The electron-phonon coupling strength of Gd3+ and Eu3+ ions in crystalline and glass phases of the same chemical composition are studied by measuring the vibronic transition probabilities of the 4f(n) transitions of these ions. The experimentally derived vibronic transition probabilities are very small. Within the experimental error, the electron-phonon coupling strength of the lanthanide ions in the different phases is the same. (C) 1998 Academic Press.