Cerium-doped alpha-SiAlON (MxSi12-(m+n)Alm+nOnN16-n) materials have been prepared by gas-pressure sintering and posthot-isostatic-press (HIP) annealing, using four powder mixtures of alpha-Si3N4, AlN, and either (i) CeO2, (ii) CeO2 + Y-alpha-SiAlON seed, (iii) CeO2 + Y2O3, or (iv) CeO2 + CaO. Cerium-containing CeAl(Si6-zAlz)(N10-zOz) (JEM) phase, rather than Ce-alpha-SiAlON phase, forms in the sample with only CeO2, whereas a single-phase alpha-SiAlON generates in samples with dual doping (CeO2 + Y2O3 and CeO2 + CaO). On ultraviolet-light excitation, JEM gives one broad emission band with maximum at 465 nm and a shoulder at 498 nm; alpha-SiAlON shows an intense and broad emission band that peaks at 500 nm. The unusual long-wavelength emissions in JEM and alpha-SiAlON are due to increases in the nephelauxetic effect and the ligand-field splitting of the 5d band, because the coordination of Ce3+ in JEM and alpha-SiAlON is nitrogen enriched.