Spectroscopy properties of Eu ³⁺ doped Ca ₉R(VO ₄) ₇ (R=Bi, La, Gd and Y) phosphors by sol-gel method

An attempt has been made to synthesize the Eu ³⁺-activated Ca ₉R(VO ₄) ₇ (R=Bi, La, Gd, and Y) red emitting phosphors by a modified sol-gel process. The phase formation processes of these samples have been characterized by thermogravimetric analysis (TGA) and x-ray diffraction (XRD). The optical excitation spectra of Ca ₉R(VO ₄) ₇ samples showed an intense charge transfer band (CTB) along with a group of typical sharp lines from Eu ³⁺, and the emission spectra have been dominated by the electric dipole ⁵D ₀- ⁷F ₂ transition peaked at 614 nm. The parameters for the synthesis of these phosphors including their annealing temperature and concentration of Eu ³⁺ ions have also been optimized. No concentration quenching is found in this class of samples, and the Ca ₉Eu(VO ₄) ₇ phosphor shows the strong red light. In addition, the thermal stability of phosphor Ca ₉Eu(VO ₄) ₇ was also investigated, and the results indicate that this class of phosphors can be served as a potential red emitting phosphor candidate for LEDs.