Delineating Mechanisms of Upconversion Enhancement by Li+ Codoping in Y2SiO5:Pr3

Codoping with Li+ has become a common method for improving optical efficiency in oxide-based upconversion luminescent materials, yet the mechanisms of enhancement have remained ambiguous. Herein, we delineate the major ways by which Li+ enhances visible-to-ultraviolet upconversion in the phosphor Y2SiO5:Pr3+ and quantify the relative contributions of each mechanism. Comparative photoluminescence spectroscopy, microscopy, and X-ray diffraction analyses show that of the total 9-fold increase in upconversion resulting from optimized Li+ doping ∼5% was due to crystallite enlargement, ∼50% due to a change in the host crystal polymorph, and ∼45% due to a reduction in activator ion clustering. Contrary to other studies, no significant upconversion enhancement arises from activator site geometry changes due to distortion by Li+, in the case of this material. To elucidate the role of Li+ doping in Y2SiO5, samples were prepared using other dopants for comparison, including Na+, Zn2+, Sc3+, and Zr4+.