Based on a model of coupled processes with differently time-dependent decay kinetics we present a critical review on photoluminescence (PL) and transient absorption (TA) experiments in undoped and Mg or Fe-doped LiNbO3, together with a comprehensive interpretation of visible radiative and parallel non-radiative decay processes on timescales ranging from 50 ns up to minutes. Analogies and peculiarities of the kinetics of mobile self-trapped and pinned excitons are investigated and compared with those of hopping polarons in the same system. Exciton hopping with an activation energy of ≈0.18 eV is shown to govern the lifetime and quenching of the short PL component above 100 K. Strong interaction between excitons and dipolar pinning defects explains the exorbitant lifetimes and large depinning energies characterizing delayed TA components in doped LiNbO3, while restricted hopping of the pinned excitons is proposed to play a role in strongly delayed PL in LiNbO3:Mg exhibiting a narrowed emission band due to locally reduced electron-phonon coupling. Atomistic models of pinned excitons are proposed corresponding to charge-compensated dipolar defects predicted by theories of dopant incorporation in LiNbO3 and are systematically assigned to absorption bands observed near the UV edge. Excitation in these bands is shown to lead directly to pinned exciton states confirming also the previously proposed two-step exciton-decay scenario in LiNbO3:Fe. Weak intrinsic sub-80 ns luminescence in congruent LiNbO3 is explained as an opposite effect of enhanced electron-phonon coupling for excitons pinned on Nb_Li antisite defects. The comparison of the different observed stretching behaviors in LiNbO3 provides an intuitive picture of the underlying physical processes. The findings are relevant not only for holographic and non-linear optical applications of LiNbO3 but are of general interest also for the treatment of stretched exponential or other time-dependent kinetics in complex condensed systems ranging from nanocrystals and polymers to liquids and biophysical systems.

中文翻译：

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基于原子模型的铌酸锂激子跳跃固定场景：同一系统中不同种类的拉伸指数动力学

基于具有不同时间相关衰减动力学的耦合过程模型，我们对未掺杂和 Mg 或 Fe 掺杂的 LiNbO3 中的光致发光 (PL) 和瞬态吸收 (TA) 实验进行了批判性回顾，同时对可见辐射和50 ns 到几分钟的时间尺度上的并行非辐射衰减过程。研究了移动自陷激子和钉扎激子动力学的类比和特性，并与同一系统中跳跃极化子的动力学进行了比较。具有 ≈0.18 eV 活化能的激子跳跃被证明可以控制 100 K 以上的短 PL 组件的寿命和猝灭。激子和偶极钉扎缺陷之间的强相互作用解释了掺杂 LiNbO3 中延迟 TA 成分的过高寿命和大脱钉能量，而提出钉扎激子的受限跳跃在 LiNbO3:Mg 中的强延迟 PL 中发挥作用，表现出较窄的发射带由于局部减少的电子 - 声子耦合。提出了钉扎激子的原子模型，对应于由掺杂剂掺入 LiNbO3 的理论预测的电荷补偿偶极缺陷，并系统地分配给在 UV 边缘附近观察到的吸收带。这些带中的激发显示直接导致钉扎激子态，这也证实了先前提出的 LiNbO3:Fe 中的两步激子衰变情况。全等 LiNbO3 中的弱本征亚 80 ns 发光被解释为固定在 Nb_Li 反位缺陷上的激子的增强电子 - 声子耦合的相反效果。在 LiNbO3 中观察到的不同拉伸行为的比较提供了潜在物理过程的直观图片。这些发现不仅与 LiNbO3 的全息和非线性光学应用相关，而且对于处理从纳米晶体和聚合物到液体和生物物理系统的复杂凝聚系统中的拉伸指数或其他时间相关动力学也具有普遍意义。