Banski M, Afzaal M, Podhorodecki A, Misiewicz J, Abdelhady A L, O'Brien P
Institute of Physics, Wroclaw University of Technology, Wyb. Wyspianskiego 27, 50-370 Wroclaw, Poland.
J Nanopart Res. 2012 Nov;14(11):1228. doi: 10.1007/s11051-012-1228-3. Epub 2012 Oct 10.
We examined in detail the optical properties of NaYF(4):Eu(3+) nanocrystals of ~9 nm in diameter. For such small nanocrystals roughly 17 % of Y(3+) ions occupy surface sites and can be efficiently substituted by optically active Eu(3+) ions. In order to determine the influence of surface Eu(3+) on the optical properties of the whole nanocrystal, small β-NaYF(4):Eu(3+) nanocrystals with homogenous size distribution were prepared using trioctylphosphine oxide as a coordinating solvent. In order to passivate the surface sites, a thin β-NaYF(4) shell was further deposited on nanocrystals core and the optical properties were investigated. For this purpose absorption, photoluminescence, photoluminescence excitation, and photoluminescence decays were recorded and analyzed. The optical characteristics of surface Eu(3+) significantly diminish for surface passivated nanocrystals. We calculated the increase of quantum yield to the value of 64 % when NaYF(4):Eu(3+) core was capped by undoped shell. The optical spectroscopy techniques were shown to be sufficient in determination of surface passivation of nanocrystals with high surface to volume ratio.
我们详细研究了直径约9纳米的NaYF₄:Eu³⁺纳米晶体的光学性质。对于如此小的纳米晶体，约17%的Y³⁺离子占据表面位点，并且可以被光学活性的Eu³⁺离子有效取代。为了确定表面Eu³⁺对整个纳米晶体光学性质的影响，使用三辛基氧化膦作为配位溶剂制备了尺寸分布均匀的小β-NaYF₄:Eu³⁺纳米晶体。为了钝化表面位点，在纳米晶体核心上进一步沉积了一层薄的β-NaYF₄壳层，并对其光学性质进行了研究。为此记录并分析了吸收、光致发光、光致发光激发和光致发光衰减。对于表面钝化的纳米晶体，表面Eu³⁺的光学特性显著减弱。当NaYF₄:Eu³⁺核心被未掺杂的壳层包覆时，我们计算出量子产率增加到了64%。结果表明，光谱技术足以确定具有高表面积与体积比的纳米晶体的表面钝化情况。
