Concentration dependent luminescence characteristics of5D 4 and5D 3 excited states of Tb3+ions in CFB glasses

Abstract

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 (A_R), radiative lifetimes (τ_R), radiative branching ratios (β_R) for the ⁵D₃ and ⁵D₄ excited states have been calculated by using the Judd-Ofelt parameters (Ω_λ=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.