Luminescence decay kinetics in homogeneously and delta-doped ZnS : Mn

The luminescence decay kinetics of homogeneously and delta-doped ZnS:Mn thi n film phosphors was investigated. A quantitative model based on the hoppin g model of energy transfer theory was developed to described the concentrat ion quenching phenomenon in ZnS:Mn. The model predicted the dependence of t he energy transfer rate on material parameters such as the Mn and defect co ncentrations. The luminescence decay of homogeneously doped ZnS:Mn consiste d of two exponential components at 10 K. The fast component of 120 mu s was attributed to exchange-coupled pair emission and the slow component of 1.6 ms to isolated Mn ions. As the temperature was increased, the exchange-cou pled pair emission disappeared and the decay became strongly nonexponential . The nonexponentiality was attributed to nonradiative energy transfer proc esses. The concentration dependence of the effective lifetime was also foun d to change with temperature. The investigation on the temperature dependen ce revealed two regimes of concentration which showed distinct temperature dependencies. From the temperature dependence, it was concluded that the en ergy transfer between Mn ions was active only when the Mn concentration was greater than 2 at. %. By comparing these results with the results of Dexte r's theory, the energy transfer between Mn ions was found to be mediated by an electric dipole-dipole interaction. The delta-doped ZnS: Mn showed fast er decay times due to the enhanced overlap between 3d and s-p host states c aused by lattice strain. From the temperature dependence, a two-dimensional confinement of energy transfer was observed when the doping planes were fa r apart. However, when the doping planes were brought close together, the d elta-doped samples behaved similarly to the homogeneously doped ZnS: Mn ind icating that the energy transfer was no longer two-dimensionally confined. (C) 1998 American Institute of Physics. [S0021-8979(98)03924-3].