Role of cross-relaxation in the formation of luminescent response of NaYF ₄ :Yb/Tm nanoluminophores at high excitation intensities

This paper presents the results of the study of the dependences of the intensity of the bands of upconversion luminescence of <i>β</i>-<i>N</i><i>a</i><i>Y</i><i>F</i>₄:<i>Y</i><i>b</i>³⁺/<i>T</i><i>m</i>³⁺ nanoluminophores in dimethyl sulfoxide on the intensity of powerful pulsed laser excitation at different concentrations of activators and sensitizers. It was found that, at low concentrations of activators, the ratio of the intensities of the luminescence bands in the region of 450 and 475 nm does not depend on the intensity of optical pumping. An explanation of the obtained results is proposed, in which the process of cross-relaxation between thulium ions plays a key role.