Tunable blue-green emission properties of Tb³⁺ doped barium tantalate phosphor

The TTB (tetragonal tungsten bronze) crystal structure with the general formula of A₄B₂C₄M₁₀O₃₀ has three tunnels (A, B, C) of different coordination numbers with a corner-shared octahedral formation. Thanks to these properties, the TTB structure enables various RE ion substitutions and different physical properties to emerge. A series of green- emitting Tb³⁺ doped barium tantalate phosphors with TTB-type structure between 0.25 and 5 mol% obtained by the solid-state reaction route is reported. The structure of Tb³⁺ doped TTB-BaTa₂O₆ was identified by XRD and SEM-EDS analyses. PL relative emission intensity increased from 0.25 to 0.5 mol% and then decreased due to concentration quenching. Depending on the increasing concentration, the colour of the luminescence of BaTa₂O₆:Tb³⁺ phosphor can be tuned from blue to green through a cross-relaxation process, where a dipole-dipole energy transfer occurs between two nearby Tb³⁺ ions. The PL emission of the BaTa₂O₆:Tb³⁺ in the CIE diagram tended towards blue to green with the increase in Tb³⁺ concentration. PL decay profiles of the ⁵D₃ and ⁵D₄ states have a double exponential. The observed lifetimes of the ⁵D₃ state decrease as the decay profiles of the ⁵D₄ state exhibit a stable tendency. Based on the cross-relaxation process, the quantum efficiency (ƞ_QE) of the phosphor was evaluated, and the ƞ_QE of the ⁵ D₃ state with the increase of Tb³⁺ concentration between 0.25 and 5 mol% varied from 61.63 to 40.85%, respectively. (author)