Red ZnGa2O4:Cr3+ powder electroluminescence co-generating sounds with a longer lifetime and no thermal quenching behaviors

The ZnGa2O4:Cr3+ powder electroluminescence (PEL) device has been demonstrated through a conventional screen printing method. The phosphor powder was prepared by a solid-state reaction in an air ambient and dispersed in an ethyl cellulose binder before screen printing in ITO glass. The PEL device consists of 20 mu m-thick BaTiO3 as an insulating layer and 30 mu m-thick ZnGa2O4:Cr3+ as an active layer. It has a comparatively lower threshold voltage (40 V) than the previous PEL device. It generates the red light peaking at 696 nm and 708 nm attributed to the forbidden transition of Cr3+ ions and the sound depending on the applied frequency due to the BaTiO3 layer. Its EL intensity was exponentially increased with voltage and linearly increased with the frequency before saturating at a frequency of 3 kHz, which is consistent with the 1/10 decay time. It has the best luminous efficiency of 0.74 lm/W and the maximum EL luminance of 1.64 cd/m2. In particular, it was not thermally quenched even at a higher temperature due to the anti-thermal quenching effect. Moreover, it shows high reliability under ultrasonic frequency (>20 kHz) and is long-lived in an accelerated aging environment (>740 min, temperature of 60 degrees C and humidity of 50%).