Department of Chemistry and ‡Clemson Light Imaging Facility, Clemson University , Clemson, South Carolina 29634, United States.
Nano Lett. 2017 Jun 14;17(6):3896-3901. doi: 10.1021/acs.nanolett.7b01440. Epub 2017 May 31.
Small semiconductor structures often exhibit "telegraph noise". If the number of charge carriers is small, then spontaneous changes in the number of carriers can lead to abrupt switching between two or more discrete levels, leading to burst noise or popcorn noise in transistors. We have observed similar behavior in the fluorescence of organic semiconductor nanoparticles, where typical carrier populations are often less than ∼10 carriers per nanoparticle. Spontaneous changes in the number of charges results in abrupt switching between 2 or more fluorescence intensity levels, because the charges act as highly efficient fluorescence quenchers. The equilibrium number of charges is determined by competition between a photodriven ionization process and spontaneous recombination. Doping with redox-active molecules also affects the balance. Nanoparticles of the conjugated polymer PFBT doped with the fullerene derivative PCBM, rapidly establish a fluctuating steady-state population of tens of hole polaron charge carriers, sufficient to nearly completely suppress nanoparticle fluorescence. However, fluctuations in the number of charges lead to occasional bursts of fluorescence. This spontaneous photoswitching phenomenon can be exploited for superresolution imaging. The repeated, spontaneous generation of short, intense bursts of fluorescence photons results in a localization precision of ∼0.6 nm, about 4 times better than typical resolution obtained by localization of dye molecules.
小型半导体结构通常会表现出“电报噪声”。如果载流子数量较少，那么载流子数量的自发变化会导致在两个或更多离散能级之间突然切换，从而导致晶体管中的突发噪声或爆米花噪声。我们在有机半导体纳米粒子的荧光中观察到了类似的行为，其中典型的载流子数通常少于每个纳米粒子约 10 个载流子。载流子数量的自发变化导致荧光强度的 2 个或更多能级之间的突然切换，因为电荷充当高效的荧光猝灭剂。电荷的平衡数量由光驱动的电离过程和自发复合之间的竞争决定。掺杂氧化还原活性分子也会影响平衡。用富勒烯衍生物 PCBM 掺杂的共轭聚合物 PFBT 的纳米粒子迅速建立起数十个空穴极化子载流子的波动稳态种群，足以几乎完全抑制纳米粒子的荧光。然而，电荷数量的波动会导致偶尔的荧光爆发。这种自发的光开关现象可用于超分辨率成像。荧光光子的重复、自发产生的短而强烈的爆发导致定位精度约为 0.6nm，比通过定位染料分子获得的典型分辨率好约 4 倍。
