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Concentration dependent luminescence characteristics of 5D4 and 5D3 excited states of Tb3+ ions in CFB glasses

Calcium fluoroborate (CFB) glasses doped with different concentrations of Tb3+ ions have been prepared with molar composition of (42-x) B2O3 + 20 CaF2 +15 CaO + 15 BaO + 8 Al2O3 + x TbF3 (x=0.05, 0.1, 0.5, 1.0, 2.0 and 4.0) by melt quenching method. Optical absorption spectrum for 1.0 mol% of Tb3+:CFB glass was recorded in UV-Vis-NIR regions. Radiative parameters such as radiative transition probabilities (AR), radiative lifetimes (τR), radiative branching ratios (βR) for the 5D3 and 5D4 excited states have been calculated by using the Judd-Ofelt parameters (Ωλ=2,4,6). The luminescence spectra recorded for different concentrations of Tb3+ ions in CFB glasses exhibit seven and four bands originating from 5D4 and 5D3 excited states respectively. As the concentration of Tb3+ ions increases the intensities of luminescence peaks originating from 5D4 state increases, whereas, the quenching of intensities has been observed for the emission peaks originating from 5D3 state due to energy transfer through cross-relaxation channel (5D3 : 7F6) → (5D4 : 7F0). The experimental lifetimes of 5D4 state for all the concentrations of Tb3+ ions are equal and exhibit single exponential decay with highest quantum efficiency which confirms that these glasses can be used for high intensity green emission even at high concentrations of Tb3+ ions.