Concentration quenching of Eu-related luminescence in Eu-doped GaN

The dependence of Europium (Eu)-related luminescence intensity on the Eu concentration in Eu-doped GaN was studied. This luminescence is observed at $622nm$ and originates from the intra-$4f$ transition of the $Eu3+$ ion. The intensity of the luminescence increased with increasing Eu concentration, up to about $2at.%$⁠, and then abruptly decreased. It was found that polycrystalline growth began to be induced at Eu concentrations of more than $2at.%$⁠. In addition, clear evidence for the formation of EuN compounds was obtained by x-ray diffraction and extended x-ray absorption fine structure analysis. The cause of the concentration quenching is likely to be related to the polycrystalline growth as well as EuN formation.