Electrical, electro-optic, temperature, and aging characteristics of green-emitting Zn₂GeO₄:Mn alternating-current thin-film electroluminescent (ACTFEL) devices are presented. The Zn₂GeO₄:Mn phosphor layers are prepared by RF sputtering. A maximum luminous efficiency of 0.45 lm/W and luminance of 105 cd/m² at 60 Hz and 40 V above threshold are obtained. Field-ionization of impact-excited Mn²⁺ luminescent impurities is found to give rise to positive space charge within the Zn₂GeO₄ phosphor, leading to unusual device behaviors such as conduction current delay, anomalous positive polarity transient luminance annihilation, transferred charge being comprised of mainly relaxation charge, and a decrease in the 60 Hz threshold voltage with increasing temperature. Low temperature aging experiments suggest that aging is at least partially due to hot electron-induced degradation. Although most Zn₂GeO₄:Mn ACTFEL devices exhibit a moderate amount of aging, certain devices are found to exhibit no measurable aging at 1 kHz when aged for 24 h.