Shihua Huang

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.

Eu3+ ion as fluorescent probe for detecting the surface effect in nanocrystals

Nanocrystalline yttrium vanadate doped with trivalent europium ions, YVO4:Eu3+, was synthesized via the microemulsion mediated hydrothermal process. Laser selective excitation spectra were employed to probe the local environments of Eu3+ ions in YVO4 nanocrystals. The local environments of the dopant ions were diversified because of the surface effect in nanocrystals, which led to an increase in linewidth in excitation and emission spectra. Furthermore, the change of site symmetry from the interior to the surface of nanoparticles was clearly exhibited in the emission spectra of Eu3+ ions under different excitation wavelengths. The results show that the fluorescent behavior of doped Eu3+ ions may be a useful probe for detecting the surface effect in nanosize materials.

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+).

Spectral difference between nanocrystalline and bulk Y2O3 : Eu3+

Abstract In this Letter spectral difference between nanocrystalline yttria doped with europium (Y2O3:Eu3+) and the bulk ones was reported. Besides a 580.6-nm line similar to that in the bulk Y2O3:Eu3+, a new broad excitation line at 579.9 nm was observed in the nanocrystals (NCs). The lifetime of the 579.9-nm line became slightly shorter than that of the 580.6-nm line. The 579.9-nm line was attributed to the Eu3+ ions near the surface of the NCs. Due to numerous surface defects, the crystal field on the surface degenerated, leading the energy levels of the electrons in 4f state to shift.

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.

Irradiation-induced luminescence enhancement effect of ZnS:Mn2+ nanoparticles in polymer films

The effects of irradiation-induced luminescence enhancement by ZnS:Mn(2+) nanoparticles in poly(vinyl butyral) films are reported. The luminescence intensity increases several times when fresh samples are irradiated by a 248-nm excimer laser. The decay time also increases with exposure time. The increase in the initial intensity of the slow component of luminescence makes the main contribution to the enhancement effect. A tentative model is proposed in which the efficiency of the energy transfer to Mn(2+) ions increases with exposure. States at interfaces are expected to play an important role in this process.

Luminescence of Mn2+ doped ZnS nanocrystallites

Abstract Optical properties of Mn2+-doped ZnS colloids are reported. The band to band excitation energy transfer to Mn2+ is more efficient compared to Mn2+ direct excitation, which is different from the case for bulk ZnS: Mn. Aging effects and the radiation-induced luminescence enhancement (RILE) effect are reported and an explanation for this behavior is presented.

Photon cascade emission and quantum efficiency of the 3P0 level in Pr3+-doped SrAl12O19 system

Abstract Photon cascade emission has been reported in Pr3+-doped SrAl12O19 system, providing a unique method for direct measuring the quantum efficiency of 3P0 in this material. The 1S0→1I6 fluorescence intensity can be taken as a measure of the initial 3P0 population. Thus the quantum efficiency of 3P0 can be calculated using the intensity ratio of the total emission from 3P0 and the emission of 1S0→1I6. The efficiency decreases as the concentration of Pr increases, indicating the effect of concentration quenching. The quantum efficiency is still substantially less than 100% even in dilute sample due to the thermal excitation of 1I6 and 3P1 states.

Temperature dependence of photoluminescence in CdS nanocrystals prepared by the sol-gel method

The temperature-dependent photoluminescence spectra of CdS semiconductor nanocrystals-doped glasses prepared by a sol-gel method were measured at different excitation intensities. Based on the temperature dependence of the peak energy, linewidth and intensity of the luminescence, the characteristics and origins of the band-edge luminescence were discussed.

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.