NIR Diffuse Reflectance Spectra Research Articles

Synthesis, structure and characterization of two new silver-iron based phosphates AgFe2(PO4)2F(H2O)2 and Ag3Fe2(PO4)(HPO4)3

Two new silver-iron based phosphates AgFe2(PO4)2F(H2O)2 (1) with monoclinic P21/n and Ag3Fe2(PO4)(HPO4)3 (2) with triclinic P-1 were synthesized by a conventional hydrothermal method, featuring a dimer structure and a twisted honeycomb-like lattice, respectively. XPS and BVS (Bond Valence Sum) calculations indicated only Fe3+ ions in both compounds, while FT-IR spectra proved the presence of [H2O] in 1 and [OH] groups in 2. Solid-state UV–vis–NIR diffuse reflectance spectra suggested their wide optical band gaps of 2.31 eV and 1.94 eV, respectively. Magnetic measurements indicated that both compounds display a long-range antiferromagnetic ordering at low temperature, showing the change of magnetic entropy of 9.59 J mol−1 K−1 in 1 and that of 14.87 J mol−1 K−1 in 2, respectively.

Oxygen vacancies based BiOBr nanoflowers saturable absorber and its application in Q-switched mode-locked infrared laser

In this work, BiOBr nanoflowers with oxygen vacancies as saturable absorber are prepared using hydrothermal method. Passively Q-switched mode-locked infrared laser is achieved. The output power reaches the maximum 312 mW. The minimum Q-switched envelope is 242 ns with the maximum repetition rate of 180.5 kHz. Meanwhile, the mode-locked pulse duration within the Q-switched envelope is approximately 315 ps with repetition rate of 232 MHz. The results of X-ray diffraction (XRD), Electron paramagnetic resonance (EPR), UV–Vis–NIR diffuse reflectance spectra, and X-ray photoelectron spectroscopy (XPS) demonstrate the oxygen vacancies introduce intermediate energy levels in the energy band of BiOBr, which enhances the optical absorption in the near-infrared region. Therefore, BiOBr saturable absorber exhibits good saturable absorption characteristics in the near-infrared region and is a promising modulation element in Q-switched mode-locked infrared lasers.

Amorphous Gallium Oxide Nanosheets with Broad Absorption and Spin Polarization for Si‐Based UV‒Vis‒NIR Photodetectors

AbstractAchieving broad light absorption and high carrier separation efficiency is crucial for wide‐bandgap semiconductors to enable broadband photodetection applications. Here, amorphous gallium oxide nanosheets feature with broad absorption and spin polarization Wis synthesized, and assembled with graphene and p‐Si, realizing UV‒vis‒NIR photodetection. Extended X‐ray absorption fine structure reveals that a‐GaOx NSs possess lower tetrahedral Ga occupation (10%) compared to crystalline β‐Ga2O3 (50%). UV‒vis‒NIR diffuse reflectance spectra and magnetic hysteresis loops demonstrate broad absorption and weak ferromagnetism of a‐GaOx NSs, respectively. Density functional theory calculation further reveals sub‐gap states and spin polarization in a‐GaOx NSs. Moreover, combined with Mott–Schottky curves, photoluminescence and time‐resolved photoluminescence spectra inferred the effective suppression of carrier recombination via spin polarization of a‐GaOx NSs. The graphene/a‐GaOx NSs/p‐Si photodetector incorporates a back‐to‐back rectifying junction, acquiring a dark current as low as 63 pA. All photogenerated carriers are in the depletion region of the photodetector favouring efficient charge separation. This photodetector exhibits a response time of τrise<60 ms and τfall<120 ms, and high specific detectivity 1013 Jones over 254–1064 nm light.

AGe2O4Q (A = Ba, Sr; Q = S, Se): A series of heteroanionic oxychalcogenides with large birefringence

Heteroanionic materials are of current research interest owing to their varied structural chemistry and properties. Recently, a number of heteroanionic materials have been synthesized that can be used for water splitting, battery materials, thermoelectrics, and nonlinear optical applications. Birefringent heteroanionic materials are still rarely researched. Herein, we report a series of new oxychalcogenides, AGe2O4Q (A = Ba, Sr; Q = S, Se), that are synthesized by solid-state reactions in fused silica tubes with their structures determined by single-crystal X-ray diffraction. Optical property measurements show that AGe2O4Q (A = Ba, Sr; Q = S, Se) exhibit large birefringences, 0.13–0.19 @ 1064 nm. These are one-order of magnitude larger than their single-anionic homologue, BaGe2O5 - 0.03 @ 1064 nm. This suggests that constructing heteroanions through using chalcogenides to partially substitute O in tetrahedral foundation building units (FBUs) is a viable method for designing new birefringent materials. Furthermore, the crystal structures, UV–vis–NIR diffuse reflectance spectra, infrared and Raman spectra as well as the first-principles calculations for AGe2O4Q (A = Ba, Sr; Q = S, Se) are also reported.

The Composite TiO2-CuOx Layers Formed by Electrophoretic Method for CO2 Gas Photoreduction.

This study demonstrates the ability to control the properties of TiO2-CuOx composite layers for photocatalytic applications by using a simple electrophoretic deposition method from isopropanol-based suspension. To obtain uniform layers with a controlled composition, the surfactant sodium lauryl sulfate was used, which influenced the electrophoretic mobility of the particles and the morphology of the deposited layers. The TiO2-CuOx composite layers with different CuOx contents (1.5, 5.5, and 11 wt.%) were obtained. It is shown that the optical band gap measured by UV-VIS-NIR diffuse reflectance spectra. When CuOx is added to TiO2, two absorption edges corresponding to TiO2 and CuOx are observed, indicating a broadening of the photosensitivity range of the material relative to pure TiO2. An open-circuit potential study shows that by changing the amount of CuOx in the composite material, one can control the ratio of free charge carriers (n and p) and, therefore, the catalytic properties of the material. As a result, the TiO2-CuOx composite layers have enhanced photocatalytic activity compared to the pure TiO2 layer: methanol yield grows with increasing CuOx content during CO2 photoreduction.

Sr14.06Gd14.63(BO3)24: A Gadolinium-Rich Borate with Magnetic Refrigeration Performance.

A single crystal of Sr14.06Gd14.63(BO3)24 has been successfully grown through a high-temperature solution technique with K2O-KF-B2O3 as the flux. It crystallizes in the Pnma space group with parameters a = 22.3153(5) Å, b = 15.9087(4) Å, c = 8.7507(2) Å, and Z = 2. Sr14.06Gd14.63(BO3)24 has a three-dimensional (3D) framework built from [GdO] chains, in which the isolate [BO3]3- groups and Sr2+ ions fill in the space of the 3D framework. The magnetic measurements revealed that the title compound exhibits a large magnetocaloric effect with the magnetic entropy change of -ΔSm = 42.2 J kg-1 K-1 at 2 K for 7 T, which is higher than that of the commercial material, Gd3Ga5O12 (GGG), with -ΔSm of 38.4 J kg-1 K-1 under the same conditions. Moreover, the infrared spectrum (IR), UV-vis-NIR diffuse reflectance spectrum, and thermal stability were investigated.

Syntheses, structures, and characterization of new heteroanionic chalcohalides: Na2Ba17In8Q21F18 (Q = S, Se), KBa2InQ3F2 (Q = S, Se)

Four new metal chalcogenides containing fluorine, Na2Ba17In8Q21F18 (Q = S, Se), KBa2InQ3F2 (Q = S, Se) were synthesized by the solid-state reactions, and their structures were determined by single crystal X-ray diffraction. To the best of our knowledge, they represent the first example of F-containing mixed alkali and alkaline earth In-based chalcogenides. Structurally, Na2Ba17In8Q21F18 (Q = S, Se), KBa2InQ3F2 (Q = S, Se) all feature one-dimensional chain-like structures composed of In-based polyhedra, but they are not isostructural. The optical property measurements indicate that KBa2InSe3F2 and Na2Ba17In8Se21F18 have relatively large birefringences (0.096 and 0.083 at 532 nm, respectively), which are larger than that of KBa2InS3F2(0.056 @ 532 nm) and Na2Ba17In8S21F18 (0.041 @ 532 nm). Their structure-property relationship demonstrates that the large difference of birefringence among these compounds mainly arises from the different connection modes of InQn (n = 4, 5) polyhedra. In addition, the first-principles calculations, UV–vis–NIR diffuse reflectance spectra and IR spectroscopy of title compounds have also been performed. The effect of MIII/cation ratios on the polymerization of In–Q (Q=S, Se) units have been discussed.

K3BaTeB7O15: A new borotellurite with mixed metal cations

Tellurium-based borates are known to exhibit good optical properties and structural diversity, which are beneficial for obtaining new multicomponent borate optical materials. Therefore, a new borotellurite K3BaTeB7O15 with an anionic framework interconnected by TeO3 groups and pseudo-layers consisting of B7O16 units, was synthesized. The compound was synthesized by the high-temperature solution method and crystallized in the P21/c (No.14) space group, which has a complex cation. The UV-–vis–NIR diffuse reflectance spectra showed that the absorption edge of K3BaTeB7O15 was approximately at 235 nm, corresponding to a large experimental band gap of 4.2 eV. Thermal property analysis indicated that the compound was stable below 570 °C. The electronic energy band structure and partial density of states were calculated and discussed, and its birefringence was approximately 0.03@1064 nm. The results of ELF prove the existence of the stereochemical activity of the TeO3 group in K3BaTeB7O15.

A non–centrosymmetric compound K7Li2Y2B15O30 by introducing more alkali metals into A7MRe2B15O30 family

A non–centrosymmetric alkali metal rare earth–based borate K7Li2Y2B15O30 was successfully obtained. The title compound is derived from A7MRe2B15O30 (M ​= ​divalent cations) family by a hetero–valent substitution, meanwhile maintaining the original anionic framework. Li1 atom in K7Li2Y2B15O30 perfectly inherits the divalent cation M site in A7MRe2B15O30; while Li2 atom, in order to compensate the hetero–valent substitution, occupies the general position (Wyckoff 18f) close to Li1 atom, which causes an increase of cell parameters: a and b. Partial occupation of Li1 and Li2, in order to alleviate the direct contact between them, leads to the generation of Li vacancies, in favor of Li transportation. In addition, SHG test indicates that K7Li2Y2B15O30 is an NLO–active material (0.8 ​× ​KDP). The UV–vis–NIR diffuse reflectance spectrum shows high optical reflectance from 244 ​nm to 2500 ​nm. Moreover, the incongruent melting property of K7Li2Y2B15O30 has been studied by differential scanning calorimetric (DSC) and thermogravimetric (TG) curves.

Crystal growth, characterization and theoretical studies of the noncentrosymmetric compound Al3(IO3)9·(HIO3)6·18H2O

Single crystals of Al3(IO3)9·(HIO3)6·18H2O with sizes up to 4 × 4 × 3 mm3 were grown by the aqua-solution method at room temperature. It crystallizes in the noncentrosymmetric (NCS) hexagonal space group P63 (No. 173) with unit cell parameters of a = 16.1149 (10) Å, c = 12.3886 (11) Å and Z = 2. Its structure features a 3D framework composed by the IO3−, HIO3 and [Al(H2O)6]3+ units. It shows a powder second harmonic generation (SHG) response of about 3.5 × KDP at the particle size of 55–88 μm. The thermal stability, IR and UV–Vis–NIR diffuse reflectance spectra of Al3(IO3)9·(HIO3)6·18H2O were studied comprehensively. In addition, the first-principles calculation was carried out in order to understand the electronic structure and the origin of the linear and nonlinear optical properties.

Correction method of effect of soil moisture on the fluorescence intensity of polycyclic aromatic hydrocarbons based on near-infrared diffuse reflection spectroscopy.

Soil moisture has a strong impact on the fluorescence intensity of PAHs, which is undoubtedly posing a challenge for the development of rapid real-time fluorescence detection technology of PAHs in soil. In this work, NIR diffuse reflectance spectroscopy was used to correct the fluorescence spectra of PAHs in order to reduce the effect of the soil moisture. To establish the correction method, eight soil samples with different moisture contents and a given phenanthrene concentration (8mg/g) were prepared. The fluorescence and NIR diffuse reflectance spectra were collected for of all samples. It was found that the fluorescence spectra of the soil samples that vary with the moisture content together with the NIR diffuse reflectance spectra were considered for the correction of the fluorescence intensity of phenanthrene related to the moisture content. The results showed that the ratio of the fluorescence intensity at 384nm to the NIR diffuse reflectance spectrum absorbance at 5184cm-1 can be used as a correction factor to reduce the effect of the soil moisture on the fluorescence intensity of phenanthrene in the soil. The validity of the correction method was verified by the quantitative analysis of PAHs with different concentrations and soil moisture contents. The results showed better linearity between the fluorescence intensity and the concentration of PAHs after the correction (with a correlation coefficient R of 0.99) than before the correction (with R of 0.86). The relative prediction errors for three unknown samples decreased from 19%, 51% and 40% before the correction to 5%, 13% and 0.44% after the correction, respectively, indicating the feasibility of the detection of PAHs in the soil by the combination of fluorescence and NIR diffuse reflectance spectroscopy.

Synthesis, crystal structures and physical properties of two new sulfates KYb(SO4)2·H2O and KYb(SO4)F2

Two new potassium ytterbium sulfates KYb(SO4)2·H2O and KYb(SO4)F2 have been obtained by a conventional hydrothermal method, which are found to crystallize in the monoclinic system with space group P21/n and P21/m, respectively. KYb(SO4)2·H2O features a three-dimensional open framework built by isolated YbO4 polyhedra and SO4 tetrahedra, while KYb(SO4)F2 exhibits a zigzag-chain structure built by YbO4F4 polyhedra running along [010] direction. Magnetic measurements indicate that both of two compounds display a paramagnetic behavior down to 2 ​K with a dominant antiferromagnetic interactions between ytterbium ions. TGA and temperature-dependent PXRD measurements verify the excellent thermal stability of their frameworks. Solid-state UV–vis–NIR diffuse reflectance spectra show that they have wide optical band gaps of 4.95 ​eV and 5.36 ​eV, respectively.

Na3AMg7(PO4)6 (A = K, Rb and Cs): Structures, properties and theoretical studies of alkali metal magnesium orthophosphates

• Na 3 KMg 7 (PO 4 ) 6 and Na 3 CsMg 7 (PO 4 ) 6 were determined for the first time. • Theoretical calculations were performed to understand the electronic structures. • The title compounds melt congruently and exhibit a wide transparent range with the ultraviolet cut-off edge below 210 nm. Abstract Two new alkali metal magnesium orthophosphates, Na 3 KMg 7 (PO 4 ) 6 and Na 3 CsMg 7 (PO 4 ) 6 , have been successfully synthesized using the high-temperature solid state method. The crystal structure has been determined by single crystal X-ray diffraction. Besides, Na 3 RbMg 7 (PO 4 ) 6 , a known compound, has also synthesized and characterized for comparison. The title compounds crystallize in the same space group, C 2 /c (No. 15). They are isostructural and feature a three-dimensional network composed of isolated PO 4 tetrahedra, AO x ( A = K, Rb and Cs, x = 8 and 12), and MgO x ( x = 5 and 6) distorted polyhedra. The thermal properties, infrared spectroscopies, and UV–Vis–NIR diffuse reflectance spectrum have been performed for the first time. Meanwhile, first-principle theoretical studies were carried out to understand the relationship between the electronic structures and optical properties. The title compounds melt congruently and exhibit a wide transparent range with the ultraviolet (UV) cut-off edge below 210 nm, which makes Na 3 AMg 7 (PO 4 ) 6 ( A = K, Rb, Cs) as potential UV optical materials. Na 3 AMg 7 (PO 4 ) 6 ( A = K, Rb, Cs) are isostructural and the structures have 3D framework composed of the isolated PO 4 and MgOx ( x = 5 and 6), then the K, Rb, Cs and Na cations locate in the tunnels to form the final structure, respectively.

Solid-state photoluminescence, energy transfer mechanism and optical band gap of two 4f-5d complexes with 1-D chain-like structure

Under hydrothermal conditions, two novel lanthanide (III)-mercury (II) compounds [Ln (IA)3(H3O)2]2n·2n (HgCl4)·n (Hg2Cl5)·nH3O·3nH2O (Ln ​= ​Eu, 1; Tm, 2; HIA ​= ​isonicotinic acid) were synthesized. The single-crystal X-ray diffraction revealed that they are isostructural and they feature a one-dimensional (1-D) chain-like structure and a three-dimensional (3-D) supramolecular network. Solid-state photoluminescence experiments revealed that they show red or blue emission bands, which can be assigned to the characteristic emissions of the 4f electron intrashell transitions of 5D0 → 7FJ (J ​= ​1, 2, 3, and 4; Eu3+, 1) or 1G4 → 3H6 (Tm3+, 2), respectively. The energy transfer mechanisms were revealed by the energy level diagrams of the Eu3+ or Tm3+ ions and isonicotinic acid ligand. Both compounds exhibit remarkable CIE chromaticity coordinates of (0.6454, 0.3543) and (0.1092, 0.1497) for 1 and 2, respectively. Solid-state UV–Vis–NIR diffuse reflectance spectra uncovered that they possess wide optical band gaps of 3.16 ​eV and 3.18 ​eV for 1 and 2, respectively.

Synthesis, structure, photoluminescence, band gap and energy transfer mechanism of a novel bimetallic thulium–mercury compound with a three-dimensional framework

Under hydrothermal conditions, a novel bimetallic thulium–mercury compound {[Tm(H2O)2(IA)3]2n[(Hg6Br13)n]}(nHgBr2)·4nH2O·nH3O (1) (IA = isonicotinato anion) was prepared and the crystal structure was characterized by single-crystal and powder X-ray diffraction. It is characterized by a three-dimensional (3D) framework with a novel two-dimensional (2D) inorganic [(Hg6Br13)n] layer. Solid-state photoluminescence measurements revealed that compound 1 emits upconversion mazarine emission bands, which are originated from the 1G4 → 3H6 and 1D2 → 3H4 characteristic emissions of the 4f electron intrashell transitions of Tm(III) ions. An energy transfer mechanism is reported. Compound 1 displays CIE chromaticity coordinates of 0.1288 and 0.0635 in the mazarine region. A solid-state UV–Vis–NIR diffuse reflectance spectrum unveiled that compound 1 has a wide optical band gap of 2.69 eV. A thermogravimetry analysis measurement is also reported. A novel bimetallic thulium–mercury compound was prepared and characterized. It features a 3D framework with a novel 2D inorganic [(Hg6Br13)n] layer. It contains many mercury(II) ions with four different coordination environments. It emits upconversion mazarine photoluminescence emission peaks, which could be attributed to the 1G4 → 3H6 and 1D2 → 3H4 characteristic emissions of the 4f electron intrashell transitions of the Tm(III) ions. An energy level diagram was used to explain the energy transfer mechanism. It has CIE chromaticity coordinates of 0.1288 and 0.0635 in the mazarine region, and it possesses a wide optical band gap of 2.69 eV.

Enhanced photoelectrochemical water splitting with template-free electrodeposition of SnS nanorods photoelectrode

In this paper, SnS nanorods were first prepared in an acidic solution by adjusting the amounts of tri-sodium citrate at room temperature using template-free electro-deposition method. The morphological characteristics and photoelectrochemical (PEC) properties of SnS nanorods thin films were investigated. The phase purity properties of deposited SnS thin films were analyzed by X-ray diffraction (XRD), energy disperse spectroscopy (EDS) and Raman spectra measurements. The morphological characteristics of SnS nanorods were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The band-gaps of SnS thin films were confirmed by UV–Vis–NIR diffuse reflectance spectrum. The PEC characterizations indicated that the photocurrent density of SnS nanorods thin films was about 46 μA/cm2 and the maximum IPCE value of SnS nanorods thin films was 9.3%. The fabrication of FTO/SnS (nanorods)/CdS/TiO2/Pt photoelectrode improved the PEC performances of SnS nanorods thin films greatly. The photocurrent density of FTO/SnS (nanorods)/CdS/TiO2/Pt reached 0.59 mA/cm2, and the maximum IPCE value of FTO/SnS (nanorods)/CdS/TiO2/Pt achieved 27.1%.

The first rare-earth lead phosphates Pb3AP3O12 (A=Sc, Gd) with remarkable SHG enhancement

Two new phosphates Pb3AP3O12 (A ​= ​Sc, Gd), have been synthesized through the high-temperature solution method. They crystallize in the same noncentrosymmetric space group I¯43d, and feature a three-dimensional A–O (A ​= ​Pb0.75Sc0.25 or Pb0.75Gd0.25) framework with the isolated PO4 tetrahedra filled in the space of framework. The UV–vis–NIR diffuse reflectance spectra show their band gaps are 4.4 and 4.3 ​eV, respectively. Interestingly, Pb3ScP3O12 exhibits a quite weak second harmonic generation (SHG) responses, less than 0.05 ​× ​KH2PO4 (KDP), whereas the isomorphic Pb3GdP3O12 shows a much larger SHG response, 0.6 ​× ​KDP. The relationship between structures and properties indicates that the enhanced SHG response of Pb3GdP3O12 originates from the effect of rare-earth on the distortion of [Pb0.75/Gd0.25O6] octahedron.

Quaternary rare-earth sulfide LaSnGa3S7: Synthesis, structure, thermal and optical properties

The quaternary rare-earth sulfide LaSnGa3S7 was prepared by reaction of La, SnS, Ga2S3, and S at 1173 K. Single-crystal X-ray diffraction analysis revealed that it adopts a new monoclinic structure type (space group P21/n, a = 11.3555(9) Å, b = 9.6177(5) Å, c = 11.5137(8), β = 115.693(9)°, Z = 4) featuring a three-dimensional (3D) anionic framework built up of two-dimensional (2D) Ga–S layers formed by corner-sharing [GaS4] tetrahedra and unique [Sn2S8] dimers formed by edge-sharing [SnS5] units, with the intervening voids filled by La cations. An optical band gap of 2.39 (2) eV, as deduced from the UV–vis–NIR diffuse reflectance spectrum, is consistent with the yellow colour of the crystals. Thermal analysis suggests that LaSnGa3S7 melts incongruently. The electronic structure of LaSnGa3S7 is obtained through the first-principle calculations.

SrI3O9H: A new alkaline earth metal iodate with two different anionic units using mild aqua-solution method

An alkaline earth metal iodate crystal, SrI3O9H, has been successfully grown by a mild aqua-solution method for the first time. It contains two different anionic units, isolated [IO3] units and [I2O6H] units. The alkali and/or alkaline earth metal hydrogenous iodates (Ⅴ) are summarized. Thermal behavior, infrared spectrum, Raman spectrum, and UV–Vis–NIR diffuse reflectance spectrum are characterized. The band gap, density of states, and birefringence of SrI3O9H are calculated as well.

High accuracy determination of Angelica dahurica origin based on near infrared spectroscopy and a random forest pruning algorithm

A near infrared spectroscopy method combined with a random forest pruning algorithm based on margin optimization and principal component analysis (PCA-MORFP) was proposed to identify the origin of Angelica dahurica. One hundred and ninety-six samples of A. dahurica were collected from four original cultivation regions; their NIR diffuse reflectance spectra were measured by a custom-built near infrared spectrometer which works in the range of 900–1700 nm with a resolution (full width at half maximum [FWHM]) of 4 nm. Combinations of Savitzky–Golay smoothing, standard normal variates, and first derivative transformations were used to preprocess the spectral data. Then the PCA-MORFP classification model was constructed. Meanwhile, the was compared with other classifying approaches, including: principal component analysis-K-nearest neighbor, principal component analysis-support vector machine, and principal component analysis-random forest. Experimental results showed that the PCA-MORFP achieved the best prediction performance over other compared methods. The recognition rates of the PCA-MORFP model were up to 100% for the calibration set and 98.2% for the prediction set, respectively. The method provides a rapid and convenient detection technique for the origin identification of A. dahurica.