Hui Gao

Facile synthesis and optical properties of nitrogen-doped carbon dots

Among the chemical doping elements, nitrogen atoms play a critical role in tuning the intrinsic properties or exploiting new phenomena of carbonaceous materials. Herein, we report a facile strategy to synthesize nitrogen-doped carbon dots (NCDs) using glutamic acid as the precursor via a one-step thermal conversion process. The as-produced NCDs exhibit bright blue photoluminescence (the quantum yield of ca. 23.2%), and the emission wavelength could be slightly tuned through changing the parameters of the synthesizing process. Interestingly, apart from their superior luminescence characters, unexpected cathodoluminescence (CL) and frequency upconverted emission properties were both observed in the NCDs.

Facile synthesis and photoluminescence of graphene oxide quantum dots and their reduction products

A simple chemical method of acid treatment has been developed for cutting graphene oxide into graphene oxide quantum dots with controllable size (∼3.0 nm). The newly produced graphene oxide quantum dots have high stability and disperse well in water for several months. Bright blue emission, as well as an excitation-dependent photoluminescence activity, is observed in the GOQDs. In contrast, the photoluminescence emission of graphene quantum dots obtained by the reduction of graphene oxide quantum dots has a distinctive blue shift when compared with that of the graphene oxide quantum dots. The difference in PL properties between graphene oxide quantum dots and graphene quantum dots can be attributed to the change of the bandgap due to the different size of the isolated sp2 cluster in the sp3 matrix of graphene.

The Role of Gd3 + in the Luminescence of Several Eu3 + Activated Borate Phosphors under VUV Excitation

The role of Gd 3+ in the luminescence of several Eu 3+ activated borate phosphors was examined. The results showed that under 147 nm excitation, the photoluminescence of Eu 3+ was improved with the incorporation of Gd 3+ in the systems of YBO 3 :Eu 3+ and YAl 3 (BO 3 ) 4 :Eu 3+ , while in the case of YAlO 3 :Eu 3+ and CaYBO 4 :EU 3+ , the luminescence of Eu 3+ was decreased when Gd 3+ was introduced into the host lattice. A simple energy band model according to the location of lanthanide energy levels relative to the conduction band and valence band of the host lattice was proposed to explain the phenomena.

Photoluminescence of new red phosphor SrZnO2:Eu3+

SrZnO2:Eu3+ has been synthesized by solid-state reaction and its photoluminescence in ultraviolet (UV)–vacuum ultraviolet (VUV) range was investigated. The broad bands around 254 nm are assigned to CT band of Eu3+–O2−. With the increasing of Eu3+ concentration, Eu3+ could occupy different sites, which leads to the broadening of CT band. A sharp band is observed in the region of 110–130 nm, which is related to the host absorption. The phosphors emit red luminescence centered at about 616 nm due to Eu3+ 5D0→7F2 both under 254 and 147 nm, but none of Eu2+ blue emission can be observed.

The buildup of the electric field during positron annihilation lifetime spectroscopy measurement

Positron annihilation lifetime spectra were measured on pure polystyrene (PS) and PS samples whose film surfaces were coated with gold, graphite (GR-PS), or MoS2. The results showed the longest lifetime remained constant with measured time in all experimental samples, whereas the corresponding intensity decreased with time at different rates. The experimental phenomena were associated with the buildup of an electric field inside the polymer during extended positron annihilation lifetime spectroscopy (PALS) measurement. The decrease in the rate was attributed to the presence of conductive film causing the neutrality between positive charges and negative charges, thereby reducing the buildup of the electric field. Additionally, we also performed PALS measurement on GR-PS under different experimental conditions, such as the conductive film being grounded or not grounded or the presence of an external electric field. These results further indicated that the buildup of the electric field was responsible for the decrease in the intensity with time.

Luminescence Properties of Metastable Phased LaVO4 ∕ Eu3 + under UV and VUV Light Region

Tetragonal-phased LaVO 4 /Eu 3+ was synthesized via the hydrothermal method. Their photoluminescence was evaluated under UV and vacuum UV (VUV) region, respectively. Under both UV and VUV excitation, the relative emission intensity of tetragonal-phased LaVO 4 /Eu 3+ was far higher than monazite-type bulk LaVO 4 /Eu 3+ and was 70% of bulk tetragonal YVO 4 /Eu 3+ , respectively. This indicated that the tetragonal-type LaVO 4 /Eu 3+ may serve as a good red phosphor candidate.

Vacuum Ultraviolet Optical Properties of ( Gd , Y ) AlO3 : Tb3 +

(Gd,Y)AlO 3 :Tb 3 + phosphors were prepared by the citrate-gel method at relatively low temperature and their photoluminescence properties were investigated under vaccum ultraviolet excitation. The bands (125-175 nm) are assigned to the host absorption, and the f-d transitions of Tb 3+ are in the region of 180-300 nm. With the increasing of Y 3+ content in (Gd,Y)AlO 3 :Tb 3+ , the host absorption bands shift to a higher energy region and the luminescent intensity is enhanced by Y 3+ incorporation into the lattice, because the emission lines of Xe in the discharge at 147 nm lie in the excitation spectrum. This makes the phosphor suitable for plasma display panel applications.

Oxidation of CVD Growth Single-Layer Graphene

Recently, oxidized chemical vapor deposition (CVD) growth graphene has drawn much attention due to its potential applications in the field of optoelectronics. In this article, we report a simple, scalable and efficient method to synthesize oxidized CVD growth single-layer graphene by the strong acid treatment. The results indicate that oxidation process successfully introduced more defects and oxygen-containing groups into the lattice of graphene.

The preparation of a three dimensional terbium doped reduced graphene oxide aerogel with photoluminescence and paramagnetic properties

A 3D reduced graphene oxide (rGO) material with good photoluminescence (PL) and magnetism properties was self-assembled using the hydrothermal method. The resultant material possessed a flower-like structure, which leads to a high surface area. To dehydrate the hydrogel for conservation, the sublimation process we use can effectively maintain the porosity as it uses the freeze drying method. Then, rGO was endowed with paramagnetism and green photoluminescence properties via the introduction of Tb ions, which also reinforces the significance of the building block. Finally, the coordination between Tb ions and the carbonyl was proven with photoluminescence excitation (PLE) spectra and the UV-vis absorption spectra, which are likely to offer an effective way to study the carbonyl compound.

Synthesis of Large-Area and Monolayer of Graphene: Role of Transition Metal Support and Growth Time by CVD Method

Continuous monolayer graphene sheet with large area has been synthesized via chemical vapor deposition (CVD) method using liquid hydrocarbon as precursor. Synthesis parameters including growth substrate and growth time have been investigated to assess their influence on monolayer graphene synthesis. Raman spectroscopy and high resolution transmission electron microscopy (HRTEM) reveal that the number of layers and quality of graphene sheet depend greatly on the varied synthesis parameter. The study could be used to improve understanding the growth of graphene by CVD method in order to meet the needs of graphene in various electronic applications.