Phase transition, electrical and luminescent properties of Dy-doped K 0.5 Na 0.5 NbO 3 -based lead-free ceramics

Dy-modified K 0.5 Na 0.5 NbO 3 -based lead-free piezoelectric ceramics of (K 0.48 Na 0.48 Li 0.04 ) 1−x Dy x/3 (Nb 0.90 Ta 0.04 Sb 0.06 )O 3 lead-free piezoelectric ceramics were prepared by a conventional ceramics technique and the effects of Dy 3+ doping on the crystal structure, microstructure, dielectric, piezoelectric and luminescent properties of the ceramics were investigated. The ceramics with low Dy levels (x ≤ 0.015) show a pure perovskite structure, while a small amount of secondary phase DyNbO 4 can be detected in the ceramics with x ≥ 0.02. The increase in the level of Dy 3+ doping leads to the shift of crystal structure of the ceramics from the coexistence of orthorhombic–tetragonal phases to pseudo-cubic phase. The addition of Dy 3+ inhibits the grain growth of the ceramics and induces the diffusive phase transition in the ceramics with high levels of Dy 3+ ions. The piezoelectric constant d 33 of the ceramics decreases from 198 to 52 pC/N with x increasing from 0 to 0.03 because of the shift of the crystal structure of the ceramics from the coexistence of orthorhombic–tetragonal phase to pseudo-cubic phase. The Dy-doped ceramics excited at 453 nm have excellent luminescent properties. Two strong emission spectral bands centered at 476 and 573 nm are observed, corresponding to the transition of the 4 F 9/2 → 6 H 15/2 and 4 F 9/2 → 6 H 13/2 levels of Dy 3+ , respectively. Our study shows that the ceramic with x = 0.015 possesses simultaneously strong ferroelectricity, good piezoelectricity and excellent luminescence, suggesting that the Dy-doped ceramics may have potential application in multifunctional devices.