Guoping Du

Enhanced Dielectric Response in Mg-doped CaCu3Ti4O12 Ceramics

CaCu 3 Ti 4 O 12 ceramics substituted by Mg for Ca were prepared by the solid state reaction method. The crystal structures, microstructures, and dielectric properties of the Ca 1- x Mg x Cu 3 Ti 4 O 12 ceramics were investigated. At lower doping concentrations, the substitution of Mg for Ca caused a decreased lattice constant, while at higher doping concentrations, some of the Mg dopants started to replace Ti and resulted in an increased lattice constant, and some could also replace Cu due to the similar ion radius between Mg and Cu ions. Mg doping was found to promote the grain growth of Ca 1- x Mg x Cu 3 Ti 4 O 12 ceramics during sintering. Grain boundary resistance of the Ca 1- x Mg x Cu 3 Ti 4 O 12 ceramics was found to be increased by Mg doping. Enhanced dielectric properties was observed in the Ca 1- x Mg x Cu 3 Ti 4 O 12 ceramics with x =0.05 for the frequency range from 1 kHz to 20 kHz. For other doping concentrations, the dielectric losses of Ca 1- x Mg x Cu 3 Ti 4 O 12 ceramics were generally lowered.

A strategy to prepare highly redispersible and strongly luminescent α-NaYF4:Eu3+ hybrid nanostructures with multi-channel excitation

Rare earth doped NaYF4 nanocrystals have received intensive attention in recent years because of their unique luminescence properties as a result of their very low phonon energy. However, their luminescence is largely limited by the low optical absorption of rare earth ions. This paper presents a novel strategy to prepare highly dispersible and strongly luminescent Eu3+ doped α-NaYF4 (α-NaYF4:Eu3+) nanocrystals, which can be intensely excited via multi-channel optical absorption. Highly dispersible α-NaYF4:Eu3+ nanocrystals are synthesized using a solvothermal method, and they are coated with a SiO2 layer to form the α-NaYF4:Eu3+@SiO2 core–shell nanostructures. These α-NaYF4:Eu3+@SiO2 core–shell nanostructures are thermally annealed and the SiO2 shell is then removed to obtain the annealed α-NaYF4:Eu3+ nanocrystals with strong O2−→Eu3+ charge transfer excitation. Luminescence of the α-NaYF4:Eu3+ nanocrystals is further enhanced by energy transfer of organic ligands after forming a type of inorganic–organic hybrid nanostructure. This strategy is also useful for developing other types of dispersible and strongly luminescent nanocrystals.

Effect of annealing and surfactant on photoluminescence of ZnS:O2− nanoparticles

Abstract ZnS:O2− (ZSO) nanoparticles were synthesized using a low temperature solid-state reaction method. The effects of annealing conditions and the content of the surfactant polyethylene glycol (PEG) on photoluminescence (PL) properties of the ZSO nanoparticles were studied. It was found that annealing and adding PEG during the synthesis did not change the crystal structure of ZSO nanoparticles, and their average crystallite size increased with increasing annealing time and temperature, but decreased with increasing PEG content. The emission intensity of ZSO nanoparticles was found to be enhanced after annealing or using PEG during the synthesis. Optimal annealing conditions both in air and vacuum and the optimal content of PEG were obtained for achieving maximum emission intensity from the ZSO nanoparticles.

Broadband UV Excited LaF3:Eu3+ Based Inorganic–Organic Mixed Hybrid Nanoparticles for Strong Luminescence

Lanthanide ion doped nanoparticles can coordinate with some organic ligands to form the inorganic-organic hybrid nanoparticles, which exhibit greatly enhanced luminescence as a result of the energy transfer from the organic ligands to the lanthanide ions. However, when coordinating with a single type of organic ligand, their luminescence excitation spectral bandwidth is still quite limited. In this work, Eu3+-doped LaF3 (LaF3:Eu3+) nanoparticles, as the model inorganic material, were synthesized using the hydrothermal method. Instead of coordinating with a single type of organic ligand as previously studied, the LaF3:Eu3+ nanoparticles simultaneously coordinate with both benzoic acid and 2-thenoyltrifluoroacetone to form the inorganic-organic mixed hybrid nanoparticles. The mixed hybrid nanoparticles possess a broadband excitation spectrum (200~400 nm) which perfectly covers the entire ultraviolet (UV) spectral range of the solar radiation. By down-converting the UV light to visible light, their broadband UV excitation spectrum will be extremely beneficial to the enhancement of the conversion efficiency of silicon solar cells.

Enhanced photovoltaic properties for rear passivated crystalline silicon solar cells by fabricating boron doped local back surface field

In order to enhance the p-type doping concentration in the LBSF, boron was added into the aluminum paste and boron doped local back surface field (B-LBSF) was successfully fabricated in this work. Through boron doping in the LBSF, much higher doping concentration was observed for the B-LBSF over the Al-LBSF. Higher doping concentration in the LBSF is expected to lead to better rear passivation and lower rear contact resistance. Based on one thousand pieces of solar cells for each type, it was found that the rear passivated crystalline silicon solar cells with B-LBSF showed statistical improvement in their photovoltaic properties over those with Al-LBSF.

Preparation, structures, thermal properties and sintering behaviors of B 2 O 3 -SiO 2 -ZnO-BaO-Al 2 O 3 glass

B2O3-SiO2-ZnO-BaO-Al2O3 glass with different Al2O3 contents (1mol%, 3mol%, 5mol%, and 7mol%) was prepared, and it was intended to be used as lead-free and low-melting glass sealants for solid oxide fuel cells. The effects of Al2O3 content on the structures, thermal properties, and sintering behaviors of the B2O3-SiO2-ZnO-BaO-Al2O3 glass were investigated in detail. The Al2O3 content largely influenced the structures and thermal properties of the glass. When the Al2O3 content 5mol%, the transition temperature of the glass decreased with the Al2O3 content, while the crystallization temperature increased with the Al2O3 content. However, higher Al2O3 content degraded the stability of the glass. The B2O3-SiO2-ZnO-BaO-Al2O3 glass with 5 mol% Al2O3 content exhibits the optimal sintering densification characteristics and can be used as glass sealants for solid oxide fuel cells.

Preparation and Properties of Aluminum-doped ZnO–SiO2 Composite Thin Films

Aluminum-doped ZnO (AZO) thin films are usually used as transparent conductors. For practical applications, however, the relatively high refractive index of AZO can lead to high optical reflection. In this work, we modified the optical properties of AZO thin films by adding different amounts of SiO2 into the AZO thin films to prepare the AZO-SiO2 composite thin films. The AZO-SiO2 films were deposited on quartz substrates using a co-sputtering deposition method. It was shown that the refractive index of the AZO-SiO2 thin films consistently decreased with the amount of SiO2 contained in the films. In the meantime, the resistivity of the AZO-SiO2 thin films was found to increase with the SiO2 content in the films. The effects of the deposition conditions on the optical and electrical properties of the AZO-SiO2 thin films were systematically investigated.