De Paoli Lacerda Silvia H, Douglas Jack F, Hudson Steven D, Roy Marc, Johnson Jerainne M, Becker Matthew L, Karim Alamgir
Polymers Division, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
ACS Nano. 2007 Nov;1(4):337-47. doi: 10.1021/nn700111c.
We exploit the polytypism of group II-VI semiconductors and the long-range dipolar interactions typical of CdSe nanoparticle formation to modulate the geometrical structure and the optical emission properties of novel branched CdSe nanocrystals through shape-dependent quantum confinement effects. X-ray diffraction confirms that these materials incorporate crystalline domains of cubic zinc-blende and hexagonal wurtzite within a polycrystalline growth form whose geometry can be controlled by varying thermodynamic conditions. In particular, labyrinthine-shaped nanoparticles of tunable dimensions are reproducibly synthesized based on a heterogeneous reaction between cadmium acetate in a solution in hexadecylamine and trioctylphosphine with Se as a solid precursor at a relatively low temperature (110 degrees C). The resulting highly branched CdSe structures resemble labyrinthine patterns observed in magnetic fluids and superconductors films in magnetic fields, and in lipid films and other materials where strong dipolar interactions "direct" large-scale pattern formation. Surprisingly, these novel maze-like structures emit light within a narrow bandwidth (full-width at half-maximum approximately equal to 33-42 nm) of the visible spectrum (508 nm < lambda < 563 nm), so the regular dimensions of the core regions of these branched structures govern their emission characteristics rather than overall nanoparticle size. This property should make these materials attractive for applications where luminescent materials having tunable emission characteristics and a narrow emission frequency range are required, along with the insensitivity of the particles' luminescent properties to environmental conditions.
我们利用II-VI族半导体的多型性以及CdSe纳米颗粒形成过程中典型的长程偶极相互作用，通过形状依赖的量子限制效应来调节新型支链CdSe纳米晶体的几何结构和光发射特性。X射线衍射证实，这些材料在多晶生长形式中包含立方闪锌矿和六方纤锌矿的晶域，其几何形状可通过改变热力学条件来控制。特别是，基于十六胺溶液中的醋酸镉与三辛基膦之间的非均相反应，以Se作为固体前驱体，在相对较低的温度（110摄氏度）下可重复合成尺寸可调的迷宫状纳米颗粒。所得的高度支化CdSe结构类似于在磁场中的磁性流体和超导薄膜，以及脂质薄膜和其他存在强偶极相互作用“引导”大规模图案形成的材料中观察到的迷宫图案。令人惊讶的是，这些新型迷宫状结构在可见光谱（508 nm < λ < 563 nm）的窄带宽（半高宽约等于33 - 42 nm）内发光，因此这些支链结构核心区域的规则尺寸决定了它们的发射特性，而非整体纳米颗粒尺寸。这种特性应使这些材料对于需要具有可调发射特性和窄发射频率范围的发光材料，以及颗粒发光特性对环境条件不敏感的应用具有吸引力。
