Shengliang Hu

One-step synthesis of fluorescent carbon nanoparticles by laser irradiation

Fluorescent carbon nanoparticles (CNPs) were synthesized by laser irradiation of a suspension of carbon powders in organic solvent. The surface modification on the CNPs was fulfilled simultaneously with the formation of the CNPs, and tunable light emission could be generated by selecting appropriate solvents. The origin of the luminescence was attributed to carboxylate ligands on the surface of the CNPs.

Chemical Regulation of Carbon Quantum Dots from Synthesis to Photocatalytic Activity

Carbon quantum dots (CQDs) were synthesized by heating various carbon sources in HNO3 solution at reflux, and the effects of HNO3 concentration on the size of the CQDs were investigated. Furthermore, the oxygen-containing surface groups of as-prepared CQDs were selectively reduced by NaBH4 , leading to new surface states. The experimental results show that the sizes of CQDs can be tuned by HNO3 concentration and then influence their photoluminescent behaviors; the photoluminescent properties are related to both the size and surface state of the CQDs, but the photocatalytic activities are determined by surface states alone. The different oxygen-containing groups on the surface of the CQDs can induce different degrees of the band bending upward, which determine the separation and combination of the electron-hole pairs. The high upward band bending, which is induced by C=O and COOH groups, facilitates separation of the electron-hole pairs and then enhances high photocatalytic activity. In contrast, the low upward band bending induced by C-OH groups hardly prevents the electron-hole pairs from surface recombination and then exhibits strong photoluminescence. Therefore, both the photocatalytic activities and optical properties of CQDs can be tuned by their surface states.

Ultrafine diamond synthesized by long-pulse-width laser

Nanodiamonds with sizes of 3–6nm were prepared by irradiating graphite suspension using a long-pulse-width (1.2ms) laser at room temperature and normal pressure. The low power density and long pulse laser generated a lower temperature and a lower pressure, which determine the stable size of nanodiamonds. On the other hand, the low degree of supercooling allows a rather low growth velocity, and a disordered structure formed at the diamond surface retards the epitaxy growth. The above two factors dynamically limit the final size of nanodiamonds. Our results suggest that the growth of nanodiamonds follows the Wilson-Frenkel law, and the long pulse laser is propitious to producing fine nanodiamonds.

Simultaneous synthesis of luminescent carbon nanoparticles and carbon nanocages by laser ablation of carbon black suspension and their optical limiting properties

Both luminescent carbon nanoparticles (CNPs) and carbon nanocages (CNCs) were simultaneously synthesized using laser ablation of carbon black suspension in poly(ethylene glycol). The formation of luminescent CNPs and CNCs depends on the size of carbon black and the laser power density. The optical limiting (OL) measurements of luminescent CNPs, CNCs and their mixture were performed using the open Z-scan technique at the laser wavelength of 532 nm. The mixture of luminescent CNPs and CNCs shows much stronger OL response than carbon black, luminescent CNPs and CNCs in the PEG500N solution. The luminescent CNPs can help to enhance the OL effects of CNC suspensions.

Carbon-Dot-Loaded Alginate Gels as Recoverable Probes: Fabrication and Mechanism of Fluorescent Detection

We prepare a solid and green film of carbon-dot-loaded alginate gels with a pore structure. Compared to carbon dot suspension, the film exhibits stronger blue light emission. The porous structure of the film enables ion diffusion and contact with the CDs incorporated in the gel network, and thus the photoluminescence (PL) behavior of the film can be influenced by ions. The PL of the film shows a sensitive and selective quenching effect to Cu(2+), and it can be repeatedly used as a fluorescent probe to recognize Cu(2+) with a detection limit of 5 ppm. A band bending mechanism is proposed to understand the effects of surface/interface states and metal ions on the PL behavior of carbon-dot-loaded alginate gels, and it has been supported by our further experimental results. This band bending mechanism provides a clear physical insight into ion detection by PL behavior.

Enhanced performance of Fe3+ detection via fluorescence resonance energy transfer between carbon quantum dots and Rhodamine B

Carbon quantum dots (CQDs) were prepared by a facile hydrothermal method and emitted a broad fluorescence covering the entire blue and green light wavelength scope. Because their emission spectra overlaped with the absoprtion spectrum of Rhodamine B (RhB) molecules, fluorescent resonance energy transfer (FRET) phenomenon between CQDs as the energy donors and RhB as the energy acceptors was observed when CQDs were mixed with RhB in a solution. To obtain the optimal FRET efficiency, the concentrations of CQDs and RhB should be adjusted to 0.559 mg mL−1 and 1.25 μM, respectively, at pH = 6.2. None of the metal ions except for Fe3+ hindered this FRET process as well as deactivated the electronic excitation energy of RhB molecules through migration, resulting in an enhancement of fluorescence quenching rates. Therefore, the developed system allowed enhancing the selectivity and sensitivity of Fe3+ detection via the FRET effects, and could be used for accurate measurements of time-dependent conformational changes and monitoring the corrosion processes of iron materials over an extended period.

Understanding the effects of the structures on the energy gaps in carbon nanoparticles from laser synthesis

The effects of the structures on the energy gaps in luminescent carbon nanoparticles (CNPs) were investigated. On the one hand, we fabricated CNPs with the different structures and a uniform size and then analyzed their photoluminescence (PL) behaviors. On the other hand, we calculated the dependence of the structures on the energy gaps in CNPs by a simple quantitative model. Both the experimental and calculated results show that the luminescent CNPs contain a mixture of sp2 and sp3 bonding and hence their PL behaviors and energy gaps are determined by the fraction of sp2-hybridized carbon atoms.

Formation and luminescent properties of face-centered-cubic Si nanocrystals in silica matrix by magnetron sputtering with substrate bias

Si nanocrystals with face-centered-cubic (fcc) structure were fabricated using common sputtering technique, but applying bias on the substrate, the thermodynamic calculation indicates that the bombardment of Ar+ ions arising from the bias should be responsible for the crystallization and phase transition of Si nanocrystals. The silica films containing fcc-Si nanocrystals give strong blue and ultraviolet light emissions, which suggest that the band structure of Si material could be modified by changing the crystal structure.

Growth dynamics of nanodiamonds synthesized by pulsed-laser ablation

We performed theoretical analysis on nanodiamonds (NDs) generated by pulsed-laser ablation to investigate its growth dynamics. The final size of NDs was calculated by combining the growth velocity with growth time. The result shows that the radius and density of plasma plume determine the cooling velocity, and the growth time correlates with the cooling velocity. Theoretical calculations are in good agreement with experimental results and give reasonable explanation on the formation of ultrafine NDs.

One-Step Synthesis of Graphitic Nanoplatelets that are Decorated with Luminescent Carbon Nanoparticles as New Optical-Limiting Materials

Graphitic nanoplatelets (GNPs) and luminescent carbon nanoparticles (CNPs) are simultaneously synthesized by controlling the laser parameters and the size of the graphite flakes. Because luminescent CNPs are attached onto GNPs, a new carbon nanostructure is obtained. Compared with carbon black, GNPs, and luminescent CNPs alone, this nanostructure shows better optical-limiting (OL) effects. The OL mechanism of GNPs that are decorated with luminescent CNPs can mainly be attributed to nonlinear scattering. The role of luminescent CNPs is to promote the formation and growth of nonlinear scattering bubbles, thereby enhancing their optical-limiting effects.