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

Abstract

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 ⁵F₄/⁵S₂ → ⁵I₈ 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 ⁵F₄/⁵S₂ 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.