PAL spectroscopy of rare-earth doped Ga–Ge–Te/Se glasses

• Positron annihilation spectroscopy to study rare-earth doping in Ga–Ge–Te/Se glasses.
• Two-state trapping model to reconstruct experimental positron lifetime spectra.
• Decaying tendency in positron trapping efficiency in glasses under rare-earth doping.
• Rare-earth activated elimination of free-volume voids related to Ga-tetrahedrons.

Positron annihilation lifetime (PAL) spectroscopy was applied for the first time to study free-volume void evolution in chalcogenide glasses of Ga–Ge–Te/Se cut-section exemplified by glassy Ga10Ge15Te75 and Ga10Ge15Te72Se3 doped with 500 ppm of Tb3+ or Pr3+. The collected PAL spectra reconstructed within two-state trapping model reveal decaying tendency in positron trapping efficiency in these glasses under rare-earth doping. This effect results in unchanged or slightly increased defect-related lifetimes τ2 at the cost of more strong decrease in I2 intensities, as well as reduced positron trapping rate in defects and fraction of trapped positrons. Observed changes are ascribed to rare-earth activated elimination of intrinsic free volumes associated mainly with negatively-charged states of chalcogen atoms especially those neighboring with Ga-based polyhedrons.