Near-Infrared Photoluminescence from Ytterbium- and Erbium-Codoped CsPbCl Perovskite Quantum Dots with Negative Thermal Quenching.

Near-infrared (NIR) luminescent phosphors hold promise for a wide range of applications, from bioimaging to light-emitting diodes (LEDs), but are typically confined to wavelengths <1300 nm and manifest substantial thermal quenching pervasive in luminescent materials. Here we observed the thermally enhanced NIR luminescence of Er (1540 nm), a 2.5-fold enhancement with increasing temperature from 298 to 356 K, from Yb- and Er-codoped CsPbCl perovskite quantum dots (PQDs) (photoexcited at ∼365 nm). Mechanistic investigations revealed that thermally enhanced phenomena originated from combined effects of thermally stable cascade energy transfer (from a photoexcited exciton to a pair of Yb and then to surrounding Er) and minimized quenching of surface-adsorbed water molecules on the I state of Er induced by the temperature increase. Importantly, these PQDs enable producing phosphor-converted LEDs emitting at 1540 nm with inherited thermally enhanced properties, having implications for a wide range of photonic applications.