White upconversion photoluminescence for Er3+–Tm3+–Yb3+ tri-codoped bismuth titanate ferroelectric thin films

• We obtained upconversion luminous thin films which can emit bright white photoluminescence.
• We found there existed significant energy transfers from Er3+ to Tm3+.
• The thin films showed properties of ferroelectric polarization simultaneously.
• The films would open the possibility of inventing novel optoelectronic integration devices.

The upconversion (UC) photoluminescence and ferroelectric properties of Er3+–Tm3+–Yb3+ tri-codoped bismuth titanate (BETYT) thin films were studied. The thin films were prepared by chemical solution deposition method. There are four emission bands in the visible UC luminescence spectra excited by 980 nm at room temperature. The 478 nm blue emission band corresponds to 1G4 → 3H6 transition of Tm3+, and the 527 nm, 548 nm green emission bands correspond to 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions of Er3+, and the 657 nm red emission band corresponds to 4F9/2 → 4I15/2 transition of Er3+ and 1G4 → 3F4 transition of Tm3+. The fluorescent color can be tuned by adjusting Er3+, Tm3+ and Yb3+ concentrations and the optimal color coordinate in these films is (0.31, 0.34), very close to the standard white-light coordinate of (0.33, 0.33) when pumped under power intensity about 2.8 W/cm2. The UC emission mechanism was discussed and there exist significant energy transfers from Er3+ to Tm3+, which will affect the relative intensity of blue, green and red emissions and their quenching concentrations. The remanent polarization (2Pr) value of BEr0.0085TYT thin film prepared on Pt/Ti/SiO2/Si substrate is 27.8 μC/cm2. The combination of UC photoluminescence and ferroelectric properties in BETYT thin films would open the possibility of inventing novel multifunctional optoelectronic integration devices.

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