UV Vis Optical Absorption Spectra Research Articles

Photoluminescence of samarium-doped TiO 2 nanotubes

Samarium (Sm)-modified TiO 2 nanotubes (TNTs) were synthesized by low-temperature soft chemical processing. X-ray powder diffraction analyses of the synthesized Sm-doped and non-doped TNTs show a broad peak near 2 θ=10°, which is typical of TNTs. The binding energy of Sm 3d 5/2 for 10 mol% Sm-doped TNT (1088.3 eV) was chemically shifted from that of Sm 2O 3 (1087.5 eV), showing that Sm existed in the TiO 2 lattice. Sm-doped TNTs clearly exhibited red fluorescence, corresponding to the doped Sm 3+ ion in the TNT lattice. The Sm-doped TNT excitation spectrum exhibited a broad curve, which was similar to the UV–vis optical absorption spectrum. Thus, it was considered that the photoluminescence emission of Sm 3+-doped TNT with UV-light irradiation was caused by the energy transfer from the TNT matrix via the band-to-band excitation of TiO 2 to the Sm 3+ ion.

Investigation on the synthesis and quantum confinement effects of pure and Mn 2+ added Zn (1− x) Cd xS nanocrystals

Zn (1− x) Cd x S and Zn (1− x) Cd x S:Mn 2+ semiconductor quantum dots (2–4 nm) have been prepared by a novel solvothermal route assisted microwave heating method. The growth parameters governing the smaller size and higher yield have been optimized. The synthesized QDs exhibit a significant blue shift as compared to their corresponding bulk counterpart in the UV–vis optical absorption spectrum. The dielectric constant value varies from 2.79 to 6.17 (at 40 °C, 1 kHz) depending upon the composition of the alloy; lower value corresponds to Zn 0.75Cd 0.25S:Mn 2+ and the higher value corresponds to Zn 0.25Cd 0.75S:Mn 2+. The crystallite size to exciton bohr radius ratio being <1 indicates a strong quantum confinement effect in both CdS and ZnS QDs. The quantum confinement effect exists in the sequence of ZnS:Mn 2+ < Zn (1− x) Cd x S:Mn 2+ ( x < 0.5) < ZnS < Zn (1− x) Cd x S < CdS < CdS:Mn 2+.

Synthesis and characterization of crystalline CuS nanorods prepared via a room temperature one-step, solid-state route

We described a novel and simple one-step, solid-state route for the synthesis of crystalline CuS nanorods using surfactant, C 18H 37(CH 2CH 2O) 10H, as shape controller. The diameters of the as-prepared CuS nanorods are in the range of 10–60 nm and lengths are up to 5 μm. The crystallinity, purity, morphology, structural features and UV–vis optical absorption spectra of the as-prepared nanorods were characterized by X-ray diffraction, transmission electron microscopy, selected area electron diffraction, high-resolution transmission electron microscopy, optical absorption spectra and X-ray photoelectron spectra. The role of surfactant, C 18H 37(CH 2CH 2O) 10H, in the formation of CuS nanorods has been discussed. The result indicated that the surfactant played a key role for the formation of CuS nanorods.

FT-IR and UV–Vis optical absorption spectra of γ-irradiated calcium phosphate glasses doped with Cr2O3, V2O5 and Fe2O3

Fourier transform infrared (FT-IR) spectra of xCaO·(100−x)P2O5 glasses, (mol%) with 45⩽x⩽55, have been studied in order to understand the bonding mechanisms, characteristic frequencies of the vibrational chemical bonds, which are liable to the structural and spectral changes. These spectra showed IR absorption bands related to the characteristic phosphate bonds especially PO, P–O–P, O–P–O, P–O–H and P–O–Ca bonds. UV–Vis spectra of the undoped and doped (with Cr2O3, V2O5 and Fe2O3) glasses have been recorded in the range 200–1000nm before and after γ-ray irradiation with various doses. The induced absorption spectra, calculated as the difference between the spectra of the irradiated and unirradiated glasses, were used to describe the irradiation induced defects. Intrinsic phosphorus–oxygen related radiation-induced defects, with hole centers POHCs absorbing in the visible region and electron trapped centers PO2- and PO3-ECs absorbing in the ultraviolet region, were found.

A phase-matchable nonlinear optical material N-(3-nitrophenyl)phthalimide: Synthesis, crystal growth and characterization

The N-(3-nitrophenyl)phthalimide (N3NP) single crystal of size 4 mm×1 mm×0.5 mm, sufficient enough to confirm the existence of phase-matching direction in the crystal using the Kurtz and Perry powder second-harmonic generation (SHG) measurements, was grown by slow evaporation solution growth technique using DMF solvent. Powder XRD, FTIR, CHN analysis and H 1NMR technique were employed to characterize N3NP single crystal. The single crystal XRD data revealed the noncentrosymmetric crystal structure of N3NP, which is an essential criterion for SHG. The main contribution to the SHG results comes from the strong hydrogen bonds, which also appear as intense IR bands of hydrogen bond vibrations in spectral characteristics. From DT/TG analysis, the N3NP was found to be thermally stable up to 246 °C. The four C–H······O hydrogen bonds, which hold the molecules of N3NP in three-dimensional crystal lattice, are responsible for the higher thermal stability. The UV–Vis optical absorption spectrum of N3NP shows the lower optical cut off at 370 nm and was transparent in the visible region. The N3NP is a phase-matchable NLO crystal. This crystal can be used as an efficient frequency doubler and optical parametric oscillator due to its high SHG conversion efficiency.

Optical Absorption and Valence Band Photoemission from Uncapped CdTe Nanocrystals

CdTe nanocrystals have been successfully fabricated by a mechanical alloying process. X-ray diffraction (XRD) patterns demonstrate that a single-phase CdTe compound with a zinc blende structure has been formed after ball milling elemental Cd and Te mixture powders for 27 h. The large broadening effect for the width of the {111} diffraction peak of uncapped CdTe nanocrystals on smaller size was observed in slowly scanned XRD patterns. The X-ray photoelectron spectrum was used to study the surface of the uncapped CdTe nanocrystals within both core level and valence band regions. The presence of tellurium oxide film on the surface of the uncapped CdTe nanocrystals has been detected in the X-ray photoelectron spectrum of the Te 3d core level, which was comparable to the observed amorphous oxide thin layer on the surface of uncapped CdTe nanocrystals in a high resolution transmission electron microscopy (HRTEM) image. The energy of the valence band maximum for uncapped CdTe powders blue shifts to the higher energy side with smaller particle sizes. In UV-visible optical absorption spectra of the suspension solution containing uncapped CdTe nanocrystals, the absorption peaks were locating within the ultraviolet region, which shifted toward the higher energy side with prolonged ball milling time. Both blue shifts of valence band maximum energy and absorption peaks with decreasing particle size provide a unique pathway to reveal the quantum confinement effect of uncapped CdTe nanocrystals.

Kinetics of photoinduced changes in Ag nanoparticles deposited on an indium tin oxide surface

An enhancement of the UV-visible optical absorption spectra of Ag nanoparticles (NPs) deposited on indium tin oxide (ITO) surfaces of different resistance by a seed-mediated growth technique is presented. A bicolour coherent beam, obtained from a pulsed Nd:YAG laser providing a 1060-nm fundamental wavelength and a double-frequency one at 530 nm, was used. A significant change in the optical density is observed for Ag NPs on low-resistance ITO surfaces (≈4 Ω/square), while almost nothing occurs with high-resistance (≈50 Ω/square surfaces). The spectral position of the maximal absorption at 440 nm is almost preserved in both cases. This result is explained in terms of a local photoinduced static field and surface-plasmon polaritons interacting with photoexcited phonons. A grating effect, arising from the coherent bicolour light forming a superstructure as for quantum crystals, could be another contribution.

Preparation and characterization of the ZnS nanospheres with narrow size distribution

Abstract In this work, we report the synthesis of ZnS nanospheres with relatively narrow size distribution using polyvinyl pyrrolidone (PVP) as a capping reagent. The nanocrystallite powers were characterized using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), electron diffraction (ED), and UV–vis optical absorption spectra. The synthesized nanocrystallite show typical lattice spacings corresponding to the cubic phase of ZnS, as confirmed from HRTEM, ED, and XRD. The UV–vis spectra shows a blue shift of the first excitonic transition band compared with bulk ZnS, probably due to the quantum size effect.

Fabrication of transition metal sulfides nanocrystallites via an ethylenediamine-assisted route

Many binary transition metal sulfides nanocrystallites MS (M = Zn, Cd, Co, Ni) with different morphologies have been successfully prepared in an ethylenediamine solution of metal salts and (NH 4) 2S (or thiourea) using a facile hydrothermal method. The products are characterized by powder X-ray electron diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and the selected area electron diffraction (SAED), respectively. UV–visible optical absorption spectra clearly indicate the presence of quantum size effects in some transition metal sulfides nanocrystallites and the possible mechanism of ethylenediamine-assisted is also briefly discussed. This method may also be extended to controllable synthesis of other metal chalcogenides with different morphologies, such as nanowires, nanorods, and nanodisks, etc.

Dimerization of zinc tetrasulfophthalocyanine in sol–gel process

The issue of dimerization is vital in determining the optical properties of dye-doped sol–gel materials and metallophthalocyanine offers an excellent opportunity to characterize dimmers from monomers because of their identified absorption bands. In this paper, zinc tetrasulfophthalocyanine (ZnTSPc) was encapsulated in silica–xerogel matrix by sol–gel technique. Dimerization of ZnTSPc was studied using UV–Vis optical absorption spectra, correlated with various stages of the sol–gel process. The results show that in the composites ZnTSPc concurrence in forms of monomer and dimmer, and dimerization behaves differently in the sol, gel and xerogel stages. Reasons are given from the change of the microenvironment of the composites in which ZnTSPc existed.

Synthesis of CdS nanoparticles by a novel and simple one-step, solid-state reaction in the presence of a nonionic surfactant

A novel and simple one-step, solid-state reaction in the presence of a nonionic surfactant, C 18H 37O(CH 2CH 2O) 10H (abbreviated as C 18EO 10), has been developed to synthesize uniform cubic-phase β-CdS nanoparticles with an average diameter of ca. 5 nm. The CdS nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), UV–VIS optical absorption spectrum and X-ray photoelectron spectrum (XPS). The roles of nonionic surfactant, C 18EO 10, in the formation of CdS nanoparticles were discussed in detail.

Defects in the reduced rutile single crystal

In this paper, the UV–VIS optical absorption spectra of oxidized and reduced rutile single crystals are measured by means of spectrophotometer and two absorption peaks around 430 and 730 nm are found. These spectral data are analyzed by using the crystal field theory. Based on these studies, we suggest that the reduced crystal contain the defect center [Ti 3+–O v], with the oxygen vacancy (O v) on one of the nearest neighbor sites of the central Ti 3+ ion.

Study of Au/Au(3+)-TiO2 photocatalysts toward visible photooxidation for water and wastewater treatment.

With an attempt to extend light absorption of TiO2-based photocatalyst toward the visible light range and eliminate the rapid recombination of excited electrons/holes during photoreaction, a new type of photocatalysts (Au/Au(3+)-TiO2) powder was prepared by a photoreduction/sol-gel process. The crystal phase composition, surface structure, and light absorption of the new photocatalysts were comprehensively examined by X-ray differential detection (XRD), UV-visible absorption spectra, X-ray photoelectron emission spectroscopy (XPS), and photoluminescence (PL) spectra. The photooxidation efficiencies of the photocatalysts were also evaluated in the photodegradation of methylene blue (MB) in aqueous solutions under visible light irradiation from a high-pressure sodium lamp (lambda > 400 nm). The results of PL analyses in this study indicated that the gold/gold ion-doping on the surface of TiO2 could eliminate the electron/holes recombination and also increase the light absorption in the visible range. The analytical results of UV-visible diffuse reflection spectra (DRS) and optical absorption spectra indicated that a new energy level below 3.2 eV generated in the Au/Au(3+)-TiO2 promoted the optical absorption in the visible region and made it possible to be excited by visible light (E < 3.2 eV). The experiment demonstrated that the photooxidation efficiency of MB using the Au/Au(3+)-TiO2 powder were significantly higher than that using conventional TiO2 powder and an optimum molar content of gold doping/deposition in the TiO2 was 0.5%. The development of such photocatalysts may be considered a breakthrough in large-scale utilization of solar energy to address environmental needs.

Antenna effect in an oxide xerogel

Silica xerogel doped with [Eu⊂cryptand]3+was prepared by the sol-gel method from a hydrolyzed tetramethoxysilane solution containing [Eu⊂cryptand](CF3SO3)2Br. UV-visible optical absorption spectra, fluorescence excitation and emission spectra, fluorescence lifetime as well as luminescence quantum yield were measured. Experiments were carried out in aqueous solution and in rigid silica xerogel at room temperature. It is shown that the excitation is centred on the ligand, but the metal ion takes part in the emission process. In other words, the antenna effect was observed in the Eu(III) cryptate studied in the solution and xerogel. The cryptate entrapped in the xerogel showed higher emission efficiency and longer lifetime than in solution.

Encapsulation of transition metal species into zeolites and molecular sieves as redox catalysts: Part I-preparation and characterisation of nanosized TiO2, CdO and ZnO semiconductor particles anchored in NaY zeolite

In this paper, we report the preparation and characterisation of nanometer-sized TiO2, CdO, and ZnO semiconductor particles trapped in zeolite NaY. Preparation of these particles was carried out via the traditional ion exchange method and subsequent calcination procedure. It was found that the smaller cations, i.e., Cd2+ and Zn2+ could be readily introduced into the SI′ and SII′ sites located in the sodalite cages, through ion exchange; while this is not the case for the larger Ti species, i.e., Ti monomer [TiO]2+ or dimer [Ti2O3]2+ which were predominantly dispersed on the external surface of zeolite NaY. The subsequent calcination procedure promoted these Ti species to migrate into the internal surface of the supercages. These semiconductor particles confined in NaY zeolite host exhibited a significant blue shift in the UV-VIS absorption spectra, in contrast to the respective bulk semiconductor materials, due to the quantum size effect (QSE). The particle sizes calculated from the UV-VIS optical absorption spectra using the effective mass approximation model are in good agreement with the atomic absorption data.

Abstract of the in vivo synthesis of labile methyl groups : S. Jonsson and W.A. Mosher ( J. Am. Chem. Soc., 72, 3316 (1950))

A series of CdS and CdS/CNTs photocatalysts were successfully prepared by hydrothermal method and they were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), UV–visible optical absorption spectra (UV–Vis), etc. By studying their photocatalytic properties, it is found that, for CdS, photocatalysts prepared in appropriate alkaline environment presented higher hydrogen production activity, reaching 794.6 μmol h−1 g−1; the photocatalytic activity of CdS was obviously enhanced by combining it with CNTs via a special two-step hydrothermal method, and the corresponding hydrogen production rate reached 1.771 mmol h−1 g−1; the photocatalytic activity was further improved by loading co-catalyst NiS, achieving 12.13 mmol h−1 g−1.