Ho3+-Yb3+ codoped tellurite based glasses in visible lasers and optical devices: Judd-Ofelt analysis and frequency upconversion

The optical absorption and frequency upconversion emission in the Ho3+/Yb3+ codoped TeO2-ZnO (TZ), TeO2-ZnO-WO3 (TZW) and TeO2-ZnO-WO3-TiO2 (TZWTi) glasses prepared by melting and quenching method has been studied. Judd-Ofelt theory has been used to calculate the Judd-Ofelt intensity parameters (Omega(2), Omega(4) and Omega(6)), transition probabilities, radiative lifetimes, absorption cross sections and the branching ratios. Upconversion (UC) emission bands centered at similar to 549 nm, similar to 658 nm and similar to 754 nm are observed upon 980 nm excitation. On codoping with the Yb3+ ions at 3.0 mol% the upconversion emission intensity enhancement of about similar to 57 times, similar to 342 times and similar to 480 times for the green band whereas for the red band arising from the Ho3+ ions it is about similar to 71 times, similar to 438 times and similar to 707 times respectively have been observed. The enhancement observed in the UC emission intensity is explained on the basis of efficient energy transfer from Yb3+ to Ho3+, larger absorption cross section, larger oscillator strengths and increase in the local field corrections factor. The spectroscopic quality factor Omega(4)/Omega(6) has been calculated to get the information about the developed materials for laser applications. The upconversion emission cross section determined on the basis of Judd-Ofelt analysis is found to be maximum for Ho-Yb-TZWTi glass. The nephelauxetic ratio, bonding and covalency parameters have been calculated to know the nature of bonding between the rare earth ions and neighbouring oxygen atoms. The high color purity 83.8% has been reported in the codoped glasses at similar to 81.2 W/cm(2) pump power density. (C) 2017 Elsevier Masson SAS. All rights reserved.