Upconversion, the ability to convert low frequency light to high frequency light, has attracted enormous attention due to its wide range of applications in solar cells, biological imaging, and data storage. Here, we focus on a newly introduced hybrid molecular-nanocrystal upconversion system. We use PbS nanocrystals capable of upconverting NIR light as the sensitizer and rubrene molecules as the annihilator. Light can be absorbed by the PbS nanocrystal, and then the energy can be transferred from the triplet state of the nanocrystal to the triplet state of the rubrene through a process called triplet-triplet energy transfer (TTET). Finally, the two excited rubrene molecules annihilate to upconvert the light during triplet-triplet annihilation. Here we study the mechanism of TTET and the effect of the nanocrystal ligand length on TTET quantum yield (QY) in the PbS/rubrene upconversion system. We synthesized PbS NPs with oleylamine ligands, and replaced the original ligands with carboxylic acid molecules that have 6 different alkane chain lengths (C<sub>n</sub>H<sub>2n+1 </sub>COOH, n= 3, 7, 9, 11, 13, 15). We observed that the upconversion QY increases exponentially with decreasing ligand length, indicative of Dexter energy transfer mechanism.

Mechanism of energy transfer between molecules and PbS nanocrystals during upconversion

251st National Meeting (2016)

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