The use of the 4f(7) ion Gd3+ as an energy transfer donor in solution is reported for the first time. The luminescence from the P-6 multiplet term of Gd3+ in chloride solution is quenched not only by increasing concentration, but also by the addition of Tb3+. The energy transfer from Gd3+ to Tb3+ in solution has been followed by selective decay measurements and the energy transfer constant shows a linear relationship with Tb3+ concentration up to similar to 0.05 M, after which value saturation is reached. The Tb3+ acceptor D-5(4) emission intensity as a function of time is well-modeled. (c) 2008 Elsevier B. V. All rights reserved.