Absorption spectra of Ag _x Al_1-x (top: a, b, c) and Ag _x In_1-x (bottom: d, e, f) for x = 0.25 (deep purple), x = 0.50 (green) and x = 0.75 (light blue). The palest continuous curves represent the experimental spectra just after the synthesis of the samples (time t ₀), as previously shown in Figure 3c and d. The samples were then exposed to air during several days (t _o + n _d d, n _d being the number of days) and their optical spectra measured (bold continuous curves). In Ag _x In_1-x BNPs, we observe a strong red-shift of the LSPR for x = 0.25 (d) and x = 0.50 (e), while for x = 0.75 (f), only a small damping occurs. For Ag-Al, we do not observe a strong evolution of the spectra, except a damping of the LSPR for x = 0.75 (c). The dotted lines represent the simulated optical responses for core@shell structures Ag _XcAl_1-Xc@Al₂O₃ and Ag _XcIn_1-Xc@In₂O₃ BNPs with fully oxidized shells. The silver atomic proportion in the cores are thus 100 % (c), 92.5 % (b), 90 % (a) for Ag-Al, and 95 % (f), 92.5 % (e) and 90 % (d) for Ag-In. The shells are made of pure Al₂O₃ or In₂O₃ and are thicker as the amount of Al and In increases. The positions of the resonance with these simulated configurations are in good agreement with the experimental aged spectra.