Number of Surface-Attached Acceptors on a Quantum Dot Impacts Energy Transfer and Photon Upconversion Efficiencies

• Published in: ACS photonics Vol. 7; no. 7; pp. 1876 - 1884
• Main Authors: Zhang, Jie, Kouno, Hironori, Yanai, Nobuhiro, Eguchi, Daichi, Nakagawa, Tatsuo, Kimizuka, Nobuo, Teranishi, Toshiharu, Sakamoto, Masanori
• Format: Journal Article
• Language: English
• Published: American Chemical Society 15.07.2020
• Subjects: quantum dots; perylene; triplet energy transfer; photon upconversion; triplet annihilation
• ISSN: 2330-4022; 2330-4022
• DOI: 10.1021/acsphotonics.0c00771

Composites of organic molecules and inorganic quantum dots (QDs) have emerged as attractive photon upconversion systems that use triplet–triplet annihilation upconversion (TTA-UC). However, the upconversion efficiency of such systems is still far from reaching their theoretical potential. The number of acceptor molecules directly coordinated on a QD (n) should determine triplet–triplet energy transfer (TTET) efficiency (ΦTTET), which consequently affects the efficiency of TTA-UC, but the research focusing on the n value has been limited. In the present report, the effect of n on TTET from CdSe or CdTe QDs to perylene-3-carboxylic acid (Pe; i.e., acceptor) were systematically investigated. The TTET and TTA-UC efficiencies increase with increasing n. The regulation of n on a QD could provide a straightforward means to realize high-performance TTA-UC. For the molecule/QDs systems, small QDs with a wide band gap are favorable for intrinsic TTET (i.e., TTET in a one-to-one QD-Pe composite system), because intrinsic TTET efficiency is detemined by the triplet energy of QDs. On the other hand, the small QDs limit the n due to the small surface area. Therefore, the proper choices of QDs and acceptors providing both sufficient free energy change for TTET and large n are important to achieve efficient TTA-UC.