Some effects of the addition of nickel oxide and of annealing on the optical absorption of sodium tetraborate glasses

A range of sodium tetraborate glasses containing nickel oxide was prepared and the optical absorption spectra measured. The differential scanning calorimetry technique was used to study compositional features of the glass formation. It was found that the addition of nickel oxide decreases the optical energy gap and introduces new absorption bands as compared with the optical absorption spectrum of pure sodium tetraborate glass. The results revealed that the decrease in the optical energy gap and the disappearance of some absorption bands of the annealed samples could be attributed to an increase in the concentration of reduced valence states of nickel ions which accompanies the microstructure formation.     

Some optical and differential scanning calorimetry studies of sodium tetraborate glasses containing vanadium oxide

A series of glass samples was prepared from mixtures of Na₂B₄O₇ and V₂O₅. Measurements were made for infrared absorption and optical absorption spectra as a function of V₂O₅ content up to 10 mol%. The addition of V₂O₅ did not introduce any new absorption band as compared with the infrared spectrum of pure sodium tetraborate glass. The addition of V₂O₅ shifted the optical absorption edges towards lower energies, and introduced a new absorption band as compared with the optical absorption of pure Na₂B₄O₇ glass. Differential scanning calorimetry as a function of V₂O₅ content was also measured.     

Optical,infrared and DSC studies of sodium tetraborate glasses containing copper oxide

The optical absorption, density, DSC and infrared absorption spectra of a series of sodium tetraborate glasses are measured as a function of copper content up to 5 mol%. It is found that the addition of CuO shifts the fundamental absorption edges towards lower energies in the range from 6.17–3.48 eV. The addition of CuO does not seem to introduce any new absorption band as compared with the spectrum of a pure sodium tetraborate glass. DSC measurements showed endothermal peaks varying from 486–476 °C depending on the CuO content.     

Spectroscopic and electrical studies of sodium tetraborate glasses containing nickel oxide

The infrared spectra. X-ray diffraction and electrical conductivity of sodium tetraborate glasses containing nickel have been studied as a function of nickel oxide content. It was found that addition of nickel oxide does not seem to introduce any new absorption band as compared with the infrared spectrum of pure sodium tetraborate glass. The electrical conductivity measurements revealed that the activation energy for conductivity increases with nickel oxide content. This could be explained on the basis of the concept of Hubbard bands, and possibly by a block effect of the nickel ion on the overall mobility of the sodium ion. Measurements were made on unannealed samples and some samples annealed at different temperatures. Annealing the samples at temperatures in the range 460 to 480° C causes the appearance of a crystalline phase, resulting in an increase of electronic conductivity.     

Surfactant effects on optical absorption spectra of iron phthalocyanine nanoparticles in water

Iron phthalocyanine (FePc) nanoparticles aqueous colloidal solutions were prepared by laser ablation in water, including surfactants. The Q band of FePc can be shifted to the longer or shorter wavelength widely by adjusting the concentration of surfactants on the basis of critical micelle concentration (CMC) with laser irradiation. The change in micelle structure of the surfactants surrounding the FePc nanoparticles may be the main reason for the shifting of the Q band.     

Ultrasonic investigation and infrared absorption of some sodium borate glasses

Ultrasonic velocities and absorption measurements in sodium borate glasses containing Na₂O have been made using the pulse echo technique at 4, 5 and 6 MHz. Results showed an increase in velocity as the sodium oxide content (mol%) increased. The ultrasonic absorption results showed the presence of very high and well-defined peak which shifts its position to lower temperatures with increasing frequency. This suggests some sort of relaxation process and the activation energy of this process increased with increasing Na₂O concentration (mol%). The infrared absorption spectra of sodium borate glasses confirmed the results obtained by ultrasonic investigations.     

Synthesis,EPR and optical spectroscopy of the Cr-doped tetraborate glasses

Electron paramagnetic resonance (EPR), optical absorption and photoluminescence spectra as well as luminescence kinetics of the Li₂B₄O₇:Cr and KLiB₄O₇:Cr tetraborate glasses were investigated at T = 300 K. The Li₂B₄O₇:Cr and KLiB₄O₇:Cr glasses containing 0.4 and 1.6 mol.% Cr₂O₃ of high optical quality were obtained from polycrystalline compounds by fast cooling of the melts. The X-band EPR spectroscopy shows that the Cr impurity is incorporated in the tetraborate glass network as isolated Cr³⁺ centers and Cr³⁺–Cr³⁺ pairs coupled by magnetic dipolar and exchange interactions. The EPR spectral parameters (g_eff and ΔB_pp) of both Cr³⁺ and Cr³⁺–Cr³⁺ centers in the Li₂B₄O₇:Cr and KLiB₄O₇:Cr glasses were measured and analyzed. All transitions in optical absorption, luminescence excitation and emission spectra of these glasses are identified. Broad complex bands that peak near 615, 405, and 350 nm in optical absorption and luminescence excitation spectra correspond to the ⁴A_2g(F) → ⁴T_2g(F), ⁴A_2g(F) → ⁴T_1g(F), and ⁴A_2g(F) → ⁴T_1g(P) spin-allowed transitions of the Cr³⁺ centers in distorted octahedral sites of the tetraborate glass network. The octahedral (cubic) crystal field strength (10Dq) and Racach parameters (B and C) for Cr³⁺ centers in Li₂B₄O₇:Cr and KLiB₄O₇:Cr glasses are estimated. Narrow and broad emission bands in red – NIR regions are assigned to the ²E_g(F) → ⁴A_2g(F) (R₁ line) and ⁴T_2g(F) → ⁴A_2g(F) (electron-vibration) transitions, which correspond to the Cr³⁺ centers in high-field and low-field sites, respectively. All observed emission bands are characterized by non-exponential decay. Measured average lifetimes and local structure of the Cr³⁺ centers in high-field and low-field sites of the Li₂B₄O₇:Cr and KLiB₄O₇:Cr glass network have been discussed.     

Excitonic effects on optical absorption spectra of doped graphene

We have performed first-principles calculations to study optical absorption spectra of doped graphene with many-electron effects included. Both self-energy corrections and electron-hole interactions are reduced due to the enhanced screening in doped graphene. However, self-energy corrections and excitonic effects nearly cancel each other, making the prominent optical absorption peak fixed around 4.5 eV under different doping conditions. On the other hand, an unexpected increase of the optical absorbance is observed within the infrared and visible-light frequency regime (1-3 eV). Our analysis shows that a combining effect from the band filling and electron-hole interactions results in such an enhanced excitonic effect on the optical absorption. These unique variations of the optical absorption of doped graphene are of importance to understand relevant experiments and design optoelectronic applications.     

Effect of cerium oxide addition on the optical absorption edge of tungsten trioxide

Thin films of WO₃/CeO₂ deposited by vacuum co-evaporation (10^–6 torr) on to Corning 7059 glass slides at room temperature have been shown to be amorphous in structure. The optical absorption spectra of amorphous WO₃/CeO₂ thin films have been measured at room temperature. The optical absorption edge of WO₃/CeO₂ and WO₃ thin films above 10⁵ cm^–1 follows the Davis and Mott equation for the non-direct optical transitions. The optical absorption coefficient, , below this obeys the Urbach exponential relation. The value of the optical band gap of amorphous WO₃ thin films is in good agreement with that found by Deb. The shift of the optical gap to lower energies and that of the Urbach energies to higher energies as the content of CeO₂ is increased, indicate that both parameters are strongly dependent on the concentration of Ce⁴⁺ present in the structure. Thus, the increase of Ce⁴⁺ is thought to lead to strong potential fluctuations which cause an increase in the density of localized states in the gap.     

A spectroscopic study of some sodium tetraborate glasses containing lead and copper

Optical absorption, infra-red absorption spectra and differential scanning calorimetry of amorphous (Na₂B₄O₇)₈₀-(Pb₃O₄)_20-x -(CuO) _x systems were studied as functions of copper content up to 10 mol%. When the Pb₃O₄ in the glasses is gradually replaced by CuO, a pronounced decrease in the optical energy gap and an increase in the optical absorption at 750 nm due to the CU²⁺ ions is observed. The change in the optical absorption may be attributed to the concentration variation of the Cu²⁺ ions in the glasses as a consequence of changing the lead content.     

Investigation of infrared absorption spectra of copper phosphate glasses containing some rare earth oxides

The spectra of copper-lutetium-phosphate and copper-erbium-phosphate glasses have been studied within the spectral range 4000 to 400 cm^– by Fourier transform infrared spectroscopy. Incorporation of a small amount of lutetium or erbium influences some band positions compared with binary copper phosphate glasses. The additional bands in the range 491 to 576 cm^–1 are attributed to the presence of Lu-O and Er-O groups. It has been observed that annealing of the samples at 500 ° C leads to a slight shift in the peak positions.     

A study of the optical absorption edge in silicate glasses containing TiO2 oxide

A detailed study of the optical absorption as a function of temperature and composition for a series of soda-lime-silica glasses doped with TiO₂ oxide is presented. The variations of the optical energy gap with temperature in the range 296 to 483 K are reported. The UV results are analysed assuming optical absorption by indirect transitions. It was found from these optical absorption data that the present glass system can be divided into three compositional regions.     

Structural and optical properties of phosphate-zinc-nickel oxide glasses for narrow band pass absorption filters

Novel two phosphate glass systems with compositions 50P₂O₅–30ZnO–20NiO and 50P₂O₅–30ZnO–20[NiCl_2–6H₂O] were prepared using a conventional melt-quench technique. The absorbance and transmittance were measured using a spectrophotometer in the spectral range between 190 and 1100 nm. The data demonstrates that the system acts as a narrow bandpass optical absorption filter, with a transmission band in the UV region of 311–376 nm, which is centred at 350 nm and has a full width half maximum (FWHM) of almost 34 nm, whereas, the red region is the UV region of 617–684 nm, and centred at 650 nm and has a full width half maximum (FWHM) of nearly 32 nm. However, the refractive index (n), optical band gap (E_opt), non-linear refractive index n₂, third order non-linear susceptibility χ⁽³⁾ and non-linear absorption coefficient β were also calculated. It was apparent that the non-linear refractive index, third order non-linear susceptibility and non-linear absorption coefficient increases by decreasing the optical energy gap. Finally, we investigated the structure of the prepared glasses by using Raman and FTIR spectra. We found that the local network structure based mainly on Q¹ and Q² tetrahedron units connected by P–O–P linkages.     

ESR and optical absorption spectra of Ni(II) ions in lithium fluoroborate glasses

The results of the investigation of the structure of Ni(II) ions in x LiF-(100–x) B₂O₃ glasses with 5x30 mol% using ESR and optical absorption techniques are reported. Electron spin resonance spectra of Ni(II) ions doped glasses exhibit a symmetric line shape centred at g=2.36±0.01 at room temperature. Remarkable changes have been observed in the intensity and line shape with changes in concentration of LiF and when the spectra were recorded in the temperature range 123–453 K. The optical absorption spectra were recorded at room temperature. The observed bands have been interpreted in terms of ligand field theory. From the spectral analysis, the crystal field parameter, Dq, and the Racah interelectronic repulsion parameters, B and C, have been evaluated. By correlating the ESR and optical absorption data, the covalency parameter has been evaluated.     

Microstructure and optical absorption of silver granules in oxide glasses produced by ion-exchange and reduction treatments

An electron micrographic investigation has been carried out on two oxide glasses containing alkali ions and subjected to a sodiumsilver ion-exchange followed by reduction treatments at various temperatures. The presence of metallic silver in the silver-rich droplet phases has been confirmed by selected-area electron diffraction. The silver-rich phases are found to have diameters ranging from 3 to 50 nm. The nucleus density of these particles is found to have a maximum value at temperatures in the range 250 to 300° C. The optical absorption spectra of the reduced glasses show a maximum around a wavelength of 400 nm. Maxwell-Garnett theory has been used to calculate the optical absorption and the predicted wavelength for maximum absorption is in reasonable agreement with the experimental value.