Efficient green emission by up-conversion in Yb3+/Er3+ co-doped monoclinic AgGdW2O8

Yb3+/Er3+ co-doped monoclinic AgGdW2O8 phosphors with intense green emission via up-conversion process were prepared by the high-temperature solid-state method. The samples were structurally characterized using X-ray powder diffraction, after which their luminescent properties were characterized via up-conversion spectroscopy. Green and red emissions centered at 525, 550, and 656 nm were observed when the phosphors were excited at 980 nm, these emissions are ascribed to H-2(11/2), S-4(3/2) -> I-4(15/2) ( green emission) and F-4(9/2) -> I-4(15/2) ( red emission) transitions of Er3+, respectively. It was also found that the green and red emissions originated from the two-photon process. By increasing sintering temperature and doping of Mo6+, the structure of monoclinic AgGdW2O8 transformed to a tetragonal one, which resulted a dramatic increase in UC intensity.