On the 6A1 ← 4T1 luminescence of Fe3+ in disordered nanocrystalline LiGa5O8 prepared by a combustion reaction

A combustion reaction yields nanocrystalline LiGa5O8 in the inverse-spinel phase (Fd3m) in contrast to previous attempts by quenching microcrystalline powders from 1350 °C. This follows from XRD, IR and luminescence spectra of Fe3+ at 298, 78 and 2.5 K. The ordered phase is obtained by calcination at 900 °C of the combustion product. The Fe3+ luminescence is assigned to the 6A1(S) ← 4T1(G) transition of ions in tetrahedral sites in both polymorphs; this is confirmed by the similar behaviour of the 4A2(F) ← 4T1(P) luminescence of Co2+ upon the order–disorder transition. The variation of the luminescence spectra is explained in terms of inhomogeneity and the Td → C3 symmetry reduction.