Mg codoping into Eu-doped GaN (GaN:Eu) changed the dominant optical site and increased the photoluminescence (PL) intensity at room temperature (RT). From the ratio of PL integrated intensity at 25 K to that at 300 K, PL efficiency of the GaN:Eu,Mg layer was evaluated to be as high as 77%. On the basis of this experiment, GaN:Eu-based LEDs grown by NH3 MBE were fabricated. Clear rectification characteristics with a turn-on voltage of 3.2 V were observed and a pure red emission was observed by the naked eye at RT. For the electroluminescence (EL) spectra, two predominant peaks of higher-efficiency optical sites A and C were selectively enhanced and the EL intensity was improved. This result suggests that GaN:Eu was very effective for realizing red-light-emitting devices using the nitride semiconductor.

Mg codoping into Eu-doped GaN strongly affects the two dominant optical sites A (620.3 nm) and B (622.3 nm) and dramatically improves the optical characteristics obtained from Eu 3þ ions. To clarify the mechanism of the enhanced emission, the effects of the Mg concentration on the excitation and emission processes were evaluated by considering the excitation power dependence of photoluminescence (PL) and time-resolved PL at various temperatures. The excitation cross section r ex , which reflected the excitation process, did not depend on the Mg concentration but strongly on the optical site, which was attributed to the different energy transfer processes of the two optical sites. r ex for site A was three times larger than that for site B, indicating higher excitation efficiency for site A. Mg codoping dramatically increased the number of Eu ions in site A that remain active at room temperature (RT) and the 5 D 0 lifetime at RT, indicating the suppression of nonradiative components during the emission process. Therefore, the optical properties were markedly enhanced by Mg codoping. V C 2013 American Institute of Physics. [http://dx.