A small quantity of Eu3+ ions were doped in the lead-free ferroelectric K0.5Na0.5NbO3-xLiNbO3 (KNN-xLN, 0 <= x <= 0.08) ceramics to investigate the NbO6 octahedral distortion induced by the increasing LN content. In addition, the phase structure, ferroelectric, and photoluminescence properties of K(0.5)Na(0.5)NbO(3-)xLiNbO3: 0.006Eu(3+) (KNN-xLN: 0.006Eu(3+)) lead-free piezoelectric ceramics were characterized. All the X-ray diffraction, Raman spectra, dielectric constant vs temperature measurements and the photoluminescence of Eu3+ ions demonstrated that the prepared ceramics undergo a polymorphic phase transition (PPT, from orthorhombic to tetragonal phase transformation) with the rising LN content, and the PPT region locates at 0.05 <= x <= 0.06. The ferroelectric properties, Raman intensity ratios and photoluminescence intensity ratios show similar variations with the increasing LN content, all with a maximum value achieved at the PPT region. We believe that the close relationship among the ferroelectric properties, Raman intensity ratios, and photoluminescence intensity ratios is caused by the NbO6 octahedral distortion. The photoluminescence of Eu3+ ion was discussed basing on the crystal-symmetry principle and Judd-Ofelt theory.