Zunming Lu

Blue emitting BCNO phosphors with high quantum yields

The blue emitting BCNO phosphors with high quantum yields were prepared at 625 °C using boric acid, melamine and hexamethylenetetramine as raw materials. The BCNO phosphors have turbostratic boron nitride structure and consist of nanocrystallites 5 nm in size. The emission and excitation spectra can be tuned by the contents of raw materials and sintering temperatures. The quantum yields of BCNO phosphors can be up to 99% with increasing boric acid. The FTIR spectra suggested that the quantum yield can be improved with increasing strength of B–N and B–N–B bonds, and formation of B–O–B bonds, while it decreased with enhancement of CC bonds. The emission decay curves indicated that the decay process was related to two luminescence centers corresponding to carbon and oxygen impurities. In addition, the high temperature emission spectra disclosed that the nitrogen vacancy would participate in the blue light emission process at a certain heating temperature. The blue emitting BCNO phosphors with high quantum yields have great potential application in luminescence and display areas.

Spectral properties and luminescence mechanism of red emitting BCNO phosphors

Red emitting (λem = 620 nm) BCNO phosphors were synthesized at 650 °C with solid state reaction method using boric acid and hexamethy lenetetramine as raw materials. The BCNO phosphors have turbostratic boron nitride structure and particle sizes are in micro scale. Carbon and oxygen elements were bonded to boron and nitrogen to form BCNO phosphors. The emission peaks were shifted from blue light (420–470 nm) to red light (590–620 nm) with increasing sintering temperature, heating time and the ratio of boric acid to hexamethy lenetetramine, which was induced by partially formed BCNO and completely formed BCNO phosphors. The decay curves and emission spectra indicated that the red emission was induced by two luminescence centers, corresponding to longer lifetime τ1 and short lifetime τ2. The ultraviolet visible absorption spectra disclosed that the optical band gap was changed from 1.75 eV to 2.0 eV with different preparation conditions. The high temperature emission spectra suggested that the nitrogen defects levels served as electron traps and attended the red emission. The luminescence mechanism of BCNO phosphors was stated by a simplified energy level diagram. The red emission BCNO phosphors have good thermal stability and great potential application on lighting, display, solar cell and biomedical fields.

BN-coated Ca1−xSrxS:Eu solid-solution nanowires with tunable red light emission

We report on the controlled growth of novel BN-coated Ca(1-x)Sr(x)S:Eu nanowires via a solid-liquid-solid process. The Ca(1-x)Sr(x)S solid solution forms as one-dimensional nanowires and has been coated with homogeneous protective BN nanolayers. The structure and luminescence properties of this new nanocomposite have been systematically investigated. High-spatial-resolution cathodoluminescence investigations reveal that effective red color tuning has been achieved by tailoring the composition of the Ca(1-x)Sr(x)S nanowires. Moreover, codoping of Ce(3+) and Eu(2+) in the CaS nanowire can induce energy transfer in the matrix and make it possible to obtain enhanced orange color in the nanowires. The BN-coated Ca(1-x)Sr(x)S:Eu solid-solution nanowires are envisaged to be valuable red-emitting nanophosphors and useful in advanced nanodevices and white LEDs.

Facile synthesis of BCNO quantum dots with applications for ion detection, chemosensor and fingerprint identification

Boron carbon oxynitride quantum dots (BCNO QDs) with blue emission were prepared via the template of SBA-15 (a typical mesoporous silica). A modulated photoluminescence sensor was developed based on the different quenching effects of Cu2+ or Hg2+ ions on the luminescence intensity of BCNO QDs. The Cu2+ or Hg2+ ions have an interaction with BCNO QDs due to the electrons transfer between the BCNO and Cu2+ or Hg2+ ions, and the detection limit of Cu2+ or Hg2+ ion concentration can be as less as 10 nM. The BCNO-Cr6+ mixture can be served as a turn-on fluorescent sensor for detecting the ascorbic acid based on the inner filter effect since overlapping of excitation and emission spectra between Cr6+ ions and BCNO QDs. Moreover, the BCNO QDs can also be applied to fingerprint identification and organic fluorescent films under ultraviolet excitation.

Luminescence Mechanism of Carbon Dots by Tailoring Functional Groups for Sensing Fe3+ Ions

In this paper, spherical carbon dots (CDs) with distinct compositions and surface states have been successfully synthesized by a facile microwave method. From the fluorescence spectra, several characteristic luminescence features have been observed: surface amino groups are dominant in the whole emission spectra centering at 445 nm, and the fingerprint emissions relevant to the impurity levels formed by some groups related to C and N elements, including C-C/C=C (intrinsic C), C-N (graphitic N), N-containing heterocycles (pyridine N) and C=O groups, are located around 305 nm, 355 nm, 410 nm, and 500 nm, respectively. Those fine luminescence features could be ascribed to the electron transition among various trapping states within the band structure caused by different chemical bonds in carbon cores, or functional groups attached to the CDs’ surfaces. According to the theoretical calculations and experimental results, a scheme of the band structure has been proposed to describe the positions of those trapping states within the band gap. Additionally, it has also been observed that the emission of CDs is sensitive to the concentration of Fe3+ ions with a linear relation in the range of Fe3+ concentration from 12.5 to 250 μM.

Surface states modulation of red emitting carbon dots for white light-emitting diode

Controlling surface states using different functional groups is an effective and facile way to modulate the fluorescence of carbon dots (CDs), but the underlying mechanisms are still unclear and urgent to solve. In this work, we synthesized red emitting CDs and achieved multiple emission states (red, green and blue emission) by tailoring the surface states with different amino groups. In particular, the luminescence mechanism and the role of surface states were studied in detail. It is found that the multiple emission states are related to the speciation of nitrogen (pyridinic N, pyrrolic N, graphitic N and amino N) on the surface of CDs, of which the fluorophore formed by the deformation of p-phenylenediamine contributes to the red emission, pyridinic N is responsible for the green emission state, and pyrrolic N enhances the blue emission. A possible energy level diagram was proposed to disclose the electron transition process and relative levels induced by different surface groups on CDs. In addition, the modulated CDs with multiple emission states can be used as single light converters to fabricate a white light-emitting diode, which has white light color coordinates of (0.31, 0.32), a high color rendering index (CRI) of 85, a luminous efficiency of 8.8 lm W−1 and good stability.

Cu/Ni nanoparticles supported on TiO2(B) nanotubes as hydrogen generation photocatalysts via hydrolysis of ammonia borane

TiO2(B) nanotubes (NTs) were used as carriers to support metal Cu/Ni nanoparticles for the catalytic hydrolysis of ammonia borane (NH3BH3, AB) under visible light. The TiO2 NTs were first prepared by the hydrothermal method and subsequently loaded with Cu/Ni metal nanoparticles by the impregnation reduction method. The structure, morphology, and chemical composition of the as-obtained catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX), transmission electron microscopy (TEM), inductively coupled plasma emission spectroscopy (ICP), and ultraviolet–visible spectroscopy (UV-Vis). The characterization results revealed that the metal nanoparticles were uniformly loaded on the surface of the TiO2 NTs, while the band gap of the catalyst was reduced significantly from 3.22 to 2.68 eV. The catalysts showed an excellent photocatalytic performance towards the hydrolysis of AB for H2 production. Thus, the H2 production rate of Cu0.64Ni0.36-TiO2 NTs reached 5763.86 mL g−1 min−1, with a total turnover frequency (TOF) of 15.90 mol H2 (mol cat)−1 min−1 for a loading volume of metal particles of 5.25 wt%. The results presented herein demonstrate that TiO2(B) can be a potential photocatalyst for effective H2 production, and also provide a cheap and effective approach to improve the light-to-H2 energy conversion.

Removal of Cr(III)/Cr(VI) from wastewater using defective porous boron nitride: a DFT study

Developing highly-efficient adsorbent materials for the removal of Cr(III)/Cr(VI) ions from industrial wastewater is of great importance for environmental pollution control. In this work, density functional theory was used to model the adsorption capacities of Cr(III)/Cr(VI) ions on defective porous boron nitride (p-BN). Our results suggest that both nitrogen (VN) and boron (VB) vacancies contribute to the adsorption of Cr(III)/Cr(VI) ions on p-BN. In the case of a VN defect, the calculated adsorption energy (Eads) values are 3.76 eV and 4.58 eV for single Cr(III) and Cr(VI) ions, respectively, whereas, in the case of a VB defect, the Eads values are 8.55 eV and 10.26 eV for Cr(III) and Cr(VI) ions, respectively. The analysis of the electronic structure reveals that defective levels in the energy gap region strongly affect the adsorption performance of p-BN as an adsorbent. More importantly, we clarify that the strong adsorption of Cr(III)/Cr(VI) ions on defective p-BN is indeed chemical adsorption and not dispersion or electrostatic attraction. High coverage of Cr(III) and Cr(VI) ions and the effect of water solvent molecules were also taken into account. These findings indicate that defective p-BN is an excellent candidate for the removal of Cr(III)/Cr(VI) ions from wastewater.