Luminescence in the alkali metavanadates

The luminescence efficiency of the alkali metavanadates has been reported to increase by several orders of magnitude in the cation series from Na to K to Rb to Cs. Measurements of luminescence efficiency and decay time as a function of temperature show that maxima occur in the luminescence efficiency at 300, 200, and 170 °K and that the decay times for the predominantly exponential decay rise from between 10 and 20 μs at room temperature to 160, 300, and > 1500 μs at 77 °K for KVO3, RbVO3, and CsVO3 respectively. These results are interpreted in terms of thermally activated exciton diffusion from the absorbing site to recombination centres along chains of (VO4) tetrahedral complexes which occur in the metavanadate structure. The lifetime of excitons and the activation energy for exciton diffusion is shown to be related to the degree of polarisation of the anionic complex induced by the cation.