Study On The Photoluminescence And Electrical Properties Of Er³⁺-doped Lead-free Na_0.5Bi_0.5TiO₃ Ferroelectric Material

Lead-free ferroelectric materials with electrical properties are being more and more attractive.Ferroelectric materials have a spontaneous electric polarization which can be reversed by adding an external electric field.So they have potential applications in non-volatile memories and other microelectronic devices.Recent researches reveal that rare-earth doped ferroelectric materials can not only improve the electrical properties of ferroelectric materials,but also can realize photoluminescence in them.So to study the influence of rare-earth doping on the properties of ferroelectric materials is becoming more interesting.Er³⁺-doped Na_0.5Bi_0.5TiO₃ thin films are prepared via a modified chemical solution method.These thin films are phase-pure and crystallized in perovskite structure.The largest remnant polarization?Pr?and highest dielectric constant???are obtained in Na0.5Bi0.5Er0.01TiO3 thin films,and their values are 22?C/cm2 and 1166,respectively.Meanwhile,strong green UCL at 525 nm and 548 nm is observed in Er³⁺doped NBT thin films.They are attributed to 2H11/2?4I15/2 and 4S3/2?4I15/2 transitions of Er³⁺ ions,respectively.All these results indicate that the Er³⁺-doped NBT ferroelectric thin films have potential use as multifunctional thin film materials.Here,we demonstrate outstanding temperature-sensing properties from Na0.5Bi0.5Er0.01TiO3?NBT:Er?thin films.The perovskite phase for them is stable in the temperature range from 80 to 440 K.Interestingly,the Er³⁺ doping enhances the ferroelectric polarization and introduces local dipolar,which are positive for temperature sensing.Pumped by a 488-nm laser,the NBT:Er thin films show strong green luminescence with two bands around 525nm and 548 nm.The intensity ratio I525/I545 can be used for temperature sensing,and the maximum sensitivity is about 2.3 × 10-3 K-1,higher than that from Er-doped silicon oxide.These suggest NBT:Er thin film is a promising candidate for temperature sensor.Compare with NBT:Er thin film,NBT:Er crystal has lower phonon energy.So we prepared NBT:Er crystal via a facile hydrothermal method.Upconversion emission at 528 nm and 547 nm from two thermodynamically coupled excited states of Er³⁺ were recorded in the temperature from 80 K to 480 K under the excitation of a 980 nm diode laser.The emission intensity ratio?I528/I547?as a function of the temperature was investigated.A sensitivity of 0.0053 K-1 is observed at 400 K,suggesting they are promising candidate for nanothermometers.In this work we demonstrate the preparation of Er³⁺ doped perovskite ferroelectric Na_0.5Bi_0.5TiO₃ nanocrystals and their application in temperature sensing.