Knappenberger Kenneth L, Wong Daryl B, Xu Wei, Schwartzberg Adam M, Wolcott Abraham, Zhang Jin Z, Leone Stephen R
Department of Chemistry, University of California, Berkeley, California 94720, USA.
ACS Nano. 2008 Oct 28;2(10):2143-53. doi: 10.1021/nn800421g.
The influence of excitation wavelength and embedding media on fluorescence blinking statistics of 4 nm x 20 nm cadmium selenide (CdSe) nanorods is investigated. Photon antibunching (PAB) experiments confirm nonclassical emission from single CdSe nanorods that exhibit a radiative lifetime of 26 +/- 13 ns. The blinking data show behaviors that can be categorized into two classes: excitation near the energy of the band gap and at energies exceeding 240 meV above the band gap. Excitation at the band gap energy (lambda >or= 560 nm) results in more pronounced "on" time probabilities in the distribution of "on" and "off" events, while those resulting from excitation exceeding the band gap by 240 meV or more (lambda <or= 560 nm) are 200 times less likely to display continuous "on" fluorescence persisting beyond 4 s. The "off" time statistics are also sensitive to the excitation wavelength, showing a similar, but inversely correlated, effect. To understand better the excitation-wavelength dependence, fluorescence measurements are obtained for single nanorods deposited both on a bare microscope coverslip and embedded in 1-ethyl-3-methylimidizolium bis(trifluoromethylsulfonyl)imide room-temperature ionic liquid (RTIL). The embedding RTIL medium has a significant influence on the resultant fluorescence statistics only when the excitation energy exceeds the 240 meV threshold. The results are explained by a threshold to access nonemissive trap states, attributed to self-trapping of hot charge carriers at the higher photon excitation energies.
研究了激发波长和包埋介质对4纳米×20纳米硒化镉（CdSe）纳米棒荧光闪烁统计的影响。光子反聚束（PAB）实验证实了单个CdSe纳米棒的非经典发射，其辐射寿命为26±13纳秒。闪烁数据显示出可分为两类的行为：在带隙能量附近激发以及在高于带隙240毫电子伏特以上的能量激发。在带隙能量处激发（λ≥560纳米）会导致“开”和“关”事件分布中更明显的“开”时间概率，而那些由超过带隙240毫电子伏特或更多（λ≤560纳米）的激发导致的事件显示持续超过4秒的连续“开”荧光的可能性要低200倍。“关”时间统计也对激发波长敏感，显示出类似但呈反相关的效应。为了更好地理解激发波长依赖性，对沉积在裸显微镜盖玻片上以及包埋在1-乙基-3-甲基咪唑双（三氟甲基磺酰）亚胺室温离子液体（RTIL）中的单个纳米棒进行了荧光测量。仅当激发能量超过240毫电子伏特阈值时，包埋的RTIL介质才会对所得荧光统计产生显著影响。结果通过进入非发射陷阱态的阈值来解释，这归因于在较高光子激发能量下热电荷载流子的自陷。
