Search

By employing the sol-gel process and “Mo-doped strontium cobaltite,” such as SrCo0.9 Mo0.1O3−δ (SCM), which has a lot of oxygen vacancies creating a charge storage material. However, a simple hydrothermal approach was used to make a cell SCM@GQDs and “Graphene Quantum Dots (GQDs).” The produced SCM@GQDs with increased conductivity have been found to be a promising electrode material for achieving larger energy densities. Through the use of the galvanostatic charge-discharge method for three electrode cells with 6.0 M potassium hydroxide as the electrolyte, the electro-chemical performance of the SCM@GQDs was examined. Due to enhanced conductivity and quicker ion diffusion between working electrodes and electrolyte, the produced electrode material for super-capacitor has a specific capacitance that is higher than GQDs at 0.65 A g−1. These outcomes demonstrate an excellent properties of SCM@GQDs material in the energy storage applications in the specific area of supercapacitors.

Bilirubin, is a tetrapyrrole yellow coloured compound found in digestive juice. It is generated from degradation of hemoglobin (Hb). The normal range of total bilirubin in serum is 0.30–1.20 mg/dl. The elevated range of serum bilirubin is considered as biomarker for finding and therapeutic administration of many liver diseases. Various analytical methods for determination of bilirubin, including spectrophotometery, thin layer chromatography, fluorometry, capillary electrophoresis, high performance liquid chromatographic, polarography and chemiluminescence have been applied for clinical purposes. These conventional methods are tedious, time-consuming, and require costly equipments and skilled person to operate. To overcome these limitations, the most popular biosensing technology has been employed at a large scale. The present review describes the principle, advantages and disadvantages of different analytic methods for measurement of bilirubin with focusing on biosensors, including electrochemical, photo-electrochemical, piezoelectric, optical and luminescent biosensors in detail. The working conditions for optimum activity and shelf life of all bilirubin biosensors have been summarized & compared and their future perspectives are discussed.

A comprehensive study of an efficient pseudocapacitor electrode material has been done for sulfur doped graphene quantum dots (S-GQDs). Two different electrode materials were prepared by selecting ...

A high- power ultrasonic method was used to prepare bilirubin oxidase nanoparticles (BOxNPs) which were immobilized on polyethylene (PE) film. The characterization of PE film bound to BOxNPs and BOxNPs was carried out using "Dynamic Light Scattering (DLS)," "Transmission Electron Microscopy (TEM)," and "Scanning Electron Microscopy (SEM)." The PE film was treated with nitric acid (HNO3) for its activation. BOxNPs bound to PE film exhibited optimal activity (pH-8), incubation time (11 s) with temperature 35 °C. A linear relationship was observed between the bilirubin concentrations (0.02-250 μM), with an apparent Km value and Vmax for PE- bound BOxNPs, at 0.015 μM and 2.56 μmol/mL/min. The mean recoveries of added serum bilirubin were 94.5 % at a level of 5 mM whereas 98.5 % were observed at 10 mM which showed the satisfactory reliability of BOxNPs immobilized on PE film. The coefficient of variation for serum bilirubin ranged between 4.52%-5.25%, measured on the first day (within batch) and after seven days of storage (between batch).This current method has showed a good correlation for bilirubin values when compared to the standard enzymatic colorimetric method using free enzyme. BOxNPs bound to PE film were reutilized 150 times with storage at 4 °C for 120 days.

This paper presents a comprehensive study of the impact of defects on quantum yield in doped graphene quantum dots by having sulfur containing compounds (S-GQDs). The facile and high yielding hydrothermal method was used to process the S-GQDs by selecting two different compounds such as conc. H2SO4 and MgSO4·7H2O containing sulfur. Initially, the synthesized samples were characterized by using High Resolution Transmission Electron Microscope (HRTEM), Raman Spectroscopy, Fourier Transform Infra-Red Spectroscopy (FT-IR), Thermogravimetric and Differential Thermal Analysis (TGA/DTA), UV–vis spectroscopy, and Photoluminescence (PL). HRTEM images suggest that the majority of the both samples were in the narrow range of 5–20 nm in diameter. Optical properties of the GQDs are altered as a result of S-doping with purple tunable PL at shorter wavelengths. As expected, by using the different excitation energy in PL, appearance of peak introduces additional energy levels between π and π* that provide alternative electron transition pathways. The most remarkable finding is that the fluorescence quantum yield (FL QY) of S-doped GQDs is higher than that of the reported doped GQDs. This clearly suggests that the defects states related to S modify the electron density, tailor the PL characteristics and improvements in quantum yield of the GQDs.

This work presents a comprehensive study of quantum yield in doped graphene quantum dots with a series of sulfur containing compounds ( S-GQDs). The facile hydrothermal method was used to synthesize S-GQDs at different temperatures (similar to 80 degrees C-140 degrees C) with ZnSO4.7H(2)O containing sulfur powder as a reducing agent. High Resolution Transmission Electron Microscope images suggest that the size of S-GQDs vary as a function of temperature during synthesis. Powdered X-Ray Diffraction confirms the crystallinity of all samples. Raman spectroscopy study reveals that the intensity ratio increases with an increase in temperature due to the presence of additional sulfur related defects that create enhanced elastic scattering. Removal of oxygen functional groups was maximized at 140 degrees C and reached to a ID/IG value of similar to 1.14. The photoluminescence measurements of doped GQDs having sulfur containing compounds at temperature of similar to 140 degrees C attributes to violet shift at lower excitation energy and a blueshift at higher excitation energy within the energy gap of S-GQDs due to the strong interaction of GQDs with high defect concentration of sulfur. The S-GQDs formed at similar to 140 degrees C demonstrated a superior fluorescence quantum yield of 51%. This is, therefore, expected to make S-GQDs more suitable for bioimaging and optoelectronic applications. (C) 2018 The Electrochemical Society.

Composites of transition metal oxides, with carbon, have been considered to be appropriate materials for enhancing their electrochemical properties in supercapacitor applications. In this study, we prepare Nickel-Cobaltite/ Graphene Quantum Dots (NiCo2O4/GQDs) composite structures that exhibit improved electrical conductivity and function as electrode materials with higher energy density in comparison to GQDs and NiCo2O4. The electrochemical performance of NiCo2O4/GQDs is confirmed through galvanostatic charge–discharge method for three electrode systems with an electrolyte of 0.1 M potassium hydroxide. The observed specific capacitance for the fabricated composite has been found to be 481.4 Fg−1 at 0.35Ag−1. It is higher than that of Graphene Quantum Dots (Csp~45.6 Fg−1). This is due to the enhancement in the electrical conductivity and diffusion of ions which become faster between electrodes and electrolyte. These findings demonstrate the unique characteristics of the fabricated composites as superior electrode materials for applications in supercapacitors.

Graphene quantum dots (GQDs) and CeO2-GQDs were synthesized by using a facile hydrothermal method at 140°C. All the synthesized materials were characterized by TEM, UV-Vis Spectroscopy, FT-IR, Rama...

Optical materials exhibiting a large third-order optical nonlinearity are in great demands because of their functional applications in optical limiting, optical switching, optical data storage etc. A well-known single Z-scan technique is employed to determine third-order nonlinear optical properties of nonlinear optical materials. Z-scan is a simple experimental technique to measure intensity dependent nonlinear susceptibilities of third-order nonlinear optical materials. It was originally introduced by Sheik Bahae et.al. In this technique, the sample is translated in the z-direction along the axis of a focused Gaussian beam, and the far field intensity is measured as function of sample position. Consequently, increases and decreases in the maximum intensity incident on the sample produce wavefront distortions created by nonlinear optical effects. This is a simple and sensitive single beam technique to measure the sign and magnitude of both real and imaginary part of the third order nonlinear susceptibility χ(3) of nonlinear optical materials.

The Graphene Quantum dots (GQDs), fragments of graphene have attracted considerable attention in recent years due to the size, edge effects, quantum confinement and heteroatom doping. The doping of graphene based materials can effectively tune their intrinsic properties, including electronic and optical properties, surface and local chemical reactivity. Herein, we present a comprehensive study of ZnO doped GQDs prepared by a facile hydrothermal method by using ZnO and Graphne Oxide (GO) as a source materials. All the synthesized materials were characterized by UV-Visible Spectroscopy (UV-Vis), Raman Spectroscopy, Fourier Transform Infrared (FT-IR) and Photoluminescence (PL). The morphological characterizations were confirmed by transmission electron microcopy images (TEM). The hydrothermally synthesized material had a size of 5-20 nm by uniform doping of zinc nanoparticles on graphene sheet. The results of PL of Zn(II)-GQDs showed a blue to purple emission with the variation in excitation wavelength from 280nm to 380nm. These doped GQDs were found to be an efficient approach with multicolor emission for biological applications and optoelectronic devices to make the environmental friendly, cost effective and easily scalable.

The current effort discuss the fabrication of improve electrode materials for supercapacitor comprise of surfactant doped polypyrrole‑carbon materials composites integrated with graphene, amine functionalized multiwalled carbon nanotubes and hybrid carbon assembly. The spectroscopic characterizations demonstrate the establishment of a well-built state of charge swap complex among surfactant doped polypyrrole and carbon materials that disclose the occurrence of polymer‑carbon phases and promote well-built polarization. The electrodes are assembled in the three electrode cell configuration with graphite sheet current collector. The composite SDBSDPPy-HC holds a specific capacitance of 1086 F g−1 at scan rate 5 mV s−1 in 6 M KOH electrolyte solution. SDBSDPPy-HC exhibit only 10% losses in specific capacitance over 2500 cycles i.e. 90% preservation of specific capacitance at a current density 1 A g−1.

An efficient electrode material (Fe (II)S-GQDs) has been prepared by co-doping of sulfur and iron atoms with Graphene quantum dots. A top down synthesis method including a facile and one-pot hydrothermal was used to develop high capacity and good stability electrode material by selecting ferrous sulphate powder (FeSO4.7H2O) and graphene oxide (GO) as a precursor material. The results obtained from TEM measurements reveal the size alters from micrometer graphene sheets of GO to nano-meter dots for GQDs and Fe (II)S-GQDs. The electrochemical studies reveal that Fe(II) S doped GQDs can exhibit a reversible redox reaction with excellent specific capacitance of 476.2 F/g as compared to that of GQDs (143F/g). It has been found that there is an improvement in electrical conductivity and electron transfer in addition to the largest charge storage capacity. More remarkably, the doped electrode material shows a small charge transfer resistance (Rct) value (30 Ω) in case of Fe(II)S-GQDs as compared to GQDs (2.5 kΩ) due to fast diffusion of ion and electron between working electrodes and electrolyte.

Copper diffusion from back contact creates semishallow and deep-level defects in n+-CdS/p-CdTe solar cells. This study analyzes the impact of copper as a function of annealing temperatures during back contact formation. The observed defect levels, formed after copper diffusion, were identified by employing the temperature-dependent capacitance–voltage (C-V) characteristics at reverse bias in the dark. Theoretical background involving recombination centers, defect density and the role of impurity defects (copper-related defects) suggests that the temperature-dependent C-V profiling is a suitable technique to investigate the copper-related defects. Samples, annealed at 160°C for 30 min, show only one energy level, whereas samples annealed at 280ºC for 30 min reveal two distinct deep levels. From the reported observations, the trap levels were identified as copper-related defects. Variation in annealing temperature can impact the defect formation process: substitutional impurities of copper (160°C) and deep levels (280°C).

For CdTe there is no real distinction between defects and impurities exists when non-shallow dopants are used. These dopants act as beneficial impurities or detrimental carrier trapping centers. Unlike Si, the common assumption that the trap energy level Et is around the middle of the band-gap Ei, is not valid for thin film CdTe. Trap energy levels in CdTe band-gap can distributed with wide range of energy levels above EF. To identify the real role of traps and dopants that limit the solar cell efficiency, a series of samples were investigated in thin film n+-CdS/p-CdTe solar cell, made with evaporated Cu as a primary back contact. It is well known that process temperatures and defect distribution are highly related. This work investigates these shallow level impurities by using temperature dependent current-voltage (I-V-T) and temperature dependent capacitance-voltage (C-V-T) measurements. I-V-T and C-V-T measurements indicate that a large concentration of defects is located in the depletion region. It further suggests that while modest amounts of Cu enhance the cell performance by improving the back contact to CdTe, the high temperature (greater than ∼100°C) process condition degrade device quality and reduce the solar cell efficiency. This is possibly because of the well-established Cu diffusion from the back contact into CdTe. Hence, measurements were performed at lower temperatures (T = 150K to 350K). The observed traps are due to the thermal ionization of impurity centers located in the depletion region of p-CdTe/n+-CdS junction. For our n+-CdS/p-CdTe thin film solar cells, hole traps were observed that are verified by both the measurement techniques. These levels are identical to the observed trap levels by other characterization techniques.

CdTe solar cells with back contacts formed by either (i) 15nm Cu evaporation followed by application of carbon conductive paste embedded with micron sized Cu particles in ZnTe powder and (ii) only with the above mentioned conducting paste, were evaluated. A Cu-related deep level defect with an activation energy of Ea ∼ 0.57 eV was observed for Cu evaporated back contact cells and an intrinsic defect with an activation energy Ea ∼ 0.89 eV was found for cells prepared only by ZnTe:Cu embedded carbon paste. Frequency dispersion in C-V measurements confirms the presence of Cu-related deep level traps for cells with Cu evaporated back contact whereas no such defects were observed in carbon paste contact. The behavior was believed to be due to diffusion of excess Cu from the contact. It was further observed that majority carrier deep level traps (Cu-related or intrinsic) contribute differently to the degradation of electronic properties of the CdTe solar cells.

Current-voltage (J-V) and Capacitance-voltage (C-V) measurements of diode devices at different temperatures and illumination intensities are used to provide valuable information about non-idealities in the pn semiconductor junction and metal-semiconductor junction. In principle, continuous monitoring of this information can be used to improve diode and solar cell performance. In this paper we characterize the n+p CdTe on CdS solar cell. The activation energy derived from the temperature dependence of our solar cell J-V curves is consistent with trap assisted tunneling being the dominant carrier transport mechanism in the pn junction. Interpretation is complicated in the particular case of thin-film CdTe, by multiple non-shallow (not fully ionized) "doping" energy levels in the CdTe band gap are in reality, which are not distinct from "trap" energy levels. We use C-V profiling to further understand the concentrations of recombination centers as well as the interplay of the double acceptor Cd vacancy and the non- shallow acceptor Cu substitute of Cd.

This paper presents a comprehensive study of the impact of defects on quantum yield in Nitrogen doped graphene quantum dots (N-GQDs). The facile and high yielding hydrothermal method was used to process the N-GQDs by selecting two different nitrogen containing powders, that is, NH4Cl (sample-I) and (NH4)2SO4(sample-II). Initially, the synthesized samples were characterized by using High Resolution Transmission Electron Microscope (HRTEM), Powdered X-Ray Diffraction, Raman Spectroscopy, and UV-Visible spectroscopy, Fourier Transform Infrared Spectroscopy, and Photoluminescence (PL) for sample integrity. HRTEM images suggest that the majority of the both sample types were in the narrow range of 5–20 nm in diameter. The samples show blue photoluminescence and excitation dependent PL emission characteristics. As expected, by using the different excitation energy in PL, appearance of peak introduces additional energy levels between π and π* that provide alternative electron transition pathways. The most remarkable finding is that the fluorescence quantum yield is up to 28% for sample-I and is 49.8% for sample-II, which is higher than that of reported GQDs (less than 25%). This clearly suggests that the defect states related to Nitrogen, Chlorine, and Sulfur that alter the band gap of the GQDs determine the PL characteristics and the quantum yield.

Two sets of samples (CdTe solar cells) were investigated at −1V within a temperature range of 300K–393K. We discuss Shockley-Read-Hall recombination /generation (SRH R-G) as applied to CdTe and the assumptions used to yield trap energy levels in CdTe. Observed activation energies of the J-V characterization made with Cu-containing back contact in one sample shows one slope while in another sample shows two distinct slopes in Arrhenius plot of ln (J 0 T−2) vs. 1000/T. Using published identification of the physical trap with energy level, we conclude that one sample does not have hole traps while the other cell shows deep levels corresponding to substitutional impurities of Cu and positive interstitial Cu i 2+.

Temperature Dependent Capacitance Spectroscopy (TDCS) was used to identify carrier trapping defects in thin film n+-CdS/p-CdTe solar cells, made with evaporated Cu as a primary back contact. By investigating the reverse bias junction capacitance, TDCS allows to identify the energy levels of depletion layer defects. The trap energy levels and trap concentrations were derived from temperature-dependent capacitance spectra. Three distinct deep level traps were observed from the high-temperature (T > 300 K) TDCS due to the ionization of impurity centers located in the depletion region of n+-CdS/p-CdTe junction. The observed levels were also reported by other characterization techniques. TDCS seems to be a much simpler characterization technique for accurate evaluation of deep defects in n+-CdS/p-CdTe solar cells.

not Available.