When a solvothermally prepared gamma-Ga2O3-Al2O3 (Ga 30 mol%) catalyst was treated with C3H6 followed by heating at 523 K, it colored yellow [J. Catal. 259 (2008) 36]. The photoluminescence (PL) spectra of the colored species showed two hands at near ultraviolet (383 nm) and blue-green (487 nm) regions under excitation at 343 nm, and a blue-green band (491 nm) under excitation at 436 nm. The former emissions were attributed to the carbenium ions on the tetrahedral Gal, sites in gamma-Ga2O3-Al2O3, and the latter, to those on the octahedral Ga3+ sites. The band intensity at 383 nm increased by heating the C3H6-loaded catalyst upto 523 K and further increase in temperature decreased the band intensity. The intensity of the emission band at 383 nm linearly correlated with the catalytic activity of gamma-Ga2O3-Al2O3 for selective catalytic reduction of NO with CH4. (C) 2009 Elsevier B.V. All rights reserved.