Tuning Photoluminescence Response by Electric Field in Electrically Soft Ferroelectrics

Abstract

We show that an electrically soft ferroelectric host can be used to tune the photoluminescence (PL) response of rare-earth emitter ions by external electric field. Photoluminescence (PL) property of lanthanide ions is a subject of continuing interest because of its enormous applications in lighting industry, Laser, fiber optics telecommunications, biological assaying and medical imaging [1,2]. The most common strategy prevalent among experimentalists is to investigate the PL response/mechanisms by placing the luminescent centers in different kinds of host matrices or ligand environments. Among others, crystallographic symmetry of the host crystal is one of the important factors that influences PL emission in solids [3]. As such, temperature, pressure, and compositional modifications which can induce crystallographic transformations can, as well, affect the PL response. In general, pressure induced phase transformations in inorganic materials occur at Giga Pascal pressure ranges which is not easily achievable under ordinary conditions. From a device point of view, it is always desirable to tune/control properties around the ambient temperature and pressure conditions. In principle, it can be argued that if, apart from temperature and pressure, other control parameters are available to change the crystal structure, this parameter can as well tune different types of structure-sensitive properties, including PL. Such a scenario does exist in electrically and elastically soft ferroelectrics in the proximity of a ferroelectric instability. The electromechanical softness of the lattice, in conjunction with the strong coupling of polarization with crystal structure, makes such systems amenable to field induced structural transformation [4][5][6][7][8][9][10][11][12][13]. The consequent change in the crystal field parameters is expected to affect the PL response of doped emitter ions, such as the rare earth ions, if they are embedded in such a ferroelectric host. Apart from serving as probes to understand the local structural changes due to external influences such as temperature, pressure, electric field, etc., rare-earth doping of soft ferroelectrics can form a new class of multifunctional materials, which may be termed as "luminescent-piezoelectric", based on which new applications can be envisaged. With this as the motivation, and to demonstrate the proof of this concept, we have studied the electric field effect

The NbO6 octahedral distortion and phase structural transition of Eu3+‐doped K0.5Na0.5NbO3–xLiNbO3 ferroelectric ceramics

“…To get deeper insight into the local crystal ordering or distortions (symmetries) inside the NbO 6 octahedrons, the photoluminescence behavior of Eu 3+ ion is employed to observe their behaviors. As well‐known, the photoluminescence performance of Eu 3+ ion is very sensitive to the phase transition or even small distortion in the crystal structure . From the radius perspective, Eu 3+ ion is expected to occupy the sites of K + and Na + because the radius of Eu 3+ ion is close to those of K + and Na + ions in the KNN– x LN ceramics.…”

“…As Rubio‐Marcos et al reported, it is useful to study the relationship between the structures and the piezoelectric properties of KNN‐based ceramics using the Raman spectroscopy. On the other hand, it has been reported that the photoluminescence spectroscopy of trivalent europium ion (Eu 3+ ) can be used as a probe for small structural distortions caused by phase transition, which have been observed in both glasses and ceramics . Thus, a promising method, by investigating the photoluminescence emission of Eu 3+ ion, is proposed to analyze the deformation of the NbO 6 octahedral distortion caused by the spontaneous electric dipole.…”

“…Thus, a promising method, by investigating the photoluminescence emission of Eu 3+ ion, is proposed to analyze the deformation of the NbO 6 octahedral distortion caused by the spontaneous electric dipole. Because the photoluminescence emission of Eu 3+ ion in solids is dominated by the asymmetric crystal field of the host crystal structure . However, the previous works on luminescence spectroscopy of Eu 3+ ion put little emphasis on the relation between the observed emission properties and structural properties in ferroelectrics …”

In-situ Electric Field-Induced Modulation of Photoluminescence in Pr-doped Ba0.85Ca0.15Ti0.90Zr0.10O3 Lead-Free Ceramics

“…Owing to the complexity (coexistence of phases) and interference arisen from the strong diffraction peaks of ITO, the Rietveld refinement method has not been used for precisely identifying the crystal structure. Instead, with the primary aim of verifying the change of crystal structure, the broad diffraction peak has been resolved by the practical peak fitting method25, giving the fitting results indicated in Fig. 2b.…”

“…The uneven components enhance the electronic coupling between 4f energy levels and higher 4f5d configuration and subsequently increase f–f transition probabilities of the dopant ions19. The common approaches for ferroelectric hosts to rationally tune structural symmetry are based on those coupling physical factors that can respond well to external electric field such as biaxial strain1420, polarization2212223, or phase transition2425.…”