Green-Emitting Ca6Sr4(Si2O7)3Cl2: Eu2+ Phosphors for White Light-Emitting Diodes

Abstract

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).