Study on ZnGa2O4:Cr3+ a.c. powder electroluminescent device

An a.c. powder electroluminescent (EL) device using ZnGa2O4:Cr3+ phosphor was fabricated by the screen printing method. Optical and electrical properties of the device were investigated. The fabricated device shows a red emission at 695 nm driven by the a.c. voltage. The emission is attributed to the energy transfer from hot electrons to Cr3+ centers via self-activated Ga–O groups. Luminance (L) versus voltage (V) matches the well-known equation of L = L0exp(− bV − 1 / 2) and luminance increases proportionally with frequency due to the increase of excitation probability of host lattice or Cr3+ centers. The diagram of the charge density (Q) versus applied voltage (V) is based on a conventional Sawyer–Tower circuit. At 280 V and 1000 Hz, the luminance and the luminous efficiency of the fabricated powder EL device are about 1.0 cd/m2 and 13 lm/W, respectively. And under the high field, the device fabricated with the oxide-based phosphor of ZnGa2O4:Cr3+ shows excellent stability in comparison with the conventional sulfide powder EL device.