Kepler R G
Appl Opt. 1969 Jan 1;8 Suppl 1:25-6.
Recent experiments have shown that immediate recombination of electron-hole pairs created by high energy radiation in anthracene crystals is a very probable process. The high recombination probability arises because the mean free path of electrons and holes in anthracene is small compared with the distance from a unit charge at which the Coulomb potential energy is equal to the thermal energy. In view of these results, the question which immediately arises is how important is immediate recombination in low energy band-to-band transitions in anthracene. A number of experiments reported recently have generally given a quantum efficiency of the order of 10(-4); since the experiments involved a variety of excited states, it appeared that immediate recombination was solely responsible for the low quantum efficiency. On the basis of this hypothesis, absorption of photons by singlet excitons in anthracene was looked for. The cross section for absorption predicted by the hypothesis, based on the measured cross section for exciton photoionization, is 10(-15) cm(2); experimentally, it was found to be less than 10(-17) cm(2) at 5300 A. Therefore, it appears that the low quantum yield observed for anthracene is not solely the result of a high probability for immediate recombination but must also involve low probabilities for autoionization of highly excited but bound states.
最近的实验表明，蒽晶体中由高能辐射产生的电子 - 空穴对的即时复合是一个非常可能的过程。复合概率高的原因是，与库仑势能等于热能时离单位电荷的距离相比，蒽中电子和空穴的平均自由程较小。鉴于这些结果，立即出现的问题是即时复合在蒽的低能带间跃迁中有多重要。最近报道的一些实验通常给出的量子效率约为10^(-4)；由于这些实验涉及多种激发态，似乎即时复合是低量子效率的唯一原因。基于这个假设，人们寻找蒽中单线态激子对光子的吸收。根据激子光电离的测量截面，该假设预测的吸收截面为10^(-15) cm²；实验发现，在5300 Å时，它小于10^(-17) cm²。因此，看来观察到的蒽的低量子产率并非仅仅是即时复合概率高的结果，还必定涉及高激发但束缚态的自电离概率低的问题。
