Recombination emission and the formation of combined electron-emitting states in garnets Y3Al5O12 and Y3Al5O12:Dy

Abstract

In Dy-doped Y₃Al₅O₁₂ garnets exposed to UV photons near the fundamental absorption region, the formation of composite electron–radiative states arising from both intrinsic and impurity-related electron–hole trapping centers has been studied. Under exposure with photons of 6.2 eV and 5.64 eV at 77 K, a new recombination emission in Y₃Al₅O₁₂ –Dy has been observed for the first time at 3.05 eV and 2.92 eV, which is excited by photon energies of 3.85 eV and 4.45 eV at 77 K. On the basis of the obtained experimental data, it is assumed that during UV irradiation near the fundamental spectral region of the matrix, transfer of charge from oxygen in the Al₅O₁₂ anionic complex of the valence band to a neighboring anion leads to the formation of intrinsic electron trapping centers (Al₅O₁₂)^3– + e^– → (Al₅O₁₂)^4– ; in a similar way, impurity electron trapping centers are formed: Dy³⁺ + e^–→ ! Dy²⁺ . The intrinsic and impurity electron trapping centers form combined electron–radiative local states below the conduction band. As the combined electron–radiative state decays, ionization of both intrinsic and impurity-related electron traps occurs. The released electrons then recombine with hole trapping centers (Al₂O₇)^2– located near the ground state of Dy³⁺ ions. This process can lead to exciton formation, and the energy released during recombination is either transferred to the Dy³⁺ impurities or emitted as recombination radiation with energies of 3.05 eV and 2.92 eV.