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Violet phosphorus quantum dots have been produced for the first time, which are effective fluorescent probes to selectively detect Cu2+. The morphology, microstructure and fluorescence properties have been tuned using synthesis parameters.

Violet phosphorus, the most stable phosphorus allotrope, has been successfully produced recently. Phonon properties of layered structures are important characteristic features to provide their stru...

Violet phosphorus is the most stable phosphorus allotrope with a layered structure. The corresponding violet phosphorene, a more stable two-dimensional semiconducting structure than black phosphorene, is a promising two-dimensional material for electronic and optoelectronic devices. The synthesis of violet phosphorus is the key factor to its experimental research. However, no clear evidence has been reported for the synthesis of violet phosphorus since its first proposal in 1865. The violet phosphorus was even debated to be a metastable intermediate phase. Until recently, the violet phosphorus crystals have just been successfully produced and exfoliated to give violet phosphorene. High yield synthesis of highly crystalline and pure violet phosphorus is crucial for the further exploration of violet phosphorus and phosphorene. In this work, highly crystalline and pure violet phosphorus crystals have been produced with a yield as high as 80%. The vapor transport, nucleation, crystal growth conditions, and synthesis mechanism have been studied to obtain violet phosphorus instead of black phosphorus. The mixture of transport agents and amorphous red phosphorus was heated to 600 °C to form P–Sn–I vapor and transported to the cooler zone (580 °C). The phosphorus was separated out from the P–Sn–I composites after cooling down to 530 °C to form violet phosphorus nuclei. The nucleation time and further cooling time correspond to the amount and crystallinity of violet phosphorus crystals. The precipitation has been demonstrated to be SnI2 crystals with a space group of C2/m (12) after the growth of violet phosphorus crystals. The synthesis of highly crystalline and pure violet phosphorus with high yield provides the application possibility of violet phosphorus and phosphorene in mechanic, electronic, optoelectronic, catalysts, and medical fields.

Violet phosphorene, a recently produced elemental 2D material, is a promising electronic and optoelectronic structure. The work function and band alignment of phosphorene nanoflakes are essential for their heterojunction structure design. The work function of violet phosphorene nanoflakes has been shown to decrease with the increase in layers from 5.16 eV to 4.79 eV and tends to be stable on a gold substrate, which has been confirmed via Kelvin probe force microscopy. The work functions measured on a silicon oxide substrate are much higher due to charge accumulation. The experimental work function of few-layer violet phosphorene is different from the intrinsic work function due to substrate doping, while that of thick violet phosphorene nanoflakes approaches the intrinsic work function value. Various functionals have been adopted for the work function calculation of few-layer violet phosphorene and the values obtained have been compared to the experimental results. The band alignments of different layered violet phosphorene materials calculated using the most accurate functional are demonstrated and compared to those of well-known materials to give a practical route for future applications. The work functions of the violet phosphorene nanoflakes have been shown to decrease due to oxidation, but they significantly improve after annealing in an argon atmosphere.

Black phosphorene has attracted much attention as a semiconducting two-dimensional material. Violet phosphorus is another layered semiconducting phosphorus allotrope with unique electronic and optoelectronic properties. However, no confirmed violet crystals or reliable lattice structure of violet phosphorus had been obtained. Now, violet phosphorus single crystals were produced and the lattice structure has been obtained by single-crystal x-ray diffraction to be monoclinic with space group of P2/n (13) (a=9.210, b=9.128, c=21.893 A, β=97.776°). The lattice structure obtained was confirmed to be reliable and stable. The optical band gap of violet phosphorus is around 1.7 eV, which is slightly larger than the calculated value. The thermal decomposition temperature was 52 °C higher than its black phosphorus counterpart, which was assumed to be the most stable form. Violet phosphorene was easily obtained by both mechanical and solution exfoliation under ambient conditions.