Fluorescence decay curves of the 3P0 and 1D2 manifolds in Pr 3+ doped PbWO4 crystal were measured at room temperature and fluorescence lifetimes of both manifolds were estimated. Combining with the radiative lifetimes of the manifolds calculated on the basis of the modified J-O theory, the main mechanisms for the fluorescence quenching of the manifolds were analyzed. The multi-phonon relaxation and the cross-relaxation energy transfer are the major reasons for the fluorescence quenching of the 3P0 and 1D2 manifolds, respectively. The Inokuti-Hirayama model was used to analyze the fluorescence decay curve of the 1D2 manifold and the cross-relaxation of dipole-dipole interaction was confirmed. Consequently, the 3P0 manifold is more favorable as an upper laser level than the 1D2 manifold.
