Combustion synthesis and luminescent properties of red-emitting Ca4−xAl6WO16:xEu3+ phosphors and photoluminescence enhancement by Bi3+ co-doping

A series of Ca4−xAl6WO16:xEu3+ and Ca4−x−yAl6WO16:xEu3+, yBi3+ red-emitting phosphors have been successfully synthesized by the combustion method and characterized with X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectra (EDS) and photoluminescence (PL). The results indicated that the samples were well crystallized with irregular lamellar-like shape and belonged to the tetragonal structure and space group P4c2. Photoluminescence spectra showed that the phosphors can be efficiently excited by near-UV light and exhibited a characteristic red luminescence corresponding to the electric dipole transition 5D0→7F2 at 618 nm. The emission intensity of Eu3+ ions in the Ca4Al6WO16 (CAWO) host largely enhanced with the concentration increasing of activator (Eu3+) ion and sensitizer (Bi3+) ion, and the emission intensity reached the maximum at x=0.4 and y=0.02 in Ca4−x−yAl6WO16:xEu3+, yBi3+ phosphor. Addition of Bi3+ ions drastically improved Eu3+ ions emission owing to its strong absorption of excitation energy and effectively energy transfer to Eu3+ emission center. It is shown that Ca4−xAl6WO16:xEu3+ phosphors are promising red-emitting candidates for near-UV LED-based solid-state-lighting (SSL).