Phase transition and luminescence properties of GdTiNbO6:Eu3+ formed by hydrothermal route

[Display omitted] •Phase transition and luminescence of hydrothermal GdTiNbO6:Eu3+ were investigated.•RE3+ radius 0.1061 nm was the boundary between the aeschynite and euxenite.•GdTiNbO6:0.30Eu3+ was preferred for UV-B excitation, 0.50Eu3+ for Vis-light excitation.•The decay lifetime of 615 nm emission (ex = 405 nm) was 570∼571 μs. The dependences of phase transition and luminescence properties upon both Eu3+ concentration and heating temperature in air were investigated for GdTiNbO6:Eu3+ fine crystals formed hydrothermally at 240 °C as aeschynite-type EuxGd1-xTiNbO6 solid solution. The as-prepared aeschynite solid solution in the concentration range x ≥ 0.70 did not show the phase transformation from an aeschynite- to an euxenite-type structure caused by heating at 1300 °C for 1 h in air. The present study suggested that the phase boundary between the aeschynite- and euxenite-type RETiNbO6 in the EuTiNbO6-GdTiNbO6 system, where RE was a rare earth, lay in the average RE3+ ionic radius 0.1061 nm. The intense emissions attributed to the 5D0→7F1 and 5D0→7F2 transitions of Eu3+ for the as-prepared samples were more improved by heating at 1100–1300°C in air. The material doped with 30 mol% Eu3+ was preferred for UV-B excitation, in contrast, the material with 50 mol% Eu3+ was preferred for visible light excitation.