The Influence of Concentrations of Sensitizers and Activators on Luminescence Kinetics Parameters of Up-Conversion Nanocomplexes NaYF₄:Yb³⁺/Tm³⁺

For colloids of NaYF4:Yb3+/Tm3+ nanoparticles in DMSO, by the method of time-resolved luminescence spectroscopy with nanosecond pulsed excitation at a wavelength of 975 nm, the photophysical processes that determine the course of kinetic curves have been revealed. It has been found that the luminescence rise time decreases with an increase in the concentration of activators and sensitizers due to the increase in the efficiency of energy transfer from sensitizers to activators. The cross-relaxation of the excited states of activators provides a decrease in the luminescence decay time with an increase in the concentration of activators and a constant concentration of the sensitizer. There is no correlation between the time of luminescence decay with the change in the concentration of sensitizers and the constant concentration of activators due to the competition of the processes of energy back transfer from activators to sensitizers and the “feeding” of activators by excitations coming from remote sensitizer ions.