Efficient multiphoton absorption of near-infrared emitting Cu-doped ZnInS/ZnS nanocrystals

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Due to their unique optoelectronic properties, doped semiconductor nanocrystals (NCs) are promising fluorescent probes for deep-tissue bioimaging applications. However, studies on the photophysical properties of cadmium-free doped NCs are scarce. In this study, we synthesized and studied the photophysical properties of one type of cadmium-free doped NCs (Cu: ZnInS/ZnS NCs), which exhibit near infrared-I (NIR-I) emission at 730 nm and long emission lifetime up to 1.38 μs. Femtosecond transient absorption spectra revealed a strong exciton coupling effect between the Cu2+ ions and the ZnInS/ZnS host, with a fast energy transfer time of ≈100 ps. More importantly, Cu: ZnInS/ZnS NCs exhibit efficient volume-normalized two- and three-photon absorption cross-sections in NIR-I (800–900 nm) and NIR-III regions (1600–1990 nm), with maximum values up to 6.9 GM nm−3 at 800 nm and 1.1 × 10−80 cm6 s2 photon−2 nm−3 at 1600 nm, respectively. This study can shed light on the exploration of novel environmentally friendly doped NCs for deep-tissue bioimaging applications.