Visible Reflectance Spectra Research Articles

Synthesis and photoluminescence properties of high thermal stability Mn4+ in orthorhombic SrLa2Mg2W2O12 red phosphor for warm w-LEDs

We successfully synthesized SrLa2Mg2W2O12:xMn4+ (x = 0.002, 0.004, 0.006, 0.008, 0.010, 0.012, 0.014) phosphors through a high-temperature solid-state reaction. The phase of sample was shown by X-ray powder diffraction (XRD). The morphology of the sample was observed by field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM), which showed the irregular morphology of SrLa2Mg2W2O12 (SLMW) powders. Additionally, the photoluminescence excitation (PLE), emission (PL) and ultraviolet–visible reflection spectra were also presented. As shown in results, the phosphor could be stimulated by the ultraviolet (UV) and near ultraviolet (NUV) light and then exhibited far-red emission (697 nm). The optimum doping concentration of Mn4+ is 1 mol%. The thermal stability of phosphors has been investigated and discussed (I423K/I298K = 64.6%), and the internal quantum efficiency (IQE) of SLMW:0.01Mn4+ phosphors is as high as 51.2%. Finally, a far-red light-emitting diodes (LEDs) was fabricated by combining a 365 nm near-ultraviolet InGaN chip with SLMW:0.01Mn4+ phosphor. The Color Rendering Index (CRI), correlated color temperature (CCT) and luminescent efficiency (LE) values were 29.5, 1159 K and 5.6 lm/W, respectively. All of these indicated that SLMW:Mn4+ as a far-red phosphor can be applied to LEDs lamp and it has enormous potential applications in white light-emitting diodes (w-LEDs).

In situ spectral measurements of space weathering by Chang'e-4 rover

Space weathering introduces confounding effects on visible and near infrared reflectance spectra of airless bodies, which considerably darkens the reflectance, reddens the continuum slope and suppresses absorption features. It's mainly attributed to the gradual formation and accumulation of submicroscopic metallic iron (SMFe) on regolith grains. In situ spectral measurements from Chang'e-4 rover provide a unique opportunity to investigate the space weathering effects on the intact lunar farside regolith. SMFe abundance at the landing site, which is 0.32±0.06 wt.%, is retrieved from in situ measured reflectance spectra by using Hapke model. The derived Is/FeO maturity index (82±15) indicates the Finsen crater ejecta-sourced regolith is mature, which is consistent with the geologic background that it had experienced about 3.7 Ga space weathering.

Study on Characteristic Spectrum and Multiple Classifier Fusion With Different Particle Size in Marine Sediments

Marine sediments record much information of the ecological process, which highly correlated with global and local environmental change. Particle size and its distributions of sediments indicate different ecological functions, thus are the key questions in marine ecology. The analysis method is tedious and laborious, which is not conducive for in-situ monitoring. Here, a spectral analysis was explored using surface sediments sampled in the intertidal zone of Dongdayang village, Qingdao, China. These samples were dried and sieved to pass through the mesh size of 0.3 mm, 0.2 mm, 0.1 mm, and 0.075 mm, respectively. Then, four types of subsamples were collected with the particle size of 0.3-0.2 mm, 0.2-0.1 mm, 0.1-0.075 mm, and <; 0.075 mm, respectively. The visible and near infrared reflectance spectra (226-975nm) of these subsamples with different particle size were measured. Results showed that there was a negative correlation between the spectral reflectance and the particle size. And the characteristic spectra for particle size classification were 926-975nm. These particle size were classified by the support vector machine algorithm. The classification accuracy for the calibration set and validation set was 100% and 89.06%, respectively. Furthermore, the fusion classifier was compared with the single classifier. Three spectral bands were selected as the single particle size classifier, that is 226-325nm, 826-925nm and 226-975nm. These three single classifiers were fused by voting method, forming multiple classifier fusion. A fusion classifier was recommended whose validation set had the classification accuracy of 93.75%, better than any single classifier. Multiple classifier fusion is a good tool for searching the characteristic spectra of the chemical and physical parameter in sediments. This method provides a solution for the division of particle size in sediment.

First-principles study on the electronic structures and optical properties of ZnV2O6

ZnV2O6 materials have been successfully prepared by solid-state synthesis. The phase of ZnV2O6 by X-ray Diffraction (XRD) characterization was carried out. The band structure, density of states (DOS) and optical properties of ZnV2O6 have been simulated by Materials Studio software based on density functional theory (DFT). The calculation results show that the bandgap of ZnV2O6 crystal is 2.104eV and it is a direct band gap semiconductor. The calculation results of optical properties show that ZnV2O6 exhibits better properties than TiO2 in visible light range, the absorption and reflection spectrum of ZnV2O6 are in the ultraviolet region, which has potential applications in the fabrication of ultraviolet semiconductor detectors, ultraviolet shielding devices and so on. Compared with the application of TiO2 with good performance in the ultraviolet region, there may be a complementary and substitutional role.

Bi2O2CO3–Bi2O2(OH)NO3/g-C3N4 heterojunction as a visible-light-driven photocatalyst with enhanced photogenerated charge separation

Constructing heterojunction to achieve efficient charge separation and transfer is a significant way to enhance photocatalytic activity. Herein, a novel ternary Bi2O2CO3–Bi2O2(OH)NO3/g-C3N4 (labeled as BOC-BON/CN) heterojunction photocatalyst was successfully synthesized by ion exchange reaction under hydrothermal conditions. The products were characterized by various analytical methods, including X-ray diffraction (XRD), Fourier transform-infrared spectrometer (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray spectrometer (SEM), UV–vis reflectance spectra (UV–vis DRS), photoluminescence (PL), photocurrent response and electrochemical impedance spectroscopy (EIS). Heterojunction formation mechanism and photocatalytic degradation mechanism were discussed in detail. The prepared BOC-BON/CN heterojunction exhibited excellent Rhodamine B (RhB) photodegradation rate of 0.0476 min−1 under visible light, which was 3.55 times of the pristine g-C3N4 (0.0134 min−1). The significant increase in photodegradation rate was attributable to the heterojunction structure, which promotes the separation of photogenerated charges. Bi2O2(OH)NO3 played an essential role as electron accelerator in the charge transfer process. The internal electric field of Bi2O2(OH)NO3 accelerates the directed transfer of electron from g-C3N4 to Bi2O2CO3. This work extends the study of g–C3N4–based photocatalytic systems and demonstrates Bi2O2(OH)NO3 as a promising cocatalyst.

Optical and dielectric properties of anodic iron oxide films

Porous iron oxide with tunable structural colors in the entire visible range has been prepared by anodizing pure iron foils at 40 V in an ethylene glycol solution. The relationship between the structural color and the anodization time and the electrolyte temperature was discussed. The results showed that the maxima of the reflected wavelengths in the UV–Vis reflectance spectra were consistent with the observed colors, and the refractive index n of the films was obtained. It was found that the n2 was about equal to the effective dielectric constant ɛ of the films, which means that the carriers in the dielectric material of the films are mainly electrons. These results provide a simple and effective method for determining the carrier type of porous materials.

Structure and luminescent properties of new Dy3+/Eu3+/Sm3+-activated InNbTiO6 phosphors for white UV-LEDs

A series of novel Dy3+/Eu3+/Sm3+-activated InNbTiO6 phosphors have been prepared by conventional solid state reaction method. Based on the structure refinement, RE3+ ions are preferred to occupy the site of In3+ (2e) in the wolframite-type host lattice. According to their UV–visible diffusion reflectance spectra, the band gap and absorption property of un-doped InNbTiO6 sample can be tuned by the dopants. Under UV–visible light excitation, Dy3+/Eu3+/Sm3+ activators in this matrix mainly show emission lines originating from their characteristic f→f transitions. The optimal excitation and emission wavelength are 385 nm and 581 nm for Dy3+, 394 nm and 616 nm for Eu3+, 406 nm and 615 nm for Sm3+. Concentration quenching occurs at 0.06 for Dy3+, 0.06 for Eu3+, and 0.04 for Sm3+, ascribed to resonant q-q, q-q, and d-q interactions, respectively. The luminescence lifetimes are determined to be 0.13, 0.50, and 0.50 ms for InNbTiO6:0.06Dy3+, InNbTiO6:0.06Eu3+, and InNbTiO6:0.04Sm3+, respectively. The Dy3+, Eu3+, and Sm3+ doped phosphors exhibited yellowish-white, red, and orange-red luminescence, respectively. The quantum yields and thermal stability of representative phosphors have been investigated. Present work shows that these new phosphors are promising for application in UV-LED solid-state lighting devices.

Improved photocatalytic property of peony-like InOOH for degrading norfloxacin

Novel peony-like InOOH photocatalyst was firstly obtained with the help of glycerol in the solvothermal process, whose optimal proportion of glycerol was determined to be 25%. X-ray diffraction, scanning electron microscope, X-ray energy dispersion spectrum, transmission electron microscopy, X-ray photoelectron spectroscopy and UV–visible diffusion reflectance spectrum were obtained and analyzed to reveal the structure, morphology, physical and chemical properties of synthesized samples. The results indicated that the synthesized InOOH was orthorhombic structure with the peony-like morphologies, whose average particle size was 2–5 µm approximately. The band-gap of the peony-like InOOH was estimated to be 3.65 eV. The photocatalytic activities of the samples were investigated by degrading norfloxacin under UV-light irradiation, which followed the first-order reaction kinetics. The degradation efficiency of peony-like InOOH could reach up to 98.84%. And the first order kinetic constant of peony-like InOOH was 0.01519 min−1, which was about 4.8 times or 1.7 times than that of hexagram-like InOOH or InOOH nanosheet. The peony-like InOOH showed the most superior photocatalytic performance compared with hexagram-like InOOH and InOOH nanosheet, which originated from its high separation efficiency and low recombination rate of photoproduction electron-hole pairs. The reduction of total organic carbon revealed the mineralization of norfloxacin during the photocatalytic process. Finally, O2− radicals were proved to be main reactive species during the degradation process of norfloxacin. Furthermore, the degradation pathway and the degradation mechanism of norfloxacin with peony-like InOOH as catalyst were discussed in detail.

Prediction of soil available water-holding capacity from visible near-infrared reflectance spectra

Sustainable land management requires reliable information about soil hydraulic properties. Among these properties, available water-holding capacity (AWC) is a key attribute, as it quantifies the amount of water available for plants that the soil can hold. Since direct measurements of AWC are costly, pedotransfer functions (PTF) are often used to estimate AWC, leveraging statistical relationships with properties that are easier to measure, such as texture, bulk density, and organic carbon content. This study evaluates visible near-infrared spectroscopy (vis-NIR) as an alternative approach to predict volumetric water content at field capacity (FC) and permanent wilting point (PWP) — AWC being the difference between PWP and FC. A suite of 970 vis-NIR soil spectra, recorded from air-dried, 2-mm, sieved soil samples, were associated with FC and PWP analytical data obtained from New Zealand’s National Soils Database. Partial least squares (PLS) regression and support vector machines on PLS latent variables (PLS-SVM) were used for spectroscopic modelling. With root mean squared errors below 7% and 5% for FC and PWP, respectively, our results indicate that vis-NIR spectroscopy can be used to quantitatively predict volumetric water content at FC and PWP.

Discrimination of flax cultivars based on visible diffusion reflectance spectra and colour parameters of whole seeds

Discrimination of yellow and brown seeded flax cultivars was made based on visible (Vis) diffusion reflectance spectra of whole seeds. Hierarchy cluster analysis (HCA) and principal component analysis (PCA) were used for the discrimination. Multivariate analyses of Vis spectra led to satisfactory discrimination of all flax cultivars of this study. The CIE L*a*b* colour parameters were calculated from the diffusion reflectance Vis spectra. The values of L* were in the range of 48.8–53.6 and 62.6–66.0% for brown and yellow seeded cultivars, respectively. Chromatic parameters a* and b* were in the range of 2.8–4.9 and 7.9–16.4%, respectively. A strong linear correlation (R&lt;sub&gt;2&lt;/sub&gt; = 0.9712) was found between a* and b* parameters for all the flaxseed samples. The L* and a* parameters were sufficient for HCA clustering of the individual flax cultivars.

Structural, optical and photocatalytic studies of Zn doped MoO3 nanobelts

In this study, we report a synthesis of nanobelts-form zinc (Zn) doped molybdenum oxide (MoO3) with different weight percentages (2%, 3.3%, 4%, and 5%). The synthesized nanobelts grain size is of 45 nm. The preparation process and characterization techniques are presented in detail. Structural properties are studied by using the X-ray diffraction technique, scanning electron microscopy and transmission electron microscopy. The optical properties are investigated by using the Fourier transform infrared spectroscopy, UV–Vis reflectance spectra analysis, Raman spectroscopy, and fluorescence techniques. It was founded that Zn doping concentration highly influences the crystallographic structure where it passes from the insertion to the substitution alloys. The band gap decreases from 2.96 eV to 2.83 eV. The good structural and optical properties were obtained for the 5%Zn. The photocatalytic effect of the materials was studied for the pure and 5%Zn doped MoO3 and it was denoted that Zn doping influences it highly.

KGaP2O7:Mn4+ deep red emitting phosphor: Synthesis, structure, concentration and temperature dependent photoluminescence characteristics

Mn4+-activated KGaP2O7 red emitting phosphor was successfully synthesized via traditional solid-state reaction method in air. The structural features of KGaP2O7:xMn4+ material were investigated by means of powder XRD & Raman, morphology from SEM, and element analysis, corresponding mapping through EDAX. In conjunction, concentration and temperature dependent spectroscopic properties were analyzed from UV–Vis reflectance, excitation, emission and lifetime decay curves. Powder XRD and photoluminescence profiles revealed that GaO6 polyhedra offer Mn4+ ions to substitute the Ga3+ sites in the crystal lattice resulting in a pure single phase structure with an efficient red emission at 702 nm (Mn4+:2Eg→4A2g) under 452 nm excitation. The emission decay curves exhibited non-exponential nature with lifetimes shortening when Mn4+ concentration is increased. Electric dipole-dipole interaction is identified to be responsible for the concentration quenching beyond 0.07 Mn4+ via energy transfer between Mn4+ ions. The temperature-dependent emission intensity for KGaP2O7:0.07Mn4+ exhibited 66% at 423 K (150 °C) displaying good thermal stability and activation energy (Ea) of ∼0.186 eV. From UV–Vis reflectance spectra using Tanabe-Sugano diagram, crystal splitting factor (Dq), two Racah parameters (B & C), Dq/B, C/B and energy of states are calculated to evaluate nephelauxetic ratio (β). In addition, the effect of Mn4+ content (concentration quenching) and temperature (thermal quenching) on emission intensity are discussed based on the Tanabe-Sugano energy diagram and configurational coordinate scheme of Mn4+. Therefore, KGaP2O7:Mn4+ phosphor can serve as a potential red emitting phosphor under blue light excitation and can also be useful to enhance plants growth.

Evaluation of Leaf N Concentration in Winter Wheat Based on Discrete Wavelet Transform Analysis

Leaf nitrogen concentration (LNC) is an important indicator for accurate diagnosis and quantitative evaluation of plant growth status. The objective was to apply a discrete wavelet transform (DWT) analysis in winter wheat for the estimation of LNC based on visible and near-infrared (400–1350 nm) canopy reflectance spectra. In this paper, in situ LNC data and ground-based hyperspectral canopy reflectance was measured over three years at different sites during the tillering, jointing, booting and filling stages of winter wheat. The DWT analysis was conducted on canopy original spectrum, log-transformed spectrum, first derivative spectrum and continuum removal spectrum, respectively, to obtain approximation coefficients, detail coefficients and energy values to characterize canopy spectra. The quantitative relationships between LNC and characteristic parameters were investigated and compared with models established by sensitive band reflectance and typical spectral indices. The results showed combining log-transformed spectrum and a sym8 wavelet function with partial least squares regression (PLS) based on the approximation coefficients at decomposition level 4 most accurately predicted LNC. This approach could explain 11% more variability in LNC than the best spectral index mSR705 alone, and was more stable in estimating LNC than models based on random forest regression (RF). The results indicated that narrowband reflectance spectroscopy (450–1350 nm) combined with DWT analysis and PLS regression was a promising method for rapid and nondestructive estimation of LNC for winter wheat across a range in growth stages.

Bi-directional reflectance and polarization measurements of pulse-laser irradiated airless body analog materials

Space weathering (SW) processes including solar wind irradiation and micrometeorite bombardment produce nano-phase iron (npFe) and amorphous layers that redden and darken the visible and near-infrared (VNIR) reflectance spectra of the surface of airless bodies. To understand how SW may affect the directional reflectance and polarization properties of regolith layers, we carried out pulsed laser irradiation experiments to simulate micrometeorite bombardment process on olivine (OL), orthopyroxene (OPX), anorthosite (AN), ilmenite (ILM), and JSC-1A Lunar Regolith Simulant (LRS). All samples have been equalized with a size distribution of (<45 μm) and the unsieved LRS with (<1 mm) was also used. Depending on each sample's difficulty level of weathering, 2 to 8 irradiations with single pulse energy of 50 mJ were used in the irradiations. We measured the spectral reflectance from 0.5 to 25 μm, bi-directional reflectance distribution function (BRDF) and polarization phase curves at 0.633 μm of the samples before and after irradiations. Scanning electron microscopic images show that the irradiated samples become rougher with produced melts and agglutinates. The VNIR reflectance spectra of all irradiated samples show prominent darkening and reddening, except for the unsieved LSR sample which shows spectral blueing. Compared to that of the original samples, the BRDF of irradiated OL and OPX have both enhanced back- and forward-scattering components, while the other 4 samples have enhanced backscattering but nearly unchanged (AN, ILM, JSC-1A (<45 μm)) or decreased (JSC-1A (<1 mm)) forward scattering. In general, the irradiated samples have larger positive polarization values DOPmax as compared to the original samples, consistent with the Umov law prediction. Within measurement uncertainties, the irradiated samples did not show systematic changes in the minimum polarization value DOPmin and the polarization inversion angle αinv. Using OL as an example, numerical radiative transfer computations verified that, the BRDF of olivine grains with npFe distributed uniformly inside the grains or coated with npFe have enhanced back- and forward scattering components as compared with that of the original grains, consistent with measurement results. A 5-parameter Hapke photometric model inversion has shown that all sample grains except OPX have become more backscattering (with smaller asymmetry parameters) upon the strongest irradiation as compared with the original ones. These results indicate that the directional reflectance properties of space weathered regolith grains of airless bodies may be more backscattering than that of fresh materials.

Multiferroic properties of Gd/Er doped chromium ferrite nano sized particles synthesized by citrate auto combustion method

The non-stoichiometric Gd/Er doped Chromium nano ferrite with uniform and tunable size has been successfully synthesized by citrate auto combustion method. The prepared samples exhibit a combination of nonstoichiometry and non electroneutrality. The neutrality in the investigated samples is well maintained via the reduction of oxygen or removal of Cr ions. The ferromagnetic as well as the ferroelectric hysteresis loops of the investigated samples were studied. The obtained data shows that the antiferromagnetic nature in CrFe2O4 (CrFeO3) is turned into weak ferromagnetism in rare earth doped chromium. The substitution of rare earth ions for Fe can dramatically improve the saturation magnetization and remnant magnetization. The band gap energy was calculated from near infrared (NIR) and visible (VIS) reflectance spectra using the Kubelka-Munk function. Special attention should be given to chromium ferrite nanoparticles which are suitable candidates to be used in many applications like non-volatile data storage and camera flashes due to their ferroelectrics properties.

Tunable blue-green color emitting Al5O6N: Eu2+, Tb3+ phosphors with energy transfer for near-UV white LEDs

A series of tunable blue-green emitting phosphors Al5O6N: Eu2+, Tb3+ were prepared via gas-pressure sintering reaction process. The morphology, UV–Vis reflectance spectra, photoluminescence properties, decay behavior, Eu2+ occupy site, energy transfer mechanism and thermal stability were investigated systematically. The Al5O6N: 0.003Eu2+, 0.01Tb3+ phosphor exhibits strong green emission under near-UV excitation due to briskly efficient energy transfer from Eu2+ to Tb3+. The maximum energy transfer efficiency calculated by decay lifetime can reach 80%. The mechanism of energy transfer from the Eu2+ to Tb3+ is considered to be a dipole−dipole type. The critical distance of the energy transfer is calculated via the concentration quenching method. Moreover, the color emission from blue to green can be obtained through controlling the concentration of Eu2+ and Tb3+. These results reveal the potential value of Al5O6N: Eu2+, Tb3+ phosphors as green light emitting material for near-UV pumped white light-emitting diodes.

Comprehensive study on morphological, structural and optical properties of Cr2O3 nanoparticle and its antibacterial activities

Chromium (III) oxide (Cr2O3) nanoparticles are generated by thermal treatment (calcination) of precursor materials such as chromium nitrate along with a poly (vinyl pyrrolidone) capping agent. The samples produced were characterised by various techniques, including X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FT-IR). Examination results obtained from XRD showed that Cr2O3 nanoparticles exhibit hexagonal crystalline structures, with the presence of Cr and O in these novel materials being confirmed by results of analyses of both EDX and FT-IR. Results of TEM have pointed out that the average nanoparticle size was noticeably increased from 28 to 46 nm in relation to increase of calcination temperature of a range between 500 and 800 °C. The surface composition and valence state of the produced nanoparticles were examined by X-ray photoelectron spectroscopy (XPS), the optical energy gap has been evaluated using UV–visible reflectance spectra with the help of Kubelka–Munk equation. The energy band gap had a reversely proportional relationship with calcination temperature with a reduction in energy band gap from 3.12 to 3.01 eV. Photoluminescence (PL) spectra indicated an increase in photoluminescence with increasing particle size. The antibacterial activity of the Cr2O3 nanoparticles was evaluated in-vitro using gram-negative Escherichia coli ATCC 25922 and gram-positive Bacillus subtilis UPMC 1175.

Validation of 2015 Lake Erie MODIS image spectral decomposition using visible derivative spectroscopy and field campaign data

Timely identification of color-producing agents (CPAs) in Lake Erie is a challenging, but vital aspect of monitoring harmful algal blooms (HABs). In particular, HABs that include large amounts of cyanobacteria (CyanoHABs) can be toxic to humans, posing a threat to drinking water, in addition to recreational and economic use of Lake Erie. The optical signal of Lake Erie is complex (Becker et al., 2009; Moore et al., 2017), typically comprised of phytoplankton, cyanobacteria, colored dissolved organic matter (CDOM), detritus, and terrigenous inorganic particles, varying in composition both spatially and temporally. The Kent State University (KSU) spectral decomposition method effectively partitions CPAs using a varimax-rotated, principal component analysis (VPCA) of visible reflectance spectra measured using lab, field or satellite instruments (Ali et al., 2013; Ortiz et al., 2017, 2013). We analyze 2015 imagery acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor and field samples collected during the early 2015 cyanoHAB season. We identified four primary CPA spectral signatures, and the spatial distribution of each identified CPA, in the reflectance spectra datasets of both the MODIS and lab-measured water samples. The KSU spectral decomposition method results in mixtures of specific pigments, pigment degradation products, and minerals that describe the optically complex water. We found very good agreement between the KSU VPCA spectral decomposition results and in situ measurements, indicating that this method may be a powerful tool for rapid CyanoHAB monitoring and assessment in large lakes using instruments that provide moderate resolution imagery (0.3 to 1 km2).

Combined Microspectroscopic Characterization of a Red-Colored Granite Rock Sample.

Combined microspectroscopic mapping have been conducted on a red-colored Tenzan granite sample by using an original visible-fluorescence-Raman microspectrometer together with a low vacuum scanning electron microscopy-energy dispersive spectrometry (SEM-EDS) without coating. Visible darkfield reflectance spectra were converted to L*a*b* color values and Kubelka-Munk (KM) spectra. Large a* value (red) positions correspond to large band areas at 500-560 nm, possibly due to hematite-like iron oxide, while large b* value (yellow) positions to large band areas at 450-500 nm, due to epidote-like mineral. Scanning electron microscopy-energy dispersive spectrometry analyses indicated that the reddish parts are Na and K-feldspars with low Fe contents (<0.5 wt%). Raman microspectroscopy could not detect hematite-like minerals. Since some hematite-like minerals were only identified by transmission electron microscope, they are considered to be submicron microcrystals disseminated in feldspar matrices. The KM spectra for prehnite-like minerals show a weak broad band around 430 nm due possibly to a ligand field band of Fe3+ without clear Fe2+-Fe3+ inter-valence charge transfer (IVCT) bands around 720 nm. Therefore, Fe in prehnite is not considered to be present as hematite-like iron oxide, but can be mainly present as Fe3+ replacing Al3+ in the crystal structure. Since determination of physicochemical states of Fe such as valence and coordination states (Fe2+ or Fe3+, oxide or in crystal lattice, etc.) and their distributions are extremely difficult, especially in complex colored materials such as rocks, the combined microspectroscopic methods are useful for their nondestructive characterization.

Structural and Optical Properties of CeO2 Nanoparticles Synthesized by Modified Polymer Complex Method

Ceria nanoparticles (Ceria-NPs) were synthesized using a modified polymer complex method and their structural and optical properties were evaluated. The solids were heated at 550 °C and characterized using Raman, UV–Vis absorption, diffuse reflectance, X-ray photoelectron and photoluminescence spectroscopies, X-ray diffraction (XRD) and scanning and transmission electron microscopy. The primary particles obtained presented a size of ~ 10 nm. The XRD indicated that CeO2 was the only crystalline phase. From the UV–Vis and diffuse reflectance spectra, energy values of 3.8 eV and 3.4 eV were obtained, values that can be associated with band—band electronic transitions and/or with those that involve ionized states located within the gap caused by defects and isolated atoms of Ce3+. Photoluminescence spectra reiterated the existence of localized states in the gap. Raman spectra revealed the existence of peroxide (O22−) and superoxide (O2−) over the surface of the ceria-NPs. The XPS results indicated that the concentrations of Ce3+ and Ce4+ were ∼ 20.5% and ∼79.5% respectively, and that the stoichiometry of oxygen was 1.9 per atom of Ce. The results obtained from the characterization of CeO2-NPs synthesized make it as promising material for environmental remediation, biomedicine, gas sensing and optoelectronic applications.