Upconversion Processes and High/Low Spin States of Lanthanide Ions

Emission spectra of KMgF₃:Dy²⁺ at 11 K

Upconversion processes involve the conversion of infrared to visible radiation and are important for the development of visible lasers, which can be converted to the infrared by laser diodes. The aim of this work is the measurement of upconversion processes that have been so far detected only in trivalent lanthanide and transition metal ions. In addition, spectroscopic analysis of ions such as Sm²⁺, Tm²⁺ and Dy²⁺ must be carried out, which has not been satisfactorily performed before due to the difficult preparation of the compounds. In our case, the compounds show very intense emission after excitation with a low-power light in the infrared range. This emission is more efficient than have been found in previously known systems.
These mentioned ions with the electron configuration 4fⁿ (n> 7) also show excited high- and low-spin states, a phenomenon previously unknown for the rare-earth ions and important for fundamental interests. In particular, the temperature dependence of the relative emission provides detailed insights into interactions of the electronic states and kinetic processes.