Fig. 3: Required conditions and mechanisms of laser-induced dot-to-superdot transformation.
From: Ultrafast photochemistry produces superbright short-wave infrared dots for low-dose in vivo imaging
a Time evolution of the NIR-II fluorescence generated by colloidal dispersions of Ag2S dots in CHCl3 under irradiation at different power densities. In all cases, pulse width and repetition rate were set to 50 fs and 1 kHz, respectively. b Time evolution of the NIR-II fluorescence generated by Ag2S dots dispersed in different solvents under laser irradiation with 50 fs, 808 nm laser pulses. c Time evolution of the NIR-II fluorescence generated by Ag2S dots under laser irradiation with 50 fs, 808 nm laser pulses in presence and absence of Ag NPs. d Time evolution of the NIR-II fluorescence intensity generated by Ag2S dots in CHCl3 as obtained for different pulse durations. For all cases in b, c, and d, the ultrafast laser power density was set to 9 W cm−2. Different samples were used in each condition used in a, b, c and d. e Schematic representation of the physicochemical mechanisms underlying the ultrafast laser-induced dot-to-superdot transformation. Upon illumination with ultrafast infrared laser pulses, multiphoton excitation of Ag NPs leads to their Coulomb explosion (step 1). The Ag+z generated in this process react with CHCl3 molecules forming AgCl (step 2), which in turn reacts with the surface of the Ag2S dots forming a protective layer (steps 3 and 4).
