Zn2GeO4:Mn alternating-current thin-film electroluminescent devices

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.