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