Optical Diffuse Reflectance Research Articles

Na2Cd7B8O20: a new noncentrosymmetric compound with special [B3O7] units

A new noncentrosymmetric compound, Na2Cd7B8O20, has been synthesized by solid-state reaction for the first time. The crystal structure has been determined from single crystal X-ray diffraction data. The compound crystallizes in the orthorhombic space group Fdd2 with a = 51.5597(7) A, b = 58.6920(8) A and c = 3.381 A. The crystal structure is composed of CdOn (n = 6, 7), Na–CdOn (n = 5, 6) NaOn (n = 4, 6) polyhedra, [B3O7] and [BO3] units. The [B3O7] unit is built up of three [BO3] groups via corner-sharing, rarely found in borate compounds. The IR spectrum, the optical diffuse reflectance spectrum and nonlinear optical properties of Na2Cd7B8O20 are reported.

Effects of Gd/Lu Ratio on the Luminescent Properties of Pr3+ Activated (Gd,Lu)3Ga3Al2O12

The (Gd,Lu)3Ga3Al2O12:Pr (GLGAG:Pr) polycrystalline powders with different Gd/Lu ratio are synthesized by solid state reaction method. A combination of optical diffuse reflectance, photoluminescence excitation and emission spectra, fluorescence decays and X-ray excitation luminescence spectra at room temperature are employed to reveal the underlying reason of Pr3+ 5d→4f luminescence quenching in GLGAG host. A mechanism based on the energy transfer is proposed. It can be safely concluded that the 5d→4f Pr3+ luminescence quenching originates from the non-radiation energy transfer pathway from Pr3+ to Gd3+ and cooperative processes of excitation from Pr3+ 5d to 4f levels, which is proved by the Pr3+ and Gd3+ emission spectra under UV and X-ray excitation, and decay curves from the excited state levels of the 4f15d1 electronic configuration of the Pr3+ in nanosecond and millisecond time scale. In addition, the trap depths of glow curves are evaluated by general-order kinetics fitting method and also found that the recombination center of traps in forbidden gap is Pr3+ ion but only 4f→4f luminescence observed.

A novel 3-D chiral bismuth–organic framework with mixed carboxylate, pyridine and thiolate donors exhibiting a semiconductive property

A novel 3D bismuth–organic framework with helical channels, {[Bi(mna)2]−·(HDMA)+}n (1, H2mna = 2-mercaptonicotinic acid, DMA = dimethylamine) based on homo-chiral Bi–mna helices was hydrothermally synthesized and characterized. The optical diffuse reflectance spectrum and the theoretical calculations indicate that compound 1 is a potentially semiconductive material.

Growth dynamics of interfacially polymerized polyamide layers by diffuse reflectance spectroscopy and Rutherford backscattering spectrometry

The synthesis of polyamide films used as active layers in reverse osmosis membranes was studied by in-situ diffuse reflectance spectroscopy, Rutherford backscattering spectrometry (RBS), and atomic force microscopy (AFM). Aromatic polyamide layers were formed by interfacial polymerization on porous polysulfone supports using varying concentrations of m-phenylenediamine (MPD) in water of 0.1–100g/L with a fixed concentration of trimesoyl chloride (TMC) in hexane of 1g/L and varying TMC concentrations of 0.1–10g/L with a fixed MPD concentration of 20g/L. Polyamide growth dynamics were monitored in real-time by diffuse optical reflectance at λ=329nm. A relationship was developed between diffuse reflectance and polyamide thickness. The diffuse reflectance data show that ∼50% of the polyamide thickness is produced in <2s for all TMC concentrations studied and for MPD concentrations >2g/L. All studied concentrations of TMC at a fixed 20g/L MPD concentration produced a polyamide thickness of ≈120nm. Polyamide thickness increased from ≈10 to 110nm with increasing concentration of MPD at 1g/L TMC. The roughness measured by AFM increased with increasing MPD concentration but decreased with increasing TMC concentration. At MPD concentrations <0.5g/L, polyamide does not grow on top of the polysulfone.

Preparation and photoluminescence characteristics of In(OH)3:xTb3+ obtained by Microwave-Assisted Hydrothermal method

Crystalline terbium-doped indium hydroxide structures were prepared by a rapid and efficient Microwave-Assisted Hydrothermal (MAH) method. Nanostructures were obtained at a low temperature. FE-SEM images confirm that these samples are composed of 3D nanostructures. XRD, optical diffuse reflectance and photoluminescence (PL) measurements were used to characterize the products. Emission spectra of terbium-doped indium hydroxide (In(OH)3:xTb3+) samples under excitation (350.7nm) presented broad band emission referent to the indium hydroxide matrix and 5D4→7F6, 5D4→7F5, 5D4→7F4, and 5D4→7F3 terbium transitions at 495, 550, 590 and 627nm, respectively. Relative intensities of the Tb3+ emissions increased as the concentration of this ion increased from 0, 1, 2, 4 and 8mol%, of Tb3+, but the luminescence is drastically quenched for the In(OH)3 matrix.

Can divalent ions co-doping strategy make Lu0.8Sc0.2BO3:Ce scintillation materials perform better?

The Lu0.8Sc0.2BO3 polycrystalline powders doped with 1at%Ce3+ and co-doped with Ca2+, Mg2+, or Sr2+ with varying concentration were fabricated by conventional solid-state reaction method. We applied X-ray diffraction, optical diffuse reflectance spectrum, luminescent spectra under UV and X-ray excitation, fluorescence decay time and X-ray absorption near edge spectroscopy to study the effects of divalent ions co-doping on the Lu0.8Sc0.2BO3:Ce scintillation materials. Through experiments, the influence of divalent ions co-doping strategy on scintillation efficiency and the action mechanism were revealed.

Eu3+/Tb3+-codoped Y2O3 nanophosphors: Rietveld refinement, bandgap and photoluminescence optimization

In this work, Eu-doped, Tb-doped and Eu, Tb-codoped Y2O3 nanophosphors were synthesized by the combustion synthesis method. The prepared phosphors were characterized by x-ray diffraction (XRD), Rietveld refinement and Fourier transform infrared (FTIR) spectroscopy. XRD studies and Rietveld refinement confirmed the body-centred cubic structure of doped and codoped phosphors. FTIR studies also confirmed the formation of these compounds. Thermal analysis results indicated that there was no phase transition for all the phosphors in the studied temperature range. In the optical properties, diffuse reflectance (DR) and photoluminescence (PL) measurements were performed. DR spectra were used to determine the bandgap and it increased in the doped and codoped samples due to the crystallite size effect. A strong characteristic emission from Eu3+ and Tb3+ ions was identified and the influence of doping concentration and annealing temperature on PL properties was systematically studied. Transfer of energy was observed from Tb3+ to Eu3+ ions in the codoped phosphor at room temperature.

Pressure-induced hydrogen bond symmetrisation in guyanaite, β-CrOOH: evidence from spectroscopy and ab initio simulations

Guyanaite, β-CrOOH, is a structural analogue of the high-pressure oxyhydroxide phases δ-AlOOH and ɛ-FeOOH. Here, it was synthesized in piston-cylinder and multi-anvil press experiments at 4–13.5 GPa and 900–1100 °C. The deuterated phase β-CrOOD was synthesized at 4 GPa and 600 °C. The samples were characterized at ambient conditions by X-ray diffraction, diffuse optical reflectance spectroscopy and infrared absorption (IR) spectroscopy. In addition, the structural evolution of β-CrOOH and β-CrOOD with increasing pressure up to about 20 GPa was studied by in situ IR spectroscopy in a diamond anvil cell (DAC). This investigation was complemented by first-principles calculations in the framework of the density-functional theory (DFT). A pronounced geometric isotope effect and very short O-H. . .O bond lengths of 2.497(3) A for β-CrOOH and 2.541(3) A for β-CrOOD are observed at ambient pressure. In the IR spectra, no bands show up above 2000 cm−1, which indicates strong hydrogen bonding. The evolution of OH- and OD-related vibrational bands with pressure studied by IR spectroscopy shows a discontinuity at about 5 GPa. The DFT calculations suggest that this change in compression mechanism is related to a second-order phase transition from the low-pressure phase with asymmetric hydrogen positions (space group P 21 nm or Pnnm ) to a high-pressure phase with space group Pnnm that is characterized by symmetric hydrogen bonds with two identical OH bond lengths of 1.20(1) A. Using density functional perturbation theory, the most prominent high-frequency modes observed in the IR spectra are assigned to O-H-O bending vibrations. The transition pressure for hydrogen bond symmetrisation in β-CrOOH is considerably lower than in other hydrous phases of recent interest, such as δ-AlOOH or phase D.

Electronic structure and optical properties of the nonlinear optical crystal Pb4O(BO3)2 by first-principles calculations

Pb4O(BO3)2 has a layered-type arrangement with optimally aligned BO3 triangles. The optical band gap is 3.317eV obtained via the extrapolation method from the UV–vis–IR optical diffuse reflectance spectrum, consequently the absorption edge is about 374nm. Density functional calculations using a generalized gradient approximation were utilized to investigate the electronic structures and optical properties of Pb4O(BO3)2. The calculated band structures show a direct gap of 2.608eV, which is in agreement with the experimental optical band gap. A delocalized π bonding of BO3 triangles and the stereo-effect of the lone pair 6s2 of lead cations are studied in electron densities. The birefringence is about 0.039–0.061 with the wavelength larger than about 375nm. The calculated second-order susceptibility d24=3.5 d36 (KDP) which is well consistent with the powder SHG intensity.

Structure of Morpholinium Tribromoplumbate C4H8ONH2PbBr3 Studied Using Single-Crystal Neutron Diffraction

The structure of inorganic–organic perovskite morpholinium tribromoplumbate C 4 H 8 ONH 2 PbBr 3 has been studied using single-crystal neutron diffraction with the time-of-flight (TOF) Laue technique. Nuclear positions and anisotropic atomic displacement parameters (ADPs) of all the atoms are determined with high accuracy without any restraints. The accuracy of bond lengths and angles in the organic part was almost one digit higher than that of X-ray data, showing the advantage of the neutron Laue technique for the structural study of the present system. It is indicated that the bond lengths and ADPs in the organic part are affected by protonation and bondings between organic and inorganic parts while the conformation of the morpholine molecule in the crystal is retained. The blue-shift in the band gap owing to the distortion in the inorganic octahedra is found in the optical diffuse reflection spectrum and in the electron density of state calculated by ab initio band calculation.

Determination of Optical Coefficients and Fractal Dimensional Parameters of Cancerous and Normal Prostate Tissues

Optical extinction and diffuse reflection spectra of cancerous and normal prostate tissues in the 750 to 860 nm spectral range were measured. Optical extinction measurements using thin ex vivo prostate tissue samples were used to determine the scattering coefficient (μ(s)), while diffuse reflection measurements using thick prostate tissue samples were used to extract the absorption coefficient (μ(a)) and the reduced scattering coefficient (μ'(s)). The anisotropy factor (g) was obtained using the extracted values of μ(s) and μ'(s). The values of fractal dimension (D(f)) of cancerous and normal prostate tissues were obtained by fitting to the wavelength dependence of μ'(s). The number of scattering particles contributing to μ(s) as a function of particle size and the cutoff diameter d(max) as a function of g were investigated using the fractal soft tissue model and Mie theory. Results show that d(max) of the normal tissue is larger than that of the cancerous tissue. The cutoff diameter d(max) is observed to agree with the nuclear size for the normal tissues and the nucleolar size for the cancerous tissues. Transmission spectral polarization imaging measurements were performed that could distinguish the cancerous prostate tissue samples from the normal tissue samples based on the differences between their absorption and scattering parameters.

Synthesis, structure, photoluminescence and theoretical calculations on a novel tetranuclear Cd(II) complex based on (2,3-f)-pyrazino(1,10)phenanthroline-2,3-dicarboxylic acid

Abstract A novel tetranuclear cadmium complex {Cd2[(CH3)2PPDA]2(CH3OH)Cl4}2 (1) [(CH3)2PPDA = dimethyl esterification of H2PPDA], was prepared from CdCl2·2.5H2O with (2,3-f)-pyrazino(1,10)phenanthroline-2,3-dicarboxylic acid (H2PPDA) by solvothermal reaction in methanol, and characterized by single-crystal X-ray diffraction analysis, optical diffuse reflectance and photoluminescence. In 1, cadmium ions are bridged by Cl− ions into a tetranuclear oligomeric chain further connected into a 3D supramolecular network by intermolecular C H⋯Cl, O H⋯Cl, and C H⋯O hydrogen bonds. Compound 1 displays fluorescence with a lifetime value of ~ 5.88 ns in the visible region under visible-light excitation, and the origin of the luminescent emission is primary assigned to the combination of intraligand π–π* transition of (CH3)2PPDA ligand and ligand to ligand charge transfer from Cl− to (CH3)2PPDA which is probed by the density of state (DOS) calculations.

Nano‐texturing of Transparent Polymers with Plasma Etching: Tailoring Topography for a Low Reflectivity

AbstractThe reflectivity of transparent polymers can be reduced with a proper nanotextured layer on the surface according to the “moth eye” effect. Plasma etching has been proved to be a reliable method to generate self‐organized nanostructures on the surface of various polymers. In the present work this method, directly carried out in one step, has been tested on polycarbonate for application as low reflective transparent material. CF4 and O2 fed plasma processes have been compared at different treatment time. Chemical (X‐ray photoelectron spectroscopy), morphological (scanning electron microscopy), and optical (diffuse and specular reflectance, normal and grazing incidence) features have been evaluated. Results indicate that the CF4‐to‐O2 feed ratio significantly affects shape and distribution of the generated structures. O2 plasma, in particular, leads to taller structures with wire‐like aspect and more homogeneous distribution, which are more effective in reducing reflectance with a broadband character (visible and near‐infrared). Treatment duration, which instead affect mainly the dimension scale of the structures, must be tailored in order to control diffuse component of reflectance.magnified image

The impact of laser ablation on optical soft tissue differentiation for tissue specific laser surgery-an experimental ex vivo study

BackgroundOptical diffuse reflectance can remotely differentiate various bio tissues. To implement this technique in an optical feedback system to guide laser surgery in a tissue-specific way, the alteration of optical tissue properties by laser ablation has to be taken into account. It was the aim of this study to evaluate the general feasibility of optical soft tissue differentiation by diffuse reflectance spectroscopy under the influence of laser ablation, comparing the tissue differentiation results before and after laser intervention.MethodsA total of 70 ex vivo tissue samples (5 tissue types) were taken from 14 bisected pig heads. Diffuse reflectance spectra were recorded before and after Er:YAG-laser ablation. The spectra were analyzed and differentiated using principal component analysis (PCA), followed by linear discriminant analysis (LDA). To assess the potential of tissue differentiation, area under the curve (AUC), sensitivity and specificity was computed for each pair of tissue types before and after laser ablation, and compared to each other.ResultsOptical tissue differentiation showed good results before laser exposure (total classification error 13.51%). However, the tissue pair nerve and fat yielded lower AUC results of only 0.75. After laser ablation slightly reduced differentiation results were found with a total classification error of 16.83%. The tissue pair nerve and fat showed enhanced differentiation (AUC: 0.85). Laser ablation reduced the sensitivity in 50% and specificity in 80% of the cases of tissue pair comparison. The sensitivity of nerve–fat differentiation was enhanced by 35%.ConclusionsThe observed results show the general feasibility of tissue differentiation by diffuse reflectance spectroscopy even under conditions of tissue alteration by laser ablation. The contrast enhancement for the differentiation between nerve and fat tissue after ablation is assumed to be due to laser removal of the surrounding lipid-rich nerve sheath. The results create the basis for a guidance system to control laser ablation in a tissue-specific way.

Three novel 2D organic–inorganic hybrid CuII–LnIII heterometallic arsenotungstates

The hydrothermal reactions of Na8[A-α-HAsW9O34]·11H2O with CuCl2·2H2O, LnCl3 in the presence of ethylenediamine (en) lead to three novel 2D organic–inorganic hybrid CuII–LnIII heterometallic arsenotungstates Na3[Cu(en)2(H2O)][Cu(en)2]1.5[H3Ln(α-AsW11O39)2]·xH2O (Ln=DyIII, x=5 (1); Ln=GdIII, x=4 (2); Ln=LaIII, x=5.5 (3)), which have been characterized by elemental analyses, IR spectra, optical diffuse reflectance spectra, thermogravimetric analyses and single-crystal X-ray diffraction. 1–3 are isomorphic and exhibit the unique 2D honeycomb (6,3)-network topology constructed from sandwich-type [H3Ln(α-AsW11O39)2]8− units through [Cu(en)2]2+ linkers. To the best of our knowledge, 1–3 represent rare 2D organic–inorganic hybrid CuII–LnIII heterometallic arsenotungstates. The photocatalytic measurements show that 1–3 can to some extent inhibit the photodegradation of rhodamine-B. Moreover, magnetic measurements demonstrate that there are the weak ferromagnetic behaviors in 1 and 2.

A new luminescent Cu(I) complex stabilized by Cu⋅⋅⋅Cu interactions

Abstract A novel luminescent Cu(I) compound, [Cu(HtrzS)]n (1 HtrzSH=1H-1,2,4-triazole-3-thiol), was hydrothermally synthesized, which features a two-dimensional (2D) inorganic–organic hybrid framework containing a inorganic [CuS]n layer. Further, this 2D framework is connected by the intermolecular hydrogen bonds into a three-dimensional (3D) supramolecular framework. Optical diffuse reflectance study reveals an optical band gap of 3.44 eV, making it a wide band gap semiconductor. Moreover, this compound exhibits strong photoluminescence at room temperature. The densities of states (DOS) calculations reveal that luminescence emission bands of the compound originate from the ligand-to-metal charge transfer.

Cation ordering and physicochemical characterization of the quaternary diamond-like semiconductor Ag2CdGeS4

The quaternary diamond-like semiconductor, Ag2CdGeS4, was synthesized via high-temperature solid-state synthesis as well as structurally and physicochemically characterized. Single crystal X-ray diffraction provided a model for Ag2CdGeS4 in the orthorhombic, noncentrosymmetric space group Pna21 with a=13.7415(8)Å, b=8.0367(5)Å and c=6.5907(4)Å, in contrast to a previously published model in Pmn21 from the Rietveld analysis of laboratory X-ray powder diffraction data. The Pna21 space group is supported by the Rietveld analysis of synchrotron X-ray powder diffraction data. Differential thermal analysis suggests that Ag2CdGeS4 exists in two polymorphs. Optical diffuse reflectance UV/vis/NIR spectroscopy indicates that the orange compound is a semiconductor with a band gap of 2.32eV. Optical microscopy, scanning electron microscopy, energy dispersive spectroscopy and inductively coupled plasma optical emission spectroscopy were used to further characterize the material.

The crystal and electronic band structure of the diamond-like semiconductor Ag 2ZnSiS 4

Single crystals of the new diamond-like semiconductor Ag 2ZnSiS 4 have been synthesized using high-temperature, solid state synthesis at 800 °C. The compound crystallizes in the monoclinic, noncentrosymmetric space group Pn with a = 6.4052(1) Å, b = 6.5484(1) Å, c = 7.9340(1) Å, β = 90.455(1)° and R1 (for all data) = 2.42%. The electronic band structure and density of states were calculated using density functional theory (DFT) and the full potential linearized augmented plane wave (LAPW) method within the Wien2k program suite. The calculated band structure suggests that Ag 2ZnSiS 4 is a direct band gap semiconductor with a calculated band gap of 1.88 eV at the Γ-point. The calculated density of states of Ag 2ZnSiS 4 is compared with that of AgGaS 2. The band gap of Ag 2ZnSiS 4 was also determined experimentally as 3.28 eV via optical diffuse reflectance spectroscopy.

Investigation of LaFeO3 perovskite growth mechanism through mechanical ball milling of lanthanum and iron oxides

LaFeO3 perovskite was synthesized mechanochemically through ball milling of La2O3 and Fe2O3 in stoichiometric ratio. X-ray powder diffraction (XRPD), simultaneous differential scanning calorimetry and thermogravimetry analysis (DSC–TGA), Mossbauer spectroscopy, scanning electron microscopy (SEM), and optical diffuse reflectance spectroscopy were combined for a detailed study of the growth mechanism of LaFeO3 perovskite during the ball milling process. The XRPD results showed that La2O3 is unstable when exposed to air. Both La2O3 and La(OH)3 phases coexist under the ball milling process, indicating that La2O3 or La(OH)3 can be used to produce LaFeO3. The formation of LaFeO3 perovskite was evident after only 2 h of milling and the amount of LaFeO3 gradually increased with the increase of ball milling time. After 12 h of ball milling, single phase LaFeO3 was formed. The Mossbauer spectroscopy studies show that the spectrum of the formed LaFeO3 phase consists of three sextets and one doublet, indicating the wide distribution of LaFeO3 particle sizes and some of the smaller particles having superparamagnetic properties. This is in good agreement with the SEM images, which show that the formed LaFeO3 phase consists of nanometer-sized particles and micrometer-sized agglomerates. The formation of LaFeO3 phase was mainly caused by the La3+ substitution of Fe3+ in Fe2O3 lattice. Optical diffuse reflectance spectroscopy studies show that the formed LaFeO3 phase has semiconductor properties, with the band gap energy ~2.67 eV.

OPTICAL MONITORING OF BLEACHING AGENTS EFFECTS ON HUMAN DENTAL REMAINS

The time evolution of the bleaching effect, of hydrogen peroxide and two different concentrations of carbamide peroxide, on partially deteriorated human dental remains was analyzed by optical diffuse reflectance in the visible region of the spectrum. The optical measurements show that, after applying the first bleaching treatment, the reflectance increases. However for successive applications, a decrease of the reflectance is observed. This effect can be attributed to enamel teeth surface etching induced by the bleaching agents, allowing the inner dentin to contribute to the optical spectra and diminishing the reflectance. Additionally, in order to compare with previous studies in dentistry, colorimetric analysis of the process was also performed. The relevance in the use of protocols for cleaning valuable dental pieces in forensics, anthropology, and archeology is discussed.