Changfeng Wu

Photoluminescence from surfactant-assembled Y2O3:Eu nanotubes

Y2O3:Eu nanotubes were fabricated by a surfactant assembly mechanism. The tubular structure was characterized by transmission electron microscopy. Under an ultraviolet-light excitation, the nanotubes show a relatively intense emission peak at 618 nm besides the 610 nm peak, different from that of single Y2O3:Eu nanocrystallites. The results of laser-selective excitation indicate that the emission centers near the surface of nanotube walls exhibit inhomogenously broadened spectra without spectral structures while the two sites (sites B and C) inside the nanotube walls present legible spectral structures. It is concluded by the number and peak positions of Stark levels that the sites B and C possess different site symmetries.

Enhancement of ultraviolet upconversion in Yb3+ and Tm3+ codoped amorphous fluoride film prepared by pulsed laser deposition

Zn0.3Al0.25Pb0.3Li0.098Yb0.1Tm0.002F2.354 amorphous fluoride film was prepared by pulsed laser deposition. Ultraviolet and blue up-conversion emissions were observed under infrared excitation at 978 nm. In comparison with the upconversion of the target, the ultraviolet emissions are enhanced greatly. The enhancement is attributed to a decrease of the Judd–Ofelt parameter Ω2 induced by pulsed laser deposition, which precludes the transition rate from 3F2 to 3F4 and enhances the energy transfer process and populates the 1D2 level: 3F2→3H6 (Tm3+):3H4→1D2 (Tm3+).

Infrared-to-violet upconversion from Yb3+ and Er3+ codoped amorphous fluoride film prepared by pulsed laser deposition

Yb3+–Er3+ codoped amorphous Zn0.3Al0.25Pb0.3Li0.09Yb0.1Er0.01F2.37 film has been prepared by pulsed-laser deposition. Violet, green, red, and ultraviolet upconversion emissions were observed under infrared excitation at 988 nm. In comparison with the upconversion of the target, the violet and ultraviolet emissions are enhanced greatly. The enhancement is attributed to the diminishing of the cross relaxation: 4G11/2→4F9/2 (Er3+): 2F7/2→2F5/2 (Yb3+) induced by the decrement of the structure parameter Ω2.

Near-infrared-to-visible photon upconversion in Mo-doped rutile titania

A broadband upconversion luminescence was observed from Mo-doped titania under a 978 nm diode laser excitation. The luminescence has been assigned to the transitions from the excited states 3 T1; 3 T2 to the ground state 1 A1 of the ½MoO4� 2� radicle. The intermediate states available for upconversion are supposed to be related with Mo 4þ and/or Mo 5þ species. The temporal evolution of the upconversion luminescence and the excitation-power dependence of the steady-state emission intensity exhibit the typical fingerprint of a photon avalanche. The dynamical process is well described using the fluorescence transfer function model. 2002 Elsevier Science B.V. All rights reserved.