The concentration dependent luminescence of the SrI₂-TmI₂ system was investigated. For Tm²⁺ concentrations up to 5 mol %, the quantum efficiency (QE) of the ²F_5/2→²F_7/2 emission exhibits a constant value above 50%. The QE drops for higher Tm²⁺ concentrations, partly due to concentration quenching, as evidenced by a decreasing luminescence lifetime of the ²F_5/2→²F_7/2 emission, and partly due to the formation of a second crystal phase with CdCl₂ structure, in which the ²F_5/2→²F_7/2 emission is quenched. The temperature and time dependent relaxation dynamics were studied to identify the origin of the limited QE for Tm²⁺-doping levels below 5 mol %. An anti-correlation between the 5d-4f (³H₆,t_2g)_S=3/2→²F_7/2 and 4f-4f ²F_5/2→²F_7/2 emission intensities was found and rationalised by non-radiative, thermally stimulated, inter-configurational 5d-4f relaxation to the emitting ²F_5/2 level of Tm²⁺. Both, the rise time of the 4f-4f and the decay time of the 5d-4f emission become shorter with increasing temperature. We suggest a similar non-radiative relaxation from the 5d level towards the ²F_7/2 ground state to limit the QE below unity. This route becomes more efficient when the 5d (³H₆,t_2g)_S=3/2 state moves closer to the 4f ²F_5/2 and ²F_7/2 states, which is the case for the CdCl₂ phase with a QE close to zero.

A high voltage is applied to the screen spacer of the Zeus panel to obtain high brightness and long phosphor lifetime. To prevent field emission due to high local field strength, the screen spacer is coated with a resistivity layer and a low secondary-electron-emission layer. Efficiently operating panels have been made with sputtered substoichiometric and stoichiometric silicon nitride films, and with sprayed chromium oxide and silicon nitride particle layers. For the sputtered layers the effect of stoichiometry, sheet resistance and layer thickness on the panel performance is discussed. In the case of the sprayed layers the effect of suspension quality, spray conditions, layer thickness and layer roughness is discussed.