Ghosh Manoranjan, Raychaudhuri A K
DST Unit for Nanoscience, S N Bose National Centre for Basic Sciences, Block-JD, Sector-3, Salt Lake, Kolkata 700098, India.
Nanotechnology. 2008 Nov 5;19(44):445704. doi: 10.1088/0957-4484/19/44/445704. Epub 2008 Sep 30.
We report that ZnO nanostructures synthesized by a chemical route undergo a shape transition at ∼20 nm from spherical to hexagonal morphology thereby changing the spectral components of the blue-green emission. Spherically shaped nanocrystals (size range 11-18 nm) show emission in the range of 555-564 nm and the emission shifts to the longer wavelength as the size increases. On the other hand, rods and hexagonal platelets (size range 20-85 nm), which are the equilibrium morphology after the shape transition, show an emission near 465-500 nm which shifts to shorter wavelength as the size increases. The shape transition also leads to relaxation of microstrain in the system. Our analysis shows that the visible emission originates from a defect layer on the nanostructure surface which is affected by the shape transition. The change in the spectral component of the blue-green emission on change of shape has been explained as arising from band bending due to a depletion layer in smaller spherical particles which is absent in the larger particles with flat faces.
我们报道，通过化学途径合成的氧化锌纳米结构在约20纳米处会发生形状转变，从球形变为六边形形态，从而改变蓝绿色发射的光谱成分。球形纳米晶体（尺寸范围为11 - 18纳米）在555 - 564纳米范围内发射，并且随着尺寸增加发射波长向更长波长移动。另一方面，棒状和六边形片状（尺寸范围为20 - 85纳米）是形状转变后的平衡形态，它们在465 - 500纳米附近发射，并且随着尺寸增加发射波长向更短波长移动。形状转变还导致系统中微应变的松弛。我们的分析表明，可见光发射源自纳米结构表面的缺陷层，该缺陷层受形状转变影响。形状改变时蓝绿色发射光谱成分的变化已被解释为是由于较小球形颗粒中的耗尽层导致的能带弯曲引起的，而具有平面的较大颗粒中不存在这种耗尽层。
