Crystal field analysis ofPm3+(4f4)andSm3+(4f5)and lattice location studies ofNd147andPm147inw−AlN

Abstract

We report a detailed crystal field analysis of ${\mathrm{Pm}}^{3+}$ and ${\mathrm{Sm}}^{3+}$ as well as lattice location studies of $^{147}\mathrm{Pm}$ and $^{147}\mathrm{Nd}$ in 2H-aluminum nitride $(w\text{\ensuremath{-}}\mathrm{AlN})$. The isotopes of mass 147 were produced by nuclear fission and implanted at an energy of $60\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$. The decay chain of interest in this work is $^{147}\mathrm{Nd}\ensuremath{\rightarrow}^{147}\mathrm{Pm}\ensuremath{\rightarrow}^{147}\mathrm{Sm}$ (stable). Lattice location studies applying the emission channeling technique were carried out using the ${\ensuremath{\beta}}^{\ensuremath{-}}$ particles and conversion electrons emitted in the radioactive decay of $^{147}\mathrm{Nd}\ensuremath{\rightarrow}^{147}\mathrm{Pm}$. The samples were investigated as implanted, and also they were investigated after annealing to temperatures of $873\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ as well as $1373\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The main fraction of about 60% of both $^{147}\mathrm{Pm}$ as well as $^{147}\mathrm{Nd}$ atoms was located on substitutional Al sites in the $\mathrm{AlN}$ lattice; the remainder of the ions were located randomly within the $\mathrm{AlN}$ lattice. Following radioactive decay of $^{147}\mathrm{Nd}$, the cathodoluminescence spectra of ${\mathrm{Pm}}^{3+}$ and ${\mathrm{Sm}}^{3+}$ were obtained between $500\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ and $1050\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ at sample temperatures between $12\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. High-resolution emission spectra, representing intra-4$f$ electron transitions, were analyzed to establish the crystal-field splitting of the energy levels of ${\mathrm{Sm}}^{3+}\phantom{\rule{0.3em}{0ex}}(4{f}^{5})$ and ${\mathrm{Pm}}^{3+}\phantom{\rule{0.3em}{0ex}}(4{f}^{4})$ in cationic sites having ${C}_{3v}$ symmetry in the $\mathrm{AlN}$ lattice. Using crystal-field splitting models, we obtained a rms deviation of $6\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ between 31 calculated-to-experimental energy (Stark) levels for ${\mathrm{Sm}}^{3+}$ in $\mathrm{AlN}$. The results are similar to those reported for ${\mathrm{Sm}}^{3+}$ implanted into $\mathrm{GaN}$. Using a set of crystal-field splitting parameters ${B}_{nm},$ for ${\mathrm{Pm}}^{3+}$ derived from the present ${\mathrm{Sm}}^{3+}$ analysis, we calculated the splitting for the $^{5}F_{1}$, $^{5}I_{4}$, and $^{5}I_{5}$ multiplet manifolds in ${\mathrm{Pm}}^{3+}$ and obtained good agreement between the calculated and the experimental Stark levels. Temperature-dependent lifetime measurements are also reported for the emitting levels $^{4}F_{5∕2}\phantom{\rule{0.3em}{0ex}}({\mathrm{Sm}}^{3+})$ and $^{5}F_{1}\phantom{\rule{0.3em}{0ex}}({\mathrm{Pm}}^{3+})$.