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超级老快木虫之王 (文学泰斗)
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[求助]
英译汉，一段文字！
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| These microstructural changes may enhance the photoluminescence intensity of dopant ions by increasing the oscillating strengths of the optical transitions and by decreasing internal reflections on crystallite surfaces. Furthermore, compared with samples lacking Li+ ions,the number of dopant ions in the vicinity of crystallite surfaces is smaller in the Li+ co-doped samples, and consequently, the emission intensity should be less degraded by surface ligands. In the present case, the structural parameters of GdVO4: Er3+/Yb3+ powders do not follow the a fore-mentioned trend when the Li+ co-doping concentration increases,as detailed in Table1. The crystallite size of the powder is almost doubled when powders are co-doped with 5mol% of Li+ ions (91nm instead of 56nm), and the size does not change with a further increase in Li+ concentration. Microstrain exhibits the same behavior as crystallite size. Its value increases from approximately 0.06% in the powder with no Li+ ions to about 0.29% in the powder co-doped with 5mol% of Li+ ions, and the value stays approximately the same at higher co-doping levels.Conversely,other structural parameters, such as the unit cell volume and lattice parameters, constantly decrease with an increase in the Li+ co-doping concentration. The different behavior for emission intensities, which vary with respect to the Li+ co-doping concentration, is observed with DC and UC luminescence. In UC luminescence, the intensity of emission is four times greater in the powder co-doped with 5mol% of Li+ ions than in then on-co-doped powder.However, the enhancement is reduced in samples with higher Li+ ion concentrations. A probable explanation of this phenomenon is that at high Li+ co-doping concentration there is afraction of Li+ ions sufficiently large to induce the fast energy transfer from the host to the Er3+ ions and hence to create an increase in the hole concentration leading to a decrease in competitive absorption. |
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