Fluorescent N-CQDs uniformly implanted into sponge-like PVDF-HFP piezoelectric film by facile two-step process for multifunctional pressure sensor

Abstract

To meet the diversified demands for the booming intelligent systems, a multifunctional pressure sensor with two basic capabilities of ultraviolet excited fluorescence and force-electricity response has been proposed, and named as fluorescent pressure sensor (FPS). Carbon quantum dots (CQDs) are being rapidly developed as an reasonable photoluminescence materials. However, the CQDs were utilized in the solid-state film along with serious aggregation-induced quenching (AIQ). Here, we developed a two-step method instead of the typical one-step method to overcome the AIQ of the CQDs in the representative piezoelectric polymer. The sponge-like poly (vinylidene) fluoride-hexafluoropropylene (PVDF-HFP) film with high porosity formed based on nonsolvent-induced phase separation was selected as the host matrix of the guest nitrogen-doped CQDs (N-CQDs). The impressive bright blue fluorescence with enhanced intensity derived from the N-CQDs is successfully implanted into the obtained N-CQDs/PVDF-HFP piezoelectric hybrid film, attributing to two key factors: (i) the sponge-like matrix supported uniform distribution of the N-CQDs and (ii) the hydrogen bonding between the N-CQDs and the matrix chains. Meanwhile, the hybrid film used in the FPS still keeps a sensitivity of 92.7 mV N−1, thanks to the β piezoelectric phase formation in the matrix. Since the hybrid film based FPS has multiple features, such as ultraviolet excited fluorescence, force-electricity response, self-powered capability and flexibility, it will show a great potential in the intelligent systems used as the multifunctional sensor and energy harvester.