To obtain the dielectric material with high dielectric constant and high breakdown field, here a new composite material based on Fe3O4@BaTiO3 shell–core particles and polyvinylidene fluoride (PVDF) has been prepared. It is proved the Fe3O4@BaTiO3 particles are good fillers with low conductivity for the percolation effect, which induces high dielectric constant and low dielectric loss in the Fe3O4@BaTiO3/PVDF composite. The maximum dielectric constant is up to 3893, and dielectric loss is suppressed below 0.9. Moreover, the shell layer of Fe3O4 can be the trap and scattering centers to injected charges, so that the polarization saturation can be delayed to higher field. Thus, the released energy density of this composite can be enhanced greatly due to higher breakdown strength and lower energy loss.

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In this paper, the polarization response of dielectric blend based on the polyvinylidene fluoride (PVDF) and aromatic polythiourea (ArPTU) was investigated. It is found that the conduction loss at high field has been reduced 2–4 times along with an interesting irreversible transition under high electric field. The loss at 700 MV/m can be kept below 20%, which is better than most other polar dielectric polymers. It is proved that the transition is a phase change from glass phase to polar β phase at a critical field. And the highly polar thiourea groups of ArPTU can act as traps for the electrons, reduce conduction loss greatly and prevent dielectric breakdown by stabilizing the electron energy.

Luminescent materials with high thermal stability and quantum efficiency are extensively desired for indoor illumination. In this research, a series of Eu3+-activated KGd2F7 red-emitting nanoparticles were prepared at room temperature and their phase structure, morphology, luminescence properties, as well as thermal stability, have been studied in detail. Excited by 393 nm, the resultant nanoparticles emitted bright red emissions and its optimal status was realized when the Eu3+ content was 30 mol%, in which the concentration quenching mechanism was triggered by electric dipole–dipole interaction. Through theoretical analysis via the Judd–Ofelt theory, one knows that Eu3+ situates at the high symmetry sites in as-prepared nanoparticles. Moreover, the internal and extra quantum efficiencies of designed nanoparticles were dependent on Eu3+ content. Furthermore, the studied nanoparticles also had splendid thermal stability and the corresponding activation energy was 0.18 eV. Additionally, via employing the designed nanoparticles as red-emitting constituents, a warm white light-emitting diode (white-LED), which exhibits low correlated color temperature (4456 K), proper luminous efficiency (17.2 lm/W) and high color rendering index (88.3), was developed. Our findings illustrate that Eu3+-activated KGd2F7 nanoparticles with bright red emissions are able to be used to promote the performance of white-LED.