Enhanced frequency upconversion and non-colour tunability in Er³⁺–Yb³⁺ codoped TeO₂–WO₃–Pb₃O₄ glasses

TeO₂–WO₃–Pb₃O₄ glasses codoped with Er³⁺–Yb³⁺ ions have been prepared by melting and quenching process. Judd–Ofelt analysis has been performed to calculate the various radiative parameters viz., radiative lifetime, branching ratio and stimulated emission crosssections by using the absorption spectra. The nephelauxetic ratio, bonding and covalency parameters have been determined to get the information about the nature of bonding between the rare earth ions and neighbouring oxygen atoms. The near infrared (NIR) to visible frequency upconversion (UC) study upon excitations with 980 nm and 808 nm diode lasers has been performed. The variations observed in the UC emission intensity arising from the Er³⁺ ions have been explained on the basis of efficient energy transfer Yb³⁺ → Er³⁺ ions and back energy transfer Er³⁺ → Yb³⁺ processes. On codoping with Yb³⁺ ions the intensity of the UC emission bands observed in the codoped glass upon excitation at 980 nm has been enhanced by many folds and explained on the basis of the oscillator strengths, UC emission crosssection and temporal evolution analysis. No tuning in the colour emitted from the codoped glass upon excitation at 980 nm is reported. The results suggested that the codoped glass may be suitable in making the NIR to visible upconverter and colour non-tunable optical devices.