Impact of sensitizer Yb and activator Tm on luminescence intensity of $\beta$-NaYF$_{4}$:Yb/Tm nanoluminophores

In this study, the impact of sensitizer and activator ions concentration on the intensity of up-conversion luminescence of nanoluminophores $\beta$-NaYF$_{4}$:Yb$^{3+}$/Tm$^{3+}$ in dimethyl sulfoxide (DMSO) was investigated. Analysis of all luminescence spectral bands allows one to establish that the ratio of concentrations of ytterbium and thulium ions strongly effects on the luminescent properties of nanoluminophores. Increase of sensitizer concentration at constant activator concentration leads to an increase of the luminescence integral intensity. Optimal concentration of activators at fixed sensitizer concentration was determined: 2 mol.% for thulium and 18 mol.% for ytterbium. The sensitivity of each luminescence spectrum band to changes in the concentration of activators and sensitizers was explained by cross-relaxation processes in activator ions.