Visible quantum cutting (QC) through downconversion was observed upon 4f(8)-4f(7)5d(1) excitation of Tb3+ in both BaGdB9O16 and Ca8MgGd(PO4)(7) compounds. The QC involves a cross relaxation process between two neighboring Tb3+. Modified and new QC models are proposed based on the QC mechanisms in Gd3+-Tb3+ system. Two calculation equations for the cross relaxation efficiency are suggested according to the energy transfer theory and spectral results. By studying the spectral characteristics of Tb3+ in hosts from fluoride to oxide, it indicates that the visible QC in Gd3+-Tb3+ system may occur mainly depending on the structural features of phosphors, rather than the phonon energies of matrixes. All of the above conclusions have meaning of guidance for investigating other phosphors with QC phenomenon. (C) 2014 AIP Publishing LLC.