Here, nitrogen-doped carbon quantum dots (N-CQDs) were successfully synthesized by the solvothermal method using graphite as the carbon source and N,N-dimethylformamide as the nitrogen source. We characterized the structure and chemical constitution of N-CQDs using X-ray diffraction, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. We investigated the pump- and temperature-dependent photoluminescence (PL) properties and the dynamic exciton recombination processes of N-CQDs, using both steady-state and time-resolved PL techniques. The spectral results show that the PL emission peak located at 518 nm at room temperature, mainly originates from the n-π^* transition on the surface of N-CQDs. The pump fluence and PL integral intensity were analyzed to demonstrate the existence of single-photon excitation under the 405 nm laser excitation. As the temperature increases, the non-radiative transition gradually increases, which decreases the PL intensity, the full width at half maxima first narrows and then widens and the PL lifetime gradually decreases. Furthermore, we combined the N-CQDs with chip to prepare light-emitting diode (LED). The resulting chromaticity coordinate was obtained to be (0.29, 0.40). This study offers a comprehensive understanding of the luminescence mechanism in N-doped CQDs and introduces a novel approach for the quickly fabrication of full-color display LEDs.

FeNi-based phosphides are one of the most hopeful electrocatalysts, whereas the significant challenge is to achieve prominent bifunctional catalytic activity with low voltage for water splitting. The morphology and electronic structure of FeNi-based phosphides can intensively dominate effective catalysis, therefore their simultaneous regulating is extremely meaningful. Herein, a robust bifunctional catalyst of Zn-implanted FeNi-P nanosheet arrays (Zn-FeNi-P) vertically well-aligned on Ni foam is successfully fabricated by Zn implanting strategy. The Zn fulfills the role of electronic donor due to its low electronegativity to enhance the electronic density of FeNi-P for optimized water dissociation kinetics. Meanwhile, the implantation of Zn into FeNi-P can effectively regulate morphology of the catalyst from thick and irregular nanosheets to ultrathin lamellar structure, which generates enriched catalytic active sites, leading to accelerating electron/mass transport ability. Accordingly, the designed Zn-FeNi-P catalyst manifests remarkable hydrogen evolution reaction (HER) activity with low overpotentials of 55 and 225 mV at 10 and 200 mA·cm⁻², which is superior to the FeNi-P (82 mV@10 mA·cm⁻² and 301 mV@200 mA·cm⁻²), and even out-performing the Pt/C catalyst at a high current density > 200 mA·cm⁻². Moreover, the oxygen evolution reaction (OER) activity of Zn-FeNi-P also has dramatically improved (207 mV@10 mA·cm⁻²) comparable to FeNi-P (221 mV@10 mA·cm⁻²) and RuO₂ (239 mV@10 mA·cm⁻²). Noticeably, an electrolyzer based on Zn-FeNi-P electrodes requires a low cell voltage of 1.47 V to achieve 10 mA·cm⁻², far beyond the catalytic activities of FeNi-P||FeNi-P (1.51 V@10 mA·cm⁻²) and the benchmark RuO₂||Pt/C couples (1.56 V@10 mA·cm⁻²). This Zn-implanting strategy paves a new perspective for the development of admirable bifunctional catalysts.