Europium-doped gallium nitride prepared by Na flux method

An aggregate of Eu-doped GaN columnar crystals was synthesized at 700°C and a N₂ pressure of 5 MPa at the surface of a Na-Ga melt with the addition of Eu metal. The color of the crystals was black at the melt-phase side, and changed to brown to colorless and transparent toward the gas-phase side. Energy-dispersive X-ray analysis revealed that the Eu content was 0.15 at. % at the black part and decreased gradually below <0.1at. % at the colorless transparent part. The colorless transparent part glowed red under ultraviolet radiation. A strong emission peak associated with the intra-4f transition of Eu³⁺ from ⁵D₀ to ⁷F₂ was observed at 621 nm in the photoluminescence spectrum and at 624 nm in the cathodoluminescence spectrum.