Luminescence from LiGa₅O₈: Cr³⁺ with varying concentrations of chromium

At high chromium concentrations additional sharp lines appear in the luminescence and absorption spectra of LiGa₅O₈ : Cr³⁺ which originate on exchange coupled pairs of chromium ions. These derive some excitation by transfer from the single ions. The spectra of the pairs are analyzed to obtain values for the ground state exchange parameters of nearest neighbour pairs. At liquid helium temperatures there is a strong increase in the luminescence intensity of the pair lines relative to the single ion luminescence.