dependant photocatalytic activity of zinc oxide has been explored in the present study. Two morphologically different structures are achieved via template assisted hydrothermal method. The prepared ZnO systems are well characterized by X-Ray diffraction analysis (XRD), Scanning Electron Microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Diffuse Reflectance UV spectroscopy and surface area analysis by BET method. It is revealed that ZnO with flowerlike morphology shows two fold increase in the photocatalytic activity when compared to the rod like ZnO system. The effect of polar and non-poalr sufaces in zinc oxide on the activity is investigated in detail.

The Effect of pH and Aging Time on the Synthesis of TiO2 – Chitosan Nanocomposites as Photocatalyst by Sol-Gel Method at Room Temperature

The synthesis of TiO2–chitosan nanocomposite photocatalyst using Titanium(IV)-Isopropoxide (TTIP) as precursors and chitosan as host material has been conducted. The synthesis was carried out using sol-gel method at room temperature and aging to grow crystal seeds and generate nanoparticles. The success of forming nano-sized anatase phase TiO2 nanocrystal was strongly influenced by the sol pH system during hydrolysis and the aging time. The effect of sol pH system and aging time to the crystallinity level and particle size were examined using X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Diffuse Reflectance UV-Spectroscopy (DR-UV). The results showed that TiO2 produced in acidic pHs (pH 2-4) tended to have higher crystallinity level than that produced in weakly alkaline (pH > 6), which prone to be amorphous. The longer aging time (> 14 days) also tended to produce the amorphous phase. Furthermore, chitosan as a host material had a notable influence in determining the crystallinity level and particle size of TiO2 in TiO2–chitosan nanocomposite.

Chemical functionalization of polyethylene surfaces by plasma-assisted carbene insertion

ABSTRACTControlled surface modification of PE is achieved by an efficient and facile approach via plasma-assisted carbene insertion generated using diazo chemistry. The combination of plasma and carbene insertion shows a synergistic effect, which leads to an obvious enhancement of surface grafting, as shown qualitatively by a combination of IR and UV reflectance spectroscopy, and XPS analysis. The chemical modification may be observed spectroscopically, and the approach provides an opportunity for the convenient modification of low surface energy materials.

Narrow Band Deep Red Photoluminescence of Y2Mg3Ge3O12:Mn4+,Li+ Inverse Garnet for High Power Phosphor Converted LEDs

This work concerns a novel red emitting Mn4+ doped phosphor showing an extraordinarily high thermal quenching temperature. The composition Y2Mg3Ge3O12:Mn4+,Li+ exhibits efficient red photoluminescence peaking at 658 nm, which can be assigned to the 2Eg → 4A2g intraconfigurational transition of Mn4+ ([Ar]3d3 configuration) located at the octahedral site in the garnet structure. Photoluminescence properties, such as temperature dependence of the luminescence intensity and luminescence lifetime are presented. Additionally, the band structure of the undoped host material were treated with Density Functional Theory (DFT) and evaluated with UV-reflectance spectroscopy. Furthermore, the energy levels of the Mn4+ ion in the Y2Mg3Ge3O12 host were calculated with the exchange charge model of crystal field theory and compared to those obtained experimentally from luminescence studies.

Poly(tetramethylene oxide)-coated silica nanoparticles incorporated into poly(4,4′-oxydiphenylene-pyromellitimide) matrix

ABSTRACTTelechelic poly(teramethylene oxide) with two isocyanate end groups (OCN-PTMO-NCO) was synthesized by the reaction of polytetrahydrofuran (Mn = 1000 g mol−1) and hexamethylene diisocyanate in 1:2 molar ratio. The resulting macrochains were then covalently grafted to the surface of silica nanoparticles (SNPs). Thus, the inorganic nanoparticles could be thoroughly coated by a thick and soft organic shell. Thermogravimetric measurements showed that up to 85 wt.% of the organically modified SNPs (OSNPs) could be formed from the organic part. Different weight ratios of OSNPs were subsequently added to a solution of 4,4′-oxydiphenylamine/pyromellitic dianhydride poly(amic acid) (PAA) in dimethylformamide. Chemical cyclodehydration of the PAA in the presence of homogeneously dispersed OSNPs resulted in poly(4,4′-oxydiphenylene-pyromellitimide) (POPI) nanocomposites, labeled by POPI/OSNP 5, POPI/OSNP 7.5, and POPI/OSNP 10. The nanocomposites obtained were fully characterized by field emission scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. According to the diffuse reflectance UV spectroscopy, in comparison with neat POPI, the POPI/OSNP series showed an appreciable redshift in the λmax values up to 15–20 nm. Moreover, POPI/OSNP series showed significant stability toward heat at temperatures above 540°C. The endothermic phase transitions occurred by the first thermodegradation of the resulting nanocomposites could be obviously seen in the differential thermal analysis.

Red emitting K2NbF7:Mn4+ and K2TaF7:Mn4+ for warm-white LED applications

Mn4+ activated luminescent materials have attracted much attention recently. In particular, alkali metal hexafluorometallates, such as K2SiF6:Mn4+ or K2TiF6:Mn4+, emit light in the red spectral range upon blue excitation and are thus applied onto phosphor converted LEDs (pcLEDs). K2NbF7:Mn4+ and K2TaF7:Mn4+ exhibit efficient red photoluminescence peaking at 627nm, which can be assigned to the 2Eg → 4A2g intraconfigurational transition of Mn4+ ([Ar]3d3 configuration) as part of the [MnF6]2- octahedra onto the niobium/tantalum site in the respective host structures. Photoluminescence properties, such as temperature dependence of the PL intensity and luminescence decay are presented. Additionally, the band structure of both undoped host materials has been treated with Density Functional Theory (DFT). The theoretical results have been evaluated experimentally with diffuse UV reflectance spectroscopy. Finally, luminous efficacy and color rendering values of simulated warm white emitting pcLEDs comprising a dichromatic phosphor blend employing K2NbF7:Mn4+ or K2TaF7:Mn4+ as the red emitting component are calculated and compared to the performance of warm white emitting pcLEDs comprising different commercial phosphors as red emitting component.

The optical properties of Sr3SiAl10O20 and Sr3SiAl10O20:Mn4+

Mn4+-activated luminescent materials have attracted significant attention recently. In particular, alkaline earth aluminates, such as Sr4Al14O25:Mn4+ and CaAl12O19:Mn4+, emit light in the red region, which can be exploited in phosphor-converted LEDs. We applied a sol-gel precursor followed by a ceramic method to synthesize highly crystalline Mn4+-doped Sr3SiAl10O20. The compound Sr3SiAl10O20:Mn4+ exhibits deep red photoluminescence that peaks at 663 nm, which can be assigned to the 2Eg → 4A2g intraconfigurational transition of Mn4+ ([Ar]3d.3 configuration) within the [MnO6]8− octahedra on the aluminum site in the Sr3SiAl10O20 (Space group C12/m1) host structure. The photoluminescence properties, such as the temperature dependence of the luminescence intensity and luminescence lifetime, are presented. Furthermore, the luminescence intensity as function of the activator concentration was investigated. Additionally, the band structure of the undoped host material was treated with Density Functional Theory (DFT). The theoretical results were evaluated experimentally with diffuse UV reflectance spectroscopy. Finally, the crystal field and Racah parameters were extracted to compare with those reported in the literature.

Layer-by-layer deposition on a heterogeneous surface: Effect of sorption kinetics on the growth of polyelectrolyte multilayers

Surface functionalization by means of controlled deposition of charged polymers or nanoparticles using the layer-by-layer (LbL) approach has been used to modify mostly engineered materials with well-defined surface chemistry and morphology. In this regard, natural and inhomogeneous interfaces have gained very little attention. Furthermore, natural substrates are susceptible to alterations by factors commonly used to control the growth of multilayers, such as pH, temperature and ionic strength. Here, we study the impact of sorption kinetics of a bilayer system (Poly(diallyldimethylammonium chloride) (PDDA) and Poly(sodium 4-styrenesulfonate) (PSS)) on a natural heterogeneous wood surface at neutral pH, without salt addition, on the multilayer buildup. To overcome analytical limitations we introduce a complementary approach based on UV reflectance spectroscopy, atomic force microscopy (AFM) and zeta potential measurements. Compared to immersion times used for ideal substrates, we found that a high surface coverage requires relatively long immersion, approximately 30min, into polyelectrolyte solutions, while a sufficient removal of polyelectrolyte excess during the washing step, requires even longer, about 100min. Based on these findings, we show that film growth can be controlled kinetically. Long immersion times provide well-defined and regular multilayers. The obtained data points to specific requirements to be considered when LbL treatments are applied to rough, porous and heterogeneous surfaces, and thereby sets a basis for a successful transfer of various surface functionalization approaches already shown on ideal surfaces.

Determining the sign of a polar surface of lithium niobate crystal by UV reflectance spectroscopy

We propose to reveal the +Z and–Z surfaces of a polar cut lithium niobate crystal by measuring its UV reflection spectrum. By the example of a congruent lithium niobate, it is shown that the intensities of light reflection from polar crystal surfaces of different signs in the region of 190—260 nm differ by up to several percent. The depth of short-wave radiation penetration into surface layers of the crystal in the spectral range of intrinsic absorption is estimated. It is shown that the proposed method can be used for determining the surface signs of polar crystal layers with thicknesses from several dozen to several hundred microns.

Combustion synthesis and characterisation of Eu<SUP align="right">3+</SUP>-activated Y<SUB align="right">2O<SUB align="right">3 red nanophosphors for display device applications

Europium activated yttrium oxide red phosphors have gathered more attention because of their good luminescent characteristics, acceptable atmospheric stability, reduced degradation under applied voltages, and lack of hazardous constituents. In order to achieve improved luminescent properties of Y2O3:Eu3+, the synthetic methods are playing an important role. In the present study, Eu3+ (2 mol %) doped Y2O3 nanophosphors were synthesised by the facile nitrate citrate gel combustion method at relatively low temperature and shorter duration (700°C for 2 h). Further samples were characterised by powder X-ray diffraction (XRD) technique. The morphology and particle size of the phosphors were studied by scanning electron microscope (SEM), UV reflectance spectroscopy and Raman spectroscopy. The photoluminescence measurements of the Y2O3:Eu3+ particles showed red emission peaks at 610-612 nm (5D0 → 7F2). CIE chromaticity diagram and CCT calculations confirmed that these nanophosphors can act as a red component in the fabrication of white light emitting diodes (WLEDs) for display and other optical device applications.