Improved Fluorescence from Tm-Ho- and Tm-Ho-Eu-Codoped Transparent PbF2 Glass-Ceramics for S+-Band Amplifiers

Tm³⁺-Ho³⁺- and Tm³⁺-Ho³⁺-Eu³⁺-ion-codoped oxyfluoride transparent glass-ceramics containing PbF₂ nanocrystals were prepared, and the near-infrared fluorescence properties of the Tm³⁺ ions were investigated for their potential use as a 1.4 μm amplifier. For all samples, the lifetime of the Tm³⁺:³ H ₄ level increased with heat treatment because of the decrease of the phonon energy as PbF₂ crystals were formed. Moreover, it was revealed that codoping with Ho³⁺ or Eu³⁺ was effective in suppressing the lifetime of the Tm³⁺:³ F ₄ level by energy transfer to the Ho³⁺:⁵ I ₇ or Eu³⁺:⁷ F ₆ level. For the codoped samples, the heat treatments decreased the Tm³⁺:³ F ₄ lifetime and increased the Tm³⁺:³ H ₄ lifetime. This was attributed to the concentration of rare-earth ions in the fluoride crystallites. These properties improved the population inversion of the 1.4 μm transition.