Ho3+-Yb3+ co-doped bismuth titanate ferroelectric thin films were prepared by a chemical solution deposition method on fused silica substrates and their up-conversion luminescence characteristics excited by a 980 nm diode laser were investigated. The two emission bands centered at 546 and 656 nm in the emission spectra can be assigned to 5F4 + 5S2 → 5I8 and 5F5 → 5I8 transitions of Ho3+ ions, respectively. A bright green emission was observed even when the laser pumping power was relatively low. The dependence of the emission intensity on the pumping power indicated that the up-conversion emission in the thin films was a two-photon process. The up-conversion emission mechanism is discussed in detail. This study suggests that Ho3+ and Yb3+ co-doped Bi4Ti3O12 thin films can be applied to the fabrication of new multifunctional photoluminescence ferroelectric thin-film devices.
The up-conversion (UC) photoluminescence and ferroelectric properties of Bi4−xErxTi3O12 (BErT) thin films were studied in terms of annealing temperature and Er3+ doping concentration. The thin films were prepared by chemical solution deposition method. There are two green emission bands centered at 527 and 548 nm, and a red emission band centered at 663 nm in UC luminescence spectra measured under a 980 nm laser excitation at room temperature, which correspond to the radiative transitions from 2H11/2, 4S3/2, and 4F9/2 to 4I15/2, respectively. The quenching concentration of Er3+ ions for green emission was as high as 20 mol % for Bi3.2Er0.8Ti3O12 thin films. The large Er3+ quenching concentration and efficient energy transfer between two neighboring Er3+ ions result in the improved UC emission. The dependence of UC emission intensity on pumping power indicated a two-photon UC emission process in the thin films. The combination of UC emission and ferroelectricity was realized in the capacitors of Pt/Bi3.25Er0.75Ti3O12/Pt/TiO2/SiO2/Si. The UC photoluminescent BErT ferroelectric thin films could be potentially applied to integrated optoelectronic devices.
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.
A strong blue up-conversion photoluminescence and a greatly enhanced ferroelectric polarization were observed in Tm 3þ -Yb 3þ -W 6þ -triply-doped bismuth titanate thin films. The thin films were prepared on fused silica and Pt=Ti=SiO 2 =Si (111) substrates by chemical solution deposition and annealed at 700 C. The strong blue up-conversion emission centered at 478 nm, corresponding to 1 G 4 ! 3 H 6 transitions of Tm 3þ ions, was confirmed to be a three-photon energy-transfer process by pumping laser power dependence of emission intensity. The enhanced ferroelectricity with a high remnant polarization (Pr) value of about 32 lC=cm 2 is attributed to the weakened domain pinning due to the reduced oxygen vacancies by W 6þ substitution for Ti 4þ ions. The thin films combining the strong blue up-conversion photoluminescence with the good ferroelectric properties would provide possibility of realizing novel multifunctional optoelectronic integration device applications.
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