Influence of ultraviolet irradiation on the optical properties of amorphous Sb10Se90 thin films

Amorphous Sb₁₀Se₉₀ thin films were prepared by thermal evaporation of the bulk glass. The changes in the optical properties (transmittance, optical gap, absorption coefficient, refractive index and extinction coefficient) have been measured in the wavelength range 500-900 nm of virgin and ultraviolet (UV) illuminated films. Analysis of the optical absorption data shows that the rule of non-direct transitions predominates. It is found that the optical energy gap decreases (photo-darkening) and the refractive index increases with the increase of UV exposure time. The dispersion of the refractive index (n) has been discussed in terms of Wemple-Didomenico single oscillator model. The oscillator energy E₀ and the dispersion energy E_d have been determined and discussed in terms of UV exposure time. The photo-darkening was discussed in terms of some of the current literature models.     

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.     

Optical properties of 60B2O3-(40-x)PbO-xMCl2 and 50B2O3-(50-x) PbO-xMCl2 (M = Pb, Cd) glasses

Optical absorption and transmittance spectra of 60B₂O₃-(40-x)PbO-xMCl₂ and 50B₂O₃-(50-x) PbO-xMCl₂ (M = Pb, Cd) (10 ≤x ≤ 20) glasses of varying composition were recorded in the UV-visible region. Various optical parameters such as optical energy gap (E _opt), Urbach energy (E _e), refractive index (n ₀), optical dielectric constant (ε∞), and ratio of carrier concentration to the effective mass (N/m*;) were determined. The variation of optical energy gap with increase in the concentration of PbCl₂ or CdCl₂ is discussed.     

Preparation and optical properties of borate glass doped with MnO<Subscript>2</Subscript>

In this contribution, MnO₂ doped borate glass matrix with ratios 0.0, 0.5, 1.0, 1.5 and 2.0 wt% were prepared utilizing melting method. The structural characterization of these glass samples was performed via X- ray diffraction measurements. Optical absorption analyses within the 200–1000 nm wavelength range were performed to characterize the samples. The direct and indirect optical energy gaps (E_opt) decreased however Urbach energy (E_U) increased with increasing MnO₂ concentration. The refractive index, and optical conductivity values are observed to increase with increasing MnO₂ concentration. FTIR spectra of borate glass doped with 0.0, 0.5, 1.0, 1.5 and 2.0 wt% MnO₂ revealed the presence of absorption bands due to Mn²⁺.     

Optical properties of lead-bismuth cuprous glasses

The optical transmission and absorption spectra in UV- VIS were recorded in the wavelength range 350–800 nm for different glass compositions in the system (CuO) _x (PbO) ₅₀−x(Bi₂O₃)₅₀ (x = 2.5, 5.0, 7.5, 10.0, 12.5, 15.0, 20.0). Absorption coefficient (α), optical energy gap (E_opt), refractive index (n_D), optical dielectric constant (ε′_∞), measure of extent of band tailing (ΔE), constant (β) and ratio of carrier concentration to the effective mass (N/m*) have been reported. The effects of compositions of glasses on these parameters have been discussed. It has been indicated that a small compositional modification of the glasses lead to an important change in all the optical properties including non-linear behaviour. The optical parameters were found to be almost the same for different glasses in the same family.     

Studies on boro cadmium tellurite glasses

To investigate the modification effect of the modifier CdO on boro tellurite glass, a series of glasses with compositions (50 − x) CdO-xTeO₂-50B₂O₃ have been prepared by conventional melt quenching technique. Optical absorption, IR and Raman structural studies are carried out on the glass system. The optical absorption studies revealed that the cutoff wave length and refractive index increase while optical band gap (E_opt) and Urbach energy decreases with increase of CdO content. The IR and Raman studies revealed that structure of glass network consists of [TeO_3]/[TeO₃₊₁], [TeO₄], [BO₃], [BO₄] and [Cd-Te] linkages .The compositional dependence of different physical parameters such as density, molar volume, oxygen packing density, optical basicity, have been analyzed and discussed.     

Linear and non-linear optics of nano-scale 2′,7′dichloro-fluorescein/FTO optical system: Bandgap and dielectric analysis

2′,7′ dichloro-Fluorescein (DCF) is a promising organic semiconductor material in different technological aspects such as solar cell, photodiode, Schottky diode. DCF thin film/conductive glass (FTO glass) was prepared by a low-cost spin coating technique. The spectrophotometric data such as the absorbance, reflectance and transmittance were cogitated in the 350–2500 nm wavelength range, at the normal incidence. The absorption (n) and linear refractive indices (k) were computed using the Fresnel's equations. The optical band gap was evaluated and it was found that there is two band gap described as follows: (1) It is related to the band gap of FTO/glass which is equal 3.4 eV and (2) the second one is related to the absorption edge of DCF equals 2.25 eV. The non-linear parameters such as the refractive index (n₂) and optical susceptibility χ⁽³⁾ were evaluated by the spectroscopic method based on the refractive index. Both (n₂) and χ⁽³⁾ increased rapidly on increasing the wavelength with redshift absorption. Our work represents a new idea about using FTO glass for a new generation of the optical device and technology.     

Optical and dielectric properties of double helix DNA thin films

In this work, the thin film of wheat DNA was deposited by spin-coating technique onto glass substrate, and the optical and dielectric properties of the double helix DNA thin film were investigated. The optical constants such as refractive index, extinction coefficient, dielectric constant, dissipation factor, relaxation time, and optical conductivity were determined from the measured transmittance spectra in the wavelength range 190–1100 nm. Meanwhile, the dispersion behavior of the refractive index was studied in terms of the single oscillator Wemple–DiDomenico (W–D) model, and the physical parameters of the average oscillator strength, average oscillator wavelength, average oscillator energy, the refractive index dispersion parameter and the dispersion energy were achieved. Furthermore, the optical band gap values were calculated by W–D model and Tauc model, respectively, and the values obtained from W–D model are in agreement with those determined from the Tauc model. The analysis of the optical absorption data indicates that the optical band gap E_g was indirect transitions. These results provide some useful references for the potential application of the DNA thin films in fiber optic, solar cell and optoelectronic devices.     

Optical properties of samarium doped zinc-tellurite glasses

Glasses with the composition, (Sm₂ O ₃) _x (ZnO)_(40-x)(TeO ₂)₍₆₀₎, were prepared by conventional melt quenching method. The density, molar volume, and optical energy band gap of these glasses have been measured. The refractive index, molar refraction and polarizability of oxide ion have been calculated by using Lorentz-Lorentz relations. Optical absorption spectra of these glasses were recorded in the range 300–700 nm at room temperature. The oxide ion polarizabilities deduced from two different quantities, viz. refractive index and optical energy band gap, agree well compared with other glasses. The nonlinear variation of the above optical parameters with respect to samarium dopant has been explained.     

Effect of NiO content on the optical band gap, refractive index, and density of TeO2–V2O5–NiO glasses

Amorphous layers and bulk glasses of 40TeO₂–(60 ? x)V₂O₅–xNiO compositions with 0 ≤ x ≤ 30 (in mol%) have been prepared using the usual blowing technique and press-melt quenching method, respectively. The optical absorption spectra of the layers have been recorded in the wavelength range 400–800 nm. The fundamental absorption edge has been identified from the optical absorption spectra. The optical band gap, width of the tail of the localized states, and refractive index have been evaluated using available theories. Results show that the values of optical band gap decrease from 2.02 to 1.64 eV as the contribution of NiO increases. The refractive index dispersion is fitted to the single oscillator model, and results show that the static refractive index increase from 1.309 to 1.673 as the NiO content increases. The glass transition temperature, density, and molar volume have been studied, indicating act of NiO as network modifier. Values of theoretical optical basicity are also reported.     

Some optical properties of Se-Ge-As amorphous chalcogenide glasses

The effects of composition, film thickness, substrate temperature, and annealing of amorphous thin films of Se₇₅Ge_25−x As _x (5⩽x⩽20) on their optical properties have been investigated. X-ray diffraction revealed the formation of amorphous films. The absorbance and transmission of vacuum-evaporated thin films were used to determine the band gap and refractive index. Optical absorption measurements showed that the fundamental absorption edge is a function of glass composition and the optical absorption is due to indirect transition. The energy gap increases linearly with increasing arsenic content. The optical band gap,E _opt, was found to be almost thickness independent. The shapes of the absorption edge of annealed samples displayed roughly the same characteristic as those of the unannealed films, but were shifted towards shorter wavelengths; as a result,E _opt increased andE _e, the width of the band tails, decreases. The increase inE _opt is believed to be associated with void removal and microstructural re-arrangement during annealing. The influence of substrate temperature on the optical parameters is discussed.     

Study of structural and optical properties of Cd1-xZnxSe thin films

Cd_1-xZn_xSe (x = 0, 0.5 and 1) thin films have been deposited onto glass substrates using thermal evaporation technique. The lattice constants, grain size, microstrain and dislocation density were studied by using X-ray diffraction. In addition the optical constants were calculated in the wavelength range 400-2500 nm. Transmittance and reflectance were used to calculate the absorption coefficient α and the optical band gap E_g. The linear relation of (αhυ)² as a function of photon energy hυ for the thin films illustrated that the films exhibit a direct band gap, which increases with increasing Zn content. This increasing of optical band gap was interpreted in accordance to the increasing in the cohesive energy. Optical constants, such as refractive index n, optical conductivity σ_opt, complex dielectric constant, relaxation time τ and dissipation factor tanδ were determined. The optical dispersion parameters E₀, E_d were determined according to Wemple and Di Domenico method.     

Optical and structural properties of flash evaporated HgTe thin films

Thin films of HgTe were thermally flash evaporated onto glass and quartz substrates at room temperature. The structural investigations showed that stoichiometric and amorphous films were produced. The transmittance, T, and reflectance, R, of thin films of HgTe have been measured over the wavelength ranges 300–2500 nm. From analysis of the transmittance and reflectance results, the refractive index, n, and the extinction coefficient, k, has been studied. Analysis of the refractive index yields a high frequency dielectric constant, ɛ_∞, and the energy of the effective oscillator, E_o, the dispersion energy, E_d, the covalent value β and the M₋₁ and M₋₃ moments of the imaginary dielectric function of optical spectrum. Also, the dependence of the real part dielectric constant ɛ₁(hν) on its imaginary part ɛ₂(hν) of HgTe films can be used to determine the molecular relaxation time τ, the distribution parameter α^\ and the macroscopic (electronic) relaxation time τ_o. The graphical representations of surface and volume energy loss functions, dielectric constant, the optical conductivity as well as the relaxation time as a function of photon energy revealed three transitions at 0.63, 2.21 and 2.76 eV.     

Optical and microstructural characterization of sol/gel derived cerium-doped PZT thin films

Optical properties of cerium-doped PZT thin films on sapphire prepared by a sol-gel technique are investigated using both transmission and reflection spectra in the wavelength range 200 to 900 nm. The refractive index, extinction coefficient and thickness of the film are determined from the measured transmission spectra. The packing density of the film is calculated from its refractive index using the effective medium approximation (EMA), and average oscillator strength and wavelength are estimated using a Sellmeir-type dispersion equation. Absorption coefficient (α) and the band gap energy (E_g) of each film composition are also calculated. Possible correlations of microstructure and phase formation behaviour with changes in band gap energy and other optical properties are discussed. This revised version was published online in November 2006 with corrections to the Cover Date.     

The fundamental absorption edge and optical constants of some charge transfer compounds

A series of the charge-transfer compounds determined as 1:1 stochiometric ratio by job method has been prepared with the interaction of 7,7,8,8-tetracyanoquinodimethane (TCNQ) and anthracene, 9-methylanthracene, 9-bromanthracene in dichloromethane at room temperature. The values of the optical band gap E_g, and Urbach energy E₀ were determined from the optical absorption. The optical absorption measurements indicate that the absorption mechanism is due to allowed direct transitions for the compounds and it is evaluated that the optical band gap and Urbach energy values changes with incorporating R group in the compounds. The optical constants such as refractive index n, and extinction coefficient k and real and imaginary part of dielectric constant and optical conductivity of the compounds were calculated. E_g and E₀ reflect the influence of different types of disorder on the absorption spectra processes. Thus, a correlation between E_g and E₀ was made. Form this correlation, G value that is proportional to the second-order deformation potential and, E_f value that depend on local coordination, parameters are found to be 0.29 and 2.37 eV, respectively.     

Optical properties of (1-x-y)B2O3-xLi2O-yMCI2 (M=Cd, Zn) glasses

Optical absorption and transmission spectra of (1-x-y)B₂O₃-xLi₂O-yMCI₂ (M=Cd, Zn) glasses of varying compositions were recorded in the UV-visible region. From the spectra, various optical parameters such as optical energy gap (E _opt), refractive index (n), optical dielectric constant (ɛ′), width of the tail of localized states in the forbidden gap (ΔE), ratio of carrier concentration to the effective mass (N/m*) and the constantB were evaluated. The effects of composition of glasses on these parameters are discussed.     

Thickness dependence of refractive index and optical gap of PMMA layers prepared under electrical field

Optical parameters (refractive index, dispersion energy, optical gap) of polymethylmethacrylate (PMMA) layers prepared by spin coating and modified by electric field have been studied. Refractive index was measured using a refractometer, internal structure was investigated as a structural parameter (E _d) within the One Oscillator Model. Optical gap width (E _g^opt) was assessed using Tauc Approximation from UV-Vis spectra. Surface morphology and roughness was investigated using an AFM. The electric field imposed during preparation of layers increases their refractive index. The highest increase in n (Δn = 0.042) was found for the thinnest PMMA layer (70 nm). Oriented layers have produced higher E _g^opt than non-oriented ones for all studied values of thickness. The electrical field applied at preparation of the oriented layer will not change its surface morphology and roughness.     

Linear and non-linear optics and FTIR characteristics of borosilicate glasses doped with gadolinium ions

Borosilicate glasses have been prepared using the high-temperature melt components of ingredients Gd₂O₃ doped borosilicate glasses. FTIR spectra were measured in the wavenumber range (4000–400 cm⁻¹) to explore the state and influence of Gd³⁺ ions in the structure of the glasses. Data indicated that B₂O₃ is acting as dual network formers (BO₃) and (BO₄) structural units whereas the gadolinium ions playing the role of network modifier in these glasses. Optical transmission spectra were recorded in the range 190–2500 nm and different optical parameters such as the direct and the indirect optical band gap, Urbach energy, refractive index and optical dielectric constant, have been determined. The molar refraction, electronic polarizability and the optical basicity results have been determined using the measured glass refractive indices. Gadolinium-doped borosilicate glasses are found to be characterized by different optical parameters.     

Optical properties and electrical resistivity of boron-doped ZnO thin films grown by sol–gel dip-coating method

Sol–gel dip-coating was used to grow ZnO thin films doped with various concentrations of B ranging from 0 to 2.5 at.% on quartz substrates. The effects of B doping on the absorption coefficient (α), optical band gap (E_g), Urbach energy (E_U), refractive index (n), refractive index at infinite wavelength (n_∞), extinction coefficient (k), single-oscillator energy (E_o), dispersion energy (E_d), average oscillator strength (S_o), average oscillator wavelength (λ_o), moments M₋₁ and M₋₃, dielectric constant (ε), optical conductivity (σ), and electrical resistivity (ρ) of the BZO thin films were investigated. The transmittance spectra of the ZnO and BZO thin films show that the transmittance of the BZO thin films was significantly higher than that of the ZnO thin films in the visible region of the spectrum and that the absorption edge of the BZO thin films was blue-shifted. The BZO thin films exhibited higher E_g, E_U, and E_o and lower E_d, λ_o, M₋₁ and M₋₃ moments, S_o, n_∞, and ρ than the ZnO thin films.     

Optical properties of metal phthalocyanines

In this study, optical properties of phthalocyanines of five metals, i.e., cobalt, nickel, iron, copper, and manganese, have been discussed in the energy (E) range of 1.5–4.1 eV. Utilizing the available data of refractive index (n) and extinction coefficient (k) of these materials in the literature, the related optical properties such as the real (ε₁), imaginary (ε₂) parts of the complex dielectric constant (ε), and reflectivity (R) are calculated. Interpretations for the energies corresponding to the peaks in ε₂ are explained in terms of the Penn gap (E _P). High-frequency dielectric constant (ε_∞) values corresponding to four models, i.e., the conventional Lorentz model, modified Lorentz model, relaxed Lorentz model, and the dual Lorentz model are used to determine E _P. It is found that the E _P values corresponding to the conventional and dual Lorentz models are in good agreement with the average of energy peaks in the R-E and the ε₂-E spectra. The oscillator energy (E ₀) and the dispersion energy (E _d) of these materials have been determined utilizing the Wemple–DiDomenico model. The calculated values of (a) E ₀ are generally in good agreement with the Penn gap E _P, the average of the energy peaks in the R-E and the ε₂-E spectra and (b) E _d are comparable to those in the literature for CoPc and NiPc.