Analysis of upconversion nanoparticles as an active medium for upconversion light sources

摘要

In the presented work, we investigated the optical and thermal stability of upconversion nanoparticles based on the threewidely used matrices (NaYF_4, Y_2O_3, LaF_3). Analysis of the upconversion emission as a function of pump power densityin a wide range revealed a multi-stage functional dependence. The stages of linear growing, saturation and degradationwith both reversible and irreversible characters were discovered. For matrices of nanoparticles with low-temperaturestability (NaYF_4), the dependence proves to be irreversible that could cause by a change in the structure and chemicalcomposition of the matrix. Reversible dependence occurs in matrices with high-temperature stability (Y_2O_3 and LaF_3) andis caused by multiphonon nonradiative relaxation, which can be temperature-stimulated because of self-heating and lowair-cooling of the crystal matrixes with low thermal conductivity.