University of Konstanz, Universitaetsstr. 10, 78464 Konstanz, Germany.
Nanoscale. 2015 Oct 28;7(40):16969-82. doi: 10.1039/c5nr02550h. Epub 2015 Sep 29.
The precise control over electronic and optical properties of semiconductor (SC) materials is pivotal for a number of important applications like in optoelectronics, photocatalysis or in medicine. It is well known that the incorporation of heteroelements (doping as a classical case) is a powerful method for adjusting and enhancing the functionality of semiconductors. Independent from that, there already has been a tremendous progress regarding the synthesis of differently sized and shaped SC nanoparticles, and quantum-size effects are well documented experimentally and theoretically. Whereas size and shape control of nanoparticles work fairly well for the pure compounds, the presence of a heteroelement is problematic because the impurities interfere strongly with bottom up approaches applied for the synthesis of such particles, and effects are even stronger, when the heteroelement is aimed to be incorporated into the target lattice for chemical doping. Therefore, realizing coincident shape control of nanoparticle colloids and their doping still pose major difficulties. Due to a special mechanism of the emulsion based synthesis method presented here, involving a gelation of emulsion droplets prior to crystallization of shape-anisotropic ZnO nanoparticles, heteroelements can be effectively entrapped inside the lattice. Different nanocrystal shapes such as nanorods, -prisms, -plates, and -spheres can be obtained, determined by the use of certain emulsification agents. The degree of morphologic alterations depends on the type of incorporated heteroelement M(n+), concentration, and it seems that some shapes are more tolerant against doping than others. Focus was then set on the incorporation of Eu(3+) inside the ZnO particles, and it was shown that nanocrystal shape and aspect ratios could be adjusted while maintaining a fixed dopant level. Special PL properties could be observed implying energy transfer from ZnO excited near its band-gap (3.3 eV) to the Eu(3+) states mediated by defect luminescence of the nanoparticles. Indications for an influence of shape on photoluminescence (PL) properties were found. Finally, rod-like Eu@ZnO colloids were used as tracers to investigate their uptake into biological samples like HeLa cells. The PL was sufficient for identifying green and red emission under visible light excitation.
半导体 (SC) 材料的电子和光学性质的精确控制对于许多重要应用至关重要，例如在光电、光催化或医学领域。众所周知，掺入杂元素（如掺杂是一种经典方法）是调节和增强半导体功能的有效方法。除此之外，对于不同尺寸和形状的 SC 纳米粒子的合成已经取得了巨大进展，并且量子尺寸效应在实验和理论上都得到了很好的证明。虽然纳米粒子的尺寸和形状控制对于纯化合物来说效果相当好，但杂元素的存在是一个问题，因为杂质会强烈干扰用于合成此类粒子的自下而上方法，当杂元素旨在被掺入目标晶格进行化学掺杂时，影响甚至更强。因此，实现纳米粒子胶体的共形形状控制及其掺杂仍然存在主要困难。由于这里提出的乳液合成方法具有特殊的机制，涉及乳液液滴在形状各向异性 ZnO 纳米粒子结晶之前凝胶化，杂元素可以有效地被捕获在晶格内。可以获得不同的纳米晶体形状，如纳米棒、-棱镜、-板和-球体，这取决于使用特定的乳化剂。形态变化的程度取决于掺入的杂元素 M(n+)的类型、浓度，并且似乎有些形状对掺杂的耐受性更强。然后将重点放在 Eu(3+)掺入 ZnO 粒子内，结果表明可以在保持固定掺杂水平的情况下调整纳米晶体形状和纵横比。可以观察到特殊的 PL 特性，这表明能量从 ZnO 的激发态（3.3 eV）转移到由纳米粒子的缺陷发光介导的 Eu(3+)态。表明形状对光致发光 (PL) 性质有影响。最后，使用棒状 Eu@ZnO 胶体作为示踪剂来研究它们在 HeLa 细胞等生物样品中的摄取情况。在可见光激发下，PL 足以识别绿色和红色发射。
