Rensheng Shen

Fluorescence quenching of 5DJ (J = 1, 2 and 3) levels and Judd–Ofelt analysis of Eu3+ in NaGdTiO4 phosphors

NaGdTiO4 phosphors with various Eu3+ concentrations were synthesized by a solid-state reaction. The crystal structure and fluorescence properties were characterized by means of x-ray diffraction and fluorospectroscopy, respectively. An effective energy transfer from the titanate matrix to the activator Eu3+ was observed. An intense red emission originating from 5D0 ? 7F2 of Eu3+ was observed while excited at the charge transfer bands or f?f absorption bands of Eu3+. The fluorescence quenching of 5DJ (J = 1, 2 and 3) levels were studied based on the Van Uitert model. Electric dipole?dipole interaction was confirmed to be the main mechanism of the fluorescence quenching of 5DJ levels, which is responsible for the cross-relaxation between Eu3+ ions. The full optical transition intensity parameters ?? (? = 2, 4, 6) of Eu3+ in the NaGdTiO4 phosphors were calculated in the framework of Judd?Ofelt theory to be 6.024 ? 10?20, 1.512 ? 10?20 and 0.374 ? 10?20?cm2.

Negative differential resistance in low Al-composition p-GaN/Mg-doped Al0.15Ga0.85N/n+-GaN hetero-junction grown by metal-organic chemical vapor deposition on sapphire substrate

Negative differential resistance (NDR) behavior was observed in low Al-composition p-GaN/Mg-doped-Al0.15Ga0.85N/n+-GaN hetero-junction grown by metal-organic chemical vapor deposition on sapphire substrate. The energy band and free carrier concentration of hetero-junction were studied by the model of the self-consistent solution of Schrodinger-Poisson equations combined with polarization engineering theory. At the forward bias of 0.95 V, the NDR effect has a high peak-to-valley current ratio of ∼9 with a peak current of 22.4 mA (∼current density of 11.4 A/cm2). An interesting phenomenon of NDR disappearance after consecutive scans and recurrence after electrical treatment was observed, which was associated with Poole-Frenkel effect.

Low Al-composition p-GaN/Mg-doped Al0.25Ga0.75N/n+-GaN polarization-induced backward tunneling junction grown by metal-organic chemical vapor deposition on sapphire substrate

Low Al-composition p-GaN/Mg-doped Al0.25Ga0.75N/n+-GaN polarization-induced backward tunneling junction (PIBTJ) was grown by metal-organic chemical vapor deposition on sapphire substrate. A self-consistent solution of Poisson-Schrödinger equations combined with polarization-induced theory was used to model PIBTJ structure, energy band diagrams and free carrier concentrations distribution. The PIBTJ displays reliable and reproducible backward tunneling with a current density of 3 A/cm2 at the reverse bias of −1 V. The absence of negative differential resistance behavior of PIBTJ at forward bias can mainly be attributed to the hole compensation centers, including C, H and O impurities, accumulated at the p-GaN/Mg-doped AlGaN heterointerface.

The lattice distortion of β-Ga2O3 film grown on c-plane sapphire

The β-Ga2O3 film is grown on c-plane sapphire (Al2O3) substrate using metal organic chemical deposition method. According to high resolution X-ray diffraction measurement results, the epitaxial relationship between β-Ga2O3 film and c-plane sapphire was confirmed. The β-Ga2O3 film is (

n-ZnO/p-GaN heterojunction light-emitting diodes with a polarization-induced graded-p-AlxGa1−xN electron-blocking layer

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Vertically conducting deep-ultraviolet light-emitting diodes with interband tunneling junction grown on 6H-SiC substrate

2¯01) preferred orientation and β-Ga2O3 〈102〉 and 〈010〉 directions are parallel to Al2O3 〈

Influence of Cu dopant on the structure and optical properties of ZnO thin films prepared by MOCVD

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