Er/Pr-doped K 0.5 Na 0.5 NbO 3 ceramics have been fabricated and the effects of Pr 3+ on their photoluminescence properties have been investigated systematically. The visible upconversion emissions, near-infrared and mid-infrared downconversion emissions of Er 3+ ions under the excitation of 980 nm have been studied in detail. The effects of Pr 3+ on PL properties and energytransfer processes have also been elucidated. By selecting an appropriate excitation source, simultaneous visible downconversion emissions of Er 3+ and Pr 3+ ions can be realized, and the emission colors of the ceramics can be tuned via the concentration of Pr 3+ ions in a wide range from yellowish green to yellow. Our results also reveal that the photoluminescence emissions of the ceramics can be enhanced by the alignment of polarization of the ferroelectric host.

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0.93Bi 0.5 Na 0.5 TiO 3-0.07BaTiO 3 ceramics doped with 0.01 mol Er 3þ have been prepared and their photoluminescence (PL), ferroelectric, dielectric, and piezoelectric properties have been studied. By doping Er 3þ at various sites, ceramics containing oxygen or cation vacancies have been prepared and their effects have been investigated. Ceramic containing no vacancy (i.e., doping Er 3þ at the Bi 3þ site) has also been prepared as a reference for the study. In addition to the reduction of the up-conversion PL emissions at 532, 547, and 660 nm, our results also reveal that oxygen vacancies can enhance, at the expense of the visible emissions, the near-infrared (1.44-1.66 lm) and mid-infrared (2.62-2.84 lm) down-conversion emissions. Similar results have also been observed for the ceramics containing cation vacancies, and the enhancement in the near-infrared emission becomes much more significant, reaching about 70% for the ceramic doped with Er 3þ at the Na þ site. These should be attributed to the looping mechanism between the 4 F 7/2 , 2 H 11/2 , 4 I 9/2 , and 4 I 11/2 levels facilitated by the cation vacancies and the efficient cross relaxations. The ceramics also exhibit reasonably good ferroelectric, dielectric, and piezoelectric properties, suggesting that they have great potential for multifunctional applications.

A sol-gel method has been utilized to prepare lead-free 2 mol% Er-doped K0.5Na0.5NbO3-xLiNbO3 (Er-KNN-xLN, x = 0, 0.08 and 0.10) ceramics. The X-ray diffraction results show that the ceramics have the perovskite structure and Er3+ ions have diffused into the host lattice. Compared to the solid-state reaction method, the sol-gel method is favor to reduce the sintering temperatures (~ 50 °C) of ceramics. Better compositional homogeneity, as well as finer and uniform grains is resulted from the sol-gel process, which have been confirmed by the scanning electron microscope images. The photoluminescence properties of ceramic bulks have been systemically studied. Under the excitation of 980 nm, the ceramics exhibit visible up-conversion green (510-570 nm) and red (640-685 nm) emissions. The emission colors of them are located in the yellowish green region. The down-conversion emissions in near-infrared (1450-1650 nm) and mid-infrared (2600-2870 nm) regions have been exhibited. The ferroelectric, dielectric and piezoelectric properties of ceramics have also been investigated. Because of the good electrical and excellent photoluminescence performances, our sol-gel-derived Er-doped KNN-LN ceramics should have great potential for multifunctional optoelectronic applications, such as optical-electro integrated materials and devices.