This work investigates the origin of novel visible photoluminescence (PL) bands observed in the spinel MgAl 2 O 4 :Co 2+ . Besides the well-known fourfold-coordinated Co 2+ (T d ) PL at 670nm [N.V. Kuleshov, V.P. Mikhailov, V.G. Scherbitsky, P.V. Prokoshin and K.V. Yumashev, J. Lumin. 55 (1993) 265.], a rich structured PL band at 686nm was also observed that we associate with uncontrolled impurities of sixfold coordinated Cr 3+ (O h ) by time-resolved spectroscopy and lifetime measurements and their variation with temperature. We also show that the lifetime of the Co 2+ (T d ) emission at 670nm varies from τ=6.7μs to 780ns on passing from T=10 to 290K. This unexpected behaviour for T d systems is related to the excited-state crossover ( 4 T 1 ↔ 2 E), making the emission band to transform from a narrow-like emission from 2 E at low temperature to a broad structureless band from 4 T 1 at room temperature.