The mechanisms leading to improved brightness, efficiency, and stability of alternating-current thin-film electroluminescent ZnS:Mn phosphors were studied. It had previously

been shown that ex situ co-doping of a sputter-deposited ZnS:Mn active layer with K and Cl resulted in a 53% improvement in brightness, a 62% improvement in efficiency, and better 100h accelerated aging stability. It was demonstrated here that these improvements resulted from a 75% increase in excitation efficiency for conduction electrons, combined with a small decrease in light out-coupling and non-radiative recombination. Electrical property data were used to determine that there was a reduced amount of static space charge in the co-doped films, resulting in a larger average field, increased excitation efficiency, and increased charge multiplication. The reduced space charge was attributed to the addition of charge-compensating Zn vacancy–Cl complexes and isolated Cl point defects, which were acceptor and donor defects, respectively, and to a reduction in Zn vacancy deep hole traps. It was suggested that higher average fields resulted in such electron multiplication or donor ionization that current for EL excitation was limited by the phosphor resistance rather than capacitance or density of interface states.

Control of Point Defects and Space Charge in Electroluminescent ZnS:Mn Thin Films. J.S.Lewis, M.R.Davidson, P.H.Holloway: Journal of Applied Physics, 2002, 92[11], 6646-57