Optical Diffuse Reflectance Spectra Research Articles

Photoluminescence emission enhancement in the LiSrVO4:Eu3+ vanadate phosphor by partial substitution of M+ ions (M+=Li+/Na+/K+); optical thermometry; and optical transition probabilities using Judd-Ofelt analysis

In solid state lighting (SSL), pcWLEDs gain more attention for various illumination applications. The Eu3+ activated LiSrVO4:xEu3+ (0–15 mol% in steps of 3) phosphors are prepared by the conventional solid state method and their phase formation is confirmed by PXRD. It suggest that the samples are in a monoclinic structure with P2/m space group. SEM results confirmed that the size of the prepared phosphor is in a micrometer range with an irregular spherical shape. The optical diffuse reflectance spectrum (DRS) consisted broad band absorption in the ultraviolet (UV) region (270–350 nm) and also, they are found to absorb strongly the NUV light (396 nm) and the blue light (466 nm). They exhibit the strongest emission at 617 nm for the samples under 326 nm excitation. The PL intensity of the phosphors are improved by co-doping. The optical transition probabilities of the LiSrVO4:9 mol% Eu3+ phosphor are also analyzed using the Judd-Ofelt theory. The optimized phosphor showed a good thermal stability and the lifetime values are in the millisecond range. The absolute and the relative sensitivities are obtained from the temperature dependent lifetime measurements. The LiSrVO4:9 mol%Eu3+ phosphor yielded CIE coordinates (x, y) of (0.5987, 0.4005), a low CCT of 1468K, and a color purity of 96.4 %. These results indicate the potential application of the LiSrVO4 based phosphors in WLEDs.

Are Selenides the Same as Sulfides? Structure, Spectroscopy, and Properties of Narrow-Gap Rare-Earth Semiconductors RE2Sn(S1-xSex)5 (RE = La, Ce; x = 0-0.8).

The ternary rare-earth sulfides RE2SnS5 (RE = La-Nd) and the partial solid solutions RE2Sn(S1-xSex)5 (RE = La, Ce; x = 0-0.8) were prepared in the form of polycrystalline samples by reaction of the elements at 900 °C and as single crystals in the presence of KBr flux. They adopt the La2SnS5-type structure (orthorhombic, space group Pbam, Z = 2) consisting of chains of edge-sharing SnCh6 octahedra separated by RE atoms. Although the cell parameters evolve smoothly in RE2Sn(S1-xSex)5, detailed structural analysis by single-crystal X-ray diffraction revealed a pronounced preference for the Se atoms to occupy two out of the three chalcogen sites, which offers a rationalization for why the all-selenide end-members RE2SnSe5 do not form. Solid-state 119Sn NMR spectra confirmed the nonrandom distribution of SnS6-nSen local environments, which could be resolved into individual resonances. The Raman spectra of RE2SnS5 compounds show an intense peak at 307-320 cm-1 assigned to a symmetric A1g mode, which is dominated by Sn-S bonds; the Raman peak intensities varied with Se substitution in La2Sn(S1-xSex)5. Optical diffuse reflectance spectra, band structure calculations, and electrochemical impedance spectra indicated that these compounds are narrow band gap semiconductors; the optical band gaps are insensitive to RE substitution in RE2SnS5 (0.7 eV) but they gradually decrease with greater Se substitution in RE2Sn(S1-xSex)5 (0.7-0.4 eV).

Internal quality evaluation of ‘Fuji’ apples during storage based on bulk optical properties or diffuse reflection and transmission spectra

The purpose of this study is to compare the performance of prediction models based either on the bulk optical properties (BOP) or with models based on the diffuse reflection and transmission spectra to assess the soluble solids content (SSC) or fruit firmness (FF) of ‘Fuji’ apples. Diffuse reflection and transmission spectra of 240 apples in 500–1000 nm were acquired using a self-constructed single integrating sphere system, from which the absorption coefficient (μa) and reduced scattering coefficient (μ′s) were determined. The relationships of μa, μ′s, and the reflection and transmission spectra with the SSC and FF were analyzed, and detection models were established using partial least squares regression coupled with characteristic wavelength selection. Results showed that neither the SSC nor the FF changed obviously during 80-days storage, and the μa and μ′s showed no monotonic increase or decrease pattern. The SSC prediction model based on μa spectra combined with the baseline correction method performed the best (R2p = 0.79, RMSEP = 0.62), while the model based on μ′s spectra was the best for FF (R2p = 0.67, RMSEP = 0.35 N). Overall, the accuracy of the model based on BOP in predicting internal quality was better than that based on reflection and transmission spectra from the same measurement.

Comparison of optical absorption and diffuse reflectance spectra techniques for determining the optical energy band gap of dried and calcined Ni0.5Mn0.5Fe2O4 nanoferrite

Ultrafine particles of Ni0.5Mn0.5Fe2O4 were synthesized by coprecipitation technique to study the effect of both physical forms (ferrofluid and powder) and thermal treatment (drying at 100 °C and calcination at 600 °C for two hours) on the structural properties of Ni0.5Mn0.5Fe2O4 nanoferrite. In addition, the work presents a comparison between using optical absorption and optical diffuse reflectance spectra in studying the optical direct energy band gap. x-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to study the phase, size, and morphology of dried and calcined Ni0.5Mn0.5Fe2O4 nanoparticles, respectively. Fourier transform infrared (FTIR) spectra revealed the characteristic peaks of the synthesized ferrite and provided further information on the functional groups. The optical absorption spectra were used to evaluate the optical direct energy band gap of dried and calcined Ni0.5Mn0.5Fe2O4 nanoferrite as a ferrofluid, whereas, the optical diffuse reflectance spectra were used to evaluate the optical direct energy band gap of dried and calcined Ni0.5Mn0.5Fe2O4 nanoferrite in powder form.

Analysis of active screen low temperature plasma-assisted deposition of iron nitride thin films on silicon (100) substrate

Thin film technology has gained significant attention in the industry due to its superior properties in comparison to bulk materials. Specifically, iron nitride-based thin films are a fascinating area of research in semiconductor technologies. The crystal structure and optical properties of these films are highly dependent on the growth method, deposition technique, gas flow, pressure, and several other factors. In this work, we prepared polycrystalline thin films of iron nitride on silicon (100) substrates by using the active screen low temperature plasma-assisted method. These films are deposited under the varying atmosphere of nitrogen and hydrogen in four proportions: 80% N2 + 15% H2; 60% N2 + 35% H2; 40% N2 + 55% H2; and 20% N2 + 75% H2, along with 5% argon to investigate its influence on the structural, morphological, and optical properties. The structural properties are determined by x-ray diffraction and revealed a mixture of ζ-Fe2N, ε-Fe3N, and γ′-Fe4N phases. Surface morphology is analyzed by scanning electron microscopy, which confirms the formation of a thin layer on the substrate. In addition, UV–Vis spectrophotometry is used to assess the optical response and bandgap energy of the samples. The result of UV–Vis optical diffuse reflectance spectra shows a decrease in the bandgap from 3.17 to 3.06 eV of substrate. For the S4 sample, we obtained a pure Fe4N phase, showing a significant decrease in the energy bandgap.

Optical spectroscopy study of damage in ion-irradiated 3C-SiC epilayers on a silicon substrate

Epitaxial cubic (100) 3C-SiC films on a (100) silicon wafer were irradiated at room temperature with 2.3-MeV Si+ or 3.0-MeV Kr+ ions up to a fluence of 1 × 1016 cm−2. The evolutions of the epilayer and the substrate were followed as a function of ion fluence by using micro-Raman spectroscopy, optical absorption, and diffuse reflectance spectroscopy in the UV-visible and near infrared range. Raman spectra evidence the amorphization of SiC films at an estimated dose of about 0.1 displacement per atom (dpa) for both ion irradiations. The narrow peaks of the Raman-allowed TO and LO modes of SiC and Si are recorded in the virgin sample, together with few peaks assigned to zone-edge modes of SiC arising from the intrinsic disorder in the strained films. Those crystal phonon peaks broaden or disappear with increasing fluence. The spectra finally exhibit broad extra peaks assigned to the formation of Si–Si and C–C wrong homonuclear bonds in the local order of the amorphous phase. The optical transmission and diffuse reflectance spectra feature interference fringe patterns in the SiC film that are smoothened out with irradiation due to the matching of refractive indices of the amorphous SiC film and Si substrate. The evolution of the refractive index of SiC and optical gap of Si are deduced from those spectra. The respective roles of ballistic effects and electronic excitations in the radiation damage of both SiC and Si are discussed for those two ions with about the same electronic stopping power and about one order-of-magnitude difference in nuclear stopping power. The damage is dominated by the nuclear collision processes and rather well correlated with the estimated irradiation dose in dpa. Optical spectra show that electronic excitations induce damage recovery of the amorphized substrate below the SiC/Si interface. Raman spectra and optical absorption/reflection spectra yield complementary pictures of the radiation damage.

CaZn(HPO3)2 and Ba2Zn(HPO3)3: novel alkaline-earth zincophosphites with diversified anionic frameworks.

Two novel alkaline-earth zincophosphites, namely CaZn(HPO3)2 and Ba2Zn(HPO3)3, were successfully synthesized under hydrothermal conditions. CaZn(HPO3)2 exhibits a three-dimensional (3D) anionic framework with a 6-connected uni-nodal pcu α-Po primitive cubic topology, constructed by unique Zn2O8 dimers and HPO3 pseudo-tetrahedra, while Ba2Zn(HPO3)3 displays one-dimensional (1D) [Zn(HPO3)3]4- anionic chains. It is worth mentioning that CaZn(HPO3)2 represents the first example of an alkaline-earth zincophosphite compound with a 3D framework structure. Our research also revealed the importance of both alkaline earth cation sizes and Zn/P ratios in anionic open-framework formation. The crystal structures of both compounds were further verified by energy dispersive spectroscopy, IR spectroscopy and Raman spectroscopy. Optical diffuse reflectance spectra, coupled with Tauc's fitting, revealed direct bandgaps with energy values of 4.33 and 4.48 eV for CaZn(HPO3)2 and Ba2Zn(HPO3)3, respectively, which differ from the prediction of theoretical calculations. Density of states calculations were conducted to reveal the origin of the bandgaps and bond interactions. Both compounds exhibited moderate birefringence values. This work may have implications for the design and synthesis of novel metal phosphites with desired properties.

Synthesis and Characterization of Gadolinium Oxide-Hematite Magnetic Ceramic Nanostructures

Mixed-oxide nanostructures of the type xGd2O3-(1-x)α-Fe2O3 (x=0.1, 0.3, 0.5 and 0.7) were synthesized by mechanochemical activation for ball milling times of 0, 2, 4, 8 and 12 hours. The systems were subsequently analyzed by Mӧssbauer spectroscopy, X-ray powder diffraction (XRPD), magnetic measurements and optical diffuse reflectance spectroscopy. The magnetic hyperfine field was studied as function of ball milling time for all sextets involved and found to be consistent with the formation of a limited solid solution in the systems investigated. The end-product was the gadolinium perovskite, represented by a doublet whose abundance was derived as function of the milling time. The XRPD patterns recorded for the equimolar composition were dominated by the diffraction peaks of GdFeO3 after 12 hours of milling. The hysteresis loops were recorded at 300 and 5 K in an applied magnetic field of 5 T and were interpreted as a superposition of paramagnetic behavior of gadolinium oxide and weak ferromagnetic behavior of hematite and gadolinium perovskite. The Morin transition of hematite was inferred from zero-field-cooling-field-cooling (ZFC-FC) curves measured with a magnetic field of 200 Oe in the 5-300 K temperature range and was found to depend on the ball milling time. Optical diffuse reflectance spectra showed that the compounds were semiconductors with an optical band gap of 2.1 eV.

Transition in the preferred orientation of RF sputtered ZnO/Si thin films by thermal annealing: Structural, morphological, and optical characteristics

Polycrystalline ZnO thin films having preferential growth along the polar (002) plane are prepared on Si (111) substrate using RF sputtering technique. A gradual build-up of the semipolar (103) plane with the dominant (002) polar plane of 400–700 °C annealed films is revealed by the Glancing incidence angle X-Ray diffraction (GXRD) pattern. However, a change in preferred orientation from polar (002) to semi-polar (103) and non-polar (100) planes is observed with further annealing in the temperature range 800–1200 °C. This occurs due to an increase in the mobility of adatoms due to annealing which encourages diffusion across grain boundaries and competitive growth among planes leading to the growth of (103) plane. This structural deviation of film from (002) plane to (103) plane leads to the change in surface morphology of annealed films around 800 °C as depicted in Field Emission Scanning Electron Microscopy (FESEM) images. The observed changes in surface morphology of films are further correlated with the variation in optical band gap values and diffuse reflectance spectra. The low reflectance values of the samples represent their anti-reflection property which makes ZnO/Si thin film a conceivable applicant in optoelectronics.

La4Ga2Se6O3: A Rare-Earth Oxyselenide Built from One-Dimensional Strips.

The oxyselenide La4Ga2Se6O3 was obtained by reaction in NaCl flux. Its monoclinic crystal structure (space group C2/c, a = 21.2832(13) Å, b = 11.6272(7) Å, c = 6.0006(4) Å, β = 106.3430(10)°, Z = 4), which is a new type, consists of strips of edge-sharing OLa4 tetrahedra and zigzag chains of corner-sharing GaSe4 tetrahedra. The separation into distinct structural blocks with mostly ionic vs covalent bonding character was supported by analysis of the electron localization function and crystal orbital bond index. An experimental band gap of 1.8 eV was extracted from optical diffuse reflectance spectra. First-principles calculations suggest that the thermoelectric power factor of this compound would be enhanced by n-doping.

Flux synthesis, crystal structure, and characterization of a gamma-vanadate selenite polymorph

Our exploration in vanadate selenites by using boric acid flux method has successfully lead into a new phase, namely, γ-V2Se2O9. Single crystal X-ray diffraction indicates its a new structure which crystallizes in monoclinic space group P21/c with a lattice parameter of a ​= ​7.4857 (12) Å, b ​= ​7.4388 (8) Å, c ​= ​13.042 (2) Å, β ​= ​106.619 (9)°. Its crystal structure features novel 2D electroneutral [V2Se2O9] layers composed of 1D [V2SeO9]4- chains that are further bridged by Se (1)O3 triangular pyramids. [V2SeO9]4- chain consist corner-sharing of VO6 and tridentate Se (2)O3. Unlike previously reported α- and β-V2Se2O9 with isolated [V4O18]16− tetramers, corner-sharing of VO6 octahedra lead into a 1D [V2O9]8- chain in γ-V2Se2O9. X-ray powder diffraction and thermal behavior analysis were performed to study its phase purity and thermal stability. Optical diffuse reflectance spectra associated with Tauc's fitting indicates a direct bandgap semiconductor with an energy value of 2.34 ​eV, which consistent with the theoretical prediction. As a compare, the electronic bandgaps of three polymorphs were studied and shows a sequence of α-V2Se2O9<β-V2Se2O9<γ-V2Se2O9. Density of states were also calculated to reveal the origin of the bandgaps and bond interactions.

Modulating trap levels via co-doping Ca2 + /Si4+ in LiTaO3:Pr3+ to improve both the intensity and threshold of mechanoluminescence

We report a novel mechanoluminescent phosphor Li1−xCaxSixTa1−xO3:0.01Pr3+ (x = 0–0.04). The crystal structure, photoluminescence (PL), optical diffuse reflectance spectra, afterglow (AG), fluorescence decay curves, and mechanoluminescence (ML) properties were investigated. To clarify the defect types and the mechanoluminescence mechanisms, an X-ray photoelectron spectroscopy (XPS) and thermoluminescence curve (TL) were measured. The dopants Ca2+ and Si4+ ions occupied the Li+ and Ta5+ sites, respectively. An optimal sample Li0.98Ca0.02Si0.02Ta0.98O3:Pr3+ was obtained with great enhancement in mechanoluminescence intensity, higher than that of non-doped sample LiTaO3:Pr3+ by 262%. And the compression threshold, over which the ML intensity could not maintain the linear increase, has also been greatly improved. Furthermore, the stable output of Tribo-L was achieved, which was visible to the naked eye. A probable mechanism was proposed to illustrate the mechanoluminescent process in Li1-xCaxSixTa1-xO3:0.01Pr3 + (x = 0–0.04). The study indicates that adjusting trap distribution by substituting host ions may be a novel way to develop high-quality mechanoluminescence.

Lost horses on the frontier: K2BiCl5 and K3Bi2Br9

Two missing members, K3Bi2Cl9 and K3Bi2Br9, within the series of Bi-containing defect perovskite halides A3Bi2X9 were sought. K3Bi2Cl9 could not be obtained, but the previously identified but uncharacterized compound K2BiCl5 was prepared. K3Bi2Br9 was successfully prepared. K2BiCl5 and K3Bi2Br9 were synthesized by reactions of binary halides at 450–500 ​°C and their structures were determined by single-crystal X-ray diffraction methods. K2BiCl5 adopts the K2PrCl5-type structure in orthorhombic space group Pnma with Z ​= ​4 and cell parameters of a ​= ​12.5461(7) Å, b ​= ​8.7630(5) Å, and c ​= ​7.9865(5) Å. This structure features one-dimensional columns of edge-sharing BiCl7 capped octahedra. K3Bi2Br9 adopts the Tl3Bi2Br9-type structure in monoclinic space group P21/c with Z ​= ​4 and cell parameters of a ​= ​18.718(3) Å, b ​= ​8.1148(13) Å, c ​= ​13.154(2) Å, and β ​= ​91.329(2)°. In this defect perovskite variant, Bi atoms occupy two-thirds of the octahedral sites formed by close-packed arrays of the K and Br atoms, and the BiBr6 octahedra are connected by corner-sharing within slabs. Among defect perovskite halides A3Bi2X9 containing corner-sharing octahedra, K3Bi2Br9 exhibits the greatest degree of distortion from the ideal cubic perovskite structure observed so far. The band gaps, as measured from optical diffuse reflectance spectra, are 2.8 ​eV for K2BiCl5 and 2.2 ​eV for K3Bi2Br9. Electronic structure calculations indicate an indirect gap for K2BiCl5 and a direct gap with rather flat bands for K3Bi2Br9.

Three Inorganic-Organic Hybrid Gallo-/Alumino-Borates with Porous-Layered Structures Containing [MB4O10(OH)] (M = Al/Ga) Cluster Units.

Three inorganic-organic hybrid gallo-/alumino-borates [Ga2B7O14(OH)]·H2dah (1, dah = 1,6-diaminohexane), K2[Ga2B7O14(OH)(en)0.5] (2, en = ethylenediamine), and K2[Al2B7O14(OH)(en)0.5]·H2O (3) were synthesized under solvothermal conditions. Compound 1 features a 3D porous-layered structure built by the alternation of [GaB4O10(OH)]6-, [B3O6]3- clusters and GaO4 tetrahedra, in which the novel [GaB4O10(OH)]6- cluster is first observed. Compounds 2 and 3 are isostructural and made by [MB4O10(OH)]6-, [B3O6(en)0.5]3- clusters and MO4 tetrahedra (M = Ga/Al); their 3D porous layers are similar to those of 1 and further bridged by en linkers through the rare B-N-C covalent bonds, resulting in the 3D inorganic-organic hybrid framework. This is the first main-group metal borate with organic molecules participating in the oxoboron frameworks through B-N bonds. Optical diffuse-reflectance spectra reveal that 1, 2, and 3 are potential wide-band-gap semiconductors.

Structural, Vibrational, Optical and Improved Photoluminescence Properties of Dy3+ Doped Ca2KZn2V3O12 Phosphors

A series of dysprosium (Dy3+) ion doped Ca2KZn2V3O12 phosphors were explored which exhibits a broad band and sharp peaks in the visible region under the ultraviolet light excitation. Fourier transform infrared (FTIR) spectra and the optical diffuse reflectance spectra were ascribing the formation of the distorted VO4 tetrahedral group due to the influence of Dy3+ ions. Moreover, a tunable luminescence color was achieved by doping of Dy3+ ion in the Ca2KZn2V3O12 phosphor. Through doping concentration optimization, the Ca2KZn1.9Dy0.1V3O12 phosphor was observed for high color rendering index (CRI) and excellent correlated color temperature (CCT) with cool white emission. Hence, in the designing of the VO4 → Dy3+ energy transfer that is capable of converting ultraviolet light into efficient white light, this phosphor is suitable for solid-state lighting applications.

Synthesis and Luminescence Investigation of Eu3+ Doped Ca2KZn2V3O12 Phosphors: A Potential Material for WLEDs Applications

A series of white light emitting Ca2KZn2–xV3O12:xEu3+ (x = 0.1, 0.2, 0.3, 0.4 and 0.5) phosphor samples were successfully synthesized by the traditional solid-state reaction method. The powder X-ray diffraction (XRD) patterns of the as-prepared sample reveal the high degree of crystallinity of the cubical structure with $$Ia\overline{3}d$$ space group and without any other phase formation. Fourier transform infrared (FTIR) spectra confirmed the occurrence of characteristic vibrational bands of garnet vanadate. The optical diffuse reflectance spectra consisting of broad band absorption in the ultraviolet (UV) region and the sharp absorption in the visible region were ascribing to the charge transfer between ligand–metal in the VO4 tetrahedral group and Eu3+ ions. Under the UV and near-UV excitation wavelengths, the broad band emission and the sharp emission were ascribing to the host material charge transfer of the VO4 tetrahedral group and f-f transitions of the rare-earth Eu3+ ions respectively. Ultimately, through the doping concentration optimization, a high Color Rendering Index (CRI) and excellent Correlated Color Temperature (CCT) were achieved with cool white emission. Therefore, the contribution of Ca2KZn1.8Eu0.2V3O12 phosphor was significant to phosphor-converted white light emitting device (WLEDs) excited with near ultraviolet.

MII2M3IIIF3(Te6F2O16) (MII = Pb, Ba; MIII = Al, Ga): New mixed anionic tellurites with isolated Te6 coplanar rings

Three new isostructural mixed anionic tellurites, namely, Pb2Al3F3(Te6F2O16) (1), Pb2Ga3F3(Te6F2O16) (2) and Ba2Ga3F3(Te6F2O16) (3), have been synthesized successfully by hydrothermal reactions. Their structures feature a novel 3D framework composed of 1D GaO4F2/AlO4F2 octahedral chains joined together with isolated (Te6F2O16)10− anionic rings. The charge-balance cations of Pb2+ or Ba2+ are located at the six-member polyhedral ring tunnels of the structures. The 0D (Te6F2O16)10− coplanar anionic ring is first reported in fluorotellurites, formed by two TeO4 and four TeO3F groups via corner-sharing. Thermogravimetric analyses revealed that their thermostabilities are in the following order: Pb2Al3F3(Te6F2O16) (1), Ba2Ga3F3(Te6F2O16) (3) and Pb2Ga3F3(Te6F2O16) (2). Optical diffuse reflectance spectra showed that these solids are wide band gap semiconductors with Eg of 4.1, 4.2 and 4.4 ​eV for compounds 1–3 respectively. The band gaps of compounds 1 and 2 are determined by O, Te and Pb atoms while the band gap of compound 3 is determined by O and Te atoms based on the theoretical calculations.

NaYTe2O7: A new compound with mixed valence of tellurium and large birefringence

A new compound with mixed valence of tellurium, namely, NaYTe2O7 has been successfully synthesized by the high−temperature solid state reaction through adopting substitution strategy. This compound crystallizes in the monoclinic space group of P21/n, and features two−dimensional [Te2O7]4− layer which is composed of TeVIO6 octahedra and TeIVO4 dispheniods. The anionic layers stack along [101] direction and interlinked by Y3+ and Na+ cations. The opposite arranged active lone pairs of TeIV and the layered anionic structure together induce the large birefringence which is estimated to be 0.18 at 1000 nm by first−principle calculation. This result indicates that the proper arrangement of lone pairs and directional covalent structure favor the increase of crystal’s birefringence. Furthermore, optical diffuse reflectance spectrum, infrared spectrum, thermal analysis and DFT calculations were also accomplished.

Construction of (3,8)-connected three-dimensional cobalt(II) and copper(II) coordination polymers with 1,3-bis[(1,2,4-triazol-4-yl)methyl]benzene and benzene-1,3,5-tricarboxylate ligands.

Coordination polymers (CPs) have been widely studied because of their diverse and adjustable topologies and wide-ranging applications in luminescence, chemical sensors, magnetism, photocatalysis, gas adsorption and separation. In the present work, two coordination polymers, namely poly[(μ5-benzene-1,3,5-tricarboxylato-κ6O1:O1':O3:O3:O5,O5'){μ3-1,3-bis[(1,2,4-triazol-4-yl)methyl]benzene-κ3N:N':N''}di-μ3-hydroxido-dicobalt(II)], [Co2(C9H3O6)(OH)(C12H12N6)]n or [Co2(btc)(OH)(mtrb)]n, (1), and poly[[diaquabis(μ3-benzene-1,3,5-tricarboxylato-κ3O1:O3:O5)bis{μ3-1,3-bis[(1,2,4-triazol-4-yl)methyl]benzene-κ3N:N':N''}tetra-μ3-hydroxido-tetracopper(II)] monohydrate], {[Cu4(C9H3O6)2(OH)2(C12H12N6)2(H2O)2]·H2O}n or {[Cu4(btc)2(OH)2(mtrb)2(H2O)2]·H2O}n, (2), were synthesized by the hydrothermal method using 1,3-bis[(1,2,4-triazol-4-yl)methyl]benzene (mtrb) and benzene-1,3,5-tricarboxylate (btc3-). CP (1) exhibits a (3,8)-coordinated three-dimensional (3D) network of the 3,8T38 topological type, with a point symbol of {4,5,6}2{42·56·616·72·82}, based on the tetranuclear hydroxide cobalt(II) cluster [Co4(μ3-OH)2]. CP (2) shows a (3,8)-coordinated tfz-d topology, with a point symbol of {43}2{46·618·84}, based on the tetranuclear hydroxide copper(II) cluster [Cu4(μ3-OH)2]. The different (3,8)-coordinated 3D networks based on tetranuclear hydroxide-metal clusters of (1) and (2) are controlled by the different central metal ions [CoII for (1) and CuII for (2)]. The thermal stabilities and solid-state optical diffuse-reflection spectra were measured. The energy band gaps (Eg) obtained for (1) and (2) were 2.72 and 2.29 eV, respectively. CPs (1) and (2) exhibit good photocatalytic degradation of the organic dyes methylene blue (MB) and rhodamine B (RhB) under visible-light irradiation.

Changes of optical transition models caused by crystal structural changes in CaSe2O5

The present work concerns calcium pyroselenites CaSe2O5 with two independent crystal structures, their difference physical properties and phase transformations. α-CaSe2O5 in orthorhombic form shows 2D calcium oxide anionic layers whereas new compound β-CaSe2O5 crystallizes in monoclinic space group C2/c. It's a new structure type with 1D calcium oxide thick chains which are further connected by Se2O5 dimers. Rietveld refinement indicates that the weight fraction for α/β-CaSe2O5 mixture phase was found to be 84.5% and 15.5% for α- and β-CaSe2O5, respectively. Optical diffuse reflectance spectrum coupled with Kubelka–Munk fit gives a result that α-CaSe2O5 adopts direct optical transition model while β-CaSe2O5 is an indirect semiconductor. The experimental result matches well with the prediction of theory calculation. The optical bandgap values were fitted to be 4.74 and 4.12 eV for α- and β-CaSe2O5, respectively. Thermal analysis coupled with variable temperature powder XRD indicates the phase transformation between these two phases.