Precise modulation of photoluminescence (PL) of nanomaterials by external control is of great interest in such diverse areas as photocatalysis, memory and sensing. Recent studies have combined colloidal quantum dots (QDs) with photochromic molecules to construct optically switchable PL systems. However, it still remains challenging to switch the PL on and off in the near-infrared (NIR) region with multi-stimuli such as light and heat. Here, we present light and heat triggered modulation of the NIR PL of PbS QDs using adjacent spiropyran derivatives. The NIR PL of PbS was reversibly switched on and off through the isomerization process of spiropyran molecules that can be triggered by either light irradiation or heating. The PL intensity of the off state is low enough to yield an on/off ratio as high as 54. Transient absorption measurements revealed ultrafast photoinduced hole transfer from PbS to spiropyran, the rate and efficiency of which depend critically on the driving force that can be deeply modulated through spiropyran isomerization. This study not only establishes a novel multi-stimuli switchable PL system in the NIR, but also provides fundamental guidelines for the design for such systems for a variety of emerging applications.

Auger recombination has been a long-standing obstacle to many prospective applications of colloidal quantum dots (QDs) ranging from lasing, light-emitting diodes to bio-labeling. As such, understanding the physical underpinnings and scaling laws for Auger recombination is essential to these applications. Previous studies of biexciton Auger recombination in various QDs established a universal scaling of biexciton lifetime (τ_XX) with QD volume (V): τ_XX = γV. However, recent measurements on perovskite nanocrystals (NCs), an emerging class of enablers for light harvesting and emitting applications, showed significant deviations from this universal scaling law, likely because the measured NCs are weakly-confined and also have relatively broad size-distributions. Here we study biexciton Auger recombination in mono-dispersed (size distributions within 1.7%-9.0%), quantum-confined CsPbBr₃ NCs (with confinement energy up to 410 meV) synthesized using a latest approach based on thermodynamic equilibrium control. Our measurements clearly reproduce the volume-scaling of τ_XX in confined CsPbBr₃ QDs. However, the scaling factor γ (0.085 ± 0.001 ps/nm³) is one order of magnitude lower than that reported for CdSe and PbSe QDs (1.00 ± 0.05 ps/nm³), suggesting unique mechanisms enhancing Auger recombination rate in perovskite NCs.