In this paper, the growth and characterizations of AlInGaN quaternary alloys on sapphire substrate are presented. The room temperature PL peaks of the quaternary layers were in the range of 335-375 nm with full-width at half-maximum (FWHM) values ranged between 50 and 69 meV. The X-ray rocking curves of quaternary layers for (0 0 0 4) diffraction exhibited narrow FWHM values ranged from 250 to 320 arcsec. To the best of our knowledge, these are the best results among those published in the literature. In additoin, anomalous blue-shift behavior was observed in PL measurement when temperature changed from 300 to 77 K, which was due to the band tail states in quaternary AlInGaN caused by alloy compositional fluctuation. (C) 2003 Elsevier B.V. All rights reserved.