Synthesis and luminescent properties of a new Eu ³⁺-doped Li _1+x (Ta _1-z Nb _z) _1-x Ti _x O ₃ Red phosphor

A new red phosphor based on the Li _1+x (Ta _1-zNb _z) _1-xTi _xO ₃ (LTNT, 0.05 ≤ x a;circ 0.25, 0 ≤ z a;circ 0.625) solid solution as a host material has been synthesized. This host material is known as an M-phase and has a superstructure similar to that of the Li _1+x-yNb _1-x-3yTi _x+4yO ₃ (LNT) solid solution. An Eu ³⁺-doped LTNT has been prepared by sintering at 1413 K-1433 K for 24 h in a conventional electric furnace; the optimal sintering temperature for obtaining higher photoluminescence (PL) intensity was found to be 1423 K. Interestingly, bright red emission due to the hypersensitive ⁵D ₀- ⁷F ₂ transition in Eu ³⁺ was observed under direct excitation of the 4f electron at 541 ( ⁷F ₀- ⁵D ₁) or 398 nm ( ⁷F ₀- ⁵L ₆). The PL intensity of the LTNT phosphor was found to be dependent on the concentration of Eu ³⁺, Ti ⁴⁺, Nb ⁵⁺, and Ta ⁵⁺ ions. The PL intensity upon excitation at 541 nm was higher than that at 398 nm with decreasing Nb ₂O ₅ content in the LTNT host material. The highest PL intensity was achieved for the composition Li _1.11Ta _0.89Ti _0.11O ₃ doped with 2.5 wt% of Eu ₂O ₃.