Jay Hyok Song

Emission properties of PbO−Bi2O3−Ga2O3−GeO2 glasses doped with Tm3+ and Ho3+

Heavy metal oxide glasses containing GeO2 were investigated as potential hosts for 1.48 μm fiber-optic amplifiers because of their low phonon energy. Addition of ⩾10 mol % GeO2 to 0.57PbO−0.25Bi2O3−0.18Ga2O3 (mole fraction) glass provided thermal stability as well as good emission properties. The optimum glass composition for 1.48 μm amplifiers, considering lifetimes and population of the Tm3+:3H4 level, was 0.8 (0.57PbO−0.25Bi2O3−0.18Ga2O3)−0.2GeO2 (mole fraction). As the concentration of codoped Ho3+ exceeded 0.2 mol %, the population density of the Tm3+:3H4 level decreased sharply and the population inversion between the 3H4 and 3F4 levels in Tm3+ was achieved.

Analysis of cross relaxation between Tm3+ ions in PbO−Bi2O3−Ga2O3−GeO2 glass

Mechanisms of cross relaxation (3H4, 3H6→3F4, 3F4) in Tm3+ -doped PbO−Bi2O3−Ga2O3−GeO2 glass were analyzed. The energy gap between the absorption (3H6→3F4) and emission (3H4→3F4) spectra was approximately 600 cm−1. A large decrease in cross relaxation rates at low temperatures indicated that cross relaxation is controlled by a phonon-assisted energy transfer. The bending vibration of the Ga–O–Ga bonds between GaO4 tetrahedra (∼550 cm−1) was directly responsible for this energy transfer. Although GeO2 was added to enhance the thermal stability of PbO−Bi2O3−Ga2O3 glass, the phonon mode associated with vibration of GeO2 (∼770 cm−1) was not involved in the cross relaxation process.

Emission properties and structure of heavy metal oxide glasses

Emissions properties of glasses in the PbO-Ga2O3-Bi2O3 system doped with a variety of different rare-earth ions were reviewed with particular attention on the applications towards the amplification of the optical signals in the fiber-optic communication systems and for mid-infrared lasers. Due to the low vibrational phonon energy of the glasses, it was possible to realize the efficient emissions for the O-band and S-band amplification by doping Pr3+, Dy3+ or Tm3+. Amplification at these communication bands has not been possible when conventional oxide glasses were used as host materials. Network structure of the glass was made of mixture of GaO4 tetrahedra and PbO3/PbO4 polyhedra as a backbone. They are connected through bridging oxygens and a portion of these oxygen atoms are connected to three cations instead of two. Pb2+ ions also act as charge compensators as evidenced from the large amount of non-bridging oxygens in the glass network. Bi2O3 form BiO6 octahedra.