Refractive Index Dispersion Curves Research Articles

Tailoring of physical, optical, and thermal properties of Se50-xTe30Ge20Sbx chalcogenide glasses: Influence of metalloids

The compositional dependence on physical and spectroscopic characteristics of chalcogenide Se50-xTe30Ge20Sbx (x = 5, 10, 15, and 20 at. wt%) bulk glassy systems has been explored in this communication. Numerous physical and optical features are rigorously examined by using the best glass sample among all the prepared samples. The XRD pattern reveals the amorphous character of the synthesized materials. Some of the physical parameters like density, and compactness are gradually increasing with the Sb addition, while the free volume percentage and excess volume follow the decreasing trend. The optical properties have been precisely inspected by UV-Vis spectroscopy in the (200–800) nm spectral range. The optical bandgap (Eopt) values are found to decline from (1.09–0.85) eV with Sb content. The observed refractive index, n values experience a subsequent decline with incident energy. By using the Wemple and DiDomenico (WDD) single oscillator model, the refractive index dispersion curve has been studied, and the dispersion parameters are discussed. The valence band (VB) and conduction band (CB) locations are estimated, and the obtained result reveals the VB potential increases from −15,089 eV to −1.3899 eV, while that of CB decreases from −0.4113 eV to −0.5303 eV with the rise of Sb-concentration. The cohesive energy (CE) values have been estimated by using the chemical bond approach (CBA). Investigation reveals the CE of the system decreases from 45.237 kcal/mole to 44.229 kcal/mole justifying the decrement in obtained band gap energy values of the studied glassy systems. Furthermore, the compositional dependency of various thermal parameters is investigated by using the DSC approach. The glass transition (Tg), and peak crystallization (Tp) were significantly affected by Sb addition. The obtained values of Tg are found to decrease from (337–305 K), while the thermal stability is found to increase with the Sb incorporation.

Optical studies on thermally evaporated Ge–Se/Ge-Sb-Se chalcogenide glass films by spectroscopic ellipsometry

The GexSb30-xSe70: x = 30, 25, 15, 10 glass films were prepared by thermal evaporation technique. The surface morphology of glass films was studied by atomic force microscopy. The samples exhibited surface roughness with a root mean square value falling within the 0.89–1.47 nm range. The optical properties were precisely characterized by spectroscopic ellipsometry in the 4.13–0.77 eV spectral range. The Cody-Lorentz dispersion model was used to fit the data across the entire spectral range and extract the optical functions of glass films. It has been observed that the refractive index, n values rise with increasing energy, reaching a peak, and then experience a subsequent decline. The refractive index values exhibit a rising trend with an increase in Sb content. The optical bandgap, Egopt was found to follow a decreasing pattern with a decrease in Ge content. The refractive index dispersion curve was analyzed using the Wemple and DiDomenico single oscillator model in the lower absorption spectral region. It has been observed the values of oscillator energy, Eo, and static refractive index, n0, exhibit a pattern consistent with that of Egopt , and n, respectively. The optical properties, such as the high-frequency dielectric constant, carrier concentration, plasma frequency, and optical conductivity were analyzed.

Structural, electronic, optical and vibrational properties of CdSiP2 from first-principles

We report the results of a first-principles research of the structural, electronic, linear and nonlinear responses, and vibrational properties of CdSiP2 based on the density functional theory using pseudopotential plane-wave approach. We calculate the energy band structure, dielectric function, absorption coefficient, reflectivity, refractive index, SHG susceptibility, and phonon dispersion curves. In order to obtain accurate band gap value of CdSiP2, the GW approximation method is used to calculate the quasiparticle band structure and the corrected band gap value is in excellent agreement with experimental measurements. Furthermore, the corrected band gap can be used as scissor shift for linear and nonlinear optical properties calculations. The linear-response theory is used to derive the phonon dispersion curves and density of states. All zone-center phonon modes are calculated and LO-TO splitting of the infrared modes are identified. The results show a good agreement with available experimental data and other calculations.

Development of high refractive index UiO-66 framework derivatives via ligand halogenation.

UiO-66 is a Zr-based metal-organic framework (MOF) with exceptional chemical and thermal stability. The modular design of a MOF allows the tuning of its electronic and optical properties to obtain tailored materials for optical applications. Making use of the halogenation of the 1,4-benzenedicarboxylate (bdc) linker, the well-known monohalogenated UiO-66 derivatives were examined. In addition, a novel diiodo bdc based UiO-66 analogue is introduced. The novel UiO-66-I2 MOF is fully characterized experimentally. By applying density functional theory (DFT), fully relaxed periodic structures of the halogenated UiO-66 derivatives are generated. Subsequently, the HSE06 hybrid DFT functional is used to calculate the electronic structures and optical properties. The obtained band gap energies are validated with UV-Vis measurements to assure a precise description of the optical properties. Finally, the calculated refractive index dispersion curves are evaluated underlining the capabilities to tailor the optical properties of MOFs by linker functionalization.

Glass formation and optical properties of Sn modified GeS2-Ga2S3-CsCl chalcogenide glasses

Chalcogenide glass is emerging as important IR materials for advanced athermal infrared (IR) optical systems because of its low thermal coefficient of refractive index. New chalcogenide glasses based on 75GeS2-15Ga2S3-10CsCl were developed through the substitution of GeS2 by SnS2. The introduction of heavier tin (Sn) results in the red shift of transmission window, both of visible and long-wavelength IR cut-off edges, the elevation of refractive index dispersion curves, and the decreasing of glass transition temperature. The formation of [SnS4-xClx] structural units, instead of [GeS4-xClx], should be responsible for the variation of these structural properties. In addition, homogeneous Sn modified GeS2-Ga2S3-CsCl chalcogenide glass of Φ30 mm was also prepared successfully, showing it of high potential for commercial applications.

Influence of Cu‐Doping on Linear and Nonlinear Optical Properties of High‐Quality ZnO Thin Films Obtained by Spin‐Coating Technique

To study the effect of Cu concentration on morphological, structural, linear and nonlinear optical properties, copper‐doped ZnO thin films are grown by sol–gel/spin‐coating technique on the glass substrates. Scanning electron microscopy (SEM) images reveal that the surface morphology is homogeneous with good adhesion to the glass substrate. The energy dispersive X‐ray spectroscopy (EDS) spectra confirm that Zn, O, and Cu elements are present in ZnO films. The X‐ray diffraction (XRD) pattern of Cu‐doped ZnO is dominated by (002) peak, indicating an upstanding ZnO nanorods array growing along the c‐axis. The optical bandgap of Cu‐doped ZnO thin films, calculated from optical transmission spectra, is found to decrease with the increase in copper concentration. The refractive index dispersion curve of ZnO films is subjected to the single‐oscillator model. The optical dispersion parameters Eo, Ed, and n∞, the nonlinear refractive index, and nonlinear optical susceptibility are calculated and interpreted.

The influence of oxygen deficiency on the dispersion parameters of TiO2 films

TiO2 thin films were deposited on quartz substrate by RF-magnetron sputtering technique. The effect of varying oxygen fraction [Formula: see text] on the surface morphology, structure, electrical and optical properties was investigated. Decreasing the oxygen fraction promotes phase transformation to the extent of isolating anatase phase with well oriented A(101) preferred crystal orientation at [Formula: see text] of 0.1%. The refractive index dispersion curves were utilized to estimate the single oscillator parameters. In addition, an enhancement in the electrical conductivity to [Formula: see text] at [Formula: see text]% was established. This enhancement was attributed to the deficiency of oxygen as well as the formation of anatase phase.

Influence of high gamma radiation on the optical and photoluminescence characteristics of ZnO thin films

In this study, the researchers attempt to investigate the effect of irradiation of gamma doses in the range 25–150 kGy on the optical properties of sputtered ZnO thin films. The samples have a hexagonal wurtzite structure. The optical properties of the samples, such as the absorbance, transmittance, and reflectance, have been studied as a function of γ- irradiation doses. Several optical parameters, such as refractive index, optical energy gap, Urbach energy, oscillatory energy, dispersion energy, oscillator strength, and dielectric constant have been found to be affected by changing the γ- irradiation doses. The refractive index dispersion curve of the γ-irradiated and non-irradiated ZnO thin films meet the criteria of the single-oscillator model. The room temperature photoluminescence spectra of the samples under excitation 400 and 437 nm showed green emission nearly at 2.597 and 2.559 eV, and yellow emission approximately at 2.15 eV. The green emission bands can be attributed to a transition from CB to VZn −2 and −1 respectively, while the yellow emission band can be attributed to a transition between a shallow donor and a deep level.

Корреляция между параметрами дисперсионных зависимостей показателей преломления и координационными числами катионов для кристаллов семейства лангасита

For optical crystals of the langasite family La3Ga5SiO14 (structural type Ca3Ga2Ge4O14, space group P321), a correlation was found between the parameters of the dispersion curves of refractive indices and the coordination numbers of cations in their structures.

Uniform Alignment of Non-π-Conjugated Species Enhances Deep Ultraviolet Optical Nonlinearity.

The precision of array of laser applications and manipulation on smaller scales are limited by the so-called 200 nm wall, and breakthroughs rely on the discovery of new materials with transparency and phase matchability in the ultraviolet and deep ultraviolet region. Herein, we discover an unprecedented alignment of the asymmetric non-π-conjugated species [PO3F] in NaNH4PO3F·H2O, which allows the best uniform P-F bond orientation that generates a remarkable enhancement of the (010) in-plane anisotropy that yields the largest birefringence (obv.: 0.053) to date in the phosphate and fluorophosphate families. The substance produces second harmonic generation lasers through direct frequency doubling with incident Yb:KGW femtosecond lasers on an as-synthesized (010) wafer with a size of 14 × 10 × 2.1 mm3. According to the calculated refractive index dispersion curve, the shortest second-harmonic generation (SHG) wavelength is estimated to be 194 nm, the shortest among phosphates and monofluorophosphate. These insights may help to design other high-performance non-π-conjugated deep-UV nonlinear optical materials.

3,3'-thiodipropanol as a versatile refractive index-matching mounting medium for fluorescence microscopy.

High resolution fluorescence microscopy requires optimization of the protocols for biological sample preparation. The optical and chemical characteristics of mounting media are among the things that could be modified to achieve optimal image formation. In our search for chemical substances that could perform as mounting media, 3,3'-thiodipropanol (TDP) emerged as a sulfide with potentially interesting characteristics. In this work, several tests of its performance as a mounting medium for fluorescence microscopy of biological samples were performed, including the labeling of filamentous actin with fluorescent phalloidins. The refractive index dispersion curve of pH-adjusted TDP was experimentally obtained in the visible range and compared to the dispersion curves of commercial and lab-made mounting media. The effects on the fluorescence of commonly used dyes were tested by using TDP as a solvent and measuring the relative fluorescence quantum yield of the dyes. By being able to mix TDP in any concentration with water and 2,2'-thiodiethanol (TDE), it was possible not only to fine-tune the refractive index of the resulting solution, but also to preserve the compatibility of TDP with the most popular and efficient fluorescent actin staining used in biological microscopy.

Multispectral surface plasmon resonance approach for ultra-thin silver layer characterization: Application to top-emitting OLED cathode

While dielectric/metal/dielectric (DMD) multilayer thin films have raised considerable interest as transparent and conductive electrodes in various optoelectronic devices, the knowledge of optical characteristics of thin metallic layers integrated in such structures is still rather approximate. The multispectral surface plasmon resonance characterization approach described in this work precisely aims at providing a rigorous methodology able to accurately determine the optical constants of ultra-thin metallic films. As a practical example, the refractive index and extinction dispersion curves of 8 to 25 nm-thick silver layers have been investigated. As a result, their extreme dependence on the layer thickness is highlighted, in particular in a thickness range close to the critical threshold value (∼10 nm) where the silver film becomes continuous and its electrical conductance/optical transmittance ratio particularly interesting. To check the validity of the revisited Ag layers constant dispersion curves deduced from this study, they were introduced into a commercial optical model software to simulate the behavior of various optoelectronic building blocks from the simplest ones (DMD electrodes) to much more complex structures [full organic light emitting device (OLED) stacks]. As a result, a much better prediction of the emission spectrum profile as well as the angular emission pattern of top-emitting OLEDs is obtained. On this basis, it is also shown how a redesign of the top encapsulation thin film of OLEDs is necessary to better take benefit from the advanced DMD electrode. These results should particularly interest the micro-OLED display field where bright and directive single color pixel emission is required.

Structural, Optical, and Electrical Characterization of β‐Ga2O3 Thin Films Grown by Plasma‐Assisted Molecular Beam Epitaxy Suitable for UV Sensing

β‐Ga2O3 thin films were grown on c‐plane sapphire substrates by plasma‐assisted molecular beam epitaxy. The films were grown using an elemental gallium source and oxygen supplied by an RF plasma source. Reflection high‐energy electron diffraction (RHEED) was used to monitor the surface quality in real time. Both in situ RHEED and ex situ X‐ray diffraction confirmed the formation of single crystal β‐phase films with excellent crystallinity on c‐plane sapphire. Spectroscopic ellipsometry was used to determine the film thicknesses, giving values in the 11.6–18.8 nm range and the refractive index dispersion curves. UV‐Vis transmittance measurements revealed that strong absorption of β‐Ga2O3 starts at ∼270 nm. Top metal contacts were deposited by thermal evaporation for I‐V characterization, which has been carried out in dark, as well as under visible and UV light illumination. The optical and electrical measurements showed that the grown thin films of β‐Ga2O3 are excellent candidates for deep‐ultraviolet detection and sensing.

Structure and optoelectrical properties of transparent conductive MGZO films deposited by magnetron sputtering

The transparent conductive Mg-Ga co-doped ZnO (MGZO) films were prepared by radio-frequency (RF) magnetron sputtering. The influence of substrate temperature on the structural and optoelectrical properties of the films is studied. The results show that all the films possess a preferential orientation along the (002) plane. With the increase of substrate temperature, the structure and optoelectrical properties of the films can be changed. When substrate temperature is 300 °C, the deposited film exhibits the best crystalline quality and optoelectrical properties, with the minimum micro strain of 1.09×10-3, the highest average visible transmittance of 82.42%, the lowest resistivity of 1.62×10-3 Ω·cm and the highest figure of merit of 3.18×103 Ω-1·cm-1. The optical bandgaps of the films are observed to be in the range of 3.342—3.545 eV. The refractive index dispersion curves obey the Sellmeier’s dispersion model.

Synthesis, Optical and Photoluminescence Properties of Cu-Doped Zno Nano-Fibers Thin Films: Nonlinear Optics

Different concentrations of copper-doped zinc oxide thin films were coated on a glass substrate by sol–gel/spin-coating technique. The structural properties of pure and Cu-doped ZnO films were characterized by different techniques, i.e., atomic force microscopy (AFM), photoluminescence and UV–Vis-NIR spectroscopy. The AFM study revealed that pure and doped ZnO films are formed as nano-fibers with a granular structure. The photoluminescence spectra of these films showed a strong ultraviolet emission peak centered at 392 nm and a strong blue emission peak cantered at 450 nm. The optical band gap of the pure and copper-doped ZnO thin films calculated from optical transmission spectra (3.29–3.23 eV) were found to be increasing with increasing copper doping concentration. The refractive index dispersion curve of pure and Cu-doped ZnO film obeyed the single-oscillator model. The optical dispersion parameters such as E o , E d , and $$n_{{\infty }}^{2}$$ were calculated. Further, the nonlinear refractive index and nonlinear optical susceptibility were also calculated and interpreted.

Optical properties of gelatin/TGS composites

Films of pure Gelatin and five Gelatin samples doped with the ferroelectric material triglycine sulphate (TGS) at various concentrations of 2, 4, 6, 8 and 10 wt. %TGS by weight have been prepared using the solvent-casting technique.Ultraviolet-visible (UV-vis) absorption spectra were measured in the range 190-900nm. The UV-Visible spectra show some shift in the absorption edge indicating change in optical band gap energy. The optical transitions were found mainly to be indirect allowed transitions and the optical band gaps (Eopt) were determined. Measuring the absorbance, transmittance and reflectance of Gelatin, TGS and their composites permitted the calculation of the refractive index (n). The refractive index dispersion curve of composite films obeys the single-effective oscillator model (Wemple-DiDomenico model).

Optical and structural properties of amorphous silicon-nitrides and silicon-oxycarbides: Application of multilayer structures for the coupling of Bloch Surface Waves

Hydrogenated amorphous silicon nitrides (a-SiNx:H) and oxycarbides (a-SiOxCy:H) have been grown by means of plasma enhanced chemical vapor deposition (PECVD) at a low power density (40–60mW/cm2) using silane, ammonia, methane and carbon dioxide as silicon, nitrogen, carbon and oxygen precursors, respectively. Their refractive index dispersion curves have been analyzed by means of specular reflectance spectroscopy and their structural properties by FTIR spectroscopy. Taking advantage of their optical properties, the alloys have been fruitfully applied in dielectric stratified structures, optimized for the propagation of surface electromagnetic waves.

Effect of growth interruptions on TiO2 films deposited by plasma enhanced chemical vapour deposition

TiO2 films of ∼300 nm were deposited at low temperature (<140 °C) and pressure (0.4 Pa) using plasma enhanced chemical vapour deposition at the floating potential (Vf) or the substrate self-bias voltage (Vb) of −50 V. The impact of growth interruptions on the morphology, microstructure and optical properties of the films was investigated. The interruptions were carried out by stopping the plasma generation and gas injection once the increase of the layer thickness during each deposition step was about ∼100 nm. In one case of Vf, the films of ∼300 nm exhibit a columnar morphology consisting of a bottom dense layer, an intermediate gradient layer and a top roughness layer. But the growth interruptions result in an increase of the dense layer thickness and a decrease of surface roughness. The film inhomogeneity has been identified by the in-situ real-time evolution of the kinetic ellipsometry (KE) parameters and the modeling process of spectroscopic ellipsometry (SE). The discrepancy of the refractive index measured by SE between bottom and upper layers can be reduced by growth interruptions. In the other case of Vb = −50 V, the films exhibit a more compact arrangement which is homogeneous along the growth direction as confirmed by KE and SE. Both of Fourier transform infrared spectra and X-ray diffraction illustrate a phase transformation from anatase to rutile with the bias of −50 V, and also evidenced on the evolution of the refractive index dispersion curves. And a greatly increase of the refractive indice in the transparent range can be identified. However, the growth interruptions seem to have no influence on the morphology and optical properties in this case.

The Formation of Fringes of Equal Chromatic Order across Double Clad Fiber in the Presence of High Power Lasers

Multiple-beam fringes of equal chromatic order interferometry is a powerful technique to extract optical properties over a continuous range of spectrum. In this paper we develop a theory for the spectral shape of the fringes of equal chromatic order (FECO) that are formed across a double-clad fiber. The modified single term Sellmeier dispersion formula is used to construct the refractive index dispersion curves for the liquid, claddings, and core. Expressions for the paraxial optical path length for several rays passing through the fiber and the liquid are developed. The condition of bright fringe is applied to get an analytical expression for the spectral shape of the FECO across a double-clad fiber with an elliptical/circular inner cladding. A potential application of this theory is to determine the dispersion of Kerr constant of the claddings and the core of the fiber. To illustrate the theory and its application, simulation examples are provided and discussed.

Optical, Structural and Morphological Properties of Photocatalytic ZnO Thin Films Deposited by Pray Pyrolysis Technique

Photocatalytic ZnO thin films have been deposited onto glass substrate by spray pyrolysis technique. The sprayed solution consists of 0.1 M of zinc acetate dihydrate dissolved in double distilled water and sprays onto ultrasonically cleaned glass substrates maintained at 350°C, through an air-atomizing nozzle. The X-ray diffraction (XRD), scanning electron microscopy (SEM), EDX and UV-VIS spectrophotometer were applied to describe the structural, morphological, compositional and optical properties of ZnO catalyst. XRD analysis confirms that the films were found to be single phase hexagonal wurtzite structure. The SEM micrograph of the films is shown highly uniform, crack free and found to be fiber like structures. The optical transmittance spectra of the ZnO thin films were found to be transparent to visible light and the average optical transmittance was greater than 85%. The direct optical band gap energy values of the films shift towards the lower energy as a consequence of the thermal annealing. The Urbach energy of the films was found to increase with annealing temperature. The refractive index of the films was calculated and the refractive index dispersion curve of the films obeys the single oscillator model. The values of oscillatory energy Eo, dispersion energy Ed, and static dielectric constant es for the ZnO thin films were determined. The films were evaluated for their ability to degrade methylene blue. The Langmuir-Hinshelwood kinetic model was used to interpret quantitatively the observed kinetic experimental result. The photocatalytic activity of ZnO thin films was enhanced by annealing temperature.