Influence of heat treatment on the colour of Au and Ag glasses produced by the sol-gel pathway

In this work, coloured glasses were produced based on the synthesis of gold and silver nanoparticles by the sol-gel process having in mind their application in art works. Gold and silver were used separately or as a mixture by varying the mole fractions in order to get a range of colours from yellow to red. The gold and silver nanoparticles were prepared by the reduction of tetrachloroauric acid and silver nitrate with sodium citrate in aqueous solutions which were further introduced in the sol-gel system. Attention was focused on the thermal treatment of the sol-gel samples. Different temperatures were used in order to determine their influence on the obtained colour. The glasses were characterized by UV-Vis absorption spectroscopy and the size of the nanoparticles was examined by transmission electron microscopy (TEM).The range of colours mentioned above is obtained either by preparing nanoparticles of each metal and mixing them or by preparing nanoparticles from solutions containing initially ions of both metals. In the former case, two surface plasmon resonance (SPR) bands were observed for temperatures below 200 °C while higher temperatures promote the formation of alloys between the Ag and Au nanoparticles. In the latter case, only one SPR band is observed and the nanoparticle size distribution is narrower. The results were explained by nanoparticle aggregation promoted by temperature. Glasses containing only Ag did not present the typical yellow colour above 300 °C but it was shown that the colour could be stabilized if Au was added in small amounts (Au/Ag molar ratio 0.1).     

Au／CdS-核／壳结构纳米复合颗粒的制备与表征

本文制备并表征了Au/CdS几何结构的纳米簇复合物.TEM和尺寸分布图显示,Au颗粒和CdS颗粒的平均粒径分别为6 nm和8 nm,Au/CdS粒径分布较窄且分散性较好,平均粒径19 nm.这种核壳结构纳米复合颗粒和单CdS颗粒一样,在485 nm和543 nm有两处发射峰.从UV-Vis上观察到,CdS的吸收边在470 nm,Au/CdS的吸收谱线上Au的吸收峰消失,吸收边相对于单CdS出现蓝移.     

Plasmonic Features in the Absorption Spectrum of a Monodisperse Ensemble of Gold Nanoislands on Sapphire

Plasmonic features in the absorption spectrum of a monodisperse ensemble of gold nanoislands on a sapphire substrate are considered. An explanation of the long-wavelength and UV bands in the absorption spectrum of the sample is proposed. The long-wavelength feature is interpreted as a consequence of surface plasmon polariton excitation under coherent scattering from a regular lattice of gold particles on sapphire, and the short-wavelength feature is considered to be a plasmon resonance, localized on individual gold nanoparticles.     

Ion implantation,luminescence, and cluster growth in silica layers

To activate silica optically our investigations are extended to ion implantation, mainly to overstoichiometric injection or isoelectronic substitution of the both constituents silicon or oxygen, i.e. by ions of the group IV (C, Si, Ge, Sn, Pb) or the group VI (O, S, Se). Such implantation produce new luminescence bands in silica layers, partially with optical electronic–vibronic transitions and respective multimodal spectra. In this context, special interest should be directed to low-dimension nanocluster formation in silica layers. Cathodoluminescence, high resolution transmission (HR-TEM) and scanning transmission electron microscopy (STEM), and energy dispersive X-ray analysis (EDX) have been used to investigate Si and Ge cluster formation in amorphous silicon dioxide layers and their respective luminescence behavior.     

Dye centres in magnesium doped corundum monocrystal

Results of absorption spectra studies in Mg doped Al₂O₃ monocrystals are described. It is shown that due to Mg doping dye centres appear together with the associated additional absorption bands with maxima at 585, 475 and 260 nm. Kinetics of the formation (destruction) of these centres) of these centres in the process of thermal treatment is considered. An assumption on the nature of dye centres and the related absorption bands is proposed together with an evaluation of oscillator strength. Dependences of diffusion coefficients of the subject centres on thermal treatment temperatures are derived.     

Relations between the optical properties of Cu–Ag:Si3N4 nanocermets and the microstructure of the metallic nanoclusters

Ion beam sputtering has been used to prepare Ag/Cu, Ag and Cu nanoclusters embedded in a Si₃N₄ dielectric matrix with the goal to correlate structural information and optical properties. The optical transmittance spectra of the bimetallic nanoclusters are compared with those obtained in the case of the single metallic nanocermets in the as-deposited state. The influence of a post annealing treatment, at different temperatures, on the optical properties of the bimetallic nanocermets is also discussed. The nanocluster structure has been investigated by X-ray absorption spectroscopy and X-ray diffraction. The chemical composition has been analysed by Rutherford backscattering spectroscopy. The surface plasmon resonance occurring after annealing in a definite temperature range is interpreted as due to the specific atomic arrangement resulting from this treatment.     

Characterization and luminescence of a-Si:H:Cl films

a-Si:H:Cl films have been deposited by glow-discharge and characterized by infrared transmission, optical absorption and photoluminescence. The influence of growth parameters on the H and Cl content has been investigated. The luminescence spectra show that three different radiative transitions can occur, at 0.75, 0.95 and ～1.3 eV. These bands have been interpreted respectively in terms of the following recombinations: defect to defect, defect to band tail, band tail to band tail.     

A pitch of helicoid of chiral liquid crystals and surface plasmon excitation: A theoretical study

ABSTRACT

Surface plasmon resonance (SPR) is widely used in different types of optical detection schemes and for light manipulation. There are a lot of experimental and theoretical investigations about the influence of different media, adjacent to the metal layer, on SPR. However, the influence of liquid crystal (LC) layer is not fully revealed. There are only few publications considering Kretshmann configuration with LC layer sandwiched between the prism and metal layer. Respectively, a lot of questions regarding the influence of LC properties on the surface plasmon resonance (SPR) are still open. The aim of this paper is to fill this gap.     

Coupled Phonon Modes and Infrared Band Shapes in Crystal SiF

The absorption intensities of combination bands in the infrared spectrum of crystal SiF₄ have been measured. One-and two-phonon energies and densities of states have been calculated with a dipole-dipole interaction potential. The contribution to absorption intensities due to non linear electric moments have been calculated. It is shown that most of the two-phonon infrared absorption is due to phonon-phonon coupling.     

Optical absorption study on radiation damage in fluoride glasses

The effect of 1.7 MeV electrons on the coloration of fluorozirconate (ZBL) and fluorohafnate (HBL) glasses has been investigated. Irradiation can produce intense broad absorption bands at 325 nm and 253 nm in the glasses. However, the size and shape of the absorption bands in zirconate-based glass (ZBLA) which has Al³⁺ ions as network stabilizers is different from those in ZBL and HBL glass. The optical absorption bands due to self-trapped hole centers can be assigned from dichroic absorption measurements. It appears that the radiolysis damage mechanism may contribute to the coloration of these fluoride glasses.     

Investigation of the optical properties of KGd(WO<Subscript>4</Subscript>)<Subscript>2</Subscript>:Nd<Superscript>3+</Superscript> crystals with allowance for absorption

The optical properties of a biaxial absorbing KGd(WO₄)₂:Nd³⁺ crystal have been investigated. The main refractive indices were measured in the visible spectral range and the absorption and transmission spectra of samples of these crystals were studied. The changes in the refractive indices were in the region of the absorption bands with the use of the Kramers-Kronig relation. Conoscopic pictures of this crystal in the regions of transparency and absorption bands were calculated and are presented.     

Vacuum ultraviolet absorption spectrum of photorefractive Sn-doped silica fiber preforms

Vacuum ultraviolet (VUV) absorption data have been obtained up to 8.3 eV on Sn-doped silica fibre preforms. Measurements have been carried out before and after exposure to 248 nm radiation from KrF excimer laser. The absorption spectrum is composed of three structures peaking at about 4.9, 5.8 and 7 eV, with the absorption edge at about 8.2 eV. The main effect of 5 eV irradiation is the decrease of the spectral components at 4.9 and 7 eV, whereas a small increase of absorption intensity is only observed just below the band at 4.9 eV. According to the observed negative absorption changes in the whole region of point-defect bands one would expect a negative refractive index change, contrary to the positive change previously reported in optical fibres of the same composition. Structural modifications accompanying the defect photoconversion process are suggested to be responsible for positive refractive index changes.     

Effect of growth temperature on the structure and optical properties of ZnO nanorod arrays grown on ITO substrate

ZnO nanorod arrays have been successfully prepared on ITO substrate by a chemical‐bath deposition method at different growth temperatures. The influence of the growth temperature on the morphology and microstructure of the ZnO nanorods was investigated by scanning electron microscopy (SEM) and X‐ray diffraction (XRD). The results showed that the diameter of the ZnO nanorods decreased and the size of the nanocrystals increased with increasing growth temperature. Optical absorption measurements showed the absorption band edge has shifted to a lower‐energy region due to the quantum size effect. Green emission and UV emission bands were observed and they are found to be temperature dependent, which indicates that the deep‐level emission and band‐edge emission of ZnO nanorods is closely related to the rod diameter, and the related mechanism is discussed.     

EPR and Optical Absorption Studies of γ-irradiated Pyrene Single Crystals

Pyrene single crystals irradiated with γ rays at room temperature have been investigated by electron paramagnetic resonance and optical absorption experiments. EPR spectra exhibit a triplet characteristic and each line of the triplet shows characteristic features with rotations of the crystals in a magnetic field. From analyses of these spectra the presence of two kinds of hydrogen added pyrene radicals, 3-H₂-pyrene and 2-H₂-pyrene radicals, is concluded. In the optical absorption spectrum nine main absorption bands have been detected. These absorption bands are compared with the theoretically calculated transition energies with SCF-CI molecular orbital calculations for 3-H₂-pyrene and 2-H₂-pyrene radicals. Reasonable correspondences are obtained between theoretical values and the experimental spectrum.     

EPR and Optical Absorption Studies of Radiation-Induced Radicals in Biphenyl Single Crystals

Biphenyl single crystals irradiated with γ rays at liquid nitrogen temperature have been investigated by electron paramagnetic resonance and optical absorption experiments. EPR spectra at room temperature exhibit a triplet characteristic separated by 39 gauss and each line of the triplet further splits to a triplet. The main triplet has been interpreted as being caused by hydrogen added biphenyl radicals. The splitting of each line of the main triplet is consistent with the calculated splittings of 2-hydro-biphenyl radicals and 4-hydro-biphenyl radicals. The presence of 3-hydro-biphenyl radicals could not be judged from the EPR spectra due to the broadness of the lines. In the optical absorption spectra at low temperature, obtained with the light polarized to the a-, b- and c'-axes of the crystals, nine bands were detected. Transition energies were calculated using SCF-C1 molecular orbital theory for the three kinds of the hydrogen added biphenyl radicals. By comparing the experimental spectra with the theoretical transitions of the three kinds of radicals, the bands at 666 nm and 424 nm have been assigned to the transitions of 2-hydro-biphenyl radicals, the 660 nm band to that of 3-hydro-biphenyl radicals, and the bands at 604 nm and 598 nm to the ones of 4-hydro-biphenyl radicals. The decays of these radicals at room temperature are very similar and upon annealing a new absorption band appears at 462 nm.     

Effects of ArF excimer irradiation on single energy and multi energy Ge ion implanted silica

Some of the effects of ArF excimer irradiation on the optical bands produced by single energy (4 MeV) and multi energy (highest energy 4 MeV) Ge implantations in silica (Type III) have been determined. Ge ions were implanted at 4 MeV with nominal doses of 1.25, 2.5 and 5.0×10¹⁵ ions/cm². A second series of samples was made using implant energies ranging from 4 to 0.7 MeV. The doses at each energy were varied to maintain an approximate constant implant species concentration with the total number of ions implanted being 10×10¹⁵ and 5×10¹⁵ cm⁻² for concentrations of 0.042 and 0.021 at.%, respectively. The optical absorption was measured from 2.8 to 6.5 eV. The absorption of samples was then measured after 6.4 eV ArF excimer radiation with a fluence of 44 mJ/cm² per pulse for pulse totals of 3, 11 and 31. We fit the observed spectra for the as-implanted samples and the samples after each ArF exposure to the minimum number of bands attributed to intrinsic states in SiO₂ required to fit the data within ±2%. The magnitude and response of these absorption bands to the ArF irradiation was a function of dose and implant conditions.     

Optical spectra of borate glasses containing Ti and Co in relation to their structure

The optical absorption spectra of borate glasses of the base composition (mol%) 35 (Na₂O+BaO)·65 B₂O₃, to which Ti and Co ions were introduced, have been measured in the range 190–900 nm. The addition of increasing amounts of TiO₂ up to 16 g/100 g glass, introduces an intense charge transfer band in the UV region that shifts towards longer wavelengths without imparting any coloration to the glass samples.Titanium ions are present as the Ti⁴ state and its addition produces glass of more coherent structure. The cobalt ions are found to be present in two symmetries; as CoO₆ units with absorption bands (denoted here as bands a and b) around 525–530 nm and 580–595 nm (respectively), and as CoO₄ units with absorption bands (denoted here as band-c) around 620–635 nm. Replacing Na ions by Ba ions or increasing the TiO₂ content favours the conversion of CoO₄ units into the CoO₆ ones.     

Colour bands of oxidized nickel dioximes

Strong colour bands are observed in the mull absorption spectra of the oxidized nickel chain dioximes bis (1,2-benzoquinonedioximato) Ni.I_0.5 and bis (diphenylglyoximato) Ni^IIIBr in the long wavelength region of the optical spectrum which are ascribed to the reduced metal-metal distance due to oxidation. The uv-visible spectra of bis (dimethylglyoximato) Ni^II and bis (diphenylglyoximato) Ni^II have also been studied in the present comparative study. All the bands in the uv-visible range are assigned. The transitions and the effects of partial oxidation on the electronic transitions are discussed.     

Radiation-induced defects in fluoride glasses

Fluorozirconate (ZBLA) and fluorohafnate (HBL) glasses have been exposed to ionizing radiation at room temperature, and the resulting defects have been characterized using optical absorption and electron spin resonance techniques. Prominent absorption bands were found to peak in the ultraviolet at 290 nm for the ZBLA glass and at 240 and 310 nm for the HBL glass. Two major electron spin resonance spectra having g values of 1.883 and 2.043 were induced in the HBL glass. Similar electron spin resonance spectra were found in the ZBLA glass. A third spectrum with a g value of 2.008 was also observed in the ZBLA material. The optical and electron spin resonance spectra in these glasses thermally annealed between room temperature and 300°C. Possible models for the defects are discussed.     

Effect of gamma-rays on some mixed alkali borate glasses containing nickel

The change of optical absorption of some irradiated mixed alkali borate glasses containing nickel has been studied by varying the gamma-ray dose or the mixed alkali oxide content. The induced bands increase as the radiation process proceeds until a certain limit after which a constancy is assumed to be reached.The investigation of the observed spectra shows that there is an induced absorption band with its maximum at 550 nm, in addition to the characteristic absorption bands of the divalent nickel ions with peaks in the visible region at 410, 640, 680 and 750 nm.