Libo Fan

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.