Thermal, structural, mechanical and 1.8 μm luminescence properties of the thulium doped Pb-K-Al-Na glasses for optical fiber amplifiers

Abstract

ABSTRACT Lead based phosphate glasses with the concentration variation of Tm3+ ions (PPbKANTm) were prepared by using melt-cast technique. These glasses are characterized by using thermal (DSC), structural (XRD and Raman), mechanical (Knoop hardness) and optical (absorption, emission and lifetime) studies. The structural geometry of the PPbKAN glasses were explored by Raman spectrum and the phonon energy was found to be 1124 cm−1. The three Judd-Ofelt parameters were obtained in order to attain information about the ligand environment, radiative lifetime as well as branching ratios of Tm3+ ion. In general, McCumber theory found to be quite successful to evaluate the cross-section of the metastable state, 3F4→3H6 (1.8 μm). Distinctive down-conversion (420–500 nm) was studied by exciting the 1G4(Tm3+) state. The decay rate of 1D2→3F4 level measured for all the concentrations under λexc = 355 nm. With λexc = 808 nm, the near-infrared emission spectra was also studied and the spectra having two emission transitions of 3H4→3F4 at 1.47 μm and 3F4→3H6 around 1.8 μm. The emission intensity increases with increasing Tm3+ ions concentration upto 1.0 mol% and decreases beyond 1.0 mol% where the optimal 1.8 μm emission is observed when Tm3+ ions concentration is 1.0 mol%. From the near-infrared emission spectra, the crucial spectroscopic parameters such as emission (1.41 × 10−20 cm2) cross-section, effective bandwidth (197 nm) and gain coefficient (277.7 × 10−27 cm3) were evaluated. The Knoop hardness was measured for all the glasses and confirms that the present lead based phosphate glasses doped with Tm3+ ions are mechanically stable. From the analysis of the outcome, it was concluded that the present PPbKANTm glasses are useful for broad band amplifications.