Luminescence mechanism and energy level structure of Eu-doped GaN powders investigated by cathodoluminescence spectroscopy

1.5at% Eu-doped GaN powders were prepared by a co-precipitation method. Powder X-ray diffraction (XRD) results shows that there is only the wurtzite phase. Cathodoluminescence spectra were measured at room temperature and liquid nitrogen temperature, respectively. The band-to-band luminescence of GaN was shifted from 373 nm to 368 nm with the temperature decreasing from room temperature to liquid nitrogen temperature. The luminescence peaks at 537, 557, 579, 590, 597, 614, 653 and 701 nm are attributed to the Eu ions related transitions in the host of GaN powders and the peak positions were not influenced by the variation of temperature. With the increase of accelerating voltage, the intensity of all luminescence peaks was increased. The strongest luminescence peak at 614 nm shows non-symmetrical shape and is composed of 612, 615 and 621 nm through Lorentzian fitting, which indicates there are oxygen and nitrogen environments of the Eu³⁺ ions in the Eu-doped GaN powders.