Continuum-subtracted spectra of 3I/ATLAS in the CN B²Σ⁺–X²Σ⁺(0–0) violet band region (3860–3890 Å) from a monitoring campaign spanning 2025 July 4–August 21. The grid displays 11 X-Shooter spectra (X1–X11) and two high-resolution UVES observations (U1 and U2), arranged by decreasing heliocentric distance, from top left to bottom right. Each panel indicates the observation date and heliocentric distance r_h (in astronomical units). CN emission is first detected in visit X6 (2025 July 27, r_h = 3.65 au) and increases in strength as the comet approaches the Sun. The green shaded region marks the CN-band feature. UVES spectra show finer spectral structure compared to the lower-resolution X-Shooter observations. The shaded regions represent 1σ uncertainties.