Sialon fluorescent materials with activated Eu or other rare earth ions have been known as fluorescent materials capable of being excited by blue light to emit yellow light. An oxynitride fluorescent material can emit light having a far wider range of wavelengths than ever before, and can be included in a light-emitting device. A fluorescent material contains as a main component a crystal phase having a general formula La.sub.3Si.sub.8N.sub.11O.sub.4 or La.sub.3Si.sub.8-xAl.sub.xN.sub.11-xO.sub.4+x where 0