Optical properties and energy transfer of Dy3+-doped transparent oxyfluoride glasses and glass–ceramics

Dysprosium-doped oxyfluoride glasses and nanocrystalline glass–ceramics have been synthesized and studied by X-ray diffraction, transmission electron microscope, optical spectroscopy and time-resolved decay curves measurements. From the absorption spectra, Judd–Ofelt intensity parameters have been obtained and are used to predict radiative properties for the excited states of Dy3+ ions. From the visible emission spectra, yellow to blue intensity ratios have been calculated and their relative variations have been discussed based on the concentration of Dy3+ ions and the heat treatment conditions used to prepare the glass–ceramics. Luminescence decay curves of the 4F9/2 emitting level are found to be single exponential for 0.01 mol% Dy3+-doped glass and non-exponential for the remaining samples. The nature of energy transfer processes between Dy3+ ions, responsible for the non-exponential behavior of the decay curves, has been analyzed in the frame work of the Inokuti–Hirayama model. Lifetimes of the 4F9/2 level are found to decrease with the concentration of Dy3+ ions as well as with the time of heat treatment.