Page 145 - Synthesis of Functional Nanoparticles Using an Atmospheric Pressure Microplasma Process - LiangLiang Lin

Rare Earth Doped Yttrium Oxide Nanophosphors Synthesis and Engineering- Controllable Photoluminescence Properties
In addition to the heat treatment, the impact of the Eu3+ concentration on the luminescent efficiency was also explored. Initially, a steady rise in the photoluminescence intensity is observed with the increase of the Eu3+ concentration, which is due to the increase of the active centers in the yttria matrices. The optimum value is reached at the Eu3+ concentration of 7%. Afterwards, the nanophosphors exhibit luminescence quenching with the further increase of the Eu3+ concentration. This effect is caused by the Coulombic repulsion between the neighboring Eu3+ in the yttria lattice.23,24 An over-saturated dopant concentration leads to a decrease in the average distance between Eu3+, and in some cases can form dopant pairs or clusters. This will promote the interactions between ions, energy migration, and cross- relaxation processes. As a consequence, the non-radiative transitions prevail, which in turn, suppresses the luminescence efficiency.
Above all, we have shown the successful synthesis of Eu3+ doped yttria nanophosphors with tunable photoluminescence properties via a plasma-assisted method. To demonstrate the versatility of this technique, it is further expanded to the production of a series of Ln3+ (Ln=Tb, Dy, Tm) doped nanophosphors. Herein we mainly focus on their luminescence properties, as shown in Figure 7.8. In addition to the prominent emission peak of Eu3+ at 612 nm, characteristic peaks of Tm3+ (455 nm, 463 nm), Tb3+ (543 nm, 550 nm) and Dy3+ (572 nm, 579 nm) were also detected, suggesting the successful doping of Ln3+ into the yttria matrix by this technique. Since lanthanide ions have specific emission wavelengths, it is expected that this approach can be readily extended to the fabrication of various Ln3+ doped/co-doped nanophosphors with desirable photoluminescence properties by selecting proper color-center elements.
Figure 7.8 Typical photoluminescence emission spectra of Ln3+ doped yttria nanophosphors: 1% Tb3+ doping, excited at 307 nm; 3% Dy3+ doping, excited at 355nm; 1% Tm3+ doping, excited at 355 nm and
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