Improved Fluorescence from Tm‐Ho‐ and Tm‐Ho‐Eu‐Codoped Transparent PbF 2 Glass‐Ceramics for S + ‐Band Amplifiers

Tm 3+ ‐Ho 3+ ‐ and Tm 3+ ‐Ho 3+ ‐Eu 3+ ‐ion‐codoped oxyfluoride transparent glass‐ceramics containing PbF 2 nanocrystals were prepared, and the near‐infrared fluorescence properties of the Tm 3+ ions were investigated for their potential use as a 1.4 μm amplifier. For all samples, the lifetime of the Tm 3+ : 3 H 4 level increased with heat treatment because of the decrease of the phonon energy as PbF 2 crystals were formed. Moreover, it was revealed that codoping with Ho 3+ or Eu 3+ was effective in suppressing the lifetime of the Tm 3+ : 3 F 4 level by energy transfer to the Ho 3+ : 5 I 7 or Eu 3+ : 7 F 6 level. For the codoped samples, the heat treatments decreased the Tm 3+ : 3 F 4 lifetime and increased the Tm 3+ : 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.