Photoluminescence Characteristics Of Er³⁺ Doped Ferroelectric Ceramics

In recent years,there have been many researches on the fluorescent ferroelectrics and piezoelectric materials.Researchers have doped light-emitting elements?mainly rare earth elements?into the lattice of these materials to explore the fluorescent characteristics in the ferroelectric lattice field.In this way,the relationships between the physical quantities,like the phase structure and the temperature,and the fluorescence spectrum maybe established.Thereby,a new non-destructive and noncontact detection method will be developed to realize the measurements that beyond the power of some traditional methods.On the other hand,it could be very helpful for the development of new multi-functional materials,which have potential applications in the field of photonics switch by developing the optical-,mechanicaland electrical coupling relationship.At present,the research in this field mainly focuse on the lead-free materials,instead of the lead-based materials that dominate in the industrial field.In addition,the research concerning the influence of phase transformation on the characteristics of the spectrum is still in the initial stage,and most of the work put their attention on the change of flourescence intensity,ignoring other spectral features.Therefore,it is particularly important to study the fluorescence characteristics of rare earth elements that embedded in the typical lead-free and leadbased ferroelectrics systematically.Er³⁺ ions as a widely studied rare earth luminescent center,has proven its great value in commercial and research fields,such as the Er³⁺ doped fiber amplifiers,etc.Meanwhile,barium titanate?BT?ceramics,potassium sodium niobate?KNN?ceramic,calcium titanate barium?KNN?ceramics,and lead megnesium niobate-lead titanate?PMN-PT?are some typical ferroelectric ceramics,which have attracted certain attention in scientific research and industrial field,are representatives of the lead-free and lead-based ferroelectric ceramics.In this paper,we studied the fluorescence efficiency of different light-emitting elements in the ferroelectric lattice field.It was found that the fluorescence efficiencies of transition metal(Fe²⁺,Fe³⁺,Cu²⁺,and Mn²⁺ ions,etc.)in PMN-PT and a variety of lead-free ferroelectric ceramics are very poor and cannot achieve effective optical measurement.It was also found that the rare earth element Eu³⁺ has a poor fluorescence efficiency both in lead-based ceramics and lead-free ceramics,making it cannot be effectively measured either,but in lithium niobate?LN?ceramics and single crystal,it shows a good fluorescence efficiency.In addition,we found that the rare earth element Er³⁺ expressed perfect fluorescence efficiency in BT ceramics,KNN ceramic,BCT ceramics,and PMN-PT ceramic,the spectra of which can be obtained effectively and accurately.Therefore,in this paper,the fluorescence characteristics of Er³⁺ in several typical ferroelectric ceramics were mainly disussed.We studied the spectrum character variations of 2H11/3,4S3/2 and 4I9/2 levels in BT ceramics,KNN ceramic,BCT ceramics,and PMN-PT ceramic in the condition of temperature-induced phase transition.The results show with the rise of temperature,the symmetry of ferroelectric lattice field increases and the fluorescence intensity suffers from the significant attenuation.What is more,there is a significant critical phenomenon at the phase transition temperature,especially at the Curie temperature.We found that the Stark effect would respond to the lattice field,leading to the shift of the fluorescence peaks.Furthermore,the response of the energy forbidden to the lattice field in the phase transition process was explored.We found that with the increase of lattice symmetry,the opened energy forbidden transition would not be allowed.Based on the critical characteristics of the spectrum of the Er³⁺,a new measurement method for phase transition was proposed,and the automatic control and measurement were realized by Labview software.This method is a nondestructive and non-contact one and may play an important role in micro-area measurement.We studied the practical application scope of the thermal sensing based on the thermally coupled energy levels 2H11/2 and 4S3/2 of Er³⁺ embedded in BT ceramics,KNN ceramics and BCT ceramics.We found that there was deviation around the transformation temperature.Consequently,researchers used to consider the application of this fluorescence intensity ratio thermometric technology based on the thermal coupling levels in the ferroelectric lattice field first.Via the different temperature responses of several pairs of levels of Er³⁺ in the PMN-PT ceramic,a new method that based on the linear temperature responses was proposed.Compared with the traditional exponential response curve,this method greatly simplifies the measurement conditions and can obtain the same sensitivity in different temperature ranges.Transparent Er³⁺ doped nimeisuanqiantaisuanqian ceramic was prepared.We carried out the experiment that how the fluorescence intensity and lifetime response to the electric field,with in-situ style.With the help of the theoretical analysis of the energy level speed equation,we found that energy transfer mechanism should be responsible for the upconverted distribution of the 4S3/2 level on which a new method for investigation of the energy transfer was establised.Finally,based on the detection of the electric hysteresis loop and electrostrictive line,we revealed the physical mechanism of the influence of the electric field on the fluorescence characteristics.