Juechen Wang

Construction of soft porous crystal with silole derivative: strategy of framework design, multiple structural transformability and mechanofluorochromism

Novel fluorescent organic soft porous crystals have been designed and prepared based on a multi-substituted silole bearing 1-phenyl-2,2-dicyanoethene moieties (molecule 8). 8 exhibited a series of emission colors, ranging from yellow to dark red with an over 70 nm shift of emission maximum. Molecule 8 also showed the ability to reversibly switch between different solid states, and a typical mechanofluorochromism was observed by cyclic operation of the grinding–heating–cooling processes. In addition, two single crystals (O and R) were successfully obtained in proper conditions, and the crystallographic data indicated that crystal O and R had reasonable hollow structures, inside which different solvent molecules were selectively encapsulated. More importantly, we have presented a proof-of-concept example of the strategy for the designation of organic soft porous crystals with a conjugated fluorophore and demonstrated the successful achievement of softness, porosity and crystallization ability. This design strategy is instructive to design and construct organic soft porous crystals with other conjugated building blocks and develop novel smart and stimuli-responsive photo/electronic materials.

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.

Ultrabroadband near-infrared luminescence and efficient energy transfer in Bi and Bi/Ho co-doped thin films

Ultrabroadband near-infrared luminescence in the 1.0–2.4 μm range has been observed in bismuth (Bi)-doped oxyfluoride germanate thin films prepared by pulsed laser deposition (PLD). The emission peak position shows a red-shift with decreasing oxygen pressure during PLD growth. Systematic investigation reveals that the origin of the luminescence could be ascribed to Bi clusters. With the sensitization of Bi near-infrared active centers, enhanced broadband ∼2 μm luminescence of Ho3+ is realized in Bi/Ho co-doped films, and a high energy transfer efficiency is obtained. These results may provide promise to realize planar waveguide lasers in the near-infrared region for integrated optics.

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.

Fabrication of the (Y2O3:Yb–Er)/Bi2S3 composite film for near-infrared photoresponse

Harvest of near infrared (NIR) radiation in photovoltaic devices is highly desirable as it is recognized as a potential pathway to break the Shockley–Queisser limit of solar conversion efficiency. Here, (Y2O3:Yb–Er)/Bi2S3 composite films with photoactive current generation under NIR light excitation were fabricated by electro-deposition and a simple successive ionic layer adsorption and reaction (SILAR) method. The composite films consist of homogeneous crystalline particles of Y2O3 with a lamellar morphology covered by Bi2S3 nanoparticles. Upon excitation by a 980 nm laser, the Y2O3:Yb–Er layer in the composite film converts NIR photons into visible emissions through upconversion, which is absorbed by the covered Bi2S3 nanoparticles and leads to the generation of photoelectrons. With the use of a standard electrochemical cell where the composite film serves as the photoanode, we demonstrate robust photocurrent generation in aqueous solution. This study suggests a promising strategy for the harvesting of NIR radiation in solar cells, photocatalysts, and infrared photo-detectors.

Effect of sodium oxide content on the formation of nanogratings in germanate glass by a femtosecond laser

We report on the formation and structural evolution of embedded self-organized, polarization-dependent nanogratings in sodium germanate glasses induced by an 800 nm, 1 kHz femtosecond laser. Optical birefringence dependent on the femtosecond laser polarization as well as the sodium oxide content is observed when the sample surface is perpendicular to the laser propagation direction. Scanning electron microscopy images of the written lines reveal the formation of periodic platelet or nanovoid arrays, which are aligned perpendicularly to the laser polarization direction after mechanical polishing. The influences of sodium oxide content on the morphology and period of the nanogratings are discussed.

Bubble Generation in Germanate Glass Induced by Femtosecond Laser

We report the observation of bubble generation and migration in a germanate glass during irradiation by a femtosecond laser of high repetition rate. Bubbles are formed around the focal area of the laser beam, and their movement indicates the presence of thermal gravity convection in the glass melt, which is beyond the existing theoretical model about temperature field of focal area. Inside the bubbles, oxygen molecules are observed by the confocal Raman micro-spectroscopy. The generation of molecular oxygen and bubbles is explained in terms of the spatial separation of Ge and O ions and micro-explosion inside the glass melt.