Alloyed Quantum Dots with Tuned Exciton Wave Function Delocalization for Enhanced Energy Transfer

Efficient exciton energy transfer from photoexcited quantum dots (QDs) is the key to achieving high performance across diverse applications. Exciton wave function delocalization favors energy transfer, yet fine-tuning the degree of delocalization remains challenging. Here, we demonstrate the modulation of exciton delocalization by engineering the exciton Bohr radius via tellurium doping in lead selenide (PbSe_1-<i>x</i>Te_<i>x</i>) alloy QDs. Using a QD-sensitized triplet-triplet annihilation upconversion system as a testing platform, we show that Te doping enhances energy transfer and boosts upconversion efficiency by up to 50-fold, before the poor stability of PbTe dominates at higher Te content. This doping strategy is also compatible with other optimizations, as shortening the surface ligands of PbSe_1-<i>x</i>Te_<i>x</i> QDs further enhances energy transfer and upconversion performance. Through femtosecond transient absorption microscopy, we further confirm that optimized Te doping accelerates early stage exciton transfer dynamics in QD thin films, indicating larger exciton delocalization. This strategy provides a versatile material-design route to optimize energy transfer in QD-based material systems.