Juan Yi

First-principles study on the doping effects of nitrogen on the electronic structure and optical properties of Cu2O

Recent experimental literature (Sol. Energ. Mat. Sol. Cells, 2012, 105, 192) has reported that nitrogen doped Cu2O is a possible material for novel intermediate band solar cells. The doping effects of nitrogen on the crystal structure, electronic structure, and optical properties of Cu2O have been studied by an ultrasoft pseudopotential plane wave method based on first-principles calculations. The results show that nitrogen doping slightly widens the band gap of Cu2O, and form an intermediate band in the gap located at about 0.9 eV from the VBM (or CBM). This intermediate band is predominantly formed by hybridization between the N-2p states and the Cu-3d states. N-doped Cu2O is very likely to absorb at a maximum across the solar light spectrum, from the near infrared region to the ultraviolet region. Based on these results, N-doped Cu2O is considered to be a perfect intermediate band material for a novel kind of solar cells.

Band‐Edge Electronic Structure of β‐In2S3: The Role of s or p Orbitals of Atoms at Different Lattice Positions

As a promising solar-energy material, the electronic structure and optical properties of Beta phase indium sulfide (β-In(2)S(3)) are still not thoroughly understood. This paper devotes to solve these issues using density functional theory calculations. β-In(2)S(3) is found to be an indirect band gap semiconductor. The roles of its atoms at different lattice positions are not exactly identical because of the unique crystal structure. Additonally, a significant phenomenon of optical anisotropy was observed near the absorption edge. Owing to the low coordination numbers of the In3 and S2 atoms, the corresponding In3-5s states and S2-3p states are crucial for the composition of the band-edge electronic structure, leading to special optical properties and excellent optoelectronic performances.

Systematic studies on YbxBi1−xVO4:Tm3+ solid solutions: experiments and DFT calculations on up-conversion photoluminescence properties

Compound solid solutions have attracted intensive attention due to their adjustable structure, electronic structure, and optical properties. Despite tremendous advances in compound solid solution preparations, combining a rare metal compound and a bismuth compound with the same crystal phase by forming a compound solid solution is still challenging but fascinating. For example, RE1−xBixVO4 with a zircon-type structure exhibits tunable band gaps and photoluminescence performance with varying RE compositions. Herein, Yb1−xBixVO4 solid solutions with continuous monophasic phase prepared by a facile synthesis strategy that is combined with co-precipitation and hydrothermal methods are reported. By doping a small amount of Tm3+, YbxBi1−xVO4 solid solutions can achieve a broad range up-conversion photoluminescence from UV-light to NIR-light. Combined with DFT calculations, the underlying mechanism of experimental observations is explained. In these up-conversion processes, the existence of Tm3+ is an essential factor. In particular, the NIR-to-UV up-conversion photoluminescence of YbxBi0.98−xVO4: 2 mol% Tm3+ solid solution is very interesting and a worthy phenomenon for further studies. As such, designing compound solid solutions may provide a new avenue for controllable up-conversion efficiencies in semiconductor nanocrystals and also a novel insight into the rational tunable up-conversion process for applications in biological labeling and imaging.

Monophasic zircon-type tetragonal Eu{sub 1−x}Bi{sub x}VO{sub 4} solid-solution: synthesis, characterization, and optical properties

Highlights: • Complete Eu{sub 1−x}Bi{sub x}VO{sub 4} with zircon-type structure was successfully synthesized. • The band gap of the samples could be adjusted and controlled by bismuth content. • Eu{sub 1−x}Bi{sub x}VO{sub 4} show strong red emission under both near UV and visible-light excitation. - Abstract: By combining the methods of co-precipitation and hydrothermal synthesis methods, the complete solid-solution of Eu{sub 1−x}Bi{sub x}VO{sub 4} with monophasic zircon-type structure was successfully synthesized. The zircon-type structure was determined by X-ray diffractometer and Raman scattering, and the optical properties were characterized by ultraviolet-visible diffuse reflectance and photoluminescence spectrophotometer. The results indicate that the band gap of Eu{sub 1−x}Bi{sub x}VO{sub 4} could be adjusted and controlled by bismuth content in the range of x = 0–0.9. Meanwhile, the Eu{sub 1−x}Bi{sub x}VO{sub 4} solid-solution phosphors show strong red light emission was shown in 619 nm under both near UV-light and visible-light excitation. Notably, the emission intensity of Eu{sub 1−x}Bi{sub x}VO{sub 4} (x = 0.4) is the strongest in all samples.