Trap state mediated triplet energy transfer from CdSe quantum dots to molecular acceptors
Trap state mediated triplet energy transfer from CdSe quantum dots to molecular acceptors
复制标题
DOI：
10.1063/5.0022061
复制
发表时间：
2020-08-21
影响因子：
4.4
通讯作者：
Lian, Tianquan
中科院分区：
文献类型：
--
作者：
Jin, Tao;Lian, Tianquan
三重态能量转移（泰特）是量子点到分子受体的一种新型的三重态敏化剂，在光子上转换中具有广阔的应用前景。与量子点带边激子相比，尽管量子点中普遍存在陷阱态，但量子点-受体复合物中陷阱态介导的泰特的作用和机制尚未得到很好的理解。本文利用稳态光致发光、瞬态吸收光谱和时间分辨光致发光研究了从CdSe量子点的陷阱态到吸附的9-蒽羧酸（ACA）的泰特。结果表明，带边激子和陷阱激子都经历直接的Dexter能量转移，形成ACA的三重激发态。对于陷阱激子，随着能量从2.25 eV减小到1.57 eV，泰特速率从（0.340 +/-0.002）ns（-1）减小到（0.124 +/- 0.004）ns（-1），而来自带边激子的泰特速率比陷阱激子快13-37倍。尽管来自带边激子的泰特量子效率（类似于100%）略高于捕获激子的量子效率（类似于95%），但是从CdSe到ACA的整个泰特过程由捕获激子主导，因为它们的相对数量较大。这一结果证明了陷阱态介导的泰特在三重态敏化三重态产生中的重要作用。
Triplet energy transfer (TET) from quantum dots (QDs) to molecular acceptors has received intense research interest because of its promising application as triplet sensitizers in photon up-conversion. Compared to QD band edge excitons, the role and mechanism of trap state mediated TET in QD-acceptor complexes have not been well understood despite the prevalence of trap states in many QDs. Herein, TET from trap states in CdSe QDs to adsorbed 9-anthracene carboxylic acid (ACA) is studied with steady state photoluminescence, transient absorption spectroscopy, and time-resolved photoluminescence. We show that both band edge and trap excitons undergo direct Dexter energy transfer to form the triplet excited state of ACA. The rate of TET decreases from (0.340 +/- 0.002) ns(-1) to (0.124 +/- 0.004) ns(-1) for trap excitons with decreasing energy from 2.25 eV to 1.57 eV, while the TET rate from band edge excitons is 13-37 times faster than trapped excitons. Despite slightly higher TET quantum efficiency from band edge excitons (similar to 100%) than trapped excitons (similar to 95%), the overall TET process from CdSe to ACA is dominated by trapped excitons because of their larger relative populations. This result demonstrates the important role of trap state mediated TET in nanocrystal sensitized triplet generation.