Thermally activated delayed photoluminescence from pyrenyl-functionalized CdSe quantum dots

The generation and transfer of triplet excitons across semiconductor nanomaterial-molecular interfaces will play an important role in emerging photonic and optoelectronic technologies, and understanding the rules that govern such phenomena is essential. The ability to cooperatively merge the photophysical properties of semiconductor quantum dots with those of well-understood and inexpensive molecular chromophores is therefore paramount. Here we show that 1-pyrenecarboxylic acid-functionalized CdSe quantum dots undergo thermally activated delayed photoluminescence. This phenomenon results from a near quantitative triplet-triplet energy transfer from the nanocrystals to 1-pyrenecarboxylic acid, producing a molecular triplet-state 'reservoir' that thermally repopulates the photoluminescent state of CdSe through endothermic reverse triplet-triplet energy transfer. The photoluminescence properties are systematically and predictably tuned through variation of the quantum dot-molecule energy gap, temperature and the triplet-excited-state lifetime of the molecular adsorbate. The concepts developed are likely to be applicable to semiconductor nanocrystals interfaced with molecular chromophores, enabling potential applications of their combined excited states.

三重态激子在半导体纳米材料 - 分子界面的产生和转移将在新兴的光子和光电子技术中发挥重要作用，理解支配此类现象的规则至关重要。因此，将半导体量子点的光物理性质与那些已被充分了解且价格低廉的分子生色团的性质协同融合的能力是至关重要的。在此我们表明，1 - 芘甲酸功能化的CdSe量子点会发生热激活延迟光致发光现象。这种现象是由于从纳米晶体到1 - 芘甲酸近乎定量的三重态 - 三重态能量转移所致，产生了一个分子三重态“库”，它通过吸热的反向三重态 - 三重态能量转移使CdSe的光致发光态重新填充。通过改变量子点 - 分子的能隙、温度以及分子吸附物的三重态激发态寿命，光致发光性质能够被系统地且可预测地调节。所提出的概念可能适用于与分子生色团连接的半导体纳米晶体，使其组合激发态具有潜在应用。