Wurtzite InP/ZnSe/ZnS Core/Shell Semiconductor Quantum Dots with Bright Near-IR Emission

Indium phosphide (InP) quantum dots (QDs) are already widely employed as heavy-metal-free materials for optoelectronic and bioimaging applications. However, common hot-injection methods produce zinc-blende phase InP QDs, and the synthesis of large-sized InP QDs with uniform size distribution and efficient near-infrared (NIR) emission has been limited. Here, starting from the cation-exchange synthesis of monodisperse wurtzite phase InP (w-InP) QDs with tunable size, we report the epitaxial growth of ZnSe/ZnS shells to significantly enhance photoluminescence (PL) efficiency and photochemical stability. The resulting w-InP/ZnSe/ZnS core/shell/shell (CSS) QDs exhibit narrow size-tunable bright NIR emission (∼740-820 nm). For example, for cores in the midrange (d = 8.7 ± 0.7 nm; peak emission wavelength at ∼780 nm), the PL quantum yield (QY) reaches 78%, with a narrow full-width at half-maximum (fwhm) of ∼33 nm (∼69 meV). Photostability studies reveal that the optical properties of both the w-InP core and the CSS QDs remain stable in ambient conditions under dark storage. Under illumination, the w-InP cores show increased PLQY due to light-induced surface oxidation, while in the presence of oxygen, CSS QDs experience a decline in PL performance due to photo-oxidation of the ZnSe shell. This degradation is lessened upon exposure to shorter wavelength light, suggesting the involvement of outer shell states in this process. These high-performance, cadmium-free NIR-emitting QDs thus hold strong potential for applications in advanced optoelectronics and bioimaging technologies.