NanoScience Technology Center, University of Central Florida, Orlando, Florida 32826, United States.
Nano Lett. 2012 Sep 12;12(9):4661-7. doi: 10.1021/nl301988v. Epub 2012 Aug 7.
Atomic clusters of metals are an emerging class of extremely interesting materials occupying the intermediate size regime between atoms and nanoparticles. Here we report the nonlinear optical (NLO) characteristics of ultrasmall, atomically precise clusters of gold, which are smaller than the critical size for electronic energy quantization (∼2 nm). Our studies reveal remarkable features of the distinct evolution of the optical nonlinearity as the clusters progress in size from the nonplasmonic regime to the plasmonic regime. We ascertain that the smallest atomic clusters do not show saturable absorption at the surface plasmon wavelength of larger gold nanocrystals (>2 nm). Consequently, the third-order optical nonlinearity in these ultrasmall gold clusters exhibits a significantly lower threshold for optical power limiting. This limiting efficiency, which is superior to that of plasmonic nanocrystals, is highly beneficial for optical limiting applications.
金属原子团簇是一类新兴的极有趣材料，处于原子和纳米粒子之间的中间尺寸范围。在这里，我们报告了超小、原子精度的金原子团簇的非线性光学（NLO）特性，其尺寸小于电子能量量子化的临界尺寸（~2nm）。我们的研究揭示了光学非线性的明显特征，即当团簇从非等离子体区域发展到等离子体区域时，其大小会发生明显的变化。我们确定最小的原子团簇在较大的金纳米晶体（>2nm）的表面等离子体波长处不显示饱和吸收。因此，这些超小金原子团簇的三阶光学非线性在光学功率限制方面具有显著更低的阈值。这种限制效率优于等离子体纳米晶体，对于光学限制应用非常有益。
