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 Tm3+ 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 GeO2 by Ga2O3 resulted in decreasing of glass transition temperature and largest phonon energy. Increasing concentration of Ga2O3 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 Ga2O3 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 (H-3(4), H-3(6), H-3(6), H-3(4)) energy migration is not phonon dependent in the quasiresonant processes, while the cross relaxation Tm -> Tm (H-3(4), H-3(6) -> F-3(4), F-3(4)) is a multiphonon mechanism dominated by one-phonon creation (similar to 96%). It is demonstrated that the stretching frequencies and the ET processes become lower when increasing the concentration of Ga2O3.