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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.

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For Abstract see ChemInform Abstract in Full Text.

One-dimensional pure cubic Y(2)O(3)/Eu(3+) nanocrystals (NCs) were synthesized by a hydrothermal method at various temperatures. The NCs prepared at 130 degrees C yielded nanotubes (NTs) with wall thickness of 5-10 nm and outer diameter of 20-40 nm. The NCs prepared at 170 and 180 degrees C yielded nanowires (NWs) with diameters of approximately 100 and approximately 300 nm, respectively. Their luminescent properties, including electronic transition processes, local environments surrounding Eu(3+) ions, electron-phonon coupling, and UV light irradiation induced spectral changes have been systematically studied and compared. The results indicate that the Y(2)O(3)/Eu(3+) NTs and NWs have strong red (5)D(0)-(7)F(2) transitions. The fluorescence lifetime of (5)D(1)-(7)F(1) hardly changes in different samples, while that of (5)D(0)-(7)F(2) decreases a small amount in Y(2)O(3)/Eu(3+) NTs. The (5)D(0)-(7)F(2) lines originate from the emissions of Eu(3+) ions occupying one C(2) site, like that in the bulk powders. The phonon sideline with a frequency shift of 40-50 cm(-1) appears at the low-energy side of the (7)F(0)-(5)D(0) zero phonon line. The relative intensity of the sideline to zero phonon line increases by varying from NTs to NWs, and the spectral position of the phonon sideline shifts red. The UV light irradiation induced spectral change in the charge-transfer band was studied. The results indicate that the spectral change is dependent on sample size and is wavelength selective. A detailed model was proposed to explain the light-induced spectral change.

Ce3+ and Tb3+ coactivated LaPO4 nanowires and micrometer rods were synthesized by hydrothermal methods. Their fluorescent spectra and dynamics were systematically studied and compared. The results indicated that the extinction coefficients of Ce3+ and Tb3+ in nanowires were higher than those in micrometer rods. The electronic transition rates of Ce3+ and Tb3+ in nanowires had little variation in contrast to those in micrometer rods, and the energy transfer rate and efficiency of Ce3+ --> Tb3+ in nanowires were reduced greatly. It is important to observe that the brightness for the 5D4-7F5 green emissions of Tb3+ via energy transfer of Ce3+ --> Tb3+ in nanowires increased several times that in micrometer rods. This was attributed to the decreased energy loss in the excited states, being higher than 5D4 due to the hindrance of the boundary.

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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.