Manganese-activated luminescence in ZnGa2O4

Abstract

Manganese-activated ZnGa2O4, prepared at a sintering temperature of 1375 °C with 0.1% MnO dopant, emitted red and green light with peaks at 666 and 508 nm when excited with a laser source (325 nm). The luminescence centers of red emission were ascribed to Mn4+ ions in the octahedral (B) sites of spinel-structure zinc gallate. Monitored at these two peaks, the sample exhibited absorption bands at 342 and 464 nm (for red) and 245 and 290 nm (for green) when excited with radiation from a xenon discharge lamp, indicating an excitation process occurring in Mn4+ ions distinct from that of Mn2+ ions (in A sites) which were known to be responsible for the green emission. Cathodoluminescence spectra showed that the integrated intensity of an UV band (peak at 349 nm) increased steadily with beam current while the green light intensity saturated at high current ranges. Several possible saturation mechanisms were discussed. The variation of the intensities versus current was interpreted and formulated based on an energy process between Ga–O groups and Mn2+ ions. Good fittings between the calculated curves and measured intensity data were attained with appropriate parameter values in the calculation. Assuming a resonant transfer process with electric dipole–dipole interaction prevailing between the Mn2+ and Ga3+ ions, a critical interaction distance of ∼9.9 Å for the ions was derived from an associated relation and the parameters used.