Structural origin and energy transfer processes of 1.8 μm emission in Tm3+ doped germanate glasses.

A detailed characterization of structural analysis and energy transfer (ET) process in Tm(3+) doped germanate glasses has been presented. The thermal stability and Raman spectroscopic analysis of the host glass structure has been discussed. It is observed that replacing GeO(2) by Ga(2)O(3) resulted in decreasing of glass transition temperature and largest phonon energy. Increasing concentration of Ga(2)O(3) decreases the density of cross-linking of the germanate glass network, and weaker Ga-O bonds result in lower phonon energy. The influences of the concentrations of Ga(2)O(3) and the glass structure on the ET have also been analyzed. The extended overlap integral method is used to calculate the microparameters of the energy transfer and the critical distance. The results show that the transference Tm → Tm ((3)H(4), (3)H(6) → (3)H(6), (3)H(4)) energy migration is not phonon dependent in the quasiresonant processes, while the cross relaxation Tm → Tm ((3)H(4), (3)H(6) → (3)F(4), (3)F(4)) is a multiphonon mechanism dominated by one-phonon creation (∼96%). It is demonstrated that the stretching frequencies and the ET processes become lower when increasing the concentration of Ga(2)O(3).