This study investigated a series of powdered NaYF4:Yb,Er
samples with varying ytterbium-ion contents. Aim of study. This study aimed to determine the change in the quantum yield of upconversion luminescence exhibited by NaYF4:Yb,Er
as a function of the ytterbium-ion content and intensity of excitation by laser irradiation at a wavelength of 975 nm. Method. The quantum yield of upconversion luminescence was determined using a spectrometer and an integrating sphere. Main results. The quantum yield of upconversion luminescence was measured for a series of powdered NaYF4:Yb,Er
samples with different ytterbium-ion contents. The optimal ytterbium-ion content, corresponding to the maximum efficiency of upconversion, was found to be 0.4 at%. Practical significance. The results obtained can be applied in optoelectronics, medicine, and the development of laser facilities.