QSO rest-frame optical continuum-subtracted spectrum (grey line) in the spectral region 4700–5400 Å. The emission lines Hβ and [O III] λλ4959,5007 Å (marked with vertical lines) are blended with the Fe II emission, which can be clearly seen at ∼3 μm. The following fitted Fe II templates are shown: Véron-Cetty et al. (2004, VC+04, red line), Boroson & Green (1992, BG+92, blue line), and Tsuzuki et al. (2006, T+06, yellow line). The lines in the bottom panel show the different residuals of the fitting.