Yanqiang Lei

Upconversion luminescence, intensity saturation effect, and thermal effect in Gd2O3:Er3,Yb3+ nanowires

In this paper, the upconversion luminescent properties of Gd2O3:Er3+,Yb3+ nanowires as a function of Yb concentration and excitation power were studied under 978-nm excitation. The results indicated that the relative intensity of the red emission (4F(9/2)-4I(15/2)) increased with increasing the Yb3+ concentration, while that of the green emission (4S(3/2)/2H(11/2)-4I(15/2)) decreased. As a function of excitation power in ln-ln plot, the green emission of 4S(3/2)-4I(15/2) yielded a slope of approximately 2, while the red emission of 4F(9/2)-4I(15/2) yielded a slope of approximately 1. Moreover, the slope decreased with increasing the Yb3+ concentration. This was well explained by the expanded theory of competition between linear decay and upconversion processes for the depletion of the intermediate excited states. As the excitation power density was high enough, the emission intensity of upconversion decreased due to thermal quenching. The thermal effect caused by the exposure of the 978-nm laser was studied according to the intensity ratio of 2H(11/2)-4I(15/2) to 4S(3/2)-4I(15/2). The practical sample temperature at the exposed spot as a function of excitation power and Yb3+ concentration was deduced. The result indicated that at the irradiated spot (0.5 x 0.5 mm2) the practical temperature considerably increased.

Luminescent enhancement in europium-doped yttria nanotubes coated with yttria

Europium-doped yttria nanotubes were coated with yttria by a simple two-step hydrothermal method, forming the Y2O3:Eu3+∕Y2O3 core-shell composite. Remarkable improvement of photoluminescence was observed in the core-shell composite under both violet and ultraviolet excitations. These characteristics were attributed to the reduced influence of surface defects on host excitation, charge transfer transitions, and f−f inner-shell transitions of the Eu3+ ions. Due to striking red luminescence under ultraviolet excitation, the core-shell structure has potential application in plasma display panel devices.

Visible light illumination-induced phase transition to the intermediate states between the metallic and insulating states for the LaAlO3/SrTiO3 interfaces

Photoexcitation usually drives the LaAlO3/SrTiO3 interface from the insulating state into a totally metallic state, without experiencing any intermediate states. Here, we reported on an illumination-induced transition of the insulating LaAlO3(3uc)/SrTiO3 interface to a series of state between a totally insulating state and a totally metallic state. We found that appropriate light illumination can cause an insulator-to-semiconductor transition in the temperature range above ∼150 K and an insulator-to-metal transition below ∼60 K, while the original state recovers immediately after the removal of the illumination, without persistent photoconductivity as previously reported. Moreover, a remarkable resistive anomaly corresponding to the structural transition of SrTiO3 at ∼105 K appears, indicating a phase-transition-induced carrier density change.

Energy dependence of H2+ ions guided through tapered capillaries in PC

Transmission of H+2 ions through tapered capillaries in insulating polycarbonate (PC) foil is reported. Guiding, focusing effects and multi-peaks phenomena on ions through capillaries have been studied.

Transmission of 200 keV H+2 Ions through Tapered Capillaries in PC

The transmission of 200 keV H+2 ions through tapered capillaries with inlet/outlet diameters of 4 μm/2 μm and a length of 30 μm is reported. The results indicate that 200 keV H+2 ions can be guided through foils tilted up to ±12.5°. The areal density of the transmitted ion beam is estimated to be ~3.7 times larger than that of incident beam.

Secondary Electron Emission from Carbon Foils under O2+ Ion Impact

Secondary electron emission yields in forward and backward direction from carbon foils (thickness of 74 nm) induced by O2+ ions of energies form 1.9 keV/u to 11.3 keV/u have been measured. We find that the forward and the backward electron emission yields increase with the projectile kinetic energy. Further studies showed that the forward and the backward electron emission yields are approximately proportional to the electronic stopping power at the exit and entrance surfaces, respectively.