The temperature dependence of the emission spectrum of Cr3+ ions in Sr0.6Ba0.4 (NbO3)2 has been systematically investigated around the ferroelectric phase transition of this crystal (~370 K). In spite of the strong thermal quenching of the luminescence occurring at these temperatures, the emission spectrum is still clearly detectable and shows dramatic changes in both line shape and intensity when passing through the phase transition temperature. A redshift of about 6 nm occurs when the crystal is driven from the polar to the nonpolar phase. In addition, this shift displays a thermal hysteresis, then providing the possibility of realizing a bistable spectral system based on this material.