Sm doped calcium orthovanadate Ca(VO) - A spectral study.

Sm-doped vanadate-based phosphors, Ca (VO):Sm(x = 0.005 ≤ x ≤ 0.095), were synthesized by the citrate-based sol-gel method. The samples were characterized with XRD, SEM, diffuse reflectance and photoluminescence spectroscopy, aiming at the development of phosphor-converted wLED applications. Using diffuse reflectance spectra and the Kubelka-Munk function, the band gap energy was calculated to be 3.28 eV for the Ca(VO):Sm phosphor. Observation of the photoluminescence excitation spectra revealed a broadband excitation from the distorted VO tetrahedron and a few narrow peaks from the 4f-4f intra-configuration transitions of the Sm ions. Upon 404 nm excitation, G → H (564 nm), G → H (601 nm), G → H (648 nm) and G → H (701 nm) transitions were observed. The optimum Sm concentration for the studied phosphor is 0.05 mol, and the estimated critical distance between Sm ions (R) is 19.1 Å. The observed quenching of Sm emission is attributed to the dipole-dipole interactions. The possible cross-relaxation process between neighboring Sm ions was discussed in detail. The CIE coordinates were calculated for all the samples, and they set on the orange region of CIE diagram. In addition, pure orange color emission was observed under 365 nm UV lamp. The results suggest that the Ca(VO):Sm phosphor could be a good candidate for the orange emitting component for wLED applications.