Observation of nonradiative energy transfer in the excitation ofNd3+luminescence in GaP

We have carried out luminescence-excitation measurements on a ${\mathrm{Nd}}^{3+}$ complex in GaP in the range 1.5–2.2 eV to determine the mechanisms by which the internal ${\mathrm{Nd}}^{3+}$ luminescence is generated. At low temperatures we observe transitions into the ${}_{}{}^4{}_{}{}^{}$ ${\mathit{S}}_{3/2}$ and ${}_{}{}^4{}_{}{}^{}$ ${\mathit{F}}_{7/2}$ excited states of ${\mathrm{Nd}}^{3+}$ and two broad excitation bands whose integrated intensities are orders of magnitude greater than that of the ${\mathrm{Nd}}^{3+}$ excited states. These broadbands demonstrate for the first time that nonradiative energy transfer from external states is the dominant low-temperature mechanism for the excitation of ${\mathrm{Nd}}^{3+}$ luminescence in GaP. Reasonable assignments have been made for the origin of the broadbands on the basis of similar work carried out on rare-earth-doped II-VI semiconductors.