A Diffusion Model for Electron-Hole Recombination in Zn₂SiO₄:(Mn, As) Phosphors

Abstract

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.