Nonradiative relaxation time (tau) and characteristic diffusion time (tau(beta)) of Nd, Er and Co doped low silica calcium aluminosilicate (LSCA) glasses were assessed by means of photoacoustic spectroscopy. The results are interpreted in terms of frequency dependence predicted by the theory of Rosencwaig and Gersho. Whereas tau varied between 7.2 ms and 36 ms, the values of tau(beta) lied between 0.25 ms and 0.7 ms. For the neodymium doped LSCA glass, a decrease in tau(beta) was observed as the ion concentration was increased. The results indicates that rare earth ion acts as network modifier, disrupting the glass lattice. (C) 2010 Published by Elsevier B.V.