Luminescence and energy-transfer mechanisms in Eu^{3+} -doped GaN epitaxial films

Abstract

We studied the photoluminescence (PL) and energy-transfer processes in Eu^{3+} -doped GaN epitaxial films by means of microscopic PL imaging spectroscopy. Eu^{3+} -doped GaN epitaxial films exhibited blue luminescence due to bound-exciton recombinations in GaN host crystals and red luminescence due to intra-4f transitions of Eu^{3+} ions. We found an anticorrelation between the exciton and Eu^{3+} PL intensities in space-resolved PL images, indicating that energy transfer from GaN crystals to Eu^{3+} ions determines the Eu^{3+} luminescence intensity. PL and PL excitation spectra showed that efficient Eu^{3+} luminescence is caused by two different excitation processes: energy transfer from the low-energy charge-transfer (CT) states to Eu^{3+} ions or from the delocalized states above the band edge of GaN crystals to Eu^{3+} ions. The energy-transfer process from the CT state to Eu^{3+} ions dominates the Eu^{3+} luminescence.