Near-Infrared Photoluminescence and Thermal Stability of PbS Nanocrystals at Elevated Temperatures

Near-infrared quantum dots (QDs) are attractive materials for biological, defense, and telecommunications applications. Many of these applications depend on QD luminescence at elevated temperatures, which has not been thoroughly explored in infrared-emitting QD materials. Here, we report a comprehensive study of the thermal stability of lead sulfide (PbS) QDs. Despite a bulk melting temperature of 1100 °C, in situ transmission electron microscopy (TEM) revealed coalescence of neighboring PbS QDs at temperatures as low as 150 °C. While TEM, X-ray diffraction, and thermogravimetric analysis showed no changes to the QD structure below 150 °C, the photoluminescence of densely packed QD films irreversibly decreased after exposure to temperatures as low as 50 °C. In contrast, embedding the QDs in cross-linked poly(lauryl methacrylate) dramatically improved the stability of photoluminescence to thermal cycling, delaying the onset of irreversible luminescence quenching beyond 120 °C and maintaining measurable photoluminescence intensity and single-exponential decay dynamics above 200 °C. Time-resolved spectroscopy revealed increased rates of nonradiative recombination at elevated temperatures, indicating more efficient phonon-mediated decay processes. These results show that PbS QDs present similar challenges to visible-emitting QDs in applications requiring operation at elevated temperatures but encourage further efforts in thermal stabilization.