Effect Of Different Doping Concentration Research Articles

Effect of different doping concentrations of X (X = O, Se, Te) on the electronic and optical properties of single layer WS2

In this paper, we study the effects of different doping concentrations of O, Se, and Te atoms on the electronic structure and optical properties of single layer WS2 based on the density generalization theory of the first principles. The most stable structure. The system doped with Te atoms shows a shift from direct to indirect band gap, and the band gap of the system doped with Se atoms increases slightly. When investigating the optical properties, we also found that the absorption of light in each doped system mostly occurs in the ultraviolet region, and the absorption of light in the system doped with O atoms decreases, while the absorption of light in the system doped with Se and Te atoms changes with different frequencies. The reflectivity is higher than the intrinsic state.

Effect of nitrogen and transition-metal co-doping on quantum capacitance enhancement of graphene as supercapacitor electrodes: A density functional theory study

Quantum capacitance plays a crucial role in determining the energy density of graphene-based supercapacitors. In this study, density functional theory calculations were conducted to investigate the enhancement of quantum capacitance and surface storage charge density through the co-doping of transition metals (TM) such as Mn, Fe, Co, Ni, Cu, Zn, Cr, V, Ti, and N atoms in graphene (TMN3-G). At a doping concentration of 2 at% (atomic percentage), all types of metal doped graphene exhibited an increase in quantum capacitance compared to pristine graphene. The highest increase was observed in CrN3-G, where the maximum quantum capacitance increased from 19.2 μF/cm2 for pristine graphene to 122.8 μF/cm2, due to the increased density of states around the Fermi level. The maximum surface storage charge density also increased from 6.4 μC/cm2 for pristine graphene to 44.4 μC/cm2 for CrN3-G. Moreover, the study investigated the effect of different doping concentrations on quantum capacitance performance by changing the doping concentration for VN3-G. It was found that the quantum capacitance for VN3-G increased with higher doping concentration, reaching up to 282 μF/cm2 when the doping concentration was increased to 12.5 at% from 2 at%. Based on our calculation results, ZnN3-G, NiN3-G, CrN3-G, and TiN3-G are suitable for the anode of supercapacitors, while CuN3-G and CoN3-G are suitable for the cathode. FeN3-G, MnN3-G, and VN3-G are suitable for both electrodes. These findings provide valuable insights for designing high-capacity graphene-based supercapacitors.

Study on the Degradation of Methylene Blue by Cu-Doped SnSe.

Treatment of organic wastewater is still a difficult problem to solve. In this paper, Cu-doped SnSe powder was synthesized by a convenient and efficient hydrothermal method. Meanwhile, the degradation effect of different doping concentrations of SnSe on methylene blue was investigated. It was found that at low doping concentrations, the degradation effect on methylene blue was not obvious because Cu was dissolved in the lattice of the SnSe matrix at low concentrations. As the doping concentration increased, SnSe changed from a layered structure to a nanocluster structure with reduced particle size, and a mixed phase of SnSe and Cu2SnSe4 appeared. In fact, the degradation effect on methylene blue was significantly enhanced, and we found that the catalytic degradation effect on methylene blue was best at a doping concentration of 10 wt.%.

K+ doping effect on grain boundary passivation and photoelectronics properties of NiOx/perovskite films

As a new type of solar cells, perovskite solar cells (PSCs) have received widespread attention. The grain growth and surface morphology of perovskite thin films are considered to have an important influence on the performance of PSCs. In this paper, the K+ was introduced into the CH3NH3PbI3 (MAPbI3) and the effect of different doping concentration on the morphology, photophysical properties, and semiconductor characteristics of the perovskite films was investigated. From experiments, we found that the incorporation of low-concentration K+ has a passivation effect on the grain boundaries, which reduces the defect density at interface. The phase transition and obvious red shift of MAPbI3 could be seen under high doping concentration in XRD pattern and absorption spectrum, respectively. The modulation of the perovskite layer major charge carrier type was observed when K+ was introduced, which laid a basis for future investigation on inverted homo-junction solar cells.

Co-operative energy transfer in Yb3+-Er3+ co-doped SrGdxOy upconverting phosphor

Upconversion nanoparticles (UCNPs) have shown considerable interest in many fields; however, low upconversion efficiency of UCNPs is still the most severe limitation of their applications. Yb3+ and Er3+ co-doped SrGd4O7/Gd2O3(SGO) upconversion (UC) phosphors were synthesized by a modified co-precipitation process. The UC properties were investigated by direct excitation with a 980nm laser. It was observed that the as prepared materials showed relatively strong green emission, while upon the incorporation of the Er3+ ion, there was an increase in the upconversion luminescence intensity for the red component. The effect of different doping concentration of Er3+on the emission spectra and X-ray diffraction patterns of the UC materials have also been studied. The luminescence lifetimes and Commission Internationale de L'Eclairage coordinates for these as prepared samples were determined to understand the energy transfer (ET) mechanisms occurring between Yb3+ and Er3+ in the SGO host matrix. The UC luminescence intensity as a function of laser pump power was monitored and it was confirmed that the UC process in SGO:Yb3+/Er3+is a two-photon absorption process. The findings reported here are expected to provide a better approach for understanding of the ET mechanisms in the oxide based Yb3+/Er3+ co-doped UC phosphors. This study might be helpful in precisely defined applications where optical transitions are essential criterion and this can be easily achieved by smart tuning of the emission properties of Yb3+/Er3+ co-doped UC phosphors.

Preparation and Luminescence Properties of Dy<sup>3+</sup> Doped Sr<sub>3</sub>Lu(PO<sub>4</sub>)<sub>3</sub> as a New Single Phase White Light Emitting Phosphor

The novel white light emitting phosphors Sr3Lu(1-x)Dyx(PO4)3 (x = 0.02, 0.04, 0.06, 0.08, 0.10) were synthesized via a conventional high-temperature solid-state reaction method at 1250°C. The excitation spectrum indicated that these phosphors had a strong absorption in near UV region in the range from 260 to 460 nm. And under 350 nm excitation, the blue emission at 483nm (4F9/2→6H15/2) and yellow emission at 576 nm (4F9/2→6H13/2) were observed in the phosphors, respectively. We studied the effect of different doping concentrations of Dy3+ activator on the luminescence properties and found that the optimum doping concentration is 6 mol%. According to the Dexter’s theory, this quenching behavior is ascribed to be electric d-d interaction. Furthermore, the chromaticity coordinate (x = 0.28, y = 0.32) of Sr3Lu (PO4)3:0.06Dy3+ phosphor was very close to the “ideal white” (x = 0.33, y = 0.33) in the chromaticity diagram. Our results indicate that the Sr3Lu (PO4)3:Dy3+ phosphor can serve as a promising candidate for single-component white light emitting phosphor under near UV excitation.

Structural and photoluminescence study of CeO2:Eu3+ phosphors

Europium doped ceria (CeO2:Eu3+) with different concentration of dopant were synthesized by solid state reaction technique. The structural properties and particle size of CeO2:Eu3+ phosphors were investigated by using X-ray diffraction (XRD) pattern which revealed the cubic fluorite crystal structure of CeO2:Eu3+ and its average particle size was found to be 46.5 nm. Luminescence properties of CeO2:Eu3+ phosphors were studied by observing photoluminescence excitation and emission spectra. Under the excitation of 295 nm, a strong emission peak at 592 nm and two shoulder peaks at 612 nm and 633 nm were found and assigned to different transitions 5D0 → 7Fj (where j = 0, 1, 2) of Eu3+. The effect of different doping concentration on photoluminescence properties of samples were also discussed in the present paper.

Preparation, characterization and photoluminescence properties of SiO2 and SiO2:Eu3+ submicron rods

SiO2 and Eu3+-doped SiO2 submicron rods were conveniently fabricated via a sol–gel process at room temperature. In this process, citric acid served as a unique structural modifier through hydrolysis of TEOS at alkaline condition to obtain the silica submicron rods. The morphology of the products was sensitive to the conditions, such as stirring, gelation time and the dropping speed of NH4OH. By sampling the products at different reaction times, we discussed the formation and growing mechanism of SiO2:Eu3+ submicron rods in detail. The weak interactions between ammonium citrate crystals and silica species may be the reasons of the rods formation. The obtained silica submicron rods were 5–6μm in length and 650–750nm in width and there was no obvious change after doping. Under UV light excitation, the undoped silica submicron rods exhibited blue emission, which may be associated with defect centers in the structures of the products. The Eu3+-doped silica submicron rods exhibited red emission, which was due to the 4f→4f transition of Eu3+. The effect of different doping concentrations of Eu3+ ions on the luminescence was investigated. The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectrum (FT-IR), Thermo-gravimetry Analysis (TGA), Scanning electron microscope (SEM), Transmission electron microscope (TEM), Energy-dispersive spectroscopy (EDS) and Photoluminescence spectrum.

Synthesis and luminescence properties of Sm-doped LDPE–Na2SO4 composite material

A series of Sm-doped LDPE–Na2SO4 composites were successfully achieved by melt mixing and hot pressing methods. Their morphology, structure and luminescent properties were characterized by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and photoexcitation (PE), photoluminescence (PL) spectra, respectively. The sizes and concentrations of free volume cavities in composites were studied by positron annihilation lifetime spectroscopy (PALS). SEM micrographs showed that Na2SO4:Sm3+ particles were well-distributed in the polymer matrix. XRD analyses revealed that the addition of Na2SO4:Sm3+ had no effect on the original crystal structure of LDPE. The dominant photoexcitation peak was observed at about 402nm. The photoluminescence spectra consisted of four main peaks at 563, 598, 644 and 706nm which could be associated to the transitions 4G5/2→6HJ (J=5/2,7/2,9/2 and 11/2, respectively) within the 4f5 electronic configuration of Sm3+. The effect of different doping concentration of Na2SO4:Sm3+ on the luminescent properties of the composites was investigated. The luminescent intensity of the composites increased with phosphor concentration.

Small molecule dye rubrene doped organic bulk heterojunction solar cells

Poly(3-hexylthiphene) (P3HT):[6,6]-phenyl C60-butyric acid methyl ester (PCBM) bulk heterojunction solar cells doped with a small molecule dye of rubrene were fabricated. The effect of different doping concentration on the performance of solar cells was investigated. The results showed that by doping 3.5wt% rubrene, the short circuit current and the power conversion efficiency (PCE) of the cell were improved by 23.1% and 23.4%, respectively. The increased light absorption and effective charge separation of blend films contributed to the enhancement of PCE in doping devices. Moreover, by simulating the photocurrent of solar cells using Onsager–Braun theory, it was found that doping rubrene was responsible for the enhancement of charge transfer generation and dissociation, thereby improving the performance of P3HT:PCBM solar cells.

Synthesis and luminescence properties of a novel red Sr3Bi(PO4)3:Sm3+ phosphor

A series of Sr3Bi1–x(PO4)3: xSm3+phosphors were prepared by solid state method at 1250 °C for 4 h. X-ray diffraction (XRD) indicated that the sample was of a pure phase of Sr3Bi(PO4)3. The main excitation peaks were located at 343 (6H5/2→4H9/2), 360 (6H5/2→4D3/2), 373 (6H5/2→6P7/2), 400 (6H5/2→4F7/2), 414 (6H5/2→6P5/2) and 467 nm (6H5/2→4I13/2). The main emission were located at 563 (4G5/2→6H5/2), 599 (4G5/2→6H7/2), 646 (4G5/2→6H9/2) and 708 nm (4G5/2→6H11/2). The intensest emission was excited by 400 nm. We studied the effect of different doping concentrations of Sm3+ activator on the luminescence properties and found that the luminescent intensity first increased with Sm3+ concentration increasing, and then decreased. The luminescent intensity had the best value when x=0.04. The chromaticity coordinates of the sample Sr3Bi0.96(PO4)3:0.04Sm3+ were (x=0.57, y=0.36), and the lifetime was 2.12 ms.

Optical absorption coefficients of semiconductor quantum-well infrared detectors

The optical absorption coefficients of semiconductor quantum-well infrared detectors have been carefully analyzed in the most general way using quantum perturbation theory. We have calculated the optical transitions between discrete subbands in quantum-well systems and between continuous energy bands of bulk materials as well as mini-subbands formed in semiconductor superlattices. Nonparabolic effects in energy spectra and the effect of different doping concentrations have also been investigated. The optimal directions, the corresponding absorption coefficients, and the quantum-well widths as functions of responding radiation frequency ℏω are listed in a table for the four most commonly used materials AlAs, GaAlSb, Si, and Ge as a guide for device designs.