Spectra and energy levels of Tm3+(4f(12)) in AlN

Abstract

We report a detailed analysis of the cathodoluminescence spectra of Tm3+-implanted 2H-aluminum nitride (AlN) covering the wavelength range between 290 and 820 nm at temperatures between 12 and 60 K. More than 200 transitions are observed, of which more than 100 of these transitions can be identified from emitting multiplet manifolds I-1(6), D-1(2), and (1)G(4). Although the emitting levels are not observed directly, emission is also attributed to the P-3(2) and P-3(1) multiplet manifolds based on analyses of transitions to terminal levels F-3(4), H-3(5), and F-3(3). The observed crystal-field splitting of the ground-state multiplet manifold, H-3(6), and manifolds F-3(4), H-3(5), H-3(4), F-3(3), F-3(2), and (1)G(4) is established from an analysis based on matching repeated energy differences between transitions. This method is similar to one used in analyzing arc and spark spectra. Temperature-dependent spectra also establish the crystal-field splitting of the P-3(1) and part of the manifold splitting of emitting levels such as I-1(6). To establish an initial set of crystal-field splitting parameters, B-nm, that can be related to a physical model, we carried out a lattice-sum calculation by computing the crystal-field components, which are the coefficients in a multipolar expansion of the crystal field about the Al3+ sites that have C-3v symmetry in the lattice. Emission channeling experiments indicate that the Al3+ sites serve as the substitutional sites for Tm3+ in AlN. With only minor adjustments to the calculated centroids to account for J-mixing, the calculated crystal-field splitting of most multiplet manifolds, L-2S+1(J), of Tm3+(4f(12)) based on the B-nm obtained from the lattice-sum calculations, is in good agreement with the reported experimental splitting.