Optical properties of inverted type-I InP quantum dots with near-infrared emission

Unlike conventional type-I InP-based quantum dots (QDs), inverted type-I QDs can push the emission wavelength to the near-infrared (NIR) range. However, the fundamental optical properties of such kinds of QDs have yet to be studied in depth. In this work, we report the optical properties of inverted type-I ZnSe/InP/ZnS QDs with photoluminescence (PL) emission in the first biological window. Using femtosecond ultrafast transient absorption, the electron-injection time, Auger lifetime, and hot-carrier cooling time of the inverted type-I QDs are determined. Their temperature-dependent PL spectrum reveals that these QDs possess a higher exciton-binding energy and weaker carrier-phonon coupling effect than conventional type-I InP-based QDs. Interestingly, the QDs have strong two-photon absorption cross sections in the second biological window, up to 5120 GM at 1200 nm. These results suggest that ZnSe/InP/ZnS QDs have potential applications for light emitting devices and deeptissue bioimaging.