High pressure responsive luminescence of flexible Eu3+ doped PVDF fibrous mats

Abstract Exploring lanthanide doped materials and their high-pressure optical properties is important from the perspective of designing pressure sensors, piezoelectric materials, scintillators, and optoelectronic devices, just to mention a few. Understanding the high-pressure optical properties of polymeric fibrous mats provides significant advantages in terms of flexibility, tunability, facile processability, and malleability. In this work, we have developed flexible polyvinylidene difluoride (PVDF) fibrous mats doped with an Eu3+ source of Eu(NO3)3·5H2O (EN-PF) or Eu2(SO4)3 (ES-PF) by a Forcespinning® method. Microstructural analysis of these two systems indicates that Eu(NO3)3·5H2O and Eu2(SO4)3 are homogeneously distributed and dispersed into the PVDF matrix. Fiber formation promotes a β-phase PVDF. Eu3+ doping increases the β-phase. Its fraction is larger for the ES-PF mats. To understand their high-pressure optical properties, their photoluminescence spectra have been taken at various pressures up to 58 GPa in a diamond anvil cell. High-pressure luminescence illustrates a clear change in asymmetry ratio, peak intensity, peak breadth, color coordinate, and color temperature of Eu3+ ions from both EN-PF and ES-PF with a different extent of changes. Specifically, Eu3+ ions in the ES-PF mats switch from asymmetric to symmetric environment as pressure increases. Those in the EN-PF mats present symmetric environment for all tested pressures. Both of the Eu3+ doped PVDF systems present irreversible changes. Therefore, the EN-PF fibrous mats present an opportunity to make pressure induced red-orange-yellow tunable phosphors for multifunctional applications.