This work described the photoluminescent (PL) and thermal stability properties of Tb3+-doped Ca-alpha-SiAlON phosphors, with the composition (Ca1-3/2xTbx)(m/2)Si12-m-nAlm+nOnN16-n (m = 1.5, n = 0.75) that can be excitable under vacuum UV (VUV) light. The concentration of Tb as a fraction of that of Ca was varied from 0.03 <= x <= 1.0. The sample with x = 0.25 had the highest emission intensity. The obtained activation energy for the sample with x = 0.25 was 0.1 eV. The major mechanism of concentration quenching was dipole-dipole interaction. The VUV PL intensities of composition-optimized x = 0.25 samples under different excitation wavelengths were compared. The results indicated that the PL intensity at lambda(ex) = 172 or lambda(ex) = 147 nm was much weaker than the obtained intensity with excitation at 258 nm, suggesting that Tb3+-doped Ca-alpha-SiAlON phosphors can be excitable by VUV but are not suitable for applications in plasma display panels. Moreover, the emission peak intensity (excitation at 258 nm and monitored at 544 nm) decreased with increasing temperature and have a slight blueshift. This phenomenon is explained by the anti-Stokes effect associated with the interaction between electron and thermal phonon. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3125135] All rights reserved.