Luminescence of excitons in single-crystal garnets

Comparative studies of the luminescence of Y₃Al₅O₁₂:Ce and Lu₃Al₅O₁₂:Ce single-crystal films and their volume analogues—Y₃Al₅O₁₂ and Y₃Al₅O₁₂:Ce single crystals, excited by synchrotron radiation with energy E=120–150 eV, have been performed. The films were grown from melt-solution by liquid-phase epitaxy and the crystals were grown from melt. The single-crystal films and single crystals studied are characterized by different degrees of structural order, in particular, different concentrations of substitutional defects of the Y _Al ³⁺ and LU _Al ³⁺ types. It was ascertained that the bands at 260 and 250 nm in the intrinsic luminescence spectra of Y₃Al₅O₁₂:Ce and Lu₃Al₅O₁₂:Ce single-crystal films and single crystals are due to the emission of self-trapped excitons. The luminescence band with λ_max=300 nm and τ=0.36 μs, which is present in the luminescence spectrum of single crystals and absent in the spectra of single-crystal films, is due to the recombination of electrons with holes localized at Y _Al ³⁺ centers. It is shown that an efficient energy transfer by excitons to activator ions occurs in Y₃Al₅O₁₂ and Lu₃Al₅O₂ single-crystal films doped with Ce³⁺ ions.