A series of new green-emitting Ca6Sr4-xEux(Si2O7)3Cl2 phosphors were synthesized using the high-temperature solid-state reaction. Thermogravimetry-differential thermal analysis (TG-DTA) and X-ray diffraction (XRD) were used in order to determine the crystallization process and crystal structure of the obtained product. Complete optical studies including the diffuse reflection, photoluminescence excitation and emission measurements were performed. Crystallographic site-occupations of Eu2+ ions in the Ca6Sr4(Si2O7)3Cl2 host were assigned and two distinguishable Eu2+ sites, viz., Eu(1)2+ and Eu(2)2+, were confirmed. The luminescence natures of the Eu2+ emission, e. g., the Stokes shift and the concentration-dependent luminescence behaviors were also investigated in detail. Based on the experimental results and theoretical calculation, the dipole-dipole interaction was dominantly involved in the energy transfer from Eu(1)2+ to Eu(2)2+ ions, and the critical distance was determined to be about 14.69 Å. The thermal-quenching behaviors were further presented. In view of its strong absorption in the near-UV region, the intense green light emission peaking at 511 nm, as well as the lower thermal quenching, the Eu2+-doped Ca6Sr4(Si2O7)3Cl2 phosphor can serve as a potential new material for phosphor-converted light-emitting diodes (LEDs).

A single crystal of Te2V2O9 with dimensions of 15×15×5 mm3 has been grown by the top‐seeded growth method. Infrared and transmission spectra indicate the transmission cutoff wavelength of Te2V2O9 crystal is about 620 nm in visible region and 6.2 μm in infrared region. In addition, band structure and density of states calculations of Te2V2O9 were carried out using the total‐energy code CASTEP based on density functional theory. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Thickness of emissive layer in organic electroluminescent device is one of the important factors affecting the device performance. In this report, a blue electroluminescent device with an active layer of 4, 4'-bis(2, 2'-diphenylvinyl) -1, 1'- biphenyl (DPVBi) is fabricated. The device performance varies with the thickness of DPVBi. With the increase of the DPVBi thickness between 1050 nm, the device luminance and efficiency at the same current density first increase and then decrease, the device with a DPVBi thickness of 40 nm exhibits the highest luminance of 15840 cd/m2 and a maximum external quantum efficiency of 3.2%, with Commission Internationale de l'Eclairage (CIE) co-ordinates being (0.15, 0.15). The luminescent spectral red shift and the color purity deteriorate when the thickness is over 40 nm, which can be attributed to a result of microcavity effect. In the meantime, the analysis from experimental results shows that the exciton diffusion length in DPVBi is between 2030 nm.