Crystal field analysis of Pm3+ (4f(4)) and Sm3+ (4f(5)) and lattice location studies of Nd-147 and Pm-147 in w-AlN

Abstract

We report a detailed crystal field analysis of Pm3+ and Sm3+ as well as lattice location studies of Pm-147 and Nd-147 in 2H-aluminum nitride (w-AlN). The isotopes of mass 147 were produced by nuclear fission and implanted at an energy of 60 keV. The decay chain of interest in this work is Nd-147 -> Pm-147 -> Sm-147 (stable). Lattice location studies applying the emission channeling technique were carried out using the beta(-) particles and conversion electrons emitted in the radioactive decay of Nd-147 -> Pm-147. The samples were investigated as implanted, and also they were investigated after annealing to temperatures of 873 K as well as 1373 K. The main fraction of about 60% of both Pm-147 as well as Nd-147 atoms was located on substitutional Al sites in the AlN lattice; the remainder of the ions were located randomly within the AlN lattice. Following radioactive decay of Nd-147, the cathodoluminescence spectra of Pm3+ and Sm3+ were obtained between 500 nm and 1050 nm at sample temperatures between 12 K and 300 K. High-resolution emission spectra, representing intra-4f electron transitions, were analyzed to establish the crystal-field splitting of the energy levels of Sm3+ (4f(5)) and Pm3+ (4f(4)) in cationic sites having C-3v symmetry in the AlN lattice. Using crystal-field splitting models, we obtained a rms deviation of 6 cm(-1) between 31 calculated-to-experimental energy (Stark) levels for Sm3+ in AlN. The results are similar to those reported for Sm3+ implanted into GaN. Using a set of crystal-field splitting parameters B-nm, for Pm3+ derived from the present Sm3+ analysis, we calculated the splitting for the F-5(1), I-5(4), and I-5(5) multiplet manifolds in Pm3+ and obtained good agreement between the calculated and the experimental Stark levels. Temperature-dependent lifetime measurements are also reported for the emitting levels F-4(5/2) (Sm3+) and F-5(1) (Pm3+).