Disorder response of 3d3 ions zero-phonon lines in the luminescence spectra of Yttrium-Aluminum-Gallium garnet solid solution ceramics

The zero-phonon R-line luminescence spectra of 3d3 ions (Cr3+ and Mn4+) in a series of Y3Al5-5yGa5yO12 (0 ≤y≤1) solid solution garnet ceramics were studied. Instead of increased inhomogeneous line broadening which is usually observed in solid solutions, discrete structure in the Cr3+ emission spectra is observed at lower values of y, whereas at high values of y the strong inhomogeneous broadening of the R-lines occurs and no discrete disorder response is observed. The results are explained based on the limited number of possible high-symmetry luminescent center geometries and the non-random preferential occupancy of tetrahedral lattice sites with gallium ions.