Transition metal ions doped InP/ZnS quantum dots: toward the application of two-photon probes and type-I photosensitizers

Semiconductor colloidal quantum dots (QDs) are technologically important for multiphoton bioimaging and photodynamic therapy applications. However, most semiconductor QDs have intrinsic cytotoxicity and small Stokes shifts, which hinder their applications in diagnosis and treatment. In this work, a series of transition metal ions doped InP/ZnS QDs, including Cu: InP/ZnS and Mn: InP/ZnS QDs, are synthesized, and their optical properties are characterized. Interestingly, these doped InP/ZnS QDs possess strong two-photon absorption cross sections at 700 nm (100 fs, 80 MHz), up to ∼1.5 × 10 4 GM for Cu: InP/ZnS QDs (0.5% Cu) and ∼8.8 × 10 3 GM for Mn: InP/ZnS QDs (40% Mn). Importantly, both undoped and doped InP/ZnS QDs can generate electron-hole pairs to produce •OH and O 2 •− under 800 nm photoexcitation, which can be used as two-photon excited type-I photosensitizers. These findings constitute a comprehensive understanding of the transitional metal ions doped InP/ZnS QDs as the two-photon fluorescence probes and type-I photosensitizers.