Energy transfer mechanisms in Tb(OH)3 from line shapes of band-to-band exciton fluorescence

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Abstract
Mechanisms of energy transfer between Tb3+ ions in Tb(OH)3 have been isolated for several states of the Tb3+ ion by means of line shape measurements of the band‐to‐band fluorescence from the two lowest exciton bands of the 5D4 manifold to one exciton band in the 7F6 (ground) and 7F5 (first excited) manifolds. The interionic energy transfer matrix elements were determined by comparing the observed line shapes with calculations of the exciton band‐to‐band transitions in which the energy dispersion was varied. A consideration of the simple nature of the single‐ion states, an examination of the selection rules on the various energy transfer mechanisms, and an analysis of the range dependence of these mechanisms has enabled us to conclude that (1) the exchange plays a major role in both the 7F5 and 7F6 bands, (2) the electric multipole interaction does not make the dominant contribution to the energy transfer matrix elements in either manifold, (3) the magnetic dipole–dipole interaction plays a small but significant role particularly in the 7F6 manifold, and (4) the virtual phonon exchange plays a role comparable to that of exchange in the 7F6 band, a result which is of special interest in view of the few cases in which its importance has been clearly demonstrated.