Dependence of quantum yield of up-conversion luminescence on the composition of fluorite-type solid solution NaY$_{1-x-y}$Yb$_{x}$Er$_{y}$F$_{4}$

A study of the properties of polycrystalline fluorite-type NaY$_{1-x-y}$Yb$_{x}$Er$_{y}$F$_{4}$ solid solutions demonstrated that NaY$_{0.87}$Yb$_{0.10}$Er$_{0.03}$F$_{4}$ and NaY$_{0.885}$Yb$_{0.1}$Er$_{0.015}$F$_{4}$ samples produced up-conversion luminescence with 3.35% and 3.62% quantum yields, which were higher than quantum yields of the other NaY$_{1-x-y}$Yb$_{x}$Er$_{y}$F$_{4}$ samples. NaY$_{1-x-y}$Yb$_{x}$Er$_{y}$F$_{4}$ specimens were prepared by co-precipitation from aqueous solutions by drop-wise addition of rare earth nitrate solutions to aqueous sodium fluoride.