Triplet Sensitization and Photon Upconversion Using InP-Based Quantum Dots.

Molecular triplet sensitization using colloidal semiconductor nanocrystals or quantum dots (QDs) is important for many photochemical and photonic applications. Current QD sensitizers often contain toxic elements such as Cd and Pb. In order to "go green" with these sensitizers, we investigate triplet energy transfer from InP-based QDs. Time-resolved spectroscopy studies revealed picosecond hole trapping in core-only QDs, which could complicate and/or inhibit energy transfer. We therefore developed InP/ZnSe/ZnS core/shell QDs that effectively suppressed hole trapping and meanwhile allowed for triplet energy transfer to surface-anchored anthracene acceptors with an efficiency of 84%. The sensitized molecular triplets participated in triplet-triplet-annihilation, enabling photon upconversion with a normalized quantum yield reaching 10.0% ± 0.1%. This study demonstrates that nontoxic InP-based QDs can be engineered to be on par with state-of-the-art Cd- or Pb-containing QDs for use as triplet sensitizers.