New results on visible quantum cutting, i.e. the emission of more than one visible photon for every photon absorbed, are presented. The 4~(fn) level structure at high energies and emission from high-lying levels was investigated for various trivalent lathanides, but no high visible quantum efficiencies were found for a single lanthanide ion. By using energy transfer between different types of ions, visible quantum cutting can be achieved. This is called downconversion. For two different combinations of rare earth ions visible quantum cutting via downconversion was found to take place: the systems Gd~(3+)-Eu~(3+)-Tb~(3+).
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