Relaxation Dynamics of Photo-excited States and Generation and Transport Processes of Carriers in Pristine C_<60> Single Crystals.

为了理解光激发后C_2晶体的整个弛豫过程<60>，我们研究了与光致发光过程有关的载流子产生机制。在本研究项目的第一阶段，我们已经明确了载流子的产生源于Frenkel激子的热解离，并且通过将Frenkel激子捕获到局域态来增强局域激子的发光。为了证实载流子产生和发光过程之间的反相关性，在同一个晶体中测量光电流和光致发光。用飞行时间法测量了光电流，用显微光谱法观察了ITO电极和云母薄膜的光致发光，光电流和光致发光强度与温度的关系服从Arrhenius公式。在高于100 K的范围内，光电流变得可观察到， ...更多信息 发光源于定域激子的辐射衰变。光电流的热激活行为表现出与光致发光猝灭的反相关性。这种关系可以解释为载流子产生的增强直接导致发光强度的降低。通过假设Frenkel激子的热激活布居转移，它们可以拟合为相同的激活能99 meV。估计的激活能表明，存在于低于120 meV的弗伦克尔激子态的局域态，不有助于载流子的产生。另一方面，获得的光电流时间响应为“色散型”，几乎随t^&lt;-□&gt;（α &lt;$1）衰减。在TOF方法中，这种响应归因于漂移载流子的反常色散。C_2晶体中载流子的输运<60>似乎服从跳跃过程，所得到的响应表明跳跃位置在势垒高度和距离上存在连续分布。少

Aiming to understanding the whole relaxation processes following optical excitation in C_<60> crystals, we have investigated the carrier generation mechanism in connection with the photoluminescence process. In the first stage of the present research project, we have made clear that the carrier generation originates from thermal dissociation of Frenkel exciton and luminescence from localized exciton is enhanced by capturing the Frenkel exciton into the localized state. In order to confirm anti-correlation between the carrier generation and the luminescence process, photocurrent and photoluminescence were measured in one and the same crystal. The photocurrent was measured by Time-of-Flight method, and the photoluminescence through ITO electrodes and mica thin films was observed by a microspectroscopy method.Temperature dependence of photocurrent and photoluminescence intensities obeys to Arrhenius formula. In the range higher than 100K where the photocurrent becomes observable, the lumi … More nescence originates from radiative decay of localized exciton. The thermally activated behavior of the photocurrent exhibits anti-correlation to quenching of the photoluminescence. This relation is interpreted by that enhancement of carrier generation directly leads reduction of luminescence intensity. They can fit with the same activation energy of 99meV by assuming thermal activated population transfers from the Frenkel exciton. The estimated activation energy suggests that the localized state, which exists below 120meV from the Frenkel exciton state, doesn't contribute to the carrier generation. On the other hand, obtained time response of photocurrent is of "dispersive-type", and almost decays as t^<-□> (α〜1). Such response in TOF method has been attributed to anomalous dispersion of drift carriers. Carrier transport in C_<60> crystals seems to obey a hopping process, and the obtained response suggests the existence of continuous distribution of hopping sites in barrier height and distance. Less