Enhanced green upconversion photoluminescence from Ho3+/Yb3+ co-doped CaZrO3 phosphor via Mg2+ doping

This paper reports enhanced green upconversion photoluminescence from Ho3+/Yb3+ co-doped CaZrO3 phosphor via Mg2+ doping synthesized through a solid state reaction method. The X-ray diffraction measurements confirm a shift in the peak position due to the presence of Mg2+ in the CaZrO3 phosphor. The scanning electron micrographs reveal an increase in the particle size for doping with Mg2+ ions. The Ho3+/Yb3+ co-doped CaZrO3 phosphor gives an intense monochromatic green upconversion emission centered at 543 nm due to F-5(4)/S-5(2) -> I-5(8) transition along with weak UV, blue, red and NIR emissions on excitation at 976 nm. The emission intensity of Ho3+ ions was optimum for 3 mol% Yb3+. The doping of Mg2+ ions slightly changes the band gap of the CaZrO3 phosphor; thereby enhancing the emission intensity significantly. When Mg2+ ions are doped in the Ho3+/Yb3+ co-doped CaZrO3 phosphor the emission intensity of the green band is enhanced by up to 4 times. This enhancement is due to substitution of Ca2+ by the Mg2+ ions, which decreased the lattice parameters and increased the crystallinity. The lifetime of the F-5(4)/S-5(2) level increases with the increase in the concentration of Mg2+ ions. Thus, the Ho3+/Yb3+/Mg2+ co-doped CaZrO3 phosphor could be a suitable candidate for intense monochromatic green light and optical devices.