فهرست مطالب حسن الله داغی

Herein, a facile, nontoxic, economic and fast green synthesis method was utilized to prepare carbon quantum dotes (CQDs). The CQDs were prepared via microwave-assisted hydrothermal method using Ferula assa-foetida. plant as carbon source. The effects of microwave power and irradiation time on optical and photoluminescence properties of CQDs were investigated. The CQDs prepared under optimum power and irradiation time (100 W, 10 min) have the average diameter of ~ 6 nm and emitted a bright blue light, when they were excited under a UV light with λex = 360 nm. The florescent quantum yield (QY) of the CQDs was 33 % which is higher than other CQDs prepared by bio-source carbons. FTIR and SEM-EDS mapping results confirmed the presence of nitrogen and sulfur elements in the CQDs structure. The CQDs were implemented into polyvinyl alcohol (PVA) matrix to prepare PVA-CQDs films. The prepared films also emitted an intense bule light with CIE index of (0.185, 0.121). The green-synthesized CQDs and PVA-CQDs film via a fast, facile and economic approach, have great potential to be used in various application fields.

In this paper, effect of gamma irradiation on structural and optical properties of CdTe/CdSe QDs were investigated for the first time. X-ray diffraction (XRD) results showed that synthesized QDs had cubic structure and gamma irradiation had no change in crystalline structure of CdTe/CdSe QDs. Also, Fourier-transform infrared spectroscopy (FT-IR) results confirmed that crystalline structure of CdTe/CdSe QDs had no change after gamma irradiation. The photoluminescence (PL) results showed that intensity of CdTe/CdSe QDs after gamma irradiation enhanced significantly. Shell thickness of CdSe and concentration of QDs were investigated as two important factor on optical properties of CdTe/CdSe QDs versus gamma irradiation. The results showed that less shell thickness and less concentration of sample make bigger changes in optical properties and band gap size of CdTe/CdSe QDs after gamma irradiation and with decreasing concentration of the QDs, the red-shift in PL peak was occurred stronger. Our obtained results showed that luminescence and absorption of CdTe/CdSe QDs have sensitivity versus gamma irradiation and CdTe/CdSe QDs are good candidate to use in dosimetry applications.

In this work, for the first time, effect of gamma irradiation on the optical properties of CdS (quantum dots) QDs in various concentrations was studied. The aqueous CdS QDs were synthesized in a facile and fast method by using domestic microwave oven.  Three concentration of QDs; 20, 2, 0.4 mg/cc after different administrated dose of gamma irradiation (0-20 kGy) were studied. The results showed increased sensitivity of QDs after gamma irradiation with decreasing of concentration, so that the PL emission was completely vanished for concentration of 0.4 mg/cc after 20 kGy dose of irradiation. The optical results showed QDs were grown under gamma irradiation. Therefore, desired dose measurement can be carried out by choosing appropriate concentration for  gamma dosimetry.

As to the crisis of energy in the recent years, devices manufacturing industry must be go toward the optimizing of energy consumption and increment in the lifetime leading to reduce production cost. Organic light emitting diodes (OLED) are one of the modern generations in the lighting industry that have many advantages such as being light and thin, flexibility, ability to be transparent, and easy to fabricate. These devices consist of hole injecting layer/electron and emissive layer. The main role of hole/electron injection layers is injection of charge carriers to emissive layer where electrons and holes recombinate and create photons. In this work we focused on optimization of hole injection in order to increase lifetime of device. We used the different composition of molybdenum oxide (MoOx) and graphene oxide (GO) in hole injection layer. The maximum efficiency of the devices owned to the composite thin film with 1:1 value ratio (MoOx:GO) that it could be reached to 7.5 lm/W.  The lifetime of the optimization of composite was compared to the standard device fabricated with PEDOT:PSS so that the results showed a 30 times enhancement in lifetime.

Lithium intercalation is a convenient method to prepare few-layer and single-layer MS2 (M=Mo, W) nanosheets. This method is, however, very time-consuming (few days) and it is difficult to control the reaction parameters. To overcome these drawbacks, we have proposed a method to use an Li battery set-up to significantly reduce the reaction time (few hours) and electrochemically intercalate lithium ions into MS2 layers in a controllable manner. Atomic force microscopy (AFM), scanning electron microscopy (SEM) and Raman spectroscopy results revealed that MoS2 and WS2 single-layer (thickness of ~ 1 nm) nanosheets with the 1T phase were prepared after intercalation in an Li battery set-up. Lateral dimensions of MoS2 and WS2 nanosheets were determined to be at about ~ 170 ± 15 and 200 ± 30 nm, respectively. The concentrations of the final solutions containing MoS2 and WS2 nanosheets were measured to be 0.012 and 0.008 mg/mL, respectively. Successful fabrication of the single-layer MS2 nanosheets using the Li battery set-up could provide an excellent opportunity to investigate the unique properties of these two-dimensional crystals for various important applications such as catalysis, solar cells, optoelectronic, etc.

In this report a facile and optimized method for polishing of fluorine doped tin oxide (FTO) was presented in which nanoparticles in toothpaste was used as polishing material. Due to being more chemically and physically stability relative to another TCO such as indium tin oxide (ITO), FTO is used in optoelectronic devices. More thickness in FTO due to have a good conductivity resulting a rough surface. Toothpaste can make smooth FTO surface due to have polisher nanoparticles. Here, FTO surface was smooth using toothpaste so that according to AFM data, the RMS surface roughness was changed from 12 nm for FTO to 3 nm for FTO after polishing. The comparing of the transmittance spectra FTO before and after polishing process showed the FTO thickness was not changed dramatically. The X-Ray photoelectron spectroscopy showed there were no effects on the chemical states of FTO surface before and after polishing process. The hybrid light emitting diode was fabricated using polished FTO that it was more efficient comparing to those fabricated with FTO and ITO.