Strong Upconversion Photoluminescence and Large Ferroelectric Polarization in Er~(3+)-Yb~(3+)-W~(6+) Triply Substituted Bismuth Titanate Thin Films Prepared by Chemical Solution Deposition

摘要

Strong upconversion photoluminescence and large ferroelectric polarization were observed for the first time in layered structure Er~(3+)-Yb~(3+)-W~(6+) triply substituted bismuth titanate thin films. The thin films were prepared on fused silica and Pt(111)/Ti/ SiO_2/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 ~2H_(11/2),~4S_(3/2), and ~4F_(9/2) to ~4I_(15/2) transitions of Er~(3+) ions, respectively. A two-photon energy-transfer process was confirmed by the power dependence of emission intensity. Compared with that of Er~(3+)-Yb~(3+)-substi-tuted bismuth titanate thin films, the improved photoluminescence is related to the reduced defects such as oxygen vacancies due to B-site (Ti~(4+)) substitution by W~(6+) 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 (Bi~(3+)) and B-site (Ti~(4+)) by Er~(3+), Yb~(3+), and W~(6+) 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.