Tunable blue–green emission properties of Tb 3+ doped barium tantalate phosphor

The TTB (tetragonal tungsten bronze) crystal structure with the general formula of A 4 B 2 C 4 M 10 O 30 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 Tb 3+ 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 Tb 3+ doped TTB–BaTa 2 O 6 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 BaTa 2 O 6 :Tb 3+ phosphor can be tuned from blue to green through a cross-relaxation process, where a dipole–dipole energy transfer occurs between two nearby Tb 3+ ions. The PL emission of the BaTa 2 O 6 :Tb 3+ in the CIE diagram tended towards blue to green with the increase in Tb 3+ concentration. PL decay profiles of the 5 D 3 and 5 D 4 states have a double exponential. The observed lifetimes of the 5 D 3 state decrease as the decay profiles of the 5 D 4 state exhibit a stable tendency. Based on the cross-relaxation process, the quantum efficiency ( η QE ) of the phosphor was evaluated, and the η QE of the 5 D 3 state with the increase of Tb 3+ concentration between 0.25 and 5 mol% varied from 61.63 to 40.85%, respectively.