The processes of the energy deactivation of electronic excitation in Yb(III) β-diketonates and their dependence on the nature of β-diketone and the second ligand as well as the environment and its state (complexes in organic solvents and polymer matrix) were studied. Taking as an example the ytterbium thenoyltrifluoroacetonate, it was shown that the energy losses in the ligand and Yb(III) ion, which is due to the high-frequency vibrations of the central C-H group of the β-diketone, can lead to the decreased quantum yield of the luminescence. The increase in the medium rigidity causes the decrease in losses in the ligand, but does not affect the deactivation of the Yb(III) ion excited level. In the mix-ligand complexes the second ligand (1,10-phenanthroline) improves the screening of the central ion providing almost full transfer of the energy, absorbed by ligand, to ytterbium ion.