Co-operative energy transfer in Yb3+-Er3+ co-doped SrGdxOy upconverting phosphor

Upconversion nanoparticles (UCNPs) have shown considerable interest in many fields; however, low upconversion efficiency of UCNPs is still the most severe limitation of their applications. Yb3+ and Er3+ co-doped SrGd4O7/Gd2O3(SGO) upconversion (UC) phosphors were synthesized by a modified co-precipitation process. The UC properties were investigated by direct excitation with a 980 nm laser. It was observed that the as prepared materials showed relatively strong green emission, while upon the incorporation of the Er3+ ion, there was an increase in the upconversion luminescence intensity for the red component. The effect of different doping concentration of Er3+on the emission spectra and X-ray diffraction patterns of the UC materials have also been studied. The luminescence lifetimes and Commission Internationale de L'Eclairage coordinates for these as prepared samples were determined to understand the energy transfer (ET) mechanisms occurring between Yb3+ and Er3+ in the SGO host matrix. The UC luminescence intensity as a function of laser pump power was monitored and it was confirmed that the UC process in SGO:Yb3+/Er3+is a two-photon absorption process. The findings reported here are expected to provide a better approach for understanding of the ET mechanisms in the oxide based Yb3+/Er3+ co-doped UC phosphors. This study might be helpful in precisely defined applications where optical transitions are essential criterion and this can be easily achieved by smart tuning of the emission properties of Yb3+/Er3+ co-doped UC phosphors.