Optical Properties Of Samples Research Articles

Nanostructured Anatase Titania Thin Films Prepared by Sol-Gel Dip Coating Technique

Anatase titania thin films were deposited on glass substrates. The substrates were dipped matched dipped into the solution under vigorous stirring. The films were dried at room temperature. Oley amine (OM) was used as a surfactant in the synthesis part and it was vigorously stirred with titanium isopropoxide (TIP) at room temperature. The film samples were annealed at 550\(^\circ\)C for 15 hours. X-ray diffraction (XRD) and Raman spectroscopy were used to study the structural properties of samples. The optical properties of samples were investigated by means of ultraviolet visible (UV vis) spectroscopy. XRD results illustrated the amorphous structure and pure anatase phase of TiO\(_2\) for as deposited and annealed thin films samples and these results were further confirmed by Raman spectroscopy. UV-visible corroborates the energy band 3.26 eV and 3.22 eV for as prepared and sintered TiO\(_2\) thin films which simply refers to the change in crystal structure of anatase titania. Furthermore, both samples had high transmittance; almost 78-86%.

Effect of ytterbium substitution on LaEr(1−x)YbxO3 optical properties

A series of LaEr(1−x)YbxO3 (x=0, 0.01 and 0.05) samples were prepared with a combustion method and characterized by FTIR, Raman spectroscopy and X-ray diffraction. The optical properties of samples were studied upon laser excitations. The upconversion emission spectra registered under excitation at 980nm show the presence of the typical erbium emission bands and that the higher intensity is given by sample with 5% of ytterbium concentration. The variation of upconversion intensity as a function of laser power of the LaEr0.95Yb0.05O3 sample reveals that two photons are implicated in the upconversion mechanism and that the lifetime of the 4S3/2→4I15/2 and 4F9/2→4I15/2 emissions of this sample is estimated to 12.3 and 97.7µs, respectively. The calculated CIE chromaticity coordinates of the phosphor samples show that the green emission is dominant, and that its intensity increases by substituting erbium with 1% or 5% of ytterbium. The effect of ytterbium concentration on optical band gap shows that the gap energy value tends to decrease from 4.25eV to 4.14eV for 0% and 5% of ytterbium concentration, respectively. The increase in intensity of green emission by adding ytterbium to LaErO3 classifies these oxides as phosphor materials that could have applications in bioimaging of cells.

Synthesis, Characterization and Optical Properties of Cd<sub>x</sub>Zn<sub>1-x</sub>S Nanocrystals

Nanocrystalline Cd1-XZnXS (X=0.0, 0.2, 0.4, 0.5, 0.6, 0.8 and 1.0) were synthesized by simple wet chemical method via co-precipitation. The formation, phase purity and crystalline size were ascertained by X-ray diffraction (XRD). The shape and surface morphology of the synthesized samples were characterized by scanning electron microscopy (SEM). The optical properties of the Cd1-XZnXS samples were investigated using UV-vis absorption spectroscopy and photoluminescence spectroscopy (PL) studies. The optical properties of the sample was dramatically changed by varying the composition of Cd1-XZnXS system, which may be due to the synergic effect originated by combining CdS and ZnS. The obtained optical behaviors suggest that the material can be suitable for the photocatalytic degradation of organic pollutants. The prsent investigation demontrated that the synthetic approach developed in this is highly reproducible and can be readily scaled up for potential industrial production.

Effect of High Density Polyethylene (HDPE) on Structural and Optical Properties of (PP/PMMA) Blends

In the present work, Polypropylene (PP) was blended with poly methyl methacrylate (PMMA) to form (PP/PMMA) polymer blends. High Density Polyethylene (HDPE) was mixed into these blends at different weight fractions (2,4,6,8) % wt to form (PP/PMMA/HDPE) blends were prepared using an one screw extruder. results obtained from Scanning Electron Microscopy (SEM) revealed that there was a reduction in surface roughness any decrease in clusters, drilling and bends, as for Fourier Transform Infrared (FT-IR) spectrometry showed no change in the wave numbers of the functional groups. The optical properties of samples are investigated by measuring optical absorption spectra in the wavelength range from 260 to 1100 nm. this results show that Eg of the blends increases with increasing high density polyethylene contents, the indirect optical band gaps for (PP/PMMA) and (PP/PMMA/HDPE) blends were estimated to be about 2.83,2.9,2.95,3and 3.1 eV for indirect allowed transitions, whereas the indirect forbidden band gaps were determined as 2,2.1,2.15,2.2 and 2.3 eV with increase high density Polyethylene contents, respectively. The absorbance, absorption coefficient, extinction coefficient and the imaginary dielectric constant of (PP/PMMA/HDPE) decreases with increasing of HDPE percentages except the transmittance, refraction index and real part of the dielectric constant increase with increasing of high density polyethylene.

Solid hemoglobin-polymer phantoms for evaluation of biophotonic systems.

Stable tissue phantoms that incorporate the spectral absorption properties of hemoglobin would benefit a wide range of biophotonic technologies. Toward this end, we have developed and validated a novel polymer material incorporating hemoglobin. Our solid hemoglobin-polymer (SHP) material is fabricated by mixing liquid silicone base with a hemoglobin solution, followed by sonication and low temperature curing. The optical properties of samples were determined over 450-1000 nm using the inverse adding-doubling method and the Beer-Lambert law. Measurements indicated SHP optical stability over four months. Near-infrared spectroscopy and hyperspectral imaging measurements of SHP samples were performed to demonstrate the utility of this approach. SHP materials have the potential to improve tissue-simulating phantoms used for development, evaluation, and standardization of optical devices for oximetry and other applications.

Sandwich-like mesoporous silica flakes for anticancer drug transport—Synthesis, characterization and kinetics release study

In this paper, we present the technology of synthesis, characterization and release kinetics of anticancer drug molecules from sandwich-like mesoporous silica nanoflakes. Mesoporous silica nanoflakes are a very attractive material due to their versatility, low cytotoxicity, large surface area, high pore volume and unique feature of containing parallel pores openon both sides. Nanosilica flakes were prepared through the formation of a mesoporous silica layer on a graphene oxide surface. After graphene oxide removal, the silica nanostructures were filled by an anticancer drug—methotrexate. Release kinetics studies were performed in different temperatures, imitating the conditions in living organisms. Release data was analyzed using the zero-order model, first-order model, Higuchi model and Korsmeyer-Peppas model. The optical properties of samples, and the kinetics of drug release from the nanostructure, were examined by UV–vis spectrophotometer. Data obtained from long term studies showed that the system can serve as an anticancer drug carrier system, since a significant amount of methotrexate was loaded to the material and released. The mechanism of MTX release from mesoporous silica nanoflakes appeared to be a parallel processes of diffusion through water-filled mesopores and degradation of the mSiO2 matrix. Physical and chemical characterization was undertaken by transmission electron microscopy (TEM) and X-ray dispersion spectroscopy (EDX). The specific surface area of the samples was measured through the adsorption of N2 isotherm, interpreted with the Brunauer–Emmett–Teller model (BET). TGA and UV–vis analyses were conducted in order to estimate the amount of the released drug.

Effect of High Density Polyethylene (HDPE) on Structural and Optical Properties of (PP/PMMA) Blends

In the present work, Polypropylene (PP) was blended with poly methyl methacrylate (PMMA) to form (PP/PMMA) polymer blends. High Density Polyethylene (HDPE) was mixed into these blends at different weight fractions (2,4,6,8) % wt to form (PP/PMMA/HDPE) blends were prepared using an one screw extruder. results obtained from Scanning Electron Microscopy (SEM) revealed that there was a reduction in surface roughness any decrease in clusters, drilling and bends, as for Fourier Transform Infrared (FT-IR) spectrometry showed no change in the wave numbers of the functional groups. The optical properties of samples are investigated by measuring optical absorption spectra in the wavelength range from 260 to 1100 nm. this results show that Eg of the blends increases with increasing high density polyethylene contents, the indirect optical band gaps for (PP/PMMA) and (PP/PMMA/HDPE) blends were estimated to be about 2.83,2.9,2.95,3and 3.1 eV for indirect allowed transitions, whereas the indirect forbidden band gaps were determined as 2,2.1,2.15,2.2 and 2.3 eV with increase high density Polyethylene contents, respectively. The absorbance, absorption coefficient, extinction coefficient and the imaginary dielectric constant of (PP/PMMA/HDPE) decreases with increasing of HDPE percentages except the transmittance, refraction index and real part of the dielectric constant increase with increasing of high density polyethylene.

Novel type of highly soluble and thermally stable poly(sulfone ether imide)s

A sulfone ether diamine was synthesized by three-step reactions. Firstly, 4-(4-nitrophenoxy) phenol was synthesized via nucleophilic substitution reaction of 1-fluoro-4-nitrobenzene with hydroquinone in the presence of K2CO3 in NMP. In the second step, 4-(4-nitrophenoxy) phenol was reduced to 4-(4-aminophenoxy) phenol by Pd/activated carbon catalyst in ethanolic hydrazine hydrate. Finally, 4-(4-aminophenoxy) phenol was reacted with 4,4′-dichlorodiphenyl sulfone (with 2:1 M ratio) to produce the sulfone ether diamine. Then three different kinds of poly(sulfone ether imide)s were prepared by solution polycondensation of synthesized diamine with commercially available aromatic dianhydrides including pyromellitic dianhydride, benzophenonetetracarboxylic dianhydride, and hexafluoroisopropylidene diphthalic anhydride. The structure of synthesized compounds, monomers, and prepared polymers was characterized using 1H NMR and FT-IR spectroscopy and also elemental analysis method. Thermal behavior and stability, solubility, solution viscosity, mechanical properties, crystallinity, water uptake, and optical properties of samples were studied.

Thermo optical properties of Ag nanoparticles produced by pulsed laser ablation

The linear and nonlinear optical properties of silver nanoparticles have been investigated experimentally. Colloidal nanoparticle samples were synthesized by laser ablation at various fluences. The samples were characterized by linear absorption spectroscopy, transmission electron microscopy and dynamic light scattering methods. The behavior of nonlinear refractive index of nanoparticles was studied using the close and open Z-scan techniques by low power CW laser beam. Observation of asymmetrical configurations of the Z-scan curve indicates that nonlinear refraction occurring in the Ag samples is related to the thermo optical process. In addition, the observed optical limiting behavior is due to nonlinear refraction of samples arising from thermal lens formation under low power CW excitation. The optimum position for samples as the optical limiter based on self-defocusing effect is the valley point. When the illumination laser power is low, the self-defocusing effect is mainly dominated. Actually laser fluence variation during the ablation procedure leads to concentration variation of nanoparticles in suspensions which in turn affect the optical properties of samples. The dependence of the nonlinear properties on morphological parameters, metal concentration, and particle size have been explained by experimental results.

Nanocrystalline TiO2 micropillar arrays grafted on conductive glass supports: microscopic and spectroscopic studies

Vertically oriented TiO2 micropillar arrays were obtained on Fluorine-doped Tin Oxide (FTO) conductive glasses by adopting a facile and cost-effective method. The process consists in the spray-coating with a polymer film containing an organo-metallic precursor (Ti isopropoxyde), followed by scratching the film surface by means of a sandpaper and an oxidative treatment. The role played by the scratching step in the formation of vertically oriented TiO2 micropillars, as well as the nanostructured scaffold nature consequent upon the oxidation, will be highlighted. The morphology, structure and optical properties of samples, were investigated by combining electron and atomic force microscopies with X-ray diffraction and UV–vis spectroscopy. Due to the robust texture of highly crystalline and cemented anatase and rutile nanoparticles and to the porous nature of TiO2 pillars covering FTO glasses, this system may find application in energy, photochemistry and photodegradation fields.

Effect of light beam on measurements of reflectance and transmittance of turbid media with integrating sphere: Monte Carlo simulation

Integrating sphere technique is widely used to measure the total reflectance and transmittance of turbid sample, but the unavoidable light loss induces some measuring error. It has never been reported whether the error depends on the shape and size of light beam. In this paper, a convolution for computing the responses to rectangular incident light beam based on the Monte Carlo method was presented. The effects of light beam shape and size, and optical properties of sample on the measurements were addressed. The results show that the light loss with rectangular incident light beam is larger than that with circular one with the same area. The more the area of light beam, the more the light loss. And the light loss induced by the optical properties of sample is much more significant than that by the shape and size of the incident light beam.

Fabrication and characterization of electrospun PVA/CdS and PVA/TiO2 nanocomposite thin films as n-type semiconductors

Poly(vinyl alcohol) (PVA)/CdS and PVA/TiO2 nanocomposite thin films were prepared at different semiconductor nanoparticles ratio (20, 30, 40 and 50 CC) by employing electrospinning method. For the former, CdS nanoparticles were first synthesized using cadmium nitrate (Cd (NO3)2) and sodium sulfide (Na2S) in a simple and economical way whereas for the latter, TiO2 was purchased. Morphology and structure of nanocomposites were characterized by X-ray diffraction (XRD) and scanning electron microscope. The results indicated the cubic and anatase structure of CdS and TiO2 nanoparticles in PVA matrix, respectively, and proved that nanoparticles were successfully coated by PVA molecules. Optical properties of samples were also characterized by diffuse reflectance spectroscopy. Particle sizes of CdS and TiO2, <9 and 15 nm, respectively, were calculated with the results obtained from XRD observation and it was found to be in agreement with the absorption spectra of both nanocomposites. The prepared films at 50:50 ratio, in both PVA/CdS and PVA/TiO2, were found to be suitable for application in solar cell as a window layer due to the crystalline phase, favorable band gap (2.53, 3.31 eV) and higher optical transmittance.

The influence of heat treatment on the crystallite size, dislocation density, stacking faults probability and optical band gap of nanostructured cadmium sulfide films

Nanocrystalline cadmium sulfide films were deposited on the ordinary glass slide substrates by chemical bath deposition. Two advanced X-ray diffraction analyses i.e. DIFFaX and eCMWP were applied and the microstructure of films was evaluated as a function of annealing temperature. The optical properties of samples were also studied, using the transmittance spectra in the wavelength range of 300–900nm. Based on our studies, we have found that with the elevation of annealing temperature, the crystallite size increases, however, the dislocation density, the fraction of stacking faults and the band gap energy decrease and the outer cut-off radius of dislocation does not appreciably change. We can also see that the energy gap follows the linear, inverse square and quadratic relation with uniform strain, crystallite size and dislocation density, respectively. Comparing the microstructure evaluated from eCMWP with the results of Scherrer formula and Williamson–Hall plot shows that there is no agreement between the results of advanced and early X-ray diffraction analysis.

Performance Improvement of Bulk Heterojunction Polymer Solar Cells with Metal Oxide Nanoparticles

We fabricated polymer solar cells with two different bulk heterojunction (BHJ), thieno(3,4-b)-thiophene/benzodithiophene copolymer:(6,6) phenylC71butyric acid methyl ester (PTB7:PC71BM), and poly (3-hexyl- thiophene):[6,6]-phenylC71 butyric acid methyl ester (P3HT:PC71BM). For the two polymer solar cell (PSC) devices, the titanium suboxide (TiOx) layer was inserted between the (BHJ) and metal electrode. The performance enhancement of the devices with / without TiOx layer was reported. X-ray diffraction (XRD) and UV-Vis measurements were used to investigate the structural and optical properties of samples. The current density–voltage (J-V) curves of the polymer solar cells were measured. We found that the TiOx layer improved the efficiency and stability of the devices compared with the same devices without TiOx layer. Also we observed that the PTB7/PC71BM/TiOx device was much stable compared with P3HT/PC71BM/TiOx device.

Performance Improvement of Bulk Heterojunction Polymer Solar Cells with Metal Oxide Nanoparticles

Polymer solar cells (PSC) based on bulk heterojunction (BHJ) materials containing conjugated polymers and fullerene derivatives have large advantages of easy fabrication, and also have considerable potential in renewable energy resources [1–3]. The polymer solar cell efficiencies and their lifetimes can be improved by using metal oxides such as titanium suboxide TiOx or zinc oxide [4]. In this study, we fabricated polymer solar cells with two different bulk heterojunction (BHJ), thieno(3,4-b)-thiophene/ benzodithiophene copolymer,(6,6)-phenyl C71 butyric acid methyl ester (PTB7/PC71BM), poly (3- hexylthiophene) and [6,6]-phenylC71butyric acid methyl ester (P3HT/PC71BM). For the two PSC devices the TiOx interlayer was inserted between the active layer (BHJ) and metal electrode. The performance enhancement of the devices with and without interlayer was investigated. X-ray diffraction (XRD) and UV-VIS measurements were used to investigate structural and optical properties of samples. The current–voltage (J-V) curves of the polymer solar cells with active area of ~ 10 mm2 were measured. We found that the TiOx layer improved the efficiency and stability of the devices compared with the same devices without TiOx interlayer. Also we observed that the PTB7/PC71BM/TiOx solar cell was much stable compared with P3HT/PC71BM/TiOx solar cell.

Packaging Technologies and Luminescence Properties of Ce:YAG Single Crystal for White Light-emitting Diode

The Ce:YAG single crystal for white light-emitting diode(WLED) application was grown by the Czochralski method. The thermal stability and optical properties of samples were characterized by absorption spectrum,photoluminescence spectra and temperature-dependent PL spectra. The photoelectric performance of WLEDs fabricated by the Ce:YAG single crystal were also measured. It is found that the Ce:YAG single crystal shows a broad emission band from 500 nm to 700 nm under blue light(wave length 466 nm). Absorption peaks,located at 202,219,247.3,347.4 and 455.5 nm,are due to 4f→5d transition,and the energy of 5d orbits is divided into 21954,29154,40437,45662 and 49505 cm-1. As the temperature increases,the PL intensity is reduced because of a higher energy of the 2F7/2,and the damping upon PL intensity by the Ce:YAG single crystal(13.28%) are much lower than that by commercially available phosphors(30%). When the current is at a standard state and the luminous flux of emission blue light is around 3.7 lm,the most suitable thickness for the Ce:YAG single crystal is 0.5 mm. Since the WLED fabricated by the Ce:YAG single crystal prepared in present work meets all requirements in related GB codes,and its performance is better in comparison with that of the commercially available one,the Ce:YAG single crystal will possibly be used to fabricate new-type WLED devices.

Correction of large birefringent effect of windows for in situ ellipsometry measurements

To extract true optical properties of samples in a chamber with entrance and exit optical windows, oftentimes the windows were approximated as simple retarders where the retardation was small and premeasured under a given condition. The proposed method allows to cope with large birefringent effect of chamber windows thanks to its capability of extracting ellipsometric parameters (Δ, Ψ) of isotropic samples as well as measuring birefringent parameters (δ, θ) of each window separately and simultaneously. This method is, however, not valid for anisotropic samples. Ex situ results and extracted ellipsometric parameters results from in situ measurements of a silicon substrate and a SiO2 film thermally grown on the silicon substrate exhibited excellent agreement and provided significance of this method.

Pyrolytic synthesis of densely packed grown CdSe nanoparticles using a dual function octylamine for hybrid solar cells

We report here a well crystallized wurtzite phased CdSe nanocrystals by utilizing only octylamine ligand without the use of standard surfactants (TOPO, Fatty acids, Long chain alkyalmines, ODE) by a pyrolytic synthesis at 270°C. The synthesized CdSe nanocrystals possess a diameter of ~6nm with a band gap of 1.85eV. Hybrid P3HT:CdSe heterojunction solar cells have been fabricated from the blends of the synthesized CdSe nanocrystals and poly (3-hexylthiophene) (P3HT) in a chloroform solvent which shows a maximum power conversion efficiency of 1.41%. However, standard CdSe quantum dot nanocrystals show a low conversion efficiency of 0.08% due to presence of a thick ligand shell. The enhanced efficiency can be attributed to the surface narrow size distribution (thin shell) and better optical properties; additionally it does not require post synthetic pyridine treatment. The details of morphological and optical properties of samples have been analyzed by TEM, XRD, UV–vis, PL, J–V and EQE techniques.

Strong tip–sample coupling in thermal radiation scanning tunneling microscopy

We analyze how a probing particle modifies the infrared electromagnetic near field of a sample. The particle, described by electric and magnetic polarizabilities, represents the tip of an apertureless scanning optical near-field microscope (SNOM). We show that the interaction with the sample can be accounted for by ascribing to the particle dressed polarizabilities that combine the effects of image dipoles with retardation. When calculated from these polarizabilities, the SNOM signal depends only on the fields without the perturbing tip. If the studied surface is not illuminated by an external source but heated instead, the signal is closely related to the projected electromagnetic local density of states (EM-LDOS). Our calculations provide the link between the measured far-field spectra and the sample's optical properties. We also analyze the case where the probing particle is hotter than the sample and evaluate the impact of the dressed polarizabilities on near-field radiative heat transfer. We show that such a heated probe above a surface performs a surface spectroscopy, in the sense that the spectrum of the heat current is closely related to the local electromagnetic density of states. The calculations agree well with available experimental data.

Pn-Junction photodiode based on GaN grown on Si (111) by plasma-assisted molecular beam epitaxy

The growth and characterization of pn-junction photodiode based on GaN grown on Si (111) by RF-plasma assisted molecular beam epitaxy (MBE) are described. The structural and optical properties of samples were studied by HR-XRD and Fourier FTIR spectroscopy, respectively. For IR reflectance analysis, GaN-like and AlN-like E2 TO optical modes have been detected. By using the thermal evaporator, Ni/Ag and Al contacts were evaporated at the front and back of samples. The application of thermal annealing treatment in oxygen ambient has been shown to significantly reduce the dark current of GaN pn-junction photodiode. The electrical characteristics of all samples were conducted using Keithley's I–V measurement system. Under 460-nm wavelength, at bias voltages of 0.5, 1, and 2V, the photocurrents rise and decay times were investigated.