Optical techniques have been used to study the extended persistence of luminescence in willemite phosphors coactivated with Mn and As. Absorption and photoluminescence excitation spectroscopy establish that the MnZn2+impurity ground state lies 3.9 ± 0.1 eV below the conduction bandedge in willemite. Laser pulse excitation at energies > 3.9 eV has been used to generate MnZn2+luminescence decay curves. At short times (t < 100 ms), the shape of these decay curves depends strongly on both temperature and As concentration in the samples (NAs). These pulse response curves have been analyzed using a bimolecular kinetic model. The behavior of the model parameters as a function of NAs is interpreted in terms of a diffusion-controlled recombination between trapped electrons and ionized Mn centers. When NAs< 1 X 1019cm-3the recombination is dominated by thermal emission of electrons to the conduction band. When NAs> 2 x 1019cm-3diffusion by intertrap tunneling is dominant. © 1985, The Electrochemical Society, Inc. All rights reserved.