Dezhi Tan

Multifunctional tunable ultra-broadband visible and near-infrared luminescence from bismuth-doped germanate glasses

Here, we present three facile approaches to achieve wavelength tunable luminescence in the same host material with single dopant, i.e., by modulating doping level, preparation temperature, and atmosphere. Based on these methods, ultra-broadband tunable near-infrared luminescence with the largest full width at half maximum of about 500nm covering the whole windows of optical communication has been obtained in bismuth-doped germanate glasses. Wavelength tunable luminescence is also observed with the change of excitation wavelength. Systematical strategy was followed to approach the physical origin of the near-infrared luminescence and we proposed that three different bismuth active centers contribute to the near-infrared luminescence in the germanate glasses. A comprehensive explanation for the tunable luminescence is given, combining the concentration, energy transfer, and chemical equilibrium of these active centers in the glasses. With the increase of melting temperatures and the increase of reducing extent of the preparation atmosphere, bismuth species transform from Bi 3þ to Bi 2þ ,B i þ ,B i 0 and bismuth clusters, and then to bismuth colloid. Of particular interest is that red tunable luminescence was also observed by modulating doping level, preparation atmosphere, and excitation wavelength. Besides, the trapped-electron centers in germanate glasses can interact with bismuth species of high valence states leading to the formation of bismuth active centers of low valence states and the decrease of trapped-electron centers. This tunable ultra-broadband luminescence is helpful for a better understanding of the origin of the near-infrared luminescence in Bi-doped glasses and may have potential applications in varieties of optical devices. V C 2013 American Institute of

Unusual luminescence quenching and reviving behavior of Bi-doped germanate glasses

Here for the first time, we report an unusual annealing temperature dependent near-infrared (NIR) luminescence quenching and reviving behavior in Bi-doped MgO-Al₂O₃-GeO₂ glasses. Systematic characterizations of the samples by using differential thermal analysis (DTA), photoluminescence and absorption spectra, X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicate that this phenomenon is associated with the reversible reaction of Bi⁺ and Bi⁰ initiated by the change of local glass structure. Excitingly, wavelength tunable luminescence is also observed and it can be ascribed to selective excitation of active Bi⁺ center in different sites. These results not only open a new way for controlling luminescence properties of main group elements in glass but also provide great value for improving practical active-fiber drawing process.

Enhanced broadband near-infrared luminescence of Bi-doped oxyfluoride glasses.

Broadband near-infrared luminescence covering 900 to 1600 nm has been observed in Bi-doped oxyfluoride silicate glasses. The partial substitution of fluoride for oxide in Bi-doped silicate glasses leads to an increase of the intensity and lifetime of the near-infrared luminescence and blue-shift of the near-infrared emission peaks. Both Bi-doped silicate and oxyfluoride silicate glasses show visible luminescence with blue, green, orange and red emission bands when excited by ultra-violet light. Careful investigation on the luminescence properties indicates that the change of near-infrared luminescence is related to optical basicity, phonon energy of the glass matrix and crystal field around Bi active centers. These results offer a valuable way to control the luminescence properties of Bi-doped materials and may find some applications in fiber amplifier and fiber laser.

Photoinduced luminescent carbon nanostructures with ultra-broadly tailored size ranges

Carbon nanoparticles (CNPs), hollow CNPs, nanodiamonds, and hybrid graphene spheres (HGSPs) are produced by using fs laser ablation in solution. These carbon nanostructures emit tunable photoluminescence and two-photon luminescence. The photoinduced layer-by-layer assembly of graphene nanosheets is observed to form HGSPs with tailored broadly-ranged sizes for the first time.

Enhanced broadband excited upconversion luminescence in Ho-doped glasses by codoping with bismuth.

We report enhanced green and red upconversion (UC) luminescence in Ho3+-doped oxyfluoride germanate glass by introducing bismuth near-infrared active centers as sensitizers. The UC excitation bands at 750 and 970 nm show a full width at half-maximum of 20 and 45 nm, respectively. Energy transfer from sensitizers, the excited-state absorption, and phonon-coupled absorption of Ho3+ jointly contribute to the enhanced UC luminescence. Our approach provides an efficient methodology to broaden the excitation bandwidth of UC luminescent materials, which may have the potential for promising application in solar cells.

Regulation of structure rigidity for improvement of the thermal stability of near-infrared luminescence in Bi-doped borate glasses

The effect of heat-treatment on the near-infrared (NIR) luminescence properties was studied in Bi-doped borate glasses. The luminescence intensity generally decreases with the increase of temperature, and the thermal stability can be improved by nearly 4.5 times with addition of 5 mol% La2O3. Collaborative studies by using steady photoluminescence (PL) and photoluminescence excitation (PLE) spectra, luminescence decay curve, differential thermal analysis (DTA), Raman spectra and X-ray diffraction (XRD) indicate that the luminescence decrement is associated with the agglomeration of Bi active centers during heat-treatment. The improvement of the thermal stability of NIR luminescence with the addition of La2O3 is benefited from the enhancement of structure rigidity due to the strong cationic field strength of La3+. The results not only provide valuable guidance for suppressing performance degradation of Bi-doped glass during fiber drawing process, but also present an effective way to control the luminescence properties of main group elements in glasses from the perspective of glass structure.

Broadband Near-Infrared Luminescence from γ-ray Irradiated Bismuth-Doped Y4GeO8 Crystals

Bismuth-Doped Y4GeO8 Crystals Beibei Xu, Dezhi Tan, Miaojia Guan, Yu Teng, Jiajia Zhou, Jianrong Qiu, and Zhanglian Hong State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou, Zhejiang 310027, P. R. China. State Key Laboratory of luminescence Physics and Chemistry, and Institute of Optical Communication Materials, South China University of Technology, Guangzhou, Guangdong 510640, P.R. China.

Effect of UV irradiation on photoluminescence of carbon dots

Effect of ultraviolet light irradiation on the photoluminescence of carbon dots (CDs) is investigated. After the ultraviolet light irradiation, CDs exhibit red shifted and enhanced green emission, and significantly enhanced emission in the wavelength region from green-yellow to red. Carbonyl groups increase remarkably originated from photochemical oxidation, resulting in more defect energy trapping (DET) states, higher electron density, and stronger n(OH)→π*(CO) interactions. Consequently, a decrease in band gap and more contribution from the DET states related radiative recombination result in an enhancement of green emission and beyond, while ultraviolet emission is reduced and blue shifted due to the decrease of sp2 carbons.

One-pot synthesis of luminescent hydrophilic silicon nanocrystals

A facile one-pot method of femtosecond laser ablation in solution to synthesize hydrophilic silicon nanocrystals is presented in this communication. These silicon nanoscrystals emit colorful photoluminescence when excited at different wavelengths. This simple method has potential applications in the preparation of luminescent silicon nanocrystals passivated with different organic molecules.

Large-scale preparation of strawberry-like, AgNP-doped SiO2 microspheres using the electrospraying method

In this paper, we report on a novel strategy for the preparation of silver nanoparticle-doped SiO(2) microspheres (Ag-SMSs) with an interesting strawberry-like morphology using a simple and efficient electrospraying method. SEM (scanning electron microscopy), TEM (transmission electron microscopy), XRD (x-ray diffraction), EDS (energy-dispersive spectroscopy) and UV-vis spectra (ultraviolet-visible spectra) were applied to investigate the morphology, structure, composition and optical properties of the hybrid microspheres, and E. coli (Escherichia coli) was used as a model microbe to evaluate their antibacterial ability. The results showed that the Ag-SMSs were environmentally stable and washing resistant. The Ag-SMSs exhibited effective inhibition against proliferation of E. coli, and their antibacterial ability could be well preserved for a long time. The environmental stability, washing resistance, efficient antibacterial ability and simple but productive preparation method endowed the Ag-SMSs with great potential for practical biomedical applications.