Site-selective photoluminescence and photoluminescence excitation spectroscopic investigations were carried out, at 6K, on Nd3+ emissions from the 4F3/2 → 4I11/2 transition in Nd-implanted samples which had been grown by using metal-organic chemical vapor deposition. The site-selective photoluminescence excitation spectra which were detected at emission wavelengths that were characteristic of each of the distinct Nd3+ photoluminescence bands included spectral features which were representative of excitation by above-gap absorption, by direct sharp-line Nd3+ 4f-shell absorption, and by broad below-gap absorption bands. These could be attributed to defects and impurities and to a possible iso-electronic trap that was associated with one of the five Nd3+ sites. It was concluded that the Nd3+ site which was excited by direct sharp-line Nd3+ 4f-shell absorption was the predominant or highest-concentration Nd3+ center. The excitation mechanisms for the other four Nd3+ sites all involved the non-radiative transfer of energy, from impurity-related or defect-related traps, to neighboring rare-earth atoms.

S.Kim, S.J.Rhee, X.Li, J.J.Coleman, S.G.Bishop: Physical Review B, 1998, 57[23], 14588-91