Shuaishuai Sun

Developing VUV spectroscopy for protein folding and material luminescence on beamline 4B8 at the Beijing Synchrotron Radiation Facility.

The new 4B8 beamline provides UV-VUV light in the wavelength range from 360 to 120 nm. It uniquely enables two kinds of spectroscopy measurements: synchrotron radiation circular dichroism spectroscopy and VUV excited fluorescence spectroscopy. The former is mainly used in protein secondary structure studies, and the latter in VUV excited luminescent materials research. Remote access to fluorescence measurement has been realised and users can collect data online. Besides steady-state measurements, fluorescence lifetime measurements have been established using the time domain method, while a laser-induced temperature jump is under development for protein folding dynamics using circular dichroism as a probe.

A high efficiency blue phosphor BaCa2MgSi2O8:Eu2+ under VUV and UV excitation

BaCa2MgSi2O8:Eu2+ phosphors have been prepared by a conventional high temperature solid state reaction technique. The emission and excitation spectra as well as the luminescence decays were investigated, showing that Eu2+ ions enter both Ba2+ and Ca2+ sites in the host. The structural refinement reveals that about 70% Eu2+ ions occupy Ba2+ sites in samples Ba1−xEuxCa2MgSi2O8 and BaCa2(1−x)Eu2xMgSi2O8. By investigation of the thermal-quenching, the schematic energy levels for Eu2+ in BaCa2MgSi2O8 were proposed. Intense blue emission was observed under 147, 172 and 254 nm excitation in comparison with the commercial blue phosphor BaMgAl10O17:Eu2+ (BAM), demonstrating the potential application of the phosphors in plasma display panels (PDPs) and tri-color fluorescent tubes.

A potential cyan-emitting phosphor Sr8(Si4O12)Cl8:Eu2+ for wide color gamut 3D-PDP and 3D-FED

The potential application of Sr8(Si4O12)Cl8:Eu2+ phosphor in wide gamut 3D-PDP and 3D-FED is demonstrated in consideration of its high emission intensity (∼148% and ∼280% of commercial BAM) under VUV light and low-voltage electron beam excitation, suitable chromaticity coordinates (0.136, 0.298) and short decay time (∼0.9 μs).

Ultraviolet-vacuum ultraviolet photoluminescence and x ray radioluminescence of Ce3+-doped Ba3MgSi2O8

Ce3+-doped Ba3MgSi2O8 phosphors were prepared by a solid-state reaction route. The photoluminescence properties in the vacuum ultraviolet-vis spectral range and the x ray excited radioluminescence were investigated. Ce3+ ions were found to enter three different sites in the host lattice. Five excitation bands and two emission bands of Ce(1)3+ centers were observed in the spectra. For Ce(2)3+ and Ce(3)3+ centers, the lowest 5d excitation bands and the emission bands were determined. The light yields of samples under x ray excitation were estimated by comparing the integrated emission intensities of our samples with that of BaF2.

Surface exciton emission of MgO crystals

MgO crystals have been exposed to vacuum ultraviolet (VUV) radiation from a synchrotron, with energies up to 9 eV, and the emitted light, at wavelengths above 200 nm, was observed. It is concluded that bulk excitons, play an important role in the diffusion of energy inside MgO crystals, resulting in 5.85 eV (212 nm) emission from the MgO terraces of large (0.2-2 mu m) MgO: F crystals. In the case of aliovalent impurity doping, then the bulk exciton energy is also transferred to the V-k centres and 5.3 eV (235 nm) light is emitted. Both fluorine and silicon doping appear to promote UV surface emission, acting similarly to an ns2 ion inside MgO, while strong scandium doping is killing the surface emission completely. The 212 nm surface UV emission and the 235 nm bulk UV emission can be excited only at the bandgap edge. Broadband visible light, centred around 400 nm, is also emitted. Contrary to the UV emission, this is not generated when excited at the bandgap edge; instead, we find that it is only excited at sub-bandgap energies, with a maximum at the 5C surface excitation energy of 5.71 eV (217 nm) for the MgO terraces.