NIR Absorption Spectra Research Articles

A Spectroscopic and Computationally Minimal Approach to the Analysis of Charge-Transfer Processes in Conformationally Fluxional Mixed-Valence and Heterobimetallic Complexes.

Class II mixed-valence bimetallic complexes {[Cp'(PP)M]C≡C-C≡N[M'(PP)'Cp']}2+ (M, M'=Ru, Fe; PP=dppe, (PPh3 )2 ; Cp'=Cp*, Cp) exist as conformational ensembles in fluid solution, with a population of structures ranging from cis- to trans-like geometries. Each conformer gives rise to its own series of low-energy intervalence charge-transfer (IVCT) and local d-d transitions, which overlap in the NIR region, giving complex band envelopes in the NIR absorption spectrum, which prevent any meaningful attempt at analysis of the band shape. However, DFT and time-dependent (TD)DFT calculations with dispersion-corrected global-hybrid (BLYP35-D3) or local hybrid (lh-SsirPW92-D3) functionals on a small number of optimised structures chosen to sample the ground state potential energy hypersurfaces of each of these complexes has proven sufficient to explain the major features of the electronic spectra. Although modest in terms of computational expense, this approach provides a more accurate description of the underlying molecular electronic structure than would be possible through analysis of the IVCT band by using the static point-charge model of Marcus-Hush theory and derivatives, or TDDFT calculations from a single (global) minimum energy geometry.

Band-gap engineering, conduction and valence band positions of thermally evaporated amorphous Ge15-x Sbx Se50 Te35 thin films: Influences of Sb upon some optical characterizations and physical parameters

Quaternary chalcogenide Ge15-xSbxSe50Te35, (0.0≤x≤15.0, at. %) thin films are prepared using the thermal evaporation process under the residual vacuum pressure of ≈ 10−3 Pa. The rate of deposition and thicknesses of the film samples are kept constant at 10 nm/s and 200 nm, respectively. X-ray diffraction is employed to examine the amorphous or crystalline structure of films. The absence of sharp and distinct peaks confirms the amorphous nature. The compositional element ratio of all prepared samples is analysed by energy-dispersion X-ray spectroscopy technique. UV–Vis–NIR absorption spectra are used to study the optical parameters of thin films. The values of the absorption coefficient for all film samples are found to be higher than 104 cm −1. The optical band-gap energy is determined both experimentally and theoretically. The band gap is due to the indirect electronic transitions, and the band gap values are found to decrease from 1.047 eV to 0.864 eV with the increase in Sb-ratio. The band-tail width increases from 0.103 eV to 0.258 eV. The optical density, skin effect and extinction coefficient increase with an increase in Sb-content. The positions of the conduction and valence bands, as well as the conduction potentials of all samples, are also evaluated. The Fermi level shifts closer to the valence band and away from the conduction band with increasing Sb content. The chemical bond approach model is applied to study the cohesive energy and average-coordination number of these a-Ge-Sb-Se-Te films. The total number of constraints, floppy modes, cross-linking density, the number of the valence electrons and the number of lone-pair electrons are also investigated. All discussed parameters are found to be strongly dependent on the Sb-content.

Influence of dopant ions concentration on the spectroscopic properties of Eu3+ doped alkaline earth oxyfluoro-borotellurite glasses for LED and red laser applications

In this present work, influence of Eu3+ ions concentration in a novel alkaline earth oxyfluoro-borotellurite glasses were synthesized with the composition (40−x)B2O3+20TeO2+ 10BaO+10BaF2+10SrO+10SrF2+xEu2O3 (where x = 0.05, 0.1, 0.5, 1, 2 and 3 in wt%) to explore the applications of laser and LEDs. Spectroscopic properties of the titled glasses have been examined through UV−Vis−NIR absorption spectra, fluorescence and decay measurements. The effective shift in the absorption band positions in the absorption spectra has been used as a tool to explore the bonding nature of Eu3+ ions with the host matrix and the obtained results suggests the presence of covalent nature of the Eu3+-ligand bonds in the glass network. Luminescence spectra of the present glasses have been characterized and the radiative properties of the emission bands were analyzed through Judd-Ofelt (JO) theory. The CIE 1931 color chromaticity diagram is used to discover the overall emission spectral features such as characteristic emission color, correlated color temperature and color purity of the prepared glasses. Luminescence decay curves of the present glasses exhibit single exponential profile for all the titled glasses and the experimental lifetime values were compared with the theoretical decay lifetime values obtained after analyzing the necessary curve fitting.

Understanding the Effects of Molecular Dopant on n‐Type Organic Thermoelectric Properties

AbstractMolecular doping is a powerful method to fine‐tune the thermoelectric properties of organic semiconductors, in particular to impart the requisite electrical conductivity. The incorporation of molecular dopants can, however, perturb the microstructure of semicrystalline organic semiconductors, which complicates the development of a detailed understanding of structure–property relationships. To better understand how the doping pathway and the resulting dopant counterion influence the thermoelectric performance and transport properties, a new dimer dopant, (N‐DMBI)2, is developed. Subsequently, FBDPPV is then n‐doped with dimer dopants (N‐DMBI)2, (RuCp*mes)2, and the hydride‐donor dopant N‐DMBI‐H. By comparing the UV–vis–NIR absorption spectra and morphological characteristics of the doped polymers, it is found that not only the doping mechanism, but also the shape of the counterion strongly influence the thermoelectric properties and transport characteristics. (N‐DMBI)2, which is a direct electron‐donating dopant with a comparatively small, relatively planar counterion, gives the best power factor among the three systems studied here. Additionally, temperature‐dependent conductivity and Seebeck coefficient measurements differ between the three dopants with (N‐DMBI)2 yielding the best thermoelectric properties. The results of this study of dopant effects on thermoelectric properties provide insight into guidelines for future organic thermoelectrics.

Improved solubility of asymmetric tetraethynylporphyrin derivatives for solution-processed organic solar cells

Abstract Asymmetric magnesium tetraethynylporphyrin derivatives bearing two diketopyrrolopyrrole (DPP) units and two different aryl units were synthesized by multistage Sonogashira coupling reactions. According to saturated UV–Vis–NIR spectra, the solubility of the asymmetric porphyrin derivatives was superior to that of symmetric porphyrin derivatives. Frontier orbital energies were investigated in the solution state by differential pulse voltammetry and in the solid state by photoelectron yield spectroscopy and UV–Vis–NIR spectroscopy. Time-dependent density functional theory calculations were carried out to simulate the UV–Vis–NIR absorption spectra and revealed splitting of the Q band into two bands at 712 nm and 650 nm. The thickness of active layers in solution-processed organic solar cells was influenced by the solubility of the porphyrin derivatives. When the compound with the highest solubility was used (2d), the film thickness was 215 nm, which is larger than-the thickness of ∼120 nm reported for symmetric porphyrin derivatives. Also, the short-circuit current density (JSC) was influenced by solubility, especially for compound 2d, compared with other asymmetric compounds 2a–c. The optimized device conditions using 2d and PC61BM gave JSC of 14.86 mA/cm2, open-circuit voltage of 0.69 V, fill factor of 0.47, and power conversion efficiency of 4.84%.

Spectroscopic investigations of near-infrared emission from Nd3+-doped zinc-phosphate glasses: Judd-Ofelt evaluation

Zinc-phosphate glasses doped with different concentrations of Nd3+ ions have been prepared by the melt quenching technique and characterized the spectroscopic properties. The physical properties by means of density and molar volume are determined. The amorphous nature of the glasses has been confirmed by X–ray diffraction analysis. FTIR spectra exhibited the fundamental stretching vibrations modes of glass network. In order to study the spectroscopic properties of fabricated glasses, absorption and emission spectroscopy has been performed. Additionally, the spectroscopic properties of Nd3+ ions were analyzed using J–O theory. UV–Vis–NIR absorption spectra of glass samples divulged twelve significant peaks. Considerable enhancement of Ω2 values with increasing neodymium content indicated an improvement in the covalency and asymmetry of Nd3+ ions environment. Under the excitation of 808 nm laser diode, two near-infrared emission bands at around 890 and 1060 nm from 4F3/2 → 4I9/2 and 4I11/2 radiative transitions respectively were observed in the Nd3+ single doped glasses. The major intensity is observed for 1060 nm for such glass samples. Nd3+ ions dopant is found to augment the luminescence intensity by a factor as much as 2.23 times as the concentration of Nd3+ ions increase up to 1.5 mol%. The lifetimes of this level has been experimentally determined through decay profile studies. The developed glass possesses high fluorescence quantum efficiency (η = 96%). The results indicate that the prepared glass system could be a suitable candidate for using it as laser gain media around 1060 nm, solid-state lasers and fiber amplifiers.

Influence of 1.25 MeV gamma rays on optical and luminescent features of Er3+ doped zinc bismuth borate glasses

Abstract Glasses based on 10ZnO-5Na2CO3-10Bi2O3-(75-x)B2O3-xEr2O3 with x = (0, 0.1, 0.3, 0.5, 0.7, 1.0) mol%, were synthesized by melt quenching technique and characterized through optical and luminescent features, before and after irradiating them with high energy (1.25 MeV) gamma rays. The amorphous nature of the glasses and the presence of various structural groups like BiO6, BO3 and BO4 were confirmed through XRD and FTIR measurements. Optical properties were studied through UV–VIS–NIR absorption spectra. Decrease in band gap values after gamma irradiation confirmed the creation of color centers in the glass matrix. Thermally stimulated Luminescence (TL) and Optically Stimulated Luminescence (OSL) spectroscopy techniques were used to study the trap centers induced after irradiation. The number of peaks and their trapping parameters were assessed using the Computerized Glow Curve Deconvolution (CGCD). The linearity in dose response proves their suitability in usage for dosimeter and shields in radiation zones within the dose.

White light-emitting Dy3+-doped transparent chloroborosilicate glass: synthesis and optical properties

ABSTRACTDy3+-doped chloroborosilicate glasses with the composition 35.7SiO2–25.5B2O3–17BaO–3.4K2O–3.4Al2O3–15BaCl2 (mol%) were prepared using melt quenching technique. The glass transition temperature (Tg) was ~610°C. In UV–vis–NIR absorption spectra, characteristic absorption bands of Dy3+ appeared at 322, 347, 364, 388, 795 and 880 nm due to spectral transitions from the 6H15/2 level to various higher levels of Dy3+ ion. The excitation spectrum was recorded at within 200–550 nm by monitoring emissions at 576 nm. The excitation bands at 392, 428, 453 and 472 nm were attributed to the 6H15/2 → 4I13/2, 4G11/2, 4I15/2 and 4F9/2 transitions, respectively. Prominent emission bands were observed at wavelengths of 484, 576, 664 and 754 nm when excited at 447 nm. The bands correspond to the transitions 4F9/2 → 6H15/2, 4F9/2 → 6H13/2, 4F9/2 → 6H11/2 and 4F9/2 → 6H9/2 6F11/2, respectively. The emitted light from all the samples was found to be white. Their color coordinates lie within the white range. The sample containing 0.5 wt% Dy2O3 emitted white light with the color coordinates x = 0.351, y = 0.335, which are the very closest to pure white light and whose color temperature of 4716 K is similar to daylight. Such white light-emitting transparent glasses promise to be enormously useful for various photonic applications.

Synthesis and characterization of Cu2CoSnS4 thin films prepared via radio-frequency (RF) magnetron sputtering

Cu2CoSnS4 (CCTS) thin films, for the first time, were successfully fabricated by RF magnetron sputtering with two different metal precursor stacking sequences followed by sulfurization treatment under kinds of temperatures. Structure, morphology, composition, chemical valence states and optical properties of the as-grown films were discussed by X-ray diffraction (XRD), Raman spectroscopy (Raman), Scanning electron microscopy (SEM), Energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and ultraviolet–visible-near-infrared spectrophotometer (UV–vis–NIR spectrophotometer) respectively. XRD and Raman analysis indicated that the as-obtained Cu2CoSnS4 thin films possess a stannite structure and the crystallinity was improved accompanying the incremental sulfurization temperature under both two depositing orders. The growth mechanism of CCTS films during vulcanization process was also discussed. XRD, Raman spectroscopy and SEM analysis showed that the precursors deposited in Cu/Co/Sn sequence had the best crystallinity after 600 °C sulfurization annealing. Under this preparation condition, XPS analysis showed that the chemical states of the four main elements in the film were Cu (I), Co (II), Sn (IV) and sulfide ions,and it exhibited the direct band gap of 1.58 eV by UV–vis–NIR absorption spectra, which is close to the ideal values for photovoltaic utilization.

Effect of Hf4+ doping on structure and enhancement of upconversion luminescence in Yb:Tm:LiNbO3 crystals**Project supported by Special Funds of Harbin Innovation Talents in Science and Technology Research, China (Grant No. 2015RQQXJ045) and Science Funds for the Young Innovative Talents of HUST, China.

A series of Yb:Tm:LiNbO3 crystals doped with x mol% Hf4+ ions (x = 2, 4, and 6) were grown by the Czochralski method. The dopant occupancy and defect structure of Hf:Yb:Tm:LiNbO3 crystals were investigated by x-ray diffraction and infrared transmission spectra. The influence of Hf4+ ions concentration on UV–VIS–NIR absorption spectra of Hf:Yb:Tm:LiNbO3 crystals was discussed. The upconversion luminescence of Hf:Yb:Tm:LiNbO3 crystals was obtained under 980 nm excitation. Strong emissions were observed at 475 nm in the blue wavelength range and 651 nm in the red wavelength range. Remarkably, enhancement of the red and blue upconversion luminescence was achieved by tridoping Hf4+ ions.

Orthometalated N-(Benzophenoxazine)-o-aminophenol: Phenolato versus Phenoxyl States.

The molecular and electronic structures of the orthometalated ruthenium(III) and osmium(III) complexes of N-(benzophenoxazine)-o-aminophenol (OXLH2) that exhibits versatile redox activities are reported. The redox chemistry of OXLH2 is remarkably different from that of N-(aryl)-o-aminophenol (APLH2). The study established that OXLH2 is redox noninnocent and is a precursor of a phenoxyl radical. One of the C–H bonds of OXLH2 is activated by ions, and OXLH2 reveals three different redox states as dianionic phenolato (OXL2–), monoanionic phenoxyl radical (OXL•–), and zwitterionic phenoxium cation (OXL±) states. The reaction of OXLH2 with [RuII(PPh3)3Cl2] in boiling toluene in air affords an orthometalated OXL2– complex of ruthenium(III), trans-[(OXL2–)RuIII(PPh3)2(Cl)] (1), whereas the similar reaction with [OsII(PPh3)3Br2] yields an orthometalated OXL•– complex, cis-[(OXL•–)OsIII(PPh3)Br2] (2). 1 and 2 exhibit ligand-based reversible redox waves due to OXL•–/OXL2–, OXL±/OXL•–, and MIII/MII couples. The 1+ ion is a OXL•– complex of ruthenium(III). 2– exhibits temperature-dependent valence tautomerism due to [OsII(OXL•–) ↔ OsIII(OXL2–)] equilibrium. 22– is a OXL2– complex of osmium(II), while 12+ and 2+ are OXL± complexes of metal(III). 2 is an oxidant and effective catalyst for oxidation of 3,5-di-tert-butylcatechol to the corresponding quinone, and the turnover number is 119.7 h–1. The UV–vis–NIR absorption spectrum of 1 displays an NIR band at 800 nm due to an intra-ligand-charge-transfer transition, which is absent in 2 incorporating a OXL•– radical. The molecular and electronic structures of 1 and 2 and their oxidized and reduced analogues were confirmed by single-crystal X-ray crystallography, variable-temperature electron paramagnetic resonance spectroscopy, spectroelectrochemical measurements, and density functional theory calculations.

Non-linearity correction in NIR absorption spectra by grouping modeling according to the content of analyte

To correct the non-linearity caused by light scattering in quantitative analysis with near infrared absorption spectra, a new modeling analysis method was proposed: grouping modeling according to the content of analyte. In this study, we tested the proposed method for non-invasive detection of human hemoglobin (Hb) based on dynamic spectrum (DS). We compared the prediction performance of the proposed method with non-grouping modeling method. Experimental results showed that the root mean square error of the prediction set (RMSEP) by the proposed method was reduced by 9.96% and relative standard deviation of the prediction set (RSDP) was reduced by 4.73%. The results demonstrated that the proposed method could reduce the effects of non-linearity on the composition analysis by spectroscopy. This research provides a new method for correcting the non-linearity stemming from light scattering. And the proposed method will accelerate the pace of non-invasive detection of blood components into clinical application.

Influence of Co-doping on the optical and magnetic properties of CdS nanoparticles

Undoped and Cobalt (Co) doped Cadmium sulfide (CdS) nanoparticles with Co in proportion of 10, 15 and 20 mol% are synthesized by chemical method at room temperature. UV–Vis–NIR absorption spectra shows blue shift in the absorption edge as compared to bulk material. The five characteristic absorption peaks at 475, 523 (513), 685, 729 and 741 nm are observable for Co doped CdS samples due to d–d transitions of Co2+ (d7) in tetrahedral symmetry and these peaks are assigned as O2−–Co2+ charge transfer process, 4A2 (F)–2E (G), 4A2 (F)–3/2 U′, 4A2 (F)–E″ and 4A2 (F)–5/2 U′ transitions respectively. The band gap values of undoped CdS nanoparticles is found to be 3.23 eV and the decrement in band gap from 3.23 to 3.18 eV due to Co concentration may be due to direct energy transfer between the semiconductor excited state and the 3d levels of the Co2+ ions. Interaction between polyvinylpyrrolidone (PVP) with CdS nanoparticles as well as conformation of the Cd–S and Co–S stretching band in Co doped CdS nanoparticles is studied by Fourier transform infrared spectroscopy. The photoluminescence (PL) spectra recorded at room temperature with 283 nm excitation wavelength show small shift in emission peak with Co doping which attribute to indirect recombination of the free electrons moving from the trap levels formed by the Co-atoms to the holes in the valence band. The luminescence intensity increases with Co2+ concentration because composite luminescence centre of Co2+ ions are formed, as a result more electrons are easily excited and enhance radiative recombination of luminescence process. The diamagnetic and paramagnetic behavior of undoped and Co doped CdS particles is confirmed by M–H curves and Gouy method. No branching is observed in both field cooled and zero field cooled curves of M–T loop, thereby removing the probability of superparamagnetism behavior of the material.

Investigation on the Growth, Structural and Third Order Nonlinear Optical Properties of 4-Ethoxy-4-N-Methyl-4-Stilbazoliumhexafluorophosphate (EMSHP) Single Crystal

The organic material 4-ethoxy-4-N-methyl-4-stilbazolium hexafluorophosphate (EMSHP) is a new NLO material and new derivative in stilbazolium tosylate family. In this work we synthesized EMSHP, the derivative of DAST, by slow evaporation method. The chromophores of the EMSHP crystal makes an angle of about 28 with repeat to a- axis which makes this material a promising terahertz (THz) wave generation and used for various electro – optic applications. The crystal system is found as monoclinic. From the UV–Vis NIR absorption spectra the good transparency is revealed. The indication at 498 nm of the crystal ascertains the blue to green emission was validated by using photo luminescence (PL) analysis. The third-order nonlinear optical properties such as nonlinear refractive index (n 2 ), absorption co-efficient (β) and susceptibility (χ (3) ) were studied by Z-scan technique at 632.8 nm using He-Ne laser. All the above studies supports the as grown EMSHP crystal is a suitable candidate for generation of THz and opto- electronic application.

Comprehensive study on compositional modification of Tb3+ doped zinc phosphate glass

Series of glass composition (60-x) P2O5 -40 ZnO –(x) Tb2O3 where x = 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 mol % are prepared by conventional melt quenching technique. X-Ray Diffraction (XRD), FTIR, UV-Vis-NIR and the photoluminescence (PL) spectroscopy are used to characterize the physical, structural and optical behavior of the glass sample. The XRD pattern confirms the amorphous nature and DTA verified the thermal stability of all the glass samples. Glass with 1.5 mol % of Tb2O3 possesses the highest thermal stability. Glass density is found to increase proportionally with increasing amount of Tb3+ while the molar volume behaves reversely. Six main IR absorption bands centered at about 540, 748, 891, 1085 and 1294 cm− 1 are evidenced. The UV-Vis NIR absorption spectra reveals the absorption center band at about 540, 376, 488 and 1920 nm corresponding to the absorption from 7F6 ground state to various excited state of Tb3+ ion. The optical band gaps for direct and indirect transition are in the range 4.53–5.07 eV and 4.30 eV-4.56 eV respectively. The Urbach energy decreases with the increasing concentration of Tb2O3. The PL emission spectra reveals several prominent peaks at 413, 435, 457, 488, 540, 585 and 620 nm due to electronic transition from 5D3→7F5, 5D3→7F4, 5D3→7F3, 5D4→7F6, 5D4→7F5, 5D4→7F3 and 5D4→7F5 respectively.

Characterization of α-Glucosidase Inhibitor/Cyclodextrin Complex Prepared by Freeze-Drying.

Miglitol (MT) is an α-glucosidase inhibitor with a postmeal blood glucose level lowering effect that is used to treat type 2 diabetes. In addition, α-cyclodextrin (αCD) has been reported to inhibit increases in postmeal blood glucose. The aim of this study was to prepare a freeze-dried product (FD) composed of MT and αCD or γCD (molar ratio of MT/αCD = 1/1, MT/γCD = 1/1) and to evaluate the physicochemical properties and biological activity of the FD. The PXRD profile of FD exhibited a halo pattern, and characteristic peaks derived from MT, αCD, and γCD were not observed. The TG-DTA results for FD indicated an increased weight loss temperature and the absence of an endothermic peak for MT. The NIR absorption spectrum measurement suggested an intermolecular interaction between MT and αCD or γCD in the FD. 1H-1H NOESY NMR spectroscopy (D2O) revealed an intermolecular interaction in the FD. The results of the α-glucosidase activity inhibition test and the α-amylase activity inhibition test indicated that the FD exhibited the same inhibition rate as MT alone and the effects of MT were not altered by the freeze-drying method.

Synthesis and characterization of multifunctional homochiral 1-D aminoacetic acid potassium metal organic framework

The multifunctional homochiral aminoacetic acid potassium (AAAP) metal organic framework was synthesized and grown by hydrothermal technique. The structural arrangement can be described by alternating organic and inorganic layers which are constructed as 1D infinite chain along the b direction. These building blocks are cross linked further by nearest metal ions formed 1D tunnels like a framework also. Functional moieties exist in AAAP were analyzed by FT-IR spectral analysis. The optical constants like; optical band gap, absorption coefficient, extinction coefficient and refractive index were calculated using UV–Vis–NIR absorption spectrum. DSC study shows that compound stable upto 250 °C. The dielectric constant and dielectric loss of the crystal were calculated as a function of frequency at room temperature, and the results are discussed. The piezoelectric charge coefficient (d33) and voltage coefficient (g33) were found. The nonlinear efficiency was determined by the Kurtz and Perry powder technique and the obtained value is 1.38 times that of KDP. BET analysis reveals the specific surface area of grown crystal is 104 m2/g and pore size distribution plot display the mesoporous nature. Thus, the sorption behavioral mesoporous, nonlinear and piezoelectric, AAAP act as a Multifunctional Metal Organic Framework material.

Syntheses, crystal structures and photophysical properties of a series of Zn-Ln coordination polymers

A series of coordination polymers, {[LnZn(2,3-pydc)(1,3-bdc)(OH)(H2O)m]·H2O}n, (Ln = Sm 1, Eu 2, Gd 3, Tb 4, Dy 5, Er 6, Yb 7, Pr 8, Nd 9), (1–7, m = 1; 8, 9, m = 2), (2,3-H2pydc = pyridine-2,3-dicarboxylic acid, 1,3-H2bdc = isophthalic acid), are synthesized by the hydrothermal method and their crystal structures are determined by single-crystal X-ray diffraction. Structural analysis shows that coordination polymers 1–9 present two-dimensional layered structures and all of them are crystalized in triclinic system with space group Pī. Hereinto polymers 1–7 are isomorphous, while polymers 8 and 9 are also isomorphous and each of them includes one more coordinated water molecule than others. All coordination polymers are characterized by IR, UV–Vis–NIR and fluorescent spectra, and the luminescent properties are the research emphasis. In addition, except for polymer 3, the other eight Zn-Ln polymers exhibit the characteristic luminescence of corresponding Ln(III) ions, which should be owing to the sensitization of the Zn-Ligand moiety. With the influence of the crystal field and the introduction of Zn(II) ion, the internal energy levels of the system are tuned, which is reflected by shift and split of the partial characteristic bands of Ln(III) ions in their UV–Vis–NIR absorption spectra and NIR emission spectra, and both can corroborate each other.

Orthorhombic (Fe2TiO5)-monoclinic (Cr2TiO5) solid solution series: Synthesis by gel routes, coloring and NIR reflectivity evaluation

CrxFe2-xTiO5 compositions of the solid solutions series from pseudobrookite Fe2TiO5 to monoclinic Cr2TiO5 have been prepared by the ceramic route and gel methods. At 1400 °C, pseudobrookite crystallizes in the x = 0–0.4 range, both pseudobrookite and monoclinic Fe-Cr2TiO5 coexist at x = 0.5, while in the range x = 0.7–1.5 monoclinic Fe-Cr2TiO5 crystallizes. Powders were 5 wt% glazed within a double-firing frit and the composition with x = 0.1 fired at 1000 °C exhibits the best red color (L*a*b* = 43.2/18.8/12.5), showing an intense band at 520 nm in the UV–Vis–NIR absorption spectrum associated with Cr4+ in octahedral coordination. The unit cell volume of the pseudobrookite decreases smoothly with the chromium amount, associated with the entrance of Cr4+ replacing Ti4+, while the volume of the Fe-Cr2TiO5 unit cell increases with the entrance of Fe3+ replacing Cr3+. The use of flux agents, the compaction pressure and the gel methods increase the crystallization of pseudobrookite but do not improve the reddish color, which is associated with the concentration of Cr4+ in the pigment. The optimized pigment composition Cr0.1Fe1.9TiO5 also shows a high NIR reflectance (55% in powder, 54% in glazed sample).

Enhanced resonant nonlinear absorption and optical limiting in Er3+ ions doped multicomponent tellurite glasses

Nonlinear optical properties of multicomponent tellurite glasses doped with Er3+ ions were investigated by open aperture Z-scan measurements. Compositional and linear optical properties of the glasses were examined by the energy dispersive X-ray spectrum and UV–vis–NIR absorption spectrum analysis respectively. The mechanism behind the optical nonlinearity and optical limiting efficiency was successfully explained by evaluating the physical properties such as density, refractive index and polarizability of the glasses. The nonlinear properties critically depend on the polarizability, which is found to increase with the addition of Er3+ ions by the creation of non-bridging oxygen ions. By the systematic addition of Er3+ ions, we have dictated the physical properties and thus tuned the optical limiting efficiency of the glasses. This makes the Er3+-doped multicomponent tellurite glasses flexible tunable optical limiters for potential device applications.