Linmei Yang

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.

Remarkable differences in photoluminescent properties between LaPO4:Eu one-dimensional nanowires and zero-dimensional nanoparticles

Photoluminescent properties of zero-dimensional LaPO4:Eu nanoparticles (NPs) and one-dimensional nanowires (NWs) prepared by the same wet-chemical synthesis technique were studied and compared. The results indicate that in NP Eu3+ occupied only one site, A, while in NW Eu3+ occupied the same site, A and an additional site B due to crystal anisotropy. Furthermore, the electronic transition rate of D15–∑JFJ7 in the NW increased from 14.9to28.9ms−1 compared to the NP, while the nonradiative transition rate of D15–D05 decreased from 24.1to19.7ms−1. The luminescent quantum efficiency thus improved from 30% to 59%. This work demonstrates that a one-dimensional NW may be a more favorable device than a zero-dimensional NP for photoluminescence.

Fabrication and photoluminescent characteristics of La2O3:Eu3+ nanowires

One-dimensional La(2)O(3):Eu(3+) nanowires (NWs) and sub-micrometer samples (SMs) were fabricated by a hydrothermal method. Their photoluminescent characteristics were studied and compared. The results indicated that the exciton band in NWs blue-shifted in contrast to SMs. In comparison with the charge transfer (CT) band, the relative intensity of the exciton band in NWs was lower than that in SMs, which was attributed to the more energy transfer from the exciton band to surface defects. Frequency-selective-excitation spectra indicated that there existed three symmetry sites of Eu(3+) ions in NWs and two sites in SMs. The results of the temperature dependence of (5)D(1)-(7)F(2) lifetimes indicated that the electronic radiative rate of (5)D(1)-Sigma(7)F(J) in the two samples had hardly any variation and the nonradiative transition rate of (5)D(1)-(5)D(0) in NWs increased slightly.

Fabrication and near-infrared photothermal conversion characteristics of Au nanoshells

In this letter, gold nanoshells with a size of ∼20nm were prepared by a wet-chemical synthesis method and the surface plasmon absorption band of gold was tuned from visible to near-infrared. The gold nanoshell hydrosol demonstrated excellent photothermal conversion property. The temperature of the hydrosol was increased to as high as 30°C under exposure of an 808nm coherent diode laser with a powder density of 5W∕cm2. This kind of gold nanoshell hydrosol is promising for use in biomedicine through photothermal conversion.

Improved photoluminescent properties in one-dimensional LaPO 4 :Eu 3+ nanowires

The photoluminescent properties of one-dimensional LaPO4:Eu nanowires were studied in contrast with the corresponding zero-dimensional nanoparticles, micrometer particles, and micrometer rods. The results indicate that in nanowires Eu3+ ions occupied two different symmetry sites, unlike in nanoparticles and micrometer particles. Furthermore, the radiative transition rate of 5D1 - sigmaJ 7FJ or 5D0 - sigmaJ 7FJ and the internal luminescent quantum efficiency of Eu3+ in the nanowires showed obvious improvement over that in the other powders.

Wet-chemical synthesis and characteristics of Au nanoshell

Gold nanoshells were prepared by an easy wet-chemical method, with Ag nanoparticles used as the templates. Transmission electron microscopy (TEM) indicated that the shells were sphere in shape, the size was homogenous, being about 20 nm, and no hard agglomerates were observed. The plasma resonance absorption of gold was tuned from visible to near-infrared (NIR) with the increased volume of HAu11CI4. The temperature grads (ΔT) of the gold nanoshell hydrosol under the exposure of an 808-nm optical fiber laser with different power densities were measured. The highest Δt was 30δC (5 W/cm2, irradiation area was 2 cm2). This kind of gold nanoshell hydrosol is a promising material to be used in biomedicine such as photothermal cancer therapy, and its special photothermal convert property will photothermally trigger drug release.