Improved photoluminescence and ferroelectric properties of (Bi3.6Eu0.4)Ti3O12 thin films via Li+ doping

(Bi_3.6Eu_0.4)Ti₃O₁₂ (BEuT) thin films with different Li⁺ doping contents were prepared on fused silica and Pt/Ti/SiO₂/Si substrates by chemical solution deposition, and the effects of Li⁺ doping contents on the photoluminescence and ferroelectric properties of the thin films were investigated in detail. The results showed that an appropriate amount of Li⁺ doping could effectively improve emission intensities for two characteristic Eu³⁺ emission transitions of ⁵D₀→⁷F₁ (594 nm) and ⁵D₀→⁷F₂ (617 nm) compared with BEuT thin films without Li doping. This photoluminescence improvement can be attributed to the dual roles of Li⁺ ions, one of which is that Li ions can act as co-activators which are helpful to the energy transfer from the host to the Eu³⁺ ions, leading to a higher quantum yield; the other is that Li ion doping can induce local distortion of crystal field surrounding the Eu³⁺ activator because Bi³⁺ and Li⁺ ions have different ionic radii. In addition, the Li⁺-doped BEuT thin films had larger remanent polarization than BEuT thin films without Li doping prepared under the same experimental conditions. These results suggest that Li⁺ doping is an effective way to improve photoluminescence and ferroelectric properties of the (Bi,Eu)₄Ti₃O₁₂ thin films.