This contribution reports on luminescence properties of divalent ytterbium in alpha-SiAlON at room temperature. Ytterbium-doped alpha-SiAlON powders, with the compositions of (M1-2x/vYbx)(m/v)Si12-m-nAlm+nOnN16-n (M = Ca, Li, Mg, and Y, v is the valency of M, 0.002 <= x <= 0.10, 0.5 <= m = 2n <= 3.5), were synthesized by sintering at 1700 degrees C for 2 h under 0.5 MPa N-2. A single, intense, broad emission band, centered at 549 nm, is observed due to the electronic transitions from the excited state 4f(13)5d to the ground state 4f(14) of Yb2+. The luminescence of Yb2+ in alpha-SiAlON occurs at relatively low energy, which is attributable to the large crystal field splitting and nephelauxetic effect due to the nitrogen-rich coordination of Yb2+. The dependence of luminescence properties on the Yb2+ concentration, chemical composition, and annealing is discussed. It is suggested that this novel green phosphor could be applied in white light-emitting diodes (LEDs) when combined with a red phosphor and a blue LED.