Managing Electron–Phonon Coupling for Single-Photon Upconversion in Perovskite Quantum Dots

Abstract

Perovskite quantum dots (PQDs) feature intriguing single-photon upconversion (SPUC) behavior, whereby anti-Stokes photoluminescence (PL) can be achieved under mild continuous-wave photoexcitation, enabling applications in optical refrigeration, background-free bioimaging, and upconversion photovoltaics. While the conventional (down-conversion) PL efficiency of PQDs can be enhanced to near-unity levels, precise control of phonon-assisted upconversion, the crucial process for SPUC-PL, remains a key challenge. Herein, we demonstrate a rational strategy to improve the upconversion efficiency in organic–inorganic hybrid PQDs compared to all-inorganic counterparts. Using temperature-dependent photoluminescence spectroscopy and femtosecond absorption spectroscopy, we reveal that this cation engineering increases the electron–phonon coupling strength by nearly threefold and shortens the upconversion time constant from 445 fs to below the temporal resolution limit of 120 fs. Consequently, the SPUC efficiency under continuous-wave photoexcitation is enhanced, leading to an average upconversion energy gain above 160 meV, which surpasses those for reported surface-engineered all-inorganic PQDs and II–VI QDs.