The role of temperature in the photoluminescence quantum yield (PLQY) of AgS-based nanocrystals.

Highly emissive AgS nanocrystals (NCs) passivated with a gradated shell incorporating Se and Zn were synthesized in air, and the temperature dependence of their photoluminescence quantum yield (PLQY) was quantified in both organic and aqueous media at ∼1200 nm. The relevance of this parameter, measured at physiological temperatures, is highlighted for applications that rely on the near infrared (NIR) photoluminescence of NCs, such as deep NIR imaging or luminescence nanothermometry. Hyperspectral NIR imaging shows that AgS-based NCs with a PLQY in organic media of about 10% are inefficient for imaging at 40 °C through 20 mm thick tissue with low laser irradiation power densities. In contrast, water-transferred AgS-based NCs with an initial PLQY of 2% in water exhibit improved robustness against temperature changes, enabling improved imaging performance.