Double-Well Colloidal Nanocrystals Featuring Two-Color Photoluminescence

Ratiometric sensing strategy relies on the ratio of the two photoluminescence (PL) signals originating from the same nano-object for detecting the changes in the surrounding media. Recently, such dual-color emission has been demonstrated in semiconductor colloids, where the PL signal from a quantum-confined domain was complemented with the secondary emission from transition metal ions or a bulk-like structure. Here, we report on the development of dual-color nanocrystal colloids featuring a combination of two quantum-confined emitters within the same nano-object. The reported morphology relies on double-well core/barrier/shell arrangement, where zero-dimensional excitons of the core component (PbS) can coexist with two-dimensional excitons of the shell domain (CdSe). As a result, the core and shell emission bands can be independently tuned across 880–1500 nm and 600–650 nm spectral windows, respectively. A CdS potential barrier at the PbS/CdSe interface was designed to suppress the energy and charge diffusion between the two domains allowing both emission bands to exhibit quantum yields over 10%. Fabricated colloids were demonstrated as dual-color probes for sensing the redox environment, where both the energetics and the timing of photoinduced charge transfer to an add-on analyte could be inferred from the ratiometric measurements.