Spectroscopy and enhanced frequency upconversion in Nd3+-Yb3+ codoped TPO glasses: energy transfer and NIR to visible upconverter

TeO2-Pb3O4 (TPO) glasses codoped with Nd3+ and Yb3+ ions have been fabricated by conventional melting technique. The absorption, emission and excitation spectra of the samples have been recorded. The optical band gap in both the doped/codoped glasses is found to be similar to 3.31 eV. Judd-Ofelt analysis has been carried out by using the absorption spectrum of 0.8 mol% Nd3+ doped glass to determine the radiative properties viz radiative transition probabilities, branching ratios, radiative lifetimes, quality factor and emission cross sections of some emitting levels for Nd3+ ions. The radiative transition probability for the (4)G(7/2)-> I-4(9/2) transition (similar to 1926 Hz) is found to be maximum compared to other (4)G(5/2)-> I-4(9/2) (similar to 1622 Hz) and F-4(5/2)-> I-4(9/2)(similar to 865 Hz) transitions. Upconversion (UC) luminescence of the samples has been examined by the 980 nmCWdiode laser excitation. Effect of addition of Yb3+ ions in the Nd3+ doped glasses onUC emission intensity has been discussed. The UCemission intensity corresponding to the green, red and NIR bands in the codoped glass has been enhanced by similar to 17,similar to 12 and similar to 42 times as compared to that of the Nd3+ singly doped glass. The quantum efficiency for the (4)G(7/2) level is found to be similar to 32%. The nephelauxetic ratio, bonding parameter and covalency of Nd3+ ions have been found positive which represents the covalent bonding between Nd3+ ion and oxygen atom. The colour tunability from yellowish-green to dominant green region has been obtained in the optimized codoped TPO glass.