White light emission from Tm/Dy co-doped oxyfluoride germanate glasses under UV light excitation

In this paper, we report on the absorption and photoluminescence properties of Tm³⁺/Dy³⁺ ions co-doped oxyfluoride germanate glasses for white light emission. The X-ray diffraction (XRD) and differential thermal analysis (DTA) profiles of the host glass have been carried out to confirm its structure and thermal stability. From the measured absorption spectra, Judd-Ofelt (J-O) intensity parameters (Ω₂, Ω₄ and Ω₆) have been evaluated for Tm³⁺ and Dy³⁺ ions. A combination of blue, yellow and red emissions has emerged in these glasses, which allows the observation of bright white light when the glasses are excited by the ultraviolet light. The white light luminescence colour could be changed by varying the excitation wavelength. Also, various colours of luminescence, including white light, can be easily tuned by adjusting the concentrations of Tm³⁺ or Dy³⁺ ions in the co-doped glasses. Concentration quenching effect was also investigated and possible energy transfer mechanism from Dy³⁺→Tm³⁺ ions was explained which is also confirmed by the decay lifetime measurements.