Strong upconversion luminescence properties of Yb3+ and Er3+ codoped Bi4Ti3O12 ferroelectric thin films

Strong upconversion green luminescence was observed in Er3+ and Yb3+ codoped Bi4Ti3O12 ferroelectric thin films. The thin films were prepared on fused silica and Pt/TiO2/SiO2/Si substrates by chemical solution deposition method. There are two strong green emission bands centered at 524 and 545 nm and a weak red emission band centered at 667 nm in the upconversion luminescence spectra pumped by 980 nm at room temperature. They correspond to the radiative relaxation of Er3+ from H211/2, S43/2, and F49/2 levels to the ground level I415/2, respectively. Bi3.65Yb0.3Er0.05Ti3O12 thin films exhibit higher green emission intensity by a factor of about 30 compared with Bi3.95Er0.05Ti3O12 thin films. The upconversion emission mechanism of the thin films has been discussed. In addition, Bi3.65Yb0.3Er0.05Ti3O12 ferroelectric thin films on Pt/TiO2/SiO2/Si substrates also show well-defined hysteresis loops with a remnant polarization (2Pr) of 28.2 μC/cm2. This study opens the possibility of constructing new integrated photoluminescent ferroelectric thin film devices.