Abstract

Luminescence and EPR measurements were done on single crystals of LiGa₅O₈ having nominal Mn concentrations of 0.4, 1.0, and 10wt%. These crystals were grown by the flux method and supplied by Deltronic Crystals Industries, Inc.^‡ The dominant fluorescent signal is due to the B-site Mn⁴⁺ ions. At 10K the emission is characterized by a sharp zero-phonon line at 721.6nm due to the ²E(G)→⁴A₂(F) transition. This fluorescence has a decay time of 450µs, and its lower-energy side bands have a very rich structure. For the more concentrated Mn samples the intensity behaviour of some of these side bands indicates the presence of pair lines. The comparison between the observed luminescence properties of Mn⁴⁺ with those of its isoelectronic Cr³⁺ in the same compound⁽¹⁾ shows that the Mn⁴⁺ zero-phonon line and its vibronics are shifted to lower energies, and that the ⁴T₂ excitation bands are shifted to higher energies, giving rise to a Dq value of 2000cm^-1. These trends are due to the fact that both covalence and crystal field parameters must have larger values with the increase of central ionic charge. The ⁴T₁ excitation band of Mn⁴⁺ is hidden at the tail of a charge transfer band shifted towards longer wavelengths. Assuming the relation C=4B for these Racah parameters one has for Mn⁴⁺ a B value of 660cm^-1 and a C value of about 2640cm^-1. Similar results for Mn⁴⁺ and Cr³⁺ emissions were obtained in the isomorphous compound LiAl₅O₈⁽²⁾.

© 1984 Optical Society of America