Strong upconversion photoluminescence and large ferroelectric polarization were observed for the first time in layered structure Er3+–Yb3+–W6+ triply substituted bismuth titanate thin films. The thin films were prepared on fused silica and Pt(111)/Ti/SiO2/Si substrates by chemical solution deposition. Two green emission bands and a red one were observed in the upconversion photoluminescence spectra for all the films pumped by a 980 nm laser diode, which correspond to 2H11/2, 4S3/2, and 4F9/2 to 4I15/2 transitions of Er3+ ions, respectively. A two-photon energy-transfer process was confirmed by the power dependence of emission intensity. Compared with that of Er3+–Yb3+-substituted bismuth titanate thin films, the improved photoluminescence is related to the reduced defects such as oxygen vacancies due to B-site (Ti4+) substitution by W6+ ions, while the large ferroelectric remnant polarization can be attributed to the increased structure distortion and the reduced oxygen vacancies due to cosubstitution of A-site (Bi3+) and B-site (Ti4+) by Er3+, Yb3+, and W6+ ions, respectively. The combination of the strong upconversion photoluminescence and the good ferroelectric properties in the thin films would open the possibility of realizing novel multifunctional optoelectronic integration device applications.
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