Low‐energy charge‐transfer state and optical properties of Eu 3+ ‐doped GaN

We argue that the charge-transfer state of Eu3+ due to an electron transfer from N to Eu plays important roles in the luminescence properties of GaN:Eu3+ grown by gas-source molecular beam epitaxy. On the basis of the excitation spectrum of the Eu3+ luminescence, the excitation mechanism of Eu3+ under the GaN interband excitation is interpreted in terms of the energy transfer from the above charge-transfer state. The intra-4f shell 5D0–7F2 transition strength of Eu3+ in GaN, which is responsible for red luminescence, is large compared with those of most Eu3+-doped oxide materials. This fact can be attributed to the low-energy position of the charge-transfer state of Eu3+ in GaN. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)