The decay kinetics of transient optical absorption of wide bandgap crystals of lithium borates Li 2B 4O7, LiB 3O 5, and Li 6Gd(BO 3) 3 and potassium (KH 2PO 4) and ammonium (NH 4H 2PO 4) dihydrogen phosphates in the visible and ultraviolet spectral regions are analyzed using the theory of diffusion-controlled tunneling recombination. A nanosecond pulsed radiation action on these crystals is shown to form defect pairs, such as polaron-type hole centers and electron centers based on interstitial cations. The relaxation kinetics of these centers over a wide time range of 10 ns-10 s is described by the proposed model of tunneling electron transfer between antimorphous defects in the cation sublattice under the thermally stimulated mobility of recombination partners. The numerical values of the kinetic parameters are determined and the time dependences of the reaction rate constants are calculated for all the crystals under study.