Y_2O_3:Eu^(3+)纳米晶与体材料在高分辨光谱上的显著区别

Remarkable Spectral Difference between Nanocrystalline Y_2O_3 :Eu^(3+) and Bulk Ones

报道了Y2O3:Eu3+纳米晶与体材料在光谱上的显著区别。除了相同于Y2O3:Eu3+体材料在580.6nm处的激发峰外,Y2O3:Eu3+纳米晶在579.9nm处出现了一新的较宽激发线。并且,该激发线的寿命要稍短于580.6nm的激发线。579.9nm激发线被归因于靠近纳米晶表面的Eu3+的发光。纳米晶中存在大量的表面缺陷,表面的晶体场因而发生退化,从而使得4f组态的电子能级发生移动。

In this paper, spectral difference between nanocrystalline yttria doped with europium (Y2O3 :Eu3+) and the bulk ones was reported. Besides a 580.6nm line similar to that in the bulk Yz03 :Eu3+, a new broad excitation line at 579.9nm was observed in the excitation spectra of nanocrystals (NCs). The 579.9nm peak relative to the 580.6nm one decreases a little as temperature increases. The fluorescent lifetime excited by 579.9nm line became slightly shorter than that of the 580.6nm line. We suggest that in nanocrystalline Y2O3:Eu3+ the broader 579.9nm excitation peak originates from the luminescence of Eu3+ions near the surface, and the 580.6nm one from the internal Eu3+ ions. The surface to volume ratio is quite small (1% ) in the micrometer particles, while it increases significantly as the particle size decreases to several nanometers. This will lead the surface effects to be effective. As well known, the energies of electrons in 4f states of rare earth ions are affected by the crystal field. In nanocrystals, rare earth ions near the particle surface are at the sites microscopically inequivalent with those close to the center. Their energy levels may shift, and the degenerated spectral lines in the bulk sample may split. Due to the appearance of numerous surface defects the crystal field in the surface of nanoparticles degenerates and the emission of 5Do→7F,shifts. Because the local environments surrounding Eu3 + ions near the surface are more disordered and surface defects may act as nonradiative transition channels, the width of the 579.9nm line is broader and the fluorescent lifetime becomes shorter.