Efficient near infrared to visible light upconversion from Er/Yb codoped PVDF fibrous mats synthesized using a direct polymer doping technique

Upconverting-materials are capable of converting near infra-red (NIR) excitation into lower wavelengths. These materials could have a myriad of promising potential applications. However, in some areas, its use has been hindered by its low upconversion luminescence (UCL) efficiency and processing/handling disadvantages from luminescent materials in powder form. This work presents a step towards overcoming this limitation, by developing polymer-based fiber membranes without adding external luminescent powders. Herein, we report on the synthesis of Yb3+ and Er3+ codoped polyvinylidene difluoride (PVDF) and its development into fiber membranes using the Forcespinning® technique. X-ray diffraction (XRD), Fourier transformed infrared (FTIR) spectroscopy were performed to confirm the phase formation, crystallinity and the presence of vibrational bands of the corresponding PVDF matrix. Scanning Electron microscopy (SEM) and thermogravimetric analysis were conducted to investigate the morphological and thermal properties of the codoped nanofibers while the X-ray photoelectron spectroscopy (XPS) showed efficient doping of the lanthanides in the PVDF fiber. Under exposure to 980 nm NIR illumination, the PVDF:Yb3+,Er3+ fibrous mats exhibited efficient UCL emission in the visible wavelength region (523, 540 and 656 nm). The observed results show a NIR to visible UCL process where the Yb3+ ions act as the sensitizer for the generation of visible upconversion emission from Er3+ ions through an excited state absorption (ESA) and two photon energy transfer (ET) mechanisms. The developed material further opens potential lighting and imaging related applications given the ease of preparation, handling, and flexibility of the developed membranes.